Lascar DPM 160 Supplement

ICl
7660 10 µ
10 µ
10 µ
4
5
3
0V
1413
7
11
8
9
312
AD595
+10V
1M
10K
14
+5V
-5V VDD (V+)
VSS (V-)
IN HI
IN LO
COM
DPM
REF -
REF LO
1M
10 µ
10K
20K
10K
+5V
ICL
8069
ICL
8069
10 µ
2k2
Panel Instrument
Application Notes
Issue 3

www.lascarelectronics.com Issue 1_10-2016
Page 2 of 22
Table of Contents
TABLE OF CONTENTS
Installation and Operation - Section A
1. Basic Principles .............................................................................................................................................3
The A to D Converter ...............................................................................................................................3
Multiplication & Division...........................................................................................................................4
Specication ......................................................................................................................................................4
2. Analogue Inputs ......................................................................................................................................6
Di󰀨erential Input ......................................................................................................................................6
Di󰀨erential Reference..............................................................................................................................6
Analogue Common..................................................................................................................................6
Common Mode Rejection Ratio CMRR...................................................................................................6
Eliminating Common Mode Errors...........................................................................................................7
3. Referring Inputs to Supply Ground................................................................................................................7
Reducing/Eliminating VCM......................................................................................................................7
Reducing Ground Loop Errors.................................................................................................................7
Noise .......................................................................................................................................................8
4. Interfacing with Linear and Digital Circuitry ...................................................................................................9
Linear........................................................................................................................................................9
Digital Signals...........................................................................................................................................10
5. Power Supplies..............................................................................................................................................11
Negative Rail Generators ........................................................................................................................11
Operation from Low Volt Supplies ...........................................................................................................11
6. Fitting an External Reference........................................................................................................................12
7. Parallel Operation..........................................................................................................................................12
8. LCD Backlighting...........................................................................................................................................12
9. Commissioning the Meter..............................................................................................................................13
Handling ..................................................................................................................................................13
Circuit Connection ...................................................................................................................................13
Bezel Fitting.............................................................................................................................................13
Using PCB Links......................................................................................................................................15
10. Troubleshooting ...........................................................................................................................................15
Typical Applications - Section B
Measuring Voltage.............................................................................................................................................16
Measuring Current.............................................................................................................................................16
Measuring Resistance.......................................................................................................................................18
Thermometer Circuits........................................................................................................................................19
Using Strain Gauges .........................................................................................................................................20
Generating an O󰀨set .........................................................................................................................................20
AC-DC Converters.............................................................................................................................................21
Autoranging .......................................................................................................................................................22
Measuring Frequency........................................................................................................................................22

www.lascarelectronics.com Issue 1_10-2016
Page 3 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
Installation Operation - Section A&
VIN
-VREF
RINT
CINT
COMP
-
+
AMP
OSC CONTROL
DISPLAY
PHASE 1
AUTO-ZERO PHASE 2
SIGNAL
INTEGRATE
PHASE 3
REFERENCE
INTEGRATE
* 1000 for 3½ Digit
10000 for 4½ Digit
LARGE V IN
SMALL V IN
FIXED SLOPE
OSC
FIXED NO. OF
CLOCK PULSES*
No. OF CLOCK PULSES
PROPORTIONAL TO VIN
1. BASIC PRINCIPLES
1.1 THE A TO D CONVERTER
The vast majority of Lascar meters operate using the Dual-Slope method of conversion. Put simply, the technique involves charging a capacitor (CINT)
from zero at a rate directly proportional to the input voltage and for a fixed time (see fig. 1.2). This is the integrate phase. Then the control connects
the reference voltage (note that it is negative) and CINT is discharged at a rate proportional to the reference voltage. This is the reference integrate (or
de-integrate) phase, the end of which is determined when the voltage on CINT is zero. The time taken for CINT to discharge is directly proportional to
VIN and the number of clock pulses counted in this period gives the digital result.
By using electronic switching and a capacitor to store the reference (CREF), the reference voltage is always applied with the opposite polarity to VIN.
Fig. 1.2. shows the result for a negative input.
In the Auto Zero phase, errors in the analogue circuitry (op-amp input offset voltages for example) are nulled by grounding the input, closing a feedback
loop and storing an error offset voltage on the auto zero capacitor (CAZ)*.
*Not illustrated.
FIG. 1.2 INTEGRATOR CONVERSION CYCLE
Fig. 1.1 INTEGRATOR BLOCK DIAGRAM
www.lascarelectronics.com 2
Installation Operation - Section A&
VIN
-VREF
RINT
CINT
COMP
-
+
AMP
OSC CONTROL
DISPLAY
PHASE 1
AUTO-ZERO PHASE 2
SIGNAL
INTEGRATE
PHASE 3
REFERENCE
INTEGRATE
* 1000 for 3½ Digit
10000 for 4½ Digit
LARGE V IN
SMALL V IN
FIXED SLOPE
OSC
FIXED NO. OF
CLOCK PULSES*
No. OF CLOCK PULSES
PROPORTIONAL TO VIN
1. BASIC PRINCIPLES
1.1 THE A TO D CONVERTER
The vast majority of Lascar meters operate using the Dual-Slope method of conversion. Put simply, the technique involves charging a capacitor (CINT)
from zero at a rate directly proportional to the input voltage and for a fixed time (see fig. 1.2). This is the integrate phase. Then the control connects
the reference voltage (note that it is negative) and CINT is discharged at a rate proportional to the reference voltage. This is the reference integrate (or
de-integrate) phase, the end of which is determined when the voltage on CINT is zero. The time taken for CINT to discharge is directly proportional to
VIN and the number of clock pulses counted in this period gives the digital result.
By using electronic switching and a capacitor to store the reference (CREF), the reference voltage is always applied with the opposite polarity to VIN.
Fig. 1.2. shows the result for a negative input.
In the Auto Zero phase, errors in the analogue circuitry (op-amp input offset voltages for example) are nulled by grounding the input, closing a feedback
loop and storing an error offset voltage on the auto zero capacitor (CAZ)*.
*Not illustrated.
FIG. 1.2 INTEGRATOR CONVERSION CYCLE
Fig. 1.1 INTEGRATOR BLOCK DIAGRAM
www.lascarelectronics.com 2
1.1 The A to D Converter
The vast majority of Lascar meters operate using the Dual-Slope method of conversion. Put simply, the technique involves charging a capacitor
(CINT) from zero at a rate directly proportional to the input voltage and for a xed time (see g. 1.2). This is the integrate phase. Then the control
connects the reference voltage (note that it is negative) and CINT is discharged at a rate proportional to the reference voltage. This is the reference
integrate (or de-integrate) phase, the end of which is determined when the voltage on CINT is zero. The time taken for CINT to discharge is directly
proportional to VIN and the number of clock pulses counted in this period gives the digital result.
By using electronic switching and a capacitor to store the reference (CREF), the reference voltage is always applied with the
opposite polarity to VIN. Fig. 1.2. shows the result for a negative input.
In the Auto Zero phase, errors in the analogue circuitry (op-amp input o󰀨set voltages for example) are nulled by grounding the
input, closing a feedback loop and storing an error o󰀨set voltage on the auto zero capacitor (CAZ)*.
*Not Illustrated
1. Basic Principles

www.lascarelectronics.com Issue 1_10-2016
Page 4 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
gnidaeR0+0+0-Vm002=elacSlluFV0=niVgnidaertupnioreZ
gnidaeR00010001/999899Vm001=ferVferV=niVgnidaercirtemoitaR
stnuoc1+2.0+1-Vm002=niV+=niV-rorrerevolloR
(Difference between equal, positive
and negative reading near full scale.)
stnuoc1+20.0+1-roVm002=elacSlluFmorfnoitaivedmumixaM(ytiraeniL
V00.2=elacSlluF)tifenilthgiartstseb
V/V1Vm0.002=elacSlluFV0=niV,V1+=mcV)RRMC(oitaRnoitcejeRedoMnommoC
Ap011V0=niVtupnitatnerrucegakaeL
C°/V12.0C°07+<aT<C°0,V0=niVtfirdgnidaeroreZ
C°/
mpp51)C°0/mpp0feRtxE(C°07<aT<C°0,Vm0.991=niVtneiciffeocerutarepmetrotcafelacS
V0=niVedulcnitonseoD(tnerrucylppuS
COMMON or REF current) 70 100 A(MAX 136)
200 500 A(MAX 138)
ylppusevitisoPdnanommoCneewtebk052egatloVNOMMOCeugolanA
)631XAM(V2.38.26.2)631XAMk52()ylppusevitisopottcepserhtiw(
2.95 3.05 3.15 (MAX 138)
ylppusevitisoPdnanommoCneewtebk052NOMMOCeugolanAfotneiciffeocerutarepmeT
)631XAM(C°/mpp08)631XAMk52(ylppusevitisopottcepserhtiw(
)831XAM(02
V654V9=-Vot+V)831XAM
/631XAM(evirDtnemgeSkP-kP
V654V9=-Vot+V)831XAM/631XAM(evirDenalpkcaBkP-kP
µ
µ
µ
µ
Am5.25.1V3=egatlovtnemgeSV0.5=+V4BAtpecxEtnerruCgnikniStnemgeS
AB4 only 35
TINU.XAM.PYT.NIMSNOITIDNOCSRETEMARAP
MAX 140 ONLY
1.2 Multiplication & Division
Most Lascar voltmeters have either 3½ or 4½ digit resolution. That is a maximum reading of either ±1999 or ±19999. This will usually correspond to
a full scale reading of ±199.9mV (VREF=100mV) or ±1.9999V (VREF=1.00V).
The relationship is given by:-
READING = 1000 x VIN (3½) (1.1) OR = 10000 x VIN (4½) (1.2)
VREF VREF
The DPM 160 achieves either 200mV or 2V full scale reading (for a 1V reference) by digitally selecting either 10000 or 1000 clock pulses during the
signal integrate period. Thus for a DPM 160 in 200mV scale:-
READING = 10000 x VIN (1.3)
VREF
The DPM 160 uses a more complex system of successive integration and de-integration to achieve the required range of 4½ digits (on the 200mV
range the resolution is 10mV). With VREF xed and VIN varied, the system will multiply (see equations 1.1 - 1.3). However, if VIN is xed and VREF
is the input, the system will divide. This can be used with e󰀨ect in applications measuring period from the output of a F-V converter for example, or
any other requiring a reciprocal function - e.g. velocity
USING THE ICL 7136
/ MAX 131
DPM 125
DPM 942-BL
DPM 2000(S)
DPM 400
DPM 500(S)
DPM 600(S)
DPM 700(S)
DPM 702S
DPM 942
DPM 950(S)
USING THE MAX 136 DPM 116
USING THE MAX 138 DPM 125-BL
DPM 1AS-BL
DPM 2AS-BL
DPM 3AS-BL
EMV 1125
DPM 742-BL
DPM 750S-BL
DPM 750S-EB-W
EMV 1025S
DPM 342
SP 200
OEM 1B
EM32 1B
SP 400
SP 400-BLUE
SP 400-EB-W
USING THE MAX 140 DOM 340
DPM 959B
OEM 1B-LED
EM32 1B-LED
SP 100
SP 8-100
SP 300-BLUE
DPM 40
SP 300
1.3 Specication
3½ DIGIT INSTRUMENT
TABLE 1 - MAX 136, 140, 138 SPECIFICATIONS

www.lascarelectronics.com Issue 1_10-2016
Page 5 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
STINU.XAM.PYT.NIMSNOITIDNOCSRETEMARAP
gnidaeR0+0+0-Vm002=elacSlluFV0=niVgnidaertupnioreZ
C°/VV5.0+C°07+<aT<C°0,V0=niVtfirdgnidaeroreZ
oitaR1000.119999.0egnaRhgiHnoV0.1=niV+egnaRwoLnoV1.0=niVycaruccaegnahcegnaR
gnidaeR0000199998999V2=egnaRVm001=ferV,ferV=niVgnidaercirtemoitaR
stnuoC15.0Vm991=niV+=niV-rorrerevolloR
stnuoC5.0Vm002=elacSlluFrorreytiraeniL
Bd011Vm002=elacSlluFV0=niV,V1+=mcVoitaRnoitcejeRedoMn
ommoC
V5.0-+V5.1+-VVm002=elacSlluFV0=niVegnaRegatloVedoMnommoC
V7Vm002=elacSlluFV0=niV)emitfo%59dedeecxetoneulavp-p(esioN
33,23niP,V0=niVtnerrucegakaeltupnI
Scale factor temperature coefficient Vin=199.0mV,0
V5.32.38.282nipot+VegatlovNOMMOC
Am6.0V1.0ybdesiarMOCegatlovknisNOMMOC
A21V1.0ybderewolMOCegatlovecruosNOMMOC
V8.53.55.4V9=-Vot+V,63nipot+VegatlovDNGD
Am2.1V5.0ybdesiarDNGDtnerrucknisDNGD
V4196-Vot+VegnaregatlovylppuS
Am4.11V9=-Vot+V)tnerrucNOMM
OCgnidulcxe(tnerrucylppuS
Clock frequency 120 360 kHz
zH001zHk021=KLCfetarxelpitlumyalpsiD
k05+VotPSIDVecnatsiserPSIDV
V7.72.73.6-Vot+VdlohserhtyrettabwoL
Continuity threshold 002001IH=72niPtuoV
004002OL=72niPtuoV mV
A01293,83,73sniPtnerrucnwodlluP
A3/3ecruoS/kniS12,02sniPtnerruc"tuptuOkaeW"
A9/3ecruoS/kniS72niPecruoskniS
Pin22 Source current 40 A
Sink current 3
µ
µ
µ
µ
µ
µ
µ
110pA
C°/mpp52C°07+<aT<C°
www.lascarelectronics.com 4
1.3.2 4 ½ Digit Instruments
DPM 160 uses the ICL 7129A
TABLE 2 - ICL 7129 SPECIFICATION.

www.lascarelectronics.com Issue 1_10-2016
Page 6 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
2. Analogue Inputs
2.1 Differential Input
The analogue inputs for VIN (IN HI and IN LO) respond to the voltage between them and not their voltage with respect to any other signal. Because
of this, the inputs are said to be “di󰀨erential”. This makes them very versatile when interfacing to various circuits because o󰀨sets can be eliminated.
The extent to which the inputs can be o󰀨set and still remain truly di󰀨erential is known as the common mode range. The limits to this range being
1.5V** below V+ and 1.5V** above V-. It is recommended not to operate either input close to the power supply rails, because of potential
non-linearity problems with the integrator section.
** This range below V+ to above V- varies depending on the IC series tted to the DPM. Full details of this can be found in the IC manufacturers’
original data.
2.2 Differential Reference
The reference voltage VREF (REF HI and REF LO) may be anywhere within the power supply voltage range of the converter. However, if there is
a large voltage between the reference input and COM there is a risk that stray capacitance in the analogue switching circuitry (see 1.1) will cause a
noticeable roll-over error (see 2.5). Roll-over error is the di󰀨erence in reading between identical positive and negative inputs.
2.3 Analogue Common
This pin is included primarily to set the common mode voltage (VCM) for battery operation (LCD), or for any system where the input signals are
oating with respect to the power supply. The COM pin sets a voltage that is approximately 2.8 volts more negative than the positive supply. This
is selected to give a minimum end of-life battery voltage of about 6V. However, COM can be used as a reference voltage. When the total supply
voltage is large enough to cause the zener to regulate (>7V), the Common voltage will have a low voltage coe󰀩cient (.001%), low output impedance
(<15W), and a temperature coe󰀩cient typically less than 80ppm/°C.
Within the IC, COM is tied to an N-channel FET that can sink 300mA or more to hold the pin 2.8 volts below the positive supply (when a load is
trying to pull COM positive). Sinking excessive current into COM can seriously damage the unit. However, there is only 1mA of source current, so
COM may easily be tied to a more negative voltage, thus overriding the internal reference.
2.4 Common Mode Rejection Ratio CMRR
This gives a measure of the quality of the di󰀨erential inputs and is expressed in dB. It means that if there is no input (VIN =0) and the CMRR is say
(-)100dB, when you impose a voltage of 1.0V between IN LO and COM.
(See fig 2.1) the resulting offset should not exceed:-
1.0 x 10 V = 10µV
or 10µV per volt of common mode voltage.
1. Note some units have IN LO and/ or REF LO linked to COM. MAX 136 based meters have REF LO permanently connected to COM.
2. All LED and S version LCD instruments generate their own negative supply that is below the 0V power supply rail. N.B. Beware
of conicting terminology here. Traditionally non ‘S’ LCD meters have power supply connections V+ and V- and were designed to
operate from 9V nominal. In contrast, ‘S’ type LCD meters often use V+ and V- as power supply connections, BUT operate from 5V
nominal (not 9V). Many have a ‘-5V’ output which is the on-board generated negative rail. For newer meters such as the SP Series,
power supply and connectors are typically referred to as V+ and GND for 5V operation (-5V is available on V-) or V+ and V- for 9V
operation.

www.lascarelectronics.com Issue 1_10-2016
Page 7 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
Installation Operation - Section A&
3. REFERRING INPUTS TO SUPPLY GROUND
In many applications the meter will need to be powered from the same supply as the circuit under test. There are three pitfalls to be avoided here.
1. Applying excessive common mode voltage (VCM) (see Section 2).
2. Ground loop errors.
3. Noise.
Referring to section 2.1, it will be seen that the negative power supply should be at least 1.5V below the analogue inputs.
We must, therefore, provide a negative supply. All LED instruments provide their own. All S-type LCD meters do likewise. If a suitable negative supply
is not available, one must be provided or a different meter chosen for the application.
If we redraw fig 3.1 we will see that small impedances (Rs) in power supply lines will cause a volt drop (Vs) which will be subtracted from the reading,
causing an offset. Furthermore, with LED meters not only do they have a much higher current consumption (causing significant offsets), but each
reading results in a different current consumption. If there is a change in current consumption there is a change in the reading which causes a change
in current consumption, etc. A good example would be a DPM 40 reading say 1001. A drop of one count gives 1000, a difference of 4 segments in
the least significant digit. Each segment consumes 8mA. Thus the total change in current is4x8=32mA. Under these conditions it only needs Rs to
be 6m to cause a 2 count offset.
Using the application in Fig. 3.3 you will reduce the effects of any supply bourne interference.
3.1 REDUCING/ELIMINATING VCM
3.2 REDUCING GROUND LOOP ERRORS
a. 4½ Digit LED b. LED/S-type LCD c. LCD
Ω
IN LO
IN LO
COM
COM
IN HI
REF LO
REF LO
V-
V-
0V
0V
V IN
V IN
V+
V+
V+
V-
IN HI
IN LO
COM
IN HI
REF LO
V-
V-
V IN
V+
V+
IN LO
COM
IN HI
REF LO
0V
V IN
V+
V-
V+
OUT
CIRCUIT
UNDER
TEST
Rs
Vs
Is
WRONG
IN LO
COM
IN HI
REF LO
V IN
V+
V-
V+
OUT
CIRCUIT
UNDER
TEST
Rs
Is
Is
RIGHT
Fig 3.1 Ideal circuit connections
Fig 3.2 Errors due to supply impedances
Fig 3.3 Eliminating the effect of supply impedances
www.lascarelectronics.com 6
Installation Operation - Section A&
3. REFERRING INPUTS TO SUPPLY GROUND
In many applications the meter will need to be powered from the same supply as the circuit under test. There are three pitfalls to be avoided here.
1. Applying excessive common mode voltage (VCM) (see Section 2).
2. Ground loop errors.
3. Noise.
Referring to section 2.1, it will be seen that the negative power supply should be at least 1.5V below the analogue inputs.
We must, therefore, provide a negative supply. All LED instruments provide their own. All S-type LCD meters do likewise. If a suitable negative supply
is not available, one must be provided or a different meter chosen for the application.
If we redraw fig 3.1 we will see that small impedances (Rs) in power supply lines will cause a volt drop (Vs) which will be subtracted from the reading,
causing an offset. Furthermore, with LED meters not only do they have a much higher current consumption (causing significant offsets), but each
reading results in a different current consumption. If there is a change in current consumption there is a change in the reading which causes a change
in current consumption, etc. A good example would be a DPM 40 reading say 1001. A drop of one count gives 1000, a difference of 4 segments in
the least significant digit. Each segment consumes 8mA. Thus the total change in current is4x8=32mA. Under these conditions it only needs Rs to
be 6m to cause a 2 count offset.
Using the application in Fig. 3.3 you will reduce the effects of any supply bourne interference.
3.1 REDUCING/ELIMINATING VCM
3.2 REDUCING GROUND LOOP ERRORS
a. 4½ Digit LED b. LED/S-type LCD c. LCD
Ω
IN LO
IN LO
COM
COM
IN HI
REF LO
REF LO
V-
V-
0V
0V
V IN
V IN
V+
V+
V+
V-
IN HI
IN LO
COM
IN HI
REF LO
V-
V-
V IN
V+
V+
IN LO
COM
IN HI
REF LO
0V
V IN
V+
V-
V+
OUT
CIRCUIT
UNDER
TEST
Rs
Vs
Is
WRONG
IN LO
COM
IN HI
REF LO
V IN
V+
V-
V+
OUT
CIRCUIT
UNDER
TEST
Rs
Is
Is
RIGHT
Fig 3.1 Ideal circuit connections
Fig 3.2 Errors due to supply impedances
Fig 3.3 Eliminating the effect of supply impedances
www.lascarelectronics.com 6
Thus for a 4½ digit display the o󰀨set will only be a fraction of one count (with 200mV FSR the least signicant digit records 10‘s of mV)
Earlier designs of panel meter circuits used COM as the ground reference during integration. These had a lower CMRR of typically 86dB and ideally
IN LO should be connected to COM to eliminate o󰀨sets. Except where COM is being used as a ground reference (see 2.3), IN LO need not be tied
to COM.
2.5 Eliminating Common Mode Errors
The following sections give advice on suitable grounding arrangements. Because of the high Common mode performance of modern A/D
converters, it is not essential to have 0V VCM. It is, however, essential that you avoid going too close to or beyond the power supplies.
3. Referring Inputs to Supply Gound
In many applications the meter will need to be powered from the same supply as the circuit under test. There are three pitfalls to be avoided here.
1. Applying excessive common mode voltage (VCM) (see Section 2).
2. Ground loop errors.
3. Noise.
3.1 Reducing/Eliminating VCM
Referring to section 2.1, it will be seen that the negative power supply should be at least 1.5V below the analogue inputs.
We must, therefore, provide a negative supply. All LED instruments provide their own. All S-type LCD meters do likewise. If a suitable negative
supply is not available, one must be provided or a di󰀨erent meter chosen for the application.
3.2 Reducing Ground Loop Errors
If we redraw g 3.1 we will see that small impedances (Rs) in power supply lines will cause a volt drop (Vs) which will be subtracted from
the reading, causing an o󰀨set. Furthermore, with LED meters not only do they have a much higher current consumption (causing signicant
o󰀨sets), but each reading results in a di󰀨erent current consumption. If there is a change in current consumption there is a change in the reading
which causes a change in current consumption, etc. A good example would be a DPM 40 reading say 1001. A drop of one count gives 1000,
a di󰀨erence of 4 segments in the least signicant digit. Each segment consumes 8mA. Thus the total change in current is 4 x 8 = 32mA. Under
these conditions it only needs Rs to be 6m Ω to cause a 2 count o󰀨set.

www.lascarelectronics.com Issue 1_10-2016
Page 8 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
3.3 Noise
Electrical noise can be generated from stray electric, magnetic and electromagnetic elds as well as from supply and signal bourne interference.
Although meters have very good line regulation and CMRR, they will be a󰀨ected by excessive amounts of noise. Remember that meter signals
are referred to V+ and any suppression capacitors should be tted between COM and V+. Each case of noise problems will have its own solution.
Below is a list (in order of importance) of possible remedies.
3.3.1. Ground Noise
Check that there are no signal errors due to ground loop impedances. See Section 3.2.
3.3.2. Power Supply
Supplies that are likely to generate noise, such as those with noisy loads or switching converters, need to be suppressed. Decouple the
meter supply at the meter and if necessary place a choke in the positive supply. Remember that electrolytic capacitors can be inductive
and it is better to decouple with solid tantalum capacitors.
3.3.3. Signals
All meters have input lters which reduce noise, however, where the signal leads to the meter are long, use twisted pair wires and place
any attenuator networks at or on the meter. In extreme cases, use screened leads but be careful not to connect the screen to any noisy
signal or power line. Only screen the lead to COM at the meter. Ferrite beads can be very e󰀨ective in reducing noise in signal lines.
3.3.4. Stray Fields
If stray electrical or magnetic elds are suspected of causing noise, physical screening of the meter may be necessary. Other measures
include placing the meter away from cables that are likely to have large and noisy currents in them. Another source of magnetic
interference will be any transformer, especially one operating at high frequency.
Installation Operation - Section A&
3. REFERRING INPUTS TO SUPPLY GROUND
In many applications the meter will need to be powered from the same supply as the circuit under test. There are three pitfalls to be avoided here.
1. Applying excessive common mode voltage (VCM) (see Section 2).
2. Ground loop errors.
3. Noise.
Referring to section 2.1, it will be seen that the negative power supply should be at least 1.5V below the analogue inputs.
We must, therefore, provide a negative supply. All LED instruments provide their own. All S-type LCD meters do likewise. If a suitable negative supply
is not available, one must be provided or a different meter chosen for the application.
If we redraw fig 3.1 we will see that small impedances (Rs) in power supply lines will cause a volt drop (Vs) which will be subtracted from the reading,
causing an offset. Furthermore, with LED meters not only do they have a much higher current consumption (causing significant offsets), but each
reading results in a different current consumption. If there is a change in current consumption there is a change in the reading which causes a change
in current consumption, etc. A good example would be a DPM 40 reading say 1001. A drop of one count gives 1000, a difference of 4 segments in
the least significant digit. Each segment consumes 8mA. Thus the total change in current is4x8=32mA. Under these conditions it only needs Rs to
be 6m to cause a 2 count offset.
Using the application in Fig. 3.3 you will reduce the effects of any supply bourne interference.
3.1 REDUCING/ELIMINATING VCM
3.2 REDUCING GROUND LOOP ERRORS
a. 4½ Digit LED b. LED/S-type LCD c. LCD
Ω
IN LO
IN LO
COM
COM
IN HI
REF LO
REF LO
V-
V-
0V
0V
V IN
V IN
V+
V+
V+
V-
IN HI
IN LO
COM
IN HI
REF LO
V-
V-
V IN
V+
V+
IN LO
COM
IN HI
REF LO
0V
V IN
V+
V-
V+
OUT
CIRCUIT
UNDER
TEST
Rs
Vs
Is
WRONG
IN LO
COM
IN HI
REF LO
V IN
V+
V-
V+
OUT
CIRCUIT
UNDER
TEST
Rs
Is
Is
RIGHT
Fig 3.1 Ideal circuit connections
Fig 3.2 Errors due to supply impedances
Fig 3.3 Eliminating the effect of supply impedances
www.lascarelectronics.com 6
Using the application in Fig. 3.3 you will reduce the e󰀨ects of any supply bourne interference.

www.lascarelectronics.com Issue 1_10-2016
Page 9 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
Installation Operation - Section A&
4. INTERFACING WITH LINEAR AND DIGITAL CIRCUITRY
4.1 LINEAR
As mentioned in Sections 2 and 3, the most important aspect is to ensure that ground voltage levels do not cause problems. For the sake of simplicity,
we shall assume the linear circuit to be an op-amp. A number of linear systems can exist:-
i. Circuit operating from ± supplies, e.g.5-0-5V(LCD).
ii. Circuit operating from a single supply but needing a ground level to be generated in between, e.g. battery operated equipment (LCD).
iii. Circuit operating from a single supply with its output referenced to the negative (GND) supply (LED, S-type LCD).
If the signal to be measured is referred to ground, then IN LO will be connected to ground and IN HI to the signal. However, ensure that IN LO is
connected as close as possible to the ground connection point of the signal.
Advice on referring inputs to ground lines is given in Section 3. Be careful not to exceed the maximum supply voltage; the maximum supply voltage
quoted in data sheets is the maximum voltage between V+ and V-. If the maximum supply voltage is 15V, the maximum split supply is ±7.5V.
If the battery is formed with separate cells it is as well to have a centre-tap in the battery for the ground (0V). However, if you are using a packaged
battery such as the PP3, then other means are needed. The solution is to use either the COM or TEST (DGND) pins on the meter as the ground. The
choice depends on the circuit that must operate with the meter but there are a few considerations:
i. Using COM eliminates all common-mode voltages and because it is approximately 3V below V+, the ground will be well separated from either
supply rail even if the battery voltage drops down to 6V.
ii. TEST (DGND) may be a better choice if running off higher supplies such as 12V vehicle batteries.
iii. COM can sink but not source current. Any load on COM must not pull COM down towards the negative supply.
iv. TEST (DGND) can sink or source up to 1mA and is the ground for the internal meter logic.
v. If a load exceeding the conditions laid out in iii. and iv. above is likely, then the ground needs to be buffered.
Using COM to generate signal ground Using TEST to generate signal ground Buffering the ground.
Many Lascar meters generate their own negative supplies internally.
All LED meters do and so do all S-type LCD meters. These supplies
may be used to power external circuitry. The maximum load depends
on the meter so consult the data sheet.
4.1.1 SPLIT SUPPLY OPERATION
4.1.2. GENERATING A GROUND LEVEL IN BATTERY POWERED EQUIPMENT
Fig. 4.2.a Fig. 4.2.b Fig. 4.2.c
4.1.3. SINGLE ENDED METER OPERATION
IN HI
IN LO
V+
V-
Input
V- (-5V)
V+
I Load
0V
POWER
IN
IN HI
IN LO
V-
V-
V+
V+
Input
IN HI IN HI IN HI
IN LO IN LO IN LO
V-
V- V- V-
V- V-
V+
V+ V+ V+
V+ V+
Input Input Input
COM TEST COM
(TEST)
3V 5V
-
+
Fig 4.1 Split supply operation
Fig.4.3 Using meter negative power output
www.lascarelectronics.com 8
Installation Operation - Section A&
4. INTERFACING WITH LINEAR AND DIGITAL CIRCUITRY
4.1 LINEAR
As mentioned in Sections 2 and 3, the most important aspect is to ensure that ground voltage levels do not cause problems. For the sake of simplicity,
we shall assume the linear circuit to be an op-amp. A number of linear systems can exist:-
i. Circuit operating from ± supplies, e.g.5-0-5V(LCD).
ii. Circuit operating from a single supply but needing a ground level to be generated in between, e.g. battery operated equipment (LCD).
iii. Circuit operating from a single supply with its output referenced to the negative (GND) supply (LED, S-type LCD).
If the signal to be measured is referred to ground, then IN LO will be connected to ground and IN HI to the signal. However, ensure that IN LO is
connected as close as possible to the ground connection point of the signal.
Advice on referring inputs to ground lines is given in Section 3. Be careful not to exceed the maximum supply voltage; the maximum supply voltage
quoted in data sheets is the maximum voltage between V+ and V-. If the maximum supply voltage is 15V, the maximum split supply is ±7.5V.
If the battery is formed with separate cells it is as well to have a centre-tap in the battery for the ground (0V). However, if you are using a packaged
battery such as the PP3, then other means are needed. The solution is to use either the COM or TEST (DGND) pins on the meter as the ground. The
choice depends on the circuit that must operate with the meter but there are a few considerations:
i. Using COM eliminates all common-mode voltages and because it is approximately 3V below V+, the ground will be well separated from either
supply rail even if the battery voltage drops down to 6V.
ii. TEST (DGND) may be a better choice if running off higher supplies such as 12V vehicle batteries.
iii. COM can sink but not source current. Any load on COM must not pull COM down towards the negative supply.
iv. TEST (DGND) can sink or source up to 1mA and is the ground for the internal meter logic.
v. If a load exceeding the conditions laid out in iii. and iv. above is likely, then the ground needs to be buffered.
Using COM to generate signal ground Using TEST to generate signal ground Buffering the ground.
Many Lascar meters generate their own negative supplies internally.
All LED meters do and so do all S-type LCD meters. These supplies
may be used to power external circuitry. The maximum load depends
on the meter so consult the data sheet.
4.1.1 SPLIT SUPPLY OPERATION
4.1.2. GENERATING A GROUND LEVEL IN BATTERY POWERED EQUIPMENT
Fig. 4.2.a Fig. 4.2.b Fig. 4.2.c
4.1.3. SINGLE ENDED METER OPERATION
IN HI
IN LO
V+
V-
Input
V- (-5V)
V+
I Load
0V
POWER
IN
IN HI
IN LO
V-
V-
V+
V+
Input
IN HI IN HI IN HI
IN LO IN LO IN LO
V-
V- V- V-
V- V-
V+
V+ V+ V+
V+ V+
Input Input Input
COM TEST COM
(TEST)
3V 5V
-
+
Fig 4.1 Split supply operation
Fig.4.3 Using meter negative power output
www.lascarelectronics.com 8
4. Interface With Linear and Digital Circuitry
4.1 Linear
As mentioned in Sections 2 and 3, the most important aspect is to ensure that ground voltage levels do not cause problems. For the sake of
simplicity, we shall assume the linear circuit to be an op-amp. A number of linear systems can exist:
Circuit operating from ± supplies, e.g. 5 - 0 - 5V (LCD).Circuit operating from a single supply but needing a ground level to be generated in between,
e.g. battery operated equipment (LCD). Circuit operating from a single supply with its output referenced to the negative (GND) supply (LED, S-type LCD).
4.1.2. Generating a Ground Level in Battery Powered Equipment
If the battery is formed with separate cells it is as well to have a centre-tap in the battery for the ground (0V). However, if you
are using a packaged battery such as the PP3, then other means are needed. The solution is to use either the COM or TEST
(DGND) pins on the meter as the ground. The choice depends on the circuit that must operate with the meter but there are a
few considerations:
i. Using COM eliminates all common-mode voltages and because it is approximately 3V below V+, the ground will be well
separated from either supply rail even if the battery voltage drops down to 6V.
ii. TEST (DGND) may be a better choice if running o󰀨 higher supplies such as 12V vehicle batteries.
iii. COM can sink but not source current. Any load on COM must not pull COM down towards the negative supply.
iv. TEST (DGND) can sink or source up to 1mA and is the ground for the internal meter logic.
v. If a load exceeding the conditions laid out in iii. and iv. above is likely, then the ground needs to be bu󰀨ered.
4.1.1 Split Supply Operation
If the signal to be measured is referred to ground, then IN LO will be connected to ground and IN HI to the signal. However,
ensure that IN LO is connected as close as possible to the ground connection point of the signal.
Advice on referring inputs to ground lines is given in Section 3. Be careful not to exceed the maximum supply voltage; the
maximum supply voltage quoted in data sheets is the maximum voltage between V+ and V-. If the maximum supply voltage
is 15V, the maximum split supply is ±7.5V.

www.lascarelectronics.com Issue 1_10-2016
Page 10 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
Installation Operation - Section A&
4.2.DIGITAL SIGNALS
4.2.1. LED INSTRUMENTS
4.2.1.1. 3½ DIGIT (DPM 343, 40, 56)
4.2.1.2. 4½ DIGIT
4.2.2 LCD INSTRUMENTS
Fig. 4.5
The only digital signal that we shall consider is the clock. The connection is provided for the user to either hold the display (by using a switch to
connect the clock signal to V+ or 0V) or to override the clock and thus re-define the conversion rate.
Note that reducing the conversion rate will lead to excessive integrator swing (see 1.1) and cause gross non-linearity at near full scale inputs. Consult
Lascar for meters with different conversion rates.
All digital inputs and outputs are TTL compatible but remember that fan-out is limited to one standard input. Also ensure that digital signal currents do
not cause interference with analogue circuitry (see 3.2.).
The digital section of all 3½ digit displays operates between V+ and TEST and on 4½ digit displays between V+ and DGND. The meters generate the
ground themselves and it can be between4-6V(TEST) and 4.5 - 5.8V (DGND) below V+. Digital signal inputs and outputs are not TTL compatible
and C-MOS must be used.
It is recommended that wherever possible, all logic is powered from the meter’s digital supplies. If the logic will draw more than 1mA, then the ground
should be buffered (see Fig. 4.4).
Where separate supplies are used, ensure that they are commoned by joining the positive supplies together and that suitable level shifting networks are
used (see Fig. 4.5).
LCD digital signal level shifting
Fig. 4.4 Buffering Digital Ground
V-
V-
V+
V+
DGND
(TEST)
-
+
DIGITAL
GROUND
V+
V+
V- V-
V- V-
V+
V+
DPM DPM
IT 1700'
100k 100k
SS
DD
DGND
Lascar Electronics Limited
Tel: [phone] Fax: [phone]
E-mail: [e-mail]
Lascar Electronics, Inc.
Tel: [phone] Fax: [phone]
E-mail: [email protected]
Lascar Electronics (HK) Limited
Tel: [phone] Fax: [phone]
E-mail: [email protected] 9
Installation Operation - Section A&
4.2.DIGITAL SIGNALS
4.2.1. LED INSTRUMENTS
4.2.1.1. 3½ DIGIT (DPM 343, 40, 56)
4.2.1.2. 4½ DIGIT
4.2.2 LCD INSTRUMENTS
Fig. 4.5
The only digital signal that we shall consider is the clock. The connection is provided for the user to either hold the display (by using a switch to
connect the clock signal to V+ or 0V) or to override the clock and thus re-define the conversion rate.
Note that reducing the conversion rate will lead to excessive integrator swing (see 1.1) and cause gross non-linearity at near full scale inputs. Consult
Lascar for meters with different conversion rates.
All digital inputs and outputs are TTL compatible but remember that fan-out is limited to one standard input. Also ensure that digital signal currents do
not cause interference with analogue circuitry (see 3.2.).
The digital section of all 3½ digit displays operates between V+ and TEST and on 4½ digit displays between V+ and DGND. The meters generate the
ground themselves and it can be between4-6V(TEST) and 4.5 - 5.8V (DGND) below V+. Digital signal inputs and outputs are not TTL compatible
and C-MOS must be used.
It is recommended that wherever possible, all logic is powered from the meter’s digital supplies. If the logic will draw more than 1mA, then the ground
should be buffered (see Fig. 4.4).
Where separate supplies are used, ensure that they are commoned by joining the positive supplies together and that suitable level shifting networks are
used (see Fig. 4.5).
LCD digital signal level shifting
Fig. 4.4 Buffering Digital Ground
V-
V-
V+
V+
DGND
(TEST)
-
+
DIGITAL
GROUND
V+
V+
V- V-
V- V-
V+
V+
DPM DPM
IT 1700'
100k 100k
SS
DD
DGND
Lascar Electronics Limited
Tel: [phone] Fax: [phone]
E-mail: [e-mail]
Lascar Electronics, Inc.
Tel: [phone] Fax: [phone]
E-mail: [email protected]
Lascar Electronics (HK) Limited
Tel: [phone] Fax: [phone]
E-mail: [email protected] 9
4.2. Digital Signals
Where separate supplies are used, ensure that they are commoned by joining the positive supplies together and that suitable level shifting networks
are used (see Fig. 4.5).
4.2.1. LED Instruments
4.2.1.1. 3½ Digit (DPM 40)
The only digital signal that we shall consider is the clock. The connection is provided for the user to either hold the display (by using a
switch to connect the clock signal to V+ or 0V) or to override the clock and thus re-dene the conversion rate.
Note that reducing the conversion rate will lead to excessive integrator swing (see 1.1) and cause gross non-linearity at near full scale
inputs. Consult Lascar for meters with di󰀨erent conversion rates.
4.2.1.2. 4½ Digit
All digital inputs and outputs are TTL compatible but remember that fan-out is limited to one standard input. Also ensure that digital signal
currents do not cause interference with analogue circuitry (see 3.2.).
4.2.2 LCD Instruments
The digital section of all 3½ digit displays operates between V+ and TEST and on 4½ digit displays between V+ and DGND. The meters
generate the ground themselves and it can be between 4 - 6V (TEST) and 4.5 - 5.8V (DGND) below V+. Digital signal inputs and outputs
are not TTL compatible and C-MOS must be used.
It is recommended that wherever possible, all logic is powered from the meter’s digital supplies. If the logic will draw more than 1mA, then
the ground should be bu󰀨ered (see Fig. 4.4).
Installation Operation - Section A&
4. INTERFACING WITH LINEAR AND DIGITAL CIRCUITRY
4.1 LINEAR
As mentioned in Sections 2 and 3, the most important aspect is to ensure that ground voltage levels do not cause problems. For the sake of simplicity,
we shall assume the linear circuit to be an op-amp. A number of linear systems can exist:-
i. Circuit operating from ± supplies, e.g.5-0-5V(LCD).
ii. Circuit operating from a single supply but needing a ground level to be generated in between, e.g. battery operated equipment (LCD).
iii. Circuit operating from a single supply with its output referenced to the negative (GND) supply (LED, S-type LCD).
If the signal to be measured is referred to ground, then IN LO will be connected to ground and IN HI to the signal. However, ensure that IN LO is
connected as close as possible to the ground connection point of the signal.
Advice on referring inputs to ground lines is given in Section 3. Be careful not to exceed the maximum supply voltage; the maximum supply voltage
quoted in data sheets is the maximum voltage between V+ and V-. If the maximum supply voltage is 15V, the maximum split supply is ±7.5V.
If the battery is formed with separate cells it is as well to have a centre-tap in the battery for the ground (0V). However, if you are using a packaged
battery such as the PP3, then other means are needed. The solution is to use either the COM or TEST (DGND) pins on the meter as the ground. The
choice depends on the circuit that must operate with the meter but there are a few considerations:
i. Using COM eliminates all common-mode voltages and because it is approximately 3V below V+, the ground will be well separated from either
supply rail even if the battery voltage drops down to 6V.
ii. TEST (DGND) may be a better choice if running off higher supplies such as 12V vehicle batteries.
iii. COM can sink but not source current. Any load on COM must not pull COM down towards the negative supply.
iv. TEST (DGND) can sink or source up to 1mA and is the ground for the internal meter logic.
v. If a load exceeding the conditions laid out in iii. and iv. above is likely, then the ground needs to be buffered.
Using COM to generate signal ground Using TEST to generate signal ground Buffering the ground.
Many Lascar meters generate their own negative supplies internally.
All LED meters do and so do all S-type LCD meters. These supplies
may be used to power external circuitry. The maximum load depends
on the meter so consult the data sheet.
4.1.1 SPLIT SUPPLY OPERATION
4.1.2. GENERATING A GROUND LEVEL IN BATTERY POWERED EQUIPMENT
Fig. 4.2.a Fig. 4.2.b Fig. 4.2.c
4.1.3. SINGLE ENDED METER OPERATION
IN HI
IN LO
V+
V-
Input
V- (-5V)
V+
I Load
0V
POWER
IN
IN HI
IN LO
V-
V-
V+
V+
Input
IN HI IN HI IN HI
IN LO IN LO IN LO
V-
V- V- V-
V- V-
V+
V+ V+ V+
V+ V+
Input Input Input
COM TEST COM
(TEST)
3V 5V
-
+
Fig 4.1 Split supply operation
Fig.4.3 Using meter negative power output
www.lascarelectronics.com 8
4.1.3. Single Ended Meter Operation
Many Lascar meters generate their own negative supplies
internally. All LED meters do and so do all S-type LCD meters.
These supplies may be used to power external circuitry. The
maximum load depends on the meter so consult the data sheet.

www.lascarelectronics.com Issue 1_10-2016
Page 11 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
Installation Operation - Section A&
5. POWER SUPPLIES
The best power supplies for meters are either batteries or linear regulated mains supplies. Ideally each meter should have its own supply and that
supply should be isolated. Where one supply is operating more than one meter or the meter is powered from the same supply as the circuit under test,
great care is needed to ensure safe and trouble free operation (see sections 6).
All mains powered meters have internal isolated supplies. Lascar manufacture a number of small PCB based supplies which are suitable for powering
meters (PSU 201**, PSU 203, PSU 206 PSU 30105, PSU 30205 and PSU 303).
When using mains power supplies and generally where the circuit being measured has several supply voltages, take care that at power-on and power-
off no harmful conditions exist that may damage the meter. The typical case is when, due to transients, the inputs to the meter are taken beyond the
supply rails to the unit and excessive current flows in the meter signal lines. Use current limiting resistors and/or clamp the inputs to the power supply
lines.
Normally we recommend that if a negative rail is needed for a meter, a meter is used with an inbuilt negative supply (LED and S-type LCD meters). If
you choose one without a negative supply, then use the circuit shown in Fig. 5.2.
Fig. 5.3. gives a suggestion for operating from a single 1.5V cell.
Fig 5.1
Fig. 5.2
Fig. 5.3
Signal input protection
5.1. NEGATIVE RAIL GENERATORS
5.2. OPERATION FROM LOW VOLT SUPPLIES
Negative rail generator
Single cell operation
V-
V+
Add Current
Limiting Resistor
Clamping
Diodes
+5V
0V
COM
10 F
µ
10 Fµ
2
4
8
3
5
7660
V+
IN HI
IN LO
V-
-5V
+
-
VIN
DPM
0V
10 F
µ
10 Fµ
10 Fµ
10 Fµ
2
2
4
4
8
8
33
5
57660
V+
IN HI
IN LO
COM
V-
+
-
VIN
DPM
66
+
-
7660
1.5V
www.lascarelectronics.com 10
Installation Operation - Section A&
5. POWER SUPPLIES
The best power supplies for meters are either batteries or linear regulated mains supplies. Ideally each meter should have its own supply and that
supply should be isolated. Where one supply is operating more than one meter or the meter is powered from the same supply as the circuit under test,
great care is needed to ensure safe and trouble free operation (see sections 6).
All mains powered meters have internal isolated supplies. Lascar manufacture a number of small PCB based supplies which are suitable for powering
meters (PSU 201**, PSU 203, PSU 206 PSU 30105, PSU 30205 and PSU 303).
When using mains power supplies and generally where the circuit being measured has several supply voltages, take care that at power-on and power-
off no harmful conditions exist that may damage the meter. The typical case is when, due to transients, the inputs to the meter are taken beyond the
supply rails to the unit and excessive current flows in the meter signal lines. Use current limiting resistors and/or clamp the inputs to the power supply
lines.
Normally we recommend that if a negative rail is needed for a meter, a meter is used with an inbuilt negative supply (LED and S-type LCD meters). If
you choose one without a negative supply, then use the circuit shown in Fig. 5.2.
Fig. 5.3. gives a suggestion for operating from a single 1.5V cell.
Fig 5.1
Fig. 5.2
Fig. 5.3
Signal input protection
5.1. NEGATIVE RAIL GENERATORS
5.2. OPERATION FROM LOW VOLT SUPPLIES
Negative rail generator
Single cell operation
V-
V+
Add Current
Limiting Resistor
Clamping
Diodes
+5V
0V
COM
10 F
µ
10 Fµ
2
4
8
3
5
7660
V+
IN HI
IN LO
V-
-5V
+
-
VIN
DPM
0V
10 F
µ
10 Fµ
10 Fµ
10 Fµ
2
2
4
4
8
8
33
5
57660
V+
IN HI
IN LO
COM
V-
+
-
VIN
DPM
66
+
-
7660
1.5V
www.lascarelectronics.com 10
Installation Operation - Section A&
5. POWER SUPPLIES
The best power supplies for meters are either batteries or linear regulated mains supplies. Ideally each meter should have its own supply and that
supply should be isolated. Where one supply is operating more than one meter or the meter is powered from the same supply as the circuit under test,
great care is needed to ensure safe and trouble free operation (see sections 6).
All mains powered meters have internal isolated supplies. Lascar manufacture a number of small PCB based supplies which are suitable for powering
meters (PSU 201**, PSU 203, PSU 206 PSU 30105, PSU 30205 and PSU 303).
When using mains power supplies and generally where the circuit being measured has several supply voltages, take care that at power-on and power-
off no harmful conditions exist that may damage the meter. The typical case is when, due to transients, the inputs to the meter are taken beyond the
supply rails to the unit and excessive current flows in the meter signal lines. Use current limiting resistors and/or clamp the inputs to the power supply
lines.
Normally we recommend that if a negative rail is needed for a meter, a meter is used with an inbuilt negative supply (LED and S-type LCD meters). If
you choose one without a negative supply, then use the circuit shown in Fig. 5.2.
Fig. 5.3. gives a suggestion for operating from a single 1.5V cell.
Fig 5.1
Fig. 5.2
Fig. 5.3
Signal input protection
5.1. NEGATIVE RAIL GENERATORS
5.2. OPERATION FROM LOW VOLT SUPPLIES
Negative rail generator
Single cell operation
V-
V+
Add Current
Limiting Resistor
Clamping
Diodes
+5V
0V
COM
10 F
µ
10 Fµ
2
4
8
3
5
7660
V+
IN HI
IN LO
V-
-5V
+
-
VIN
DPM
0V
10 F
µ
10 Fµ
10 Fµ
10 Fµ
2
2
4
4
8
8
33
5
57660
V+
IN HI
IN LO
COM
V-
+
-
VIN
DPM
66
+
-
7660
1.5V
www.lascarelectronics.com 10
5. Power Supplies
The best power supplies for meters are either batteries or linear regulated mains supplies. Ideally each meter should have its own supply and that
supply should be isolated. Where one supply is operating more than one meter or the meter is powered from the same supply as the circuit under
test, great care is needed to ensure safe and trouble free operation (see sections 6).
All mains powered meters have internal isolated supplies. Lascar manufacture a number of small PCB based supplies which are suitable for
powering meters (PSU 201, PSU 203, PSU 206 PSU 30105, PSU 30205 and PSU 303).
When using mains power supplies and generally where the circuit being measured has several supply voltages, take care that at power-on and
power- o󰀨 no harmful conditions exist that may damage the meter. The typical case is when, due to transients, the inputs to the meter are taken
beyond the supply rails to the unit and excessive current ows in the meter signal lines. Use current limiting resistors and/or clamp the inputs to the
power supply lines.
5.1. Negative Rail Generators
Normally we recommend that if a negative rail is needed for a meter, a meter is used with an inbuilt negative supply (LED and S-type LCD meters).
If you choose one without a negative supply, then use the circuit shown in Fig. 5.2.
5.2. Operation From Low Volt Supplies
Fig. 5.3. gives a suggestion for operating from a single 1.5V cell.

www.lascarelectronics.com Issue 1_10-2016
Page 12 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
Installation Operation - Section A&
6. FITTING AN EXTERNAL REFERENCE
Sometimes a different calibration range may be needed or a more precise reference fitted, for example, where the meter does not have a bandgap
reference.
Zener Diode Reference Using a Bandgap Reference.
How not to use common supplies How to use common supplies
Fig. 6.a Fig. 6.b
Fig 7.1 Fig. 7.2
7. PARALLEL OPERATION
8. LCD BACKLIGHTING
Some applications will have more than one meter measuring in a circuit. It is very easy in these circumstances to have erroneous readings or worse.
Fig. 7.1. gives an example of how, even with an isolated supply, it is possible to destroy at least one meter. With shunts in each of the ±24V supplies,
there will be 48V between the meter IN LO inputs. Fig. 7.2. shows a better arrangement. The general rule is don't use the same supply if you cannot
use the same signal ground.
Ensure that when meters with internal references are parallel and COM is used as the ground, (e.g. in battery powered equipment) the references do
not 'fight' each other; the meter with the highest COM - V+ voltage will pull all the other COM voltages lower and only one meter will be accurate. In
these cases, use one meter to define the ground and leave the others with their COM pins unconnected. Check that programming links do not connect
COM to IN LO inside the meter.
Several Lascar LCD displays feature LED backlighting. This is an option on the DPM 1, 2, 3, 100, 125, 500 and standard on the DPM 700 and the 900
series. The DPM 100, 500 and 900 series lamps operate from 5V d.c.. The DPM 700 is supplied with either 5V or 9V backlighting. The 900 series will
take 50mA (nominally) from the supply but can be supplied at up to 90mA from a higher voltage, provided care is taken to limit the current.
PSU PSU
+24V +24V
0V 0V
-24V -24V
METER
SUPPLY
METER
SUPPLY
+
--
--
+
+
+
DPM1
DPM2
48V
LOAD 1
LOAD 1
LOAD 2
LOAD 2
DPM1
DPM2
V+ V+
REF LO
REF LO
COM
REF HI
REF HI
Iz
6.8V
ZENER 1.2V
REF
6.8K
2K
V+ V+
V-
6
RBIAS
18K
1F
µ
RBIAS
Rs1
Rs2
Rs1
Rs2
Lascar Electronics Limited
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Installation Operation - Section A&
6. FITTING AN EXTERNAL REFERENCE
Sometimes a different calibration range may be needed or a more precise reference fitted, for example, where the meter does not have a bandgap
reference.
Zener Diode Reference Using a Bandgap Reference.
How not to use common supplies How to use common supplies
Fig. 6.a Fig. 6.b
Fig 7.1 Fig. 7.2
7. PARALLEL OPERATION
8. LCD BACKLIGHTING
Some applications will have more than one meter measuring in a circuit. It is very easy in these circumstances to have erroneous readings or worse.
Fig. 7.1. gives an example of how, even with an isolated supply, it is possible to destroy at least one meter. With shunts in each of the ±24V supplies,
there will be 48V between the meter IN LO inputs. Fig. 7.2. shows a better arrangement. The general rule is don't use the same supply if you cannot
use the same signal ground.
Ensure that when meters with internal references are parallel and COM is used as the ground, (e.g. in battery powered equipment) the references do
not 'fight' each other; the meter with the highest COM - V+ voltage will pull all the other COM voltages lower and only one meter will be accurate. In
these cases, use one meter to define the ground and leave the others with their COM pins unconnected. Check that programming links do not connect
COM to IN LO inside the meter.
Several Lascar LCD displays feature LED backlighting. This is an option on the DPM 1, 2, 3, 100, 125, 500 and standard on the DPM 700 and the 900
series. The DPM 100, 500 and 900 series lamps operate from 5V d.c.. The DPM 700 is supplied with either 5V or 9V backlighting. The 900 series will
take 50mA (nominally) from the supply but can be supplied at up to 90mA from a higher voltage, provided care is taken to limit the current.
PSU PSU
+24V +24V
0V 0V
-24V -24V
METER
SUPPLY
METER
SUPPLY
+
--
--
+
+
+
DPM1
DPM2
48V
LOAD 1
LOAD 1
LOAD 2
LOAD 2
DPM1
DPM2
V+ V+
REF LO
REF LO
COM
REF HI
REF HI
Iz
6.8V
ZENER 1.2V
REF
6.8K
2K
V+ V+
V-
6
RBIAS
18K
1F
µ
RBIAS
Rs1
Rs2
Rs1
Rs2
Lascar Electronics Limited
Tel: [phone] Fax: [phone]
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E-mail: [email protected] 11
6. Fitting an External Reference
Sometimes a di󰀨erent calibration range may be needed or a more precise reference tted, for example, where the meter does not have a bandgap
reference.
7. Parallel Operation
Some applications will have more than one meter measuring in a circuit. It is very easy in these circumstances to have erroneous readings or
worse. Fig. 7.1. gives an example of how, even with an isolated supply, it is possible to destroy at least one meter. With shunts in each of the ±24V
supplies, there will be 48V between the meter IN LO inputs. Fig. 7.2. shows a better arrangement. The general rule is don’t use the same supply if
you cannot use the same signal ground.
Ensure that when meters with internal references are parallel and COM is used as the ground, (e.g. in battery powered equipment) the references
do not ‘ght’ each other; the meter with the highest COM - V+ voltage will pull all the other COM voltages lower and only one meter will be accurate.
In these cases, use one meter to dene the ground and leave the others with their COM pins unconnected. Check that programming links do not
connect COM to IN LO inside the meter.
8. LCD Backlighting
Several Lascar LCD displays feature LED backlighting you should review the operating mode for the backlight on the data sheet for each display.

www.lascarelectronics.com Issue 1_10-2016
Page 13 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
Installation Operation - Section A&
9. COMMISSIONING THE METER
9.1 HANDLING
9.2 CIRCUIT CONNECTION
9.3 BEZEL FITTING
Lascar meters do not normally need special handling precautions but they do contain CMOS circuitry and static should be avoided. When soldering,
use irons with earthed tips and avoid applying excessive heat to the meter's PCB. The recommended tip diameter should be between 1 and 2mm and
flat, not pointed. Large tips can transfer too much heat to the PCB and thin ones physically damage it whilst being inefficient at bridging solder across
programming links. If it is necessary to transport meters, e.g. via carrier, post, etc. then ensure that the unit is well packed. This is especially important
in the case of LCD panel meters. Keep bezel materials away from the glass and do not use such packaging as 'padded' bags. Firm cardboard boxes
should be used. Padded bags may protect against impact but not against crushing.
It is recommended that all connections to the meter be made with a socket. Meters such as the DPM 200 can have solder connections. Do not solder
to meters which have IC type pins on them. In some cases the meter is supplied with sockets.
Below are illustrations of the various techniques used to mount meters in panel cut-outs.
Always check that the power supply is correct and that the signals will not destroy the meter before connecting the unit. Take care that power-
on transients will not apply destructive voltages to the meter.
Fig. 9.1 Moulded window type fitting
Fig. 9.2 Din case panel fitting - screw type
Fig. 9.3 10 Series modules
Locate the meter by passing it through the front of the
panel cut-out, gently pushing until the rear of the bezel is
flush with the panel (DO NOT PUSH ON THE LCD). The
snap-in lugs will now automatically hold the meter firmly
in position.
1. Turns lugs to fit thick or thin panels.
2. Screw lugs loosely into the bezel.
3. Fit bezel to the panel and turn lugs to grip the rear of
the panel.
4. Fit the meter.
In some cases it may be easier to fit the meter to the bezel
before fitting the assembly to the panel.
This type of housing can be fitted with or without a bezel. To
remove bezel apply pressure to the bottom of the enclosure whilst
lifting the bezel.
To fit the module insert screws into both side clamps. Place the
module through the front of the panel and locate the side clamps
into the groove on either side of the module housing, until they
click into position. Tighten screws whilst holding the module flush
to the panel to ensure a secure fit.
www.lascarelectronics.com 12
9. Commissioning the Meter
9.1 Handling
Lascar meters do not normally need special handling precautions but they do contain CMOS circuitry and static should be avoided. When
soldering, use irons with earthed tips and avoid applying excessive heat to the meter’s PCB. The recommended tip diameter should be between
1 and 2mm and at, not pointed. Large tips can transfer too much heat to the PCB and thin ones physically damage it whilst being ine󰀩cient
at bridging solder across programming links. If it is necessary to transport meters, e.g. via carrier, post, etc. then ensure that the unit is well
packed. This is especially important in the case of LCD panel meters. Keep bezel materials away from the glass and do not use such packaging
as ‘padded’ bags. Firm cardboard boxes should be used. Padded bags may protect against impact but not against crushing.
9.2 Circuit Connection
It is recommended that all connections to the meter be made with a socket. Do not solder to meters which have IC type pins on them. In some
cases the meter is supplied with sockets.
Always check that the power supply is correct and that the signals will not destroy the meter before connecting the unit. Take care that power- on
transients will not apply destructive voltages to the meter.
9.3 Bezel Fitting
Below are illustrations of the various techniques used to mount meters in panel cut-outs.
Installation Operation - Section A&
9. COMMISSIONING THE METER
9.1 HANDLING
9.2 CIRCUIT CONNECTION
9.3 BEZEL FITTING
Lascar meters do not normally need special handling precautions but they do contain CMOS circuitry and static should be avoided. When soldering,
use irons with earthed tips and avoid applying excessive heat to the meter's PCB. The recommended tip diameter should be between 1 and 2mm and
flat, not pointed. Large tips can transfer too much heat to the PCB and thin ones physically damage it whilst being inefficient at bridging solder across
programming links. If it is necessary to transport meters, e.g. via carrier, post, etc. then ensure that the unit is well packed. This is especially important
in the case of LCD panel meters. Keep bezel materials away from the glass and do not use such packaging as 'padded' bags. Firm cardboard boxes
should be used. Padded bags may protect against impact but not against crushing.
It is recommended that all connections to the meter be made with a socket. Meters such as the DPM 200 can have solder connections. Do not solder
to meters which have IC type pins on them. In some cases the meter is supplied with sockets.
Below are illustrations of the various techniques used to mount meters in panel cut-outs.
Always check that the power supply is correct and that the signals will not destroy the meter before connecting the unit. Take care that power-
on transients will not apply destructive voltages to the meter.
Fig. 9.1 Moulded window type fitting
Fig. 9.2 Din case panel fitting - screw type
Fig. 9.3 10 Series modules
Locate the meter by passing it through the front of the
panel cut-out, gently pushing until the rear of the bezel is
flush with the panel (DO NOT PUSH ON THE LCD). The
snap-in lugs will now automatically hold the meter firmly
in position.
1. Turns lugs to fit thick or thin panels.
2. Screw lugs loosely into the bezel.
3. Fit bezel to the panel and turn lugs to grip the rear of
the panel.
4. Fit the meter.
In some cases it may be easier to fit the meter to the bezel
before fitting the assembly to the panel.
This type of housing can be fitted with or without a bezel. To
remove bezel apply pressure to the bottom of the enclosure whilst
lifting the bezel.
To fit the module insert screws into both side clamps. Place the
module through the front of the panel and locate the side clamps
into the groove on either side of the module housing, until they
click into position. Tighten screws whilst holding the module flush
to the panel to ensure a secure fit.
www.lascarelectronics.com 12

www.lascarelectronics.com Issue 1_10-2016
Page 14 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
Installation Operation - Section A&
Fig. 9.6 900 Series modules
Fig. 9.7 Din Cased Series modules
Fig. 9.8 EM Series modules
Locate the meter by passing it through the front panel cut-
out , gently pushing until the rear of the bezel is flush with
the panel. The snap-in lugs will now automatically hold
the meter firmly in position.
Drill a hole in the panel. Fit the module to the front of the
panel, threading the wires through the hole. Add the
washer and nut from the rear, taking care not to
overtighten the nut. Do not trap any of the wires.
Locate the four posts on the rear of the bezel
into the holes in the front of the module.
Place the module into the panel cut-out until
the bezel is flush with the panel. align the
mounting clips at each side of the module and
secure in place with screws provided.
an IP67 / NEMA 4X bezel (BEZ 900-IP)
is available - shown right.
Note:
Fig. 9.5 700 Series modules
Fig. 9.4 100 Series modules
Fit the bezel to the front of the panel and then locate the
meter into the bezel from behind. Alternatively the meter
and bezel may be assembled before fitting into the front of
the panel but care must be taken not to use excessive
force. Finally fit the window into the front of the bezel.
Fit the bezel to the front of the panel, then locate the
meter to the bezel from behind the panel. Using the
screws provided, secure the two plastic spring clips to the
rear of the meter. The meter is designed to fit directly onto
OKW Type M, P and Veronex size 3 enclosures.
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E-mail: [email protected] 13
Installation Operation - Section A&
Fig. 9.6 900 Series modules
Fig. 9.7 Din Cased Series modules
Fig. 9.8 EM Series modules
Locate the meter by passing it through the front panel cut-
out , gently pushing until the rear of the bezel is flush with
the panel. The snap-in lugs will now automatically hold
the meter firmly in position.
Drill a hole in the panel. Fit the module to the front of the
panel, threading the wires through the hole. Add the
washer and nut from the rear, taking care not to
overtighten the nut. Do not trap any of the wires.
Locate the four posts on the rear of the bezel
into the holes in the front of the module.
Place the module into the panel cut-out until
the bezel is flush with the panel. align the
mounting clips at each side of the module and
secure in place with screws provided.
an IP67 / NEMA 4X bezel (BEZ 900-IP)
is available - shown right.
Note:
Fig. 9.5 700 Series modules
Fig. 9.4 100 Series modules
Fit the bezel to the front of the panel and then locate the
meter into the bezel from behind. Alternatively the meter
and bezel may be assembled before fitting into the front of
the panel but care must be taken not to use excessive
force. Finally fit the window into the front of the bezel.
Fit the bezel to the front of the panel, then locate the
meter to the bezel from behind the panel. Using the
screws provided, secure the two plastic spring clips to the
rear of the meter. The meter is designed to fit directly onto
OKW Type M, P and Veronex size 3 enclosures.
Lascar Electronics Limited
Tel: [phone] Fax: [phone]
E-mail: [e-mail]
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E-mail: [email protected] 13

www.lascarelectronics.com Issue 1_10-2016
Page 15 of 22
PANEL INSTRUMENT APPLICATION NOTES
Installation & Operation - Section A
Installation Operation - Section A&
9.4 USING PCB LINKS
Many Lascar meters have programming pads to make circuit configuration quick and easy. Some pads are almost always closed by the customer and in
these cases the pad will have a small PCB link across it. If you need to cut the link, use a sharp scalpel and be careful not to damage adjacent tracks.
The basic technique is to dig the link out rather than slice through it (see Figs. 9.5 and 9.6).
Fig. 9.5 Fig. 9.6How not to cut PCB links How to cut PCB links
Take care not to apply excessive force to fine blades which can break. Wear eye protection.
10. TROUBLESHOOTING
The majority of difficulties stem from application problems. If a meter is suspected of malfunctioning, remove it from the circuit and connect it up on
its own in the 'Floating Supply Mode (see meter data sheet - back page) and apply an isolated signal. If the meter works satisfactorily, check the circuit,
otherwise contact a Lascar Applications Engineer. The most common problem occurs when the meter is subjected to signals outside its common mode
range or where there is a ground supply error (see sections 2 and 3).
The Frequently Asked Questions section of our website contains a more detailed section on trouble-shooting DPMs.Note:
Fig. 9.10 V Series modules
Fig. 9.9 SP Series modules
Slide the seal over the rear of the meter and fit round the
meter rim. Locate the meter by passing it through the front of
the panel cut-out and push until the rear of the bezel is flush
with the panel. Slide the fixing clip over the rear of the
module and press firmly into place.
Fit the module to the bezel and slide the
assembly through the panel. Fit the
retaining clip over the bezel pillars and fix
using push-on fasteners.
www.lascarelectronics.com 14
Installation Operation - Section A&
9.4 USING PCB LINKS
Many Lascar meters have programming pads to make circuit configuration quick and easy. Some pads are almost always closed by the customer and in
these cases the pad will have a small PCB link across it. If you need to cut the link, use a sharp scalpel and be careful not to damage adjacent tracks.
The basic technique is to dig the link out rather than slice through it (see Figs. 9.5 and 9.6).
Fig. 9.5 Fig. 9.6How not to cut PCB links How to cut PCB links
Take care not to apply excessive force to fine blades which can break. Wear eye protection.
10. TROUBLESHOOTING
The majority of difficulties stem from application problems. If a meter is suspected of malfunctioning, remove it from the circuit and connect it up on
its own in the 'Floating Supply Mode (see meter data sheet - back page) and apply an isolated signal. If the meter works satisfactorily, check the circuit,
otherwise contact a Lascar Applications Engineer. The most common problem occurs when the meter is subjected to signals outside its common mode
range or where there is a ground supply error (see sections 2 and 3).
The Frequently Asked Questions section of our website contains a more detailed section on trouble-shooting DPMs.Note:
Fig. 9.10 V Series modules
Fig. 9.9 SP Series modules
Slide the seal over the rear of the meter and fit round the
meter rim. Locate the meter by passing it through the front of
the panel cut-out and push until the rear of the bezel is flush
with the panel. Slide the fixing clip over the rear of the
module and press firmly into place.
Fit the module to the bezel and slide the
assembly through the panel. Fit the
retaining clip over the bezel pillars and fix
using push-on fasteners.
www.lascarelectronics.com 14
Installation Operation - Section A&
9.4 USING PCB LINKS
Many Lascar meters have programming pads to make circuit configuration quick and easy. Some pads are almost always closed by the customer and in
these cases the pad will have a small PCB link across it. If you need to cut the link, use a sharp scalpel and be careful not to damage adjacent tracks.
The basic technique is to dig the link out rather than slice through it (see Figs. 9.5 and 9.6).
Fig. 9.5 Fig. 9.6How not to cut PCB links How to cut PCB links
Take care not to apply excessive force to fine blades which can break. Wear eye protection.
10. TROUBLESHOOTING
The majority of difficulties stem from application problems. If a meter is suspected of malfunctioning, remove it from the circuit and connect it up on
its own in the 'Floating Supply Mode (see meter data sheet - back page) and apply an isolated signal. If the meter works satisfactorily, check the circuit,
otherwise contact a Lascar Applications Engineer. The most common problem occurs when the meter is subjected to signals outside its common mode
range or where there is a ground supply error (see sections 2 and 3).
The Frequently Asked Questions section of our website contains a more detailed section on trouble-shooting DPMs.Note:
Fig. 9.10 V Series modules
Fig. 9.9 SP Series modules
Slide the seal over the rear of the meter and fit round the
meter rim. Locate the meter by passing it through the front of
the panel cut-out and push until the rear of the bezel is flush
with the panel. Slide the fixing clip over the rear of the
module and press firmly into place.
Fit the module to the bezel and slide the
assembly through the panel. Fit the
retaining clip over the bezel pillars and fix
using push-on fasteners.
www.lascarelectronics.com 14
9.4 Using PCB Links
Many Lascar meters have programming pads to make circuit conguration quick and easy. Some pads are almost always closed by the customer
and in these cases the pad will have a small PCB link across it. If you need to cut the link, use a sharp scalpel and be careful not to damage
adjacent tracks. The basic technique is to dig the link out rather than slice through it (see Figs. 9.5 and 9.6).
Take care not to apply excessive force to ne blades which can break. Wear eye protection.
10. Troubleshooting
The majority of di󰀩culties stem from application problems. If a meter is suspected of malfunctioning, remove it from the circuit and connect it up
on its own in the ‘Floating Supply Mode (see meter data sheet - back page) and apply an isolated signal. If the meter works satisfactorily, check
the circuit, otherwise contact a Lascar Applications Engineer. The most common problem occurs when the meter is subjected to signals outside its
common mode range or where there is a ground supply error (see sections 2 and 3).

www.lascarelectronics.com Issue 1_10-2016
Page 16 of 22
Typical Applications - Section B
PANEL INSTRUMENT APPLICATION NOTES
Typical Applications - Section B
1. MEASURING VOLTAGE
Because all meters measure d.c. voltage this is the simplest parameter to measure. The most common interface circuit is a voltage attenuator. Fig. 1.
gives an example of a multi-range attenuator.
200mV Full Scale
9M *Ω
900k*
90k
9k
1k
VIN
2V F.S.
200V F.S.
20V F.S.
2000V F.S.
IN HI
IN LO
* These resistors
must be rated to
withstand high
voltages.
2. MEASURING CURRENT
Although measuring current simply means measuring the voltage across a low value resistor which has been placed in series with the current, there are
some potential pitfalls (see Chapter 1, section 6). The thing to remember is to ensure that the signal to the meter is within its common mode range.
The commonest mistake is to place the shunt in the positive supply with the meter referred to ground. If it is possible, place the shunt in the ground
line, but be careful not to superimpose the meter supply current in the reading. Always use the 'Four Terminal' technique to avoid errors due to
terminal resistance, etc. If it is essential to have the shunt in the positive supply, use an isolated meter supply or the circuit shown in Fig. 2.a.
0V
220nF 470nF
79L05
8
7660
53
2
-5V
-
+
SHUNT
+3.8V IN HI
V+
IN LO
COM
V-
DPM
10 Fµ10 Fµ10 Fµ
OUTPUT
Fig. 1 Multi-range Voltmeter
Fig. 2.a Positive Supply Shunt (LCD only)
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E-mail: [email protected] 15
Typical Applications - Section B
1. MEASURING VOLTAGE
Because all meters measure d.c. voltage this is the simplest parameter to measure. The most common interface circuit is a voltage attenuator. Fig. 1.
gives an example of a multi-range attenuator.
200mV Full Scale
9M *Ω
900k*
90k
9k
1k
VIN
2V F.S.
200V F.S.
20V F.S.
2000V F.S.
IN HI
IN LO
* These resistors
must be rated to
withstand high
voltages.
2. MEASURING CURRENT
Although measuring current simply means measuring the voltage across a low value resistor which has been placed in series with the current, there are
some potential pitfalls (see Chapter 1, section 6). The thing to remember is to ensure that the signal to the meter is within its common mode range.
The commonest mistake is to place the shunt in the positive supply with the meter referred to ground. If it is possible, place the shunt in the ground
line, but be careful not to superimpose the meter supply current in the reading. Always use the 'Four Terminal' technique to avoid errors due to
terminal resistance, etc. If it is essential to have the shunt in the positive supply, use an isolated meter supply or the circuit shown in Fig. 2.a.
0V
220nF 470nF
79L05
8
7660
53
2
-5V
-
+
SHUNT
+3.8V IN HI
V+
IN LO
COM
V-
DPM
10 Fµ10 Fµ10 Fµ
OUTPUT
Fig. 1 Multi-range Voltmeter
Fig. 2.a Positive Supply Shunt (LCD only)
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E-mail: [email protected] 15
1. Measuring Voltage
Because all meters measure d.c. voltage this is the simplest parameter to measure. The most common interface circuit is a voltage attenuator.
Fig. 1. gives an example of a multi-range attenuator.
2. Measuring Current
Although measuring current simply means measuring the voltage across a low value resistor which has been placed in series with the current, there
are some potential pitfalls (see Chapter 1, section 6). The thing to remember is to ensure that the signal to the meter is within its common mode
range.
The commonest mistake is to place the shunt in the positive supply with the meter referred to ground. If it is possible, place the shunt in the ground
line, but be careful not to superimpose the meter supply current in the reading. Always use the ‘Four Terminal’ technique to avoid errors due to
terminal resistance, etc. If it is essential to have the shunt in the positive supply, use an isolated meter supply or the circuit shown in Fig. 2.a.

www.lascarelectronics.com Issue 1_10-2016
Page 17 of 22
Typical Applications - Section B
PANEL INSTRUMENT APPLICATION NOTES
Typical Applications - Section B
Always ensure IN LO is not connected to COM. Fig. 2.b. gives the preferred application for LED and S-type LCD meters.
LED and S-type LCD Current Monitoring
Normal LCD Current Monitoring
Fig. 2.b
Fig. 2.c
220nF 470nF
+5V
-
+
SHUNT
IN HI
V+
IN LO
COM
V- (GND)
“S-TYPE”
DPM
10 Fµ
OUTPUT
78L05
(7805)
220nF
470nF
+5V
-
+
SHUNT
IN HI
V+
IN LO
COM
V-
DPM
10 Fµ
10 Fµ
10 Fµ
OUTPUT
0V
2
4
8
3
5
-5V
7660
78L05
200 A F.S.µ
900Ω
90Ω
9Ω
0.9Ω
0.1Ω
2mA F.S.
200mA
20mA
2A
DPM IN HI
IN LO
I IN
I OUT
Fig. 2.d Multi-range Current Measurement
www.lascarelectronics.com 16
Always ensure IN LO is not connected to COM. Fig. 2.b. gives the preferred application for LED and S-type LCD meters.

www.lascarelectronics.com Issue 1_10-2016
Page 18 of 22
Typical Applications - Section B
PANEL INSTRUMENT APPLICATION NOTES
Typical Applications - Section B
3. MEASURING RESISTANCE
There are two basic methods of measuring the value of a resistor. The first is to pass a known current through it and measure the volt drop. While this
method is accurate, it usually means constructing a constant current generator with a voltage reference and some active elements.
The second is easier, requires few external components and, provided the reference resistor used is accurate, needs no calibration. Known as the
ratiometric method, it uses a known resistor to generate a reference voltage and the unknown resistor to supply the input.
Referring to Chapter 1, section 1.2:-
READING = 1000 x VIN 3½ (1.1)
VREF
Refer to Fig 3.1 and rewriting equation 1.1:-
READING = 1000 x Vu (3.1)
Vs
Now Vs = IL.Rs and Vu = IL.Ru. Substituting in 3.1:-
READING = 1000 x Ru.IL (3.2)
Rs.IL
Thus:-
READING = 1000 x Ru (3.3)
Rs
*R should be chosen to set the value of Vs in the range 50 - 200mV. Tip, if R is to be switched (multi-range or multimeter type application),
then in order to avoid the need to change R as each range is selected, R can be replaced by 3-4 (forward biased) diodes in series. Only use meters
that can have their own reference circuits disconnected and which have access to the Reference inputs.
Below follows a table as a guide to suitable DPMs for this method. Note, whilst not shown in the table, parts where REF LO is hardwired to COMMON
may still be used by re-configuring the R and R divider sequence. For example DPM 116, DPM 443, DPM 443M, DPM 45, DPM
850S, EMV 1125, SP 100 and SP200. Alternatively the DMM 939 is available where resistors etc are already provided on-board.
L STANDARD
LL
STANDARD UNKNOWN
Fig. 3.1 Ratiometric Resistance Measurement
VOLTAGE ACROSS
STANDARD (Vs)
VOLTAGE ACROSS
UNKNOWN (Vu)
V+
V+
REF HI
REF LO
IN HI
IN LO
COMMON
RL*
RSTANDARD
RUNKNOWN
IL
DPM 1
LCD 3½ LED 3½ LCD 4½
DPM 340 DPM 160**
DPM 125 DPM 390 DPM 300**
DPM 1760 DPM 959 DPM 60**
DPM 1763
DPM 2
DPM 200(S)
DPM 2000(S)
DPM 3
DPM 400
DPM 500(S)
DPM 600(S)
DPM 700(S)
DPM 950(S)
OEM 1
Lascar Electronics Limited
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E-mail: [e-mail]
Lascar Electronics, Inc.
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E-mail: [email protected]
Lascar Electronics (HK) Limited
Tel: [phone] Fax: [phone]
E-mail: [email protected] 17
3. Measuring Resistance
There are two basic methods of measuring the value of a resistor. The rst is to pass a known current through it and measure the volt drop. While
this method is accurate, it usually means constructing a constant current generator with a voltage reference and some active elements.
The second is easier, requires few external components and, provided the reference resistor used is accurate, needs no calibration. Known as the
ratiometric method, it uses a known resistor to generate a reference voltage and the unknown resistor to supply the input.
Referring to Chapter 1, section 1.2:-
READING = 1000 x VIN 3½ (1.1)
VREF
Refer to Fig 3.1 and rewriting equation 1.1:-
READING = 1000 x Vu (3.1)
Vs
Now Vs = IL.Rs and Vu = IL.Ru. Substituting in 3.1:-
READING = 1000 x Ru.IL (3.2)
Rs.IL
Thus:-
READING = 1000 x Ru (3.3)
Rs
*RL should be chosen to set the value of Vs in the range 50 - 200mV. Tip, if RSTANDARD is to be switched (multi-range or multimeter type
application), then in order to avoid the need to change RL as each range is selected, RL can be replaced by 3-4 (forward biased) diodes in series.
Only use meters that can have their own reference circuits disconnected and which have access to the Reference inputs.
Below follows a table as a guide to suitable DPMs for this method. Note, whilst not shown in the table, parts where REF LO is hardwired to
COMMON may still be used by re-conguring the RSTANDARD and RUNKNOWN divider sequence. For example DPM 116, DPM 443, DPM 443M,
DPM 45, DPM 850S, EMV 1125, SP 100 and SP200. Alternatively the DMM 939 is available where resistors etc are already provided on-board.

www.lascarelectronics.com Issue 1_10-2016
Page 19 of 22
Typical Applications - Section B
PANEL INSTRUMENT APPLICATION NOTES
Typical Applications - Section B
7.5V - 15V I/P
0V
+5V
470n 220n IN4148
ICl
7660
10µ
10µ
10µ
10µ
10µ
IN4148
82
4
5
3
0V
+IN
-IN
K-TYPE THERMOCOUPLE
INPUT*
*SHORT CIRCUIT
+IN & - IN IF YOU
ARE USING THE
INTERNAL SENSOR
CLOSE FOR
INTERNAL SENSOR 14
1413
7
11
8
9
312
AD595 +10V
1M
10K
+5V
-5V VDD (V+)
VSS (V-)
IN HI
IN LO
COM
DPM
REF -
REF LO
10K
20K
10K
-5V
1M
+5V
ALM I/O
mV/°C I/O
7805
4. THERMOMETER CIRCUITS
The simplest way is to use a Lascar panel mounted temperature meter (DTM 910, DTM 995 or EMT 1900). However it is also possible to use a DPM
with front end circuitry.
For “S-TYPE” meters
Fig. 4.1
Fig. 4.2
Using a Transistor as the Sensor
For “NON S-TYPE” meters
Thermometer using the AD590
V+
V-
REF HI
DPM
REF LO
IN HI
IN LO
COMMON
22kΩ1MΩ220kΩ
100kΩ
100kΩ
1MΩ0.1 F
µ
TEMP. SENSOR
≈
0V
1k
4k3
15k
10µ
1k
+AD590
ICL
8069
9V
PUSH TO
READ
+9V
V+
IN LO
REF LO
IN HI
COMMON
REF-
TEST V-
DPM
≈
0V
2k
15k
1µf
1k
+AD590
ICL
8069
+5V
V+
IN LO
REF LO
IN HI
COM
V- (GND)
“S-TYPE”
DPM
1k
REF HI
2k
4k3
OFFSET
18k7
CAL
PRECISION
RESISTOR
LOW TEMPCO
ICL
8069
ICL
8069
10µ
2k2
10k
Fig. 4.3 Using the AD595
www.lascarelectronics.com 18
Typical Applications - Section B
7.5V - 15V I/P
0V
+5V
470n 220n IN4148
ICl
7660
10µ
10µ
10µ
10µ
10µ
IN4148
82
4
5
3
0V
+IN
-IN
K-TYPE THERMOCOUPLE
INPUT*
*SHORT CIRCUIT
+IN & - IN IF YOU
ARE USING THE
INTERNAL SENSOR
CLOSE FOR
INTERNAL SENSOR 14
1413
7
11
8
9
312
AD595 +10V
1M
10K
+5V
-5V VDD (V+)
VSS (V-)
IN HI
IN LO
COM
DPM
REF -
REF LO
10K
20K
10K
-5V
1M
+5V
ALM I/O
mV/°C I/O
7805
4. THERMOMETER CIRCUITS
The simplest way is to use a Lascar panel mounted temperature meter (DTM 910, DTM 995 or EMT 1900). However it is also possible to use a DPM
with front end circuitry.
For “S-TYPE” meters
Fig. 4.1
Fig. 4.2
Using a Transistor as the Sensor
For “NON S-TYPE” meters
Thermometer using the AD590
V+
V-
REF HI
DPM
REF LO
IN HI
IN LO
COMMON
22kΩ1MΩ220kΩ
100kΩ
100kΩ
1MΩ0.1 F
µ
TEMP. SENSOR
≈
0V
1k
4k3
15k
10µ
1k
+AD590
ICL
8069
9V
PUSH TO
READ
+9V
V+
IN LO
REF LO
IN HI
COMMON
REF-
TEST V-
DPM
≈
0V
2k
15k
1µf
1k
+AD590
ICL
8069
+5V
V+
IN LO
REF LO
IN HI
COM
V- (GND)
“S-TYPE”
DPM
1k
REF HI
2k
4k3
OFFSET
18k7
CAL
PRECISION
RESISTOR
LOW TEMPCO
ICL
8069
ICL
8069
10µ
2k2
10k
Fig. 4.3 Using the AD595
www.lascarelectronics.com 18
Typical Applications - Section B
7.5V - 15V I/P
0V
+5V
470n 220n IN4148
ICl
7660
10µ
10µ
10µ
10µ
10µ
IN4148
82
4
5
3
0V
+IN
-IN
K-TYPE THERMOCOUPLE
INPUT*
*SHORT CIRCUIT
+IN & - IN IF YOU
ARE USING THE
INTERNAL SENSOR
CLOSE FOR
INTERNAL SENSOR 14
1413
7
11
8
9
312
AD595 +10V
1M
10K
+5V
-5V VDD (V+)
VSS (V-)
IN HI
IN LO
COM
DPM
REF -
REF LO
10K
20K
10K
-5V
1M
+5V
ALM I/O
mV/°C I/O
7805
4. THERMOMETER CIRCUITS
The simplest way is to use a Lascar panel mounted temperature meter (DTM 910, DTM 995 or EMT 1900). However it is also possible to use a DPM
with front end circuitry.
For “S-TYPE” meters
Fig. 4.1
Fig. 4.2
Using a Transistor as the Sensor
For “NON S-TYPE” meters
Thermometer using the AD590
V+
V-
REF HI
DPM
REF LO
IN HI
IN LO
COMMON
22kΩ1MΩ220kΩ
100kΩ
100kΩ
1MΩ0.1 F
µ
TEMP. SENSOR
≈
0V
1k
4k3
15k
10µ
1k
+AD590
ICL
8069
9V
PUSH TO
READ
+9V
V+
IN LO
REF LO
IN HI
COMMON
REF-
TEST V-
DPM
≈
0V
2k
15k
1µf
1k
+AD590
ICL
8069
+5V
V+
IN LO
REF LO
IN HI
COM
V- (GND)
“S-TYPE”
DPM
1k
REF HI
2k
4k3
OFFSET
18k7
CAL
PRECISION
RESISTOR
LOW TEMPCO
ICL
8069
ICL
8069
10µ
2k2
10k
Fig. 4.3 Using the AD595
www.lascarelectronics.com 18
4. Thermocouple Circuits
The simplest way is to use a Lascar panel mounted temperature meter (DTM 995 or EMT 1900). However it is also possible to use a DPM with front
end circuitry.

www.lascarelectronics.com Issue 1_10-2016
Page 20 of 22
Typical Applications - Section B
PANEL INSTRUMENT APPLICATION NOTES
5. USING STRAIN GAUGES
The strain gauge circuit is a variation of the resistance circuit as seen in section 3 above. It gives a reading of bridge imbalance as a ratio of the applied
voltage and is thus independent of supply voltage. As with the resistance circuit, ensure you choose a meter with separate input and reference
connections and which can have the meter reference disconnected. Arrange the ratio of R1 to R2 to give approximately 100mV across R2.
Fig. 5 Strain Gauge Application
Some applications need the meter to have an offset (eg. tare). The basic method is to apply the signal between IN HI and COM and apply the offset
between COM and IN LO.
6. GENERATING AN OFFSET
Typical Applications - Section B
REF HI
IN HI
REF LO
DPM
IN LO
V-
V+
V+
R1
R2
R1
V-
V+
I IN
I OUT
6R2
SET
ZERO
220k
5k
IN HI
DPM
IN LO
COM
Fig. 6 4-20mA Reading (200mV FSR meter)
Lascar Electronics Limited
Tel: [phone] Fax: [phone]
E-mail: [e-mail]
Lascar Electronics, Inc.
Tel: [phone] Fax: [phone]
E-mail: [email protected]
Lascar Electronics (HK) Limited
Tel: [phone] Fax: [phone]
E-mail: [email protected] 19
5. USING STRAIN GAUGES
The strain gauge circuit is a variation of the resistance circuit as seen in section 3 above. It gives a reading of bridge imbalance as a ratio of the applied
voltage and is thus independent of supply voltage. As with the resistance circuit, ensure you choose a meter with separate input and reference
connections and which can have the meter reference disconnected. Arrange the ratio of R1 to R2 to give approximately 100mV across R2.
Fig. 5 Strain Gauge Application
Some applications need the meter to have an offset (eg. tare). The basic method is to apply the signal between IN HI and COM and apply the offset
between COM and IN LO.
6. GENERATING AN OFFSET
Typical Applications - Section B
REF HI
IN HI
REF LO
DPM
IN LO
V-
V+
V+
R1
R2
R1
V-
V+
I IN
I OUT
6R2
SET
ZERO
220k
5k
IN HI
DPM
IN LO
COM
Fig. 6 4-20mA Reading (200mV FSR meter)
Lascar Electronics Limited
Tel: [phone] Fax: [phone]
E-mail: [e-mail]
Lascar Electronics, Inc.
Tel: [phone] Fax: [phone]
E-mail: [email protected]
Lascar Electronics (HK) Limited
Tel: [phone] Fax: [phone]
E-mail: [email protected] 19
5. Using Strain Gauges
The strain gauge circuit is a variation of the resistance circuit as seen in section 3 above. It gives a reading of bridge imbalance as a ratio of the
applied voltage and is thus independent of supply voltage. As with the resistance circuit, ensure you choose a meter with separate input and
reference connections and which can have the meter reference disconnected. Arrange the ratio of R1 to R2 to give approximately 100mV across R2.
6. Generating an Offset
Some applications need the meter to have an o󰀨set (eg. tare). The basic method is to apply the signal between IN HI and COM and apply the o󰀨set
between COM and IN LO.