RDP DR7DC User manual

RDP Customer Document
Technical Manual
TRANSDUCER AMPLIFIER
TYPE DR7DC
Doc. Ref CD2401L
Affirmed by Declaration
of Conformity
USA & Canada
All other countries
RDP Electrosense Inc.
RDP Electronics Ltd
2216 Pottstown Pike
Pottstown, PA 19465
U.S.A.
Grove Street, Heath Town,
Wolverhampton, WV10 0PY
United Kingdom
Tel [phone]
Fax [phone]
Tel: [phone]
Fax: [phone]
E-mail [email protected]
www.rdpe.com
E-mail: [email protected]
www.rdpe.com

2
INDEX
1.0 INTRODUCTION.....................................................................................................3
1.1 Certificate of EMC conformity..................................................................................4
2.0 INSTALLATION INSTRUCTIONS...........................................................................5
2.1 EMC Requirements.................................................................................................5
2.2 Unit Mounting..........................................................................................................5
3.0 CONNECTIONS......................................................................................................6
3.1 Connections General ..............................................................................................6
3.2 Internal Controls......................................................................................................6
3.3 Transducer connections..........................................................................................7
3.4 Full bridge Strain Gauge Transducer......................................................................7
3.5 1/4 or 1/2 bridge transducer connections................................................................7
3.6 Potentiometric Transducers ....................................................................................7
4.0 CONTROLS............................................................................................................8
4.1 Voltage/Current Output: ..........................................................................................8
4.2 Excitation ................................................................................................................8
4.3 Zero.........................................................................................................................8
4.4 Fine Gain ................................................................................................................8
4.5 Gain Range (X1 to X1250)......................................................................................8
4.6 Shunt Calibration.....................................................................................................8
4.7 Bandwidth/Noise Sliders .........................................................................................8
4.8 4-20mA Offset Jumper Link J1................................................................................9
5.0 SETTING-UP PROCEDURE FOR VOLTAGE OUTPUT ........................................9
6.0 SETTING-UP PROCEDURE, 4-20MA OUTPUT ....................................................9
7.0 SHUNT CALIBRATION FACILITY........................................................................10
8.0 SPECIFICATION...................................................................................................11
9.0 FUNCTIONAL CHECKS .......................................................................................11
10.0 WARRANTY AND SERVICE ................................................................................12
Table of figures
Fig. 1 Connections...........................................................................................................6
Fig. 2 Internal Controls....................................................................................................6

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1.0 INTRODUCTION
The DR7DC is a single channel DC amplifier intended to provide variable excitation and
signal amplification for strain gauge type transducers. It provides up to 10V output (or 4-
20mA) with transducer signals from 10 mV to 10V. This allows operation with some high
output transducers (DCTH, etc); for example, to provide 4-20mA outputs with signal inputs
up to 10V.
This unit accepts both uni-polar (eg 0 to 4mV) or bi-polar (eg 4mV) input signals and can
produce corresponding uni-polar or bi-polar voltage outputs (ie 0 to 10V or 10V).
Sensitivities and gains given in this document refer to both. Current outputs (4 to 20mA)
are uni-polar.
The DR7DC incorporates a DC-DC converter ensuring that the output of the unit is
electrically isolated from the supply.
The unit is housed in a DIN-rail mounting thermoplastics case with recessed screw-clamp
terminals for all connections and 25-turn front-panel-accessible, zero and fine gain
adjustments. There is also a front panel push switch and a facility to connect remotely an
internal shunt calibration resister.
All other controls are internal including excitation coarse gain and switches to filter the
output.

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1.1 Certificate of EMC conformity
DECLARATION OF CONFORMITY
RDP ELECTRONICS LTD.
Grove Street Heath Town
Wolverhampton West Midlands
WV10 0PY
United Kingdom
We declare that the product described in this technical manual is
manufactured by RDP Electronics Limited and performs in conformity
to the following:
The Electromagnetic Compatibility Directive 2014/30/EU
RoHS2 Directive 2011/65/EU
R D Garbett
Director
RDP Electronics Limited

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2.0 INSTALLATION INSTRUCTIONS
2.1 EMC Requirements
For optimum EMC performance use shielded multi-core cables for connection to this
instrument; the cable shield may be terminated by means of a short "pig-tail" and
connected to the terminals marked:
(a) Pin 5 –Transducer cable
(b) Pin 15 –Supply/Output cable
The DIN-rail to which the unit is attached should be earthed.
The screw clamp terminals can accept either solid or stranded wire sizes from 0.2 mm (24
AWG) to 2.5 mm (12 AWG).
NOTES:
1. Cable shields to be grounded at only one end - the DR7DC end, although
grounding at both ends may reduce the effects of high frequency EMI.
2. When the DR7DC is a small part of a large electrical installation, ensure the cables
to and from the DR7DC are segregated from electrically noisy cables.
3. ESD precautions should be used when working on the instrument with the lid
removed. The user should ensure he is "grounded" by use of a grounded wrist
strap or at least touching ground before touching any component, including wires,
terminals or switches.
4. Segregate signal/supply/output cables. Route signal cables away from possible
sources of EMI, e.g. motor/solenoid/relay cables, etc.
5. The transducer body should be grounded. The transducer body being clamped or
bolted to grounded metalwork, e.g. on a machine usually achieves this. Where this
does not apply and also where there is no grounding connection via the connection
cable to the DR7DC, then a separate grounding wire should be connected from the
transducer body to the DR7DC SCN terminal.
2.2 Unit Mounting
The DR7DC housing is a standard DIN rail enclosure which can clip directly to a 35 mm top
hat rail. The units can be mounted side by side if an ambient temperature up to 40C.
Above this temperature, a gap of 15 mm should be left in between each unit.

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3.0 CONNECTIONS
3.1 Connections General
Transducer, supply and output connections are
made by 4 x 4 way screw-clamp terminals as
shown in Fig 1.
To reverse output polarity, reverse signal
hi/signal lo. Voltage output is between Volts
Out and common, current output is between
current out and common.
WARNING: INCORRECT SUPPLY
CONNECTION, E.G.CONNECTING SUPPLY
WIRE TO OUTPUT (O/P) MAY DAMAGE THE
UNIT AND INVALIDATE THE WARRANTY.
Fig. 1 Connections
1
Excitation Hi
2
Excitation Lo
3
Signal Hi
4
Signal Lo
5
Screen
6
R. Cal com
7
R. Cal
8
CAL
9
Volts Out
10
Common
11
Common
12
Current Out
13
Supply +
14
Supply -
15
Screen
16
N/C
3.2 Internal Controls
To access internal controls the front part of the DR7DC case needs to be removed. To do
this, use a small screw driver to gently press in the clips behind terminal 1-4 and 13-16. At
the same time pull forward the front of the case. The front of the case and pcb assembly
should now slide forward.
Fig. 2 Internal Controls
To put case back together, gently slide pcb assembly into case guide slots. Ensure pcb
earth pad CG1 is lined up with the earth clip inside the case, and push back until the front
of the case clicks back into place.
Shunt Calibration Resistor
1-4 Coarse Gain (section 4.5)
5-6 Bandwidth/Noise filter (section 4.7)
Transducer excitation (section 4.2)
4-20mA Offset Link J1 (section 4.8)
Bridge Completion Resistors (section 3.5)

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EXC-
A
B
C
D
EXC+
SIG+
SIG-
EXC+
SIG+
SIG-
EXC-
R24
POTENTIOMETER
3.3 Transducer connections
Before connecting the transducer, check the excitation
voltage.
Applying an excitation voltage that is too high may
destroy the transducer
3.4 Full bridge Strain Gauge Transducer
Transducer connector details are as shown in Fig. 1. (Section 3.1)
3.5 1/4 or 1/2 bridge transducer connections
For 1/4 bridge transducers, 3 bridge completion resistors are required. The active gauge
should be fitted on arm 'C' and the bridge completion resistors in arms D, A & B.
For 1/2 bridge systems, the active gauges should be C and D, and 2 completion resistors
are required.
The bridge completion resistors should be high stability, the same resistance as the active
gauge and may be fitted either in the transducer connector, or in the designated position on
the DR7DC PCB. This requires removal of the PCB from the case.
R22 replaces bridge arm D, R23 replaces bridge arm A, R24 replaces bridge arm B
Note: Mounting these resistors in the instrument is a compromise. To reduce temperature
and long lead effects, completion resistors should preferably be mounted at the
transducer and be of close tolerance and low t.c., e.g. 0.1%, 15 ppm..
3.6 Potentiometric Transducers
Select R24 value to drop at least 1.5V.
For example, with an excitation of say
10V and a potentiometer resistance of
500 ohms and R24 value of 100 Ohms,
the voltage drop across R24 = 10V /
(500+100) X 100 = 1.7V.
This raises terminal 4 to within the
common mode voltage range of the
amplifier.
Input signal = 10-1.7 = 8.3V so use the lowest gain range for ±10V output. For lower output
voltage or 4-20mA output, use lower excitation, e.g. 5V.
R24 can be added either in the location on the PCB, or more easily into the transducer
screw terminals, between pin 4 (sig LO) and pin 2 (EXC LO).

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4.0 CONTROLS
4.1 Voltage/Current Output:
Voltage output is between pins 9 and 10 (common). Current output is between pins
12 and 11 (common). Pins 10 and 11 are internally connected.
4.2 Excitation
allowing continuous variation of excitation between 3v and 10v.
4.3 Zero
allowing a fine adjustment of output zero of approximately ±2V (or 0-10mA)
depending on Fine Gain setting.
4.4 Fine Gain
allowing a 4:1 variation in amplifier gain, used in conjunction with 4.5.
4.5 Gain Range (X1 to X1250)
sliders 1 to 4 of the 6-slider DIL switch, when used with the fine gain control,
provide an output of 5V or 4-20mA with an input signal range of approx. 4mV to 5V
as shown below: (also output ± 5v for input ±4 mV to ±5v).
SLIDERS
ON
INPUT SIGNAL RANGE
Note:
for the two lowest gain
ranges (with slider 4
off), the excitation
voltage must be ≥5V to
provide signals within
the required common
mode voltage range of
the amplifier.
for: 5V or 4-20mA OUTPUT
For ±10V OUTPUT
4 + 3 + 2
4 –16mV
±8 to ±32mV
4 + 3
5 –20mV
±10 to ±40mV
4 + 2
18 –70mV
±35 to ±140mV
4 + 1
65 –270mV
±130 to ±500mV
4
0.25 –1V
±0.5 to ±2V
1
0.34 –1.35V
±0.7 to ±2.7V
None
1.25 –5V
±2.5 to ±10V
4.6 Shunt Calibration
The front panel push-button switch ‘CAL’, when pressed connects an internal 59kΩ
0.1% resistor across one arm of the bridge.
Remote Cal. - an internal relay may be used to remotely connect the 59kΩresistor.
To operate this relay, connect the R-Cal. terminal (pin 7) to R. Cal com (pin 6), (lead
length is irrelevant) via a switch, etc.
If long cables are used, then cable voltage drop may cause significant shunt
calibration errors. In this case, remove SP1 on PCB and connect pin 8 via a
separate wire to the relevant bridge node as near as possible to the transducer.
4.7 Bandwidth/Noise Sliders
slider 5 (filter 1) and slider 6 (filter 2) when
switched to ‘ON’ reduce the units output
bandwidth as shown in the table.
Slider
Bandwidth
5+6 OFF
5 kHz
5 ON
500 Hz
6 ON
20 Hz

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4.8 4-20mA Offset Jumper Link J1
Normally, with J1 set B-D, the relationship between input signal, voltage output and
current output, is zero to full scale input signal 0 to 5V or 4-20mA output.
For bipolar operation, e.g. for compressive/tensile load applications, J1 may be
changed to A-C which makes the relationship ± full scale input signal = ± 2.5V or 4-
20mA O/P.
i.e. J1 provides a ½ F.S. offset for the current output and increases the voltage
head room in the amplifier.
5.0 SETTING-UP PROCEDURE FOR VOLTAGE OUTPUT
Refer also to Section 7 for Shunt Calibration Method.
5.1 Determine the transducer bridge output from the manufacturer's data sheet and
adjust the coarse gain control as shown in Section 4.5. Check that sliders 5 and 6
are set to OFF.
5.2 Connect the monitor and supply as detailed in Sections 2 and 3. With transducer
DISCONNECTED switch ON power. Set excitation voltage, via the EXCIT(ATION)
control, to the value indicated in the transducer data.
Note, excessive excitation voltage or incorrect connection may irreparably damage
the transducer.
Connect transducer and allow a 20-minute warm-up period (for maximum accuracy)
5.3 With zero load (pressure, etc.) applied to the transducer, adjust the ZERO control
for zero output.
5.4 Apply a precise load (pressure, etc.) to the transducer and adjust the F.GAIN
control for the desired output.
5.5 Repeat steps 3 and 4 until repeatable readings are obtained.
5.6 Operate the Cal. switch or Remote Cal. (Sections 4.6 and 7) and note output for
future reference.
6.0 SETTING-UP PROCEDURE, 4-20mA OUTPUT
6.1 Refer to Section 4.8 for bipolar input signal operation.
6.2 Proceed with 5.1 and 5.2 above, then:
6.3 With transducer output approximately zero, adjust the ZERO control for an output
current of 4mA approx.
6.4 Apply a known value to the transducer and adjust FINE GAIN for the desired output
(preferably full scale for 20ma output). Repeat steps 3 & 4 for consistent results.
6.5 Operate the Cal. switch or Remote Cal. (see Section 4.6) and note output for future
reference. Refer to Section 7. Reference may be made to Section 7.2 but note that
full scale of output is 20-4 = 16mA.

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7.0 SHUNT CALIBRATION FACILITY
Refer to Section 4.6 for Operation
This is applicable to resistance bridge transducers only, e.g. most load cells and
pressure transducers (not semi-conductor gauges).
The Shunt Calibration Facility can be used as:-
7.1 A Calibration Check. When the prime calibration has been made by applying a
precise known pressure or load to the transducers as described in Section 5 or 6,
the R-CAL relay can be operated (normally with zero pressure or load applied) and
the output recorded as the Calibration Check figure. A quick check can then be
made at anytime by comparing new CAL outputs with the original.
Note that if the output is not at zero when the CAL switch is operated, the true CAL
CHECK figure is the CAL output plus or minus the initial output.
7.2 A Shunt Calibration. The shunt calibration method can be used to calibrate the
transducer and electronics without having to apply a known pressure or load to the
transducer.
7.2.1 Calculate the shunt calibration figure required from the data given on the transducer
Calibration Record Sheet (CRS).
From CRS - output for 100% = WmV
- output with shunt = YmV
Therefore output required in CAL is Y/W x required full scale output.
Note: If CRS states shunt resistor different from the one fitted (59k ohm is
standard, other values to order) then it may still be possible to obtain a
calibration from:
CAL figure calculated x (R shunt / 59k) = new CAL figure
7.2.2 Set the COARSE GAIN switch for the required input sensitivity (see Section 4.5).
7.2.3 Connect the monitor and supply as detailed in Sections 2 and 3. With transducer
DISCONNECTED switch ON power. Set excitation voltage, via the EXCIT control,
to the value indicated in the transducer data.
Note, excessive excitation voltage or incorrect connection may irreparably damage
the transducer.
Connect transducer and allow a 20-minute warm-up period (for maximum accuracy)
7.2.4 Ensure no load or pressure applied to the transducer.
7.2.5 Operate CAL relay and adjust FINE GAIN control to give the required output as
calculated in 7.21.