RDP DR7AC User manual

RDP CUSTOMER DOCUMENT
Technical Manual
TRANSDUCER AMPLIFIER
TYPE DR7AC
Doc. Ref CD2402M
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
I N D E X
1. INTRODUCTION................................................................................................ 3
1.1 Certificate of EMC conformity....................................................................... 4
2. INSTALLATION INSTRUCTIONS...................................................................... 5
2.1 EMC Requirements...................................................................................... 5
2.2 Unit Mounting ............................................................................................... 5
2.3 Connections General.................................................................................... 6
2.4 Internal Controls........................................................................................... 6
2.5 Transducer connections (LVDT and half bridge).......................................... 7
3. CONTROLS ....................................................................................................... 8
3.1 Voltage/Current Output................................................................................. 8
3.2 Coarse Gain Selection.................................................................................. 8
3.3 Fine Gain (On front panel, labelled GAIN).................................................... 8
3.4 Coarse Zero.................................................................................................. 8
3.5 Zero Input..................................................................................................... 9
3.6 Fine Zero (On front panel, labelled ZERO)................................................... 9
3.7 Over-Range Indicator................................................................................... 9
3.8 Excitation Voltage......................................................................................... 9
3.9 Excitation Frequency.................................................................................... 9
3.10 Master/Slave................................................................................................. 9
4.0 SETTING UP PROCEDURES.......................................................................... 10
4.1 LVDT & Half Bridge (Differential Inductance) Transducers ........................ 10
5. SPECIFICATION.............................................................................................. 11
6WARRANTY AND SERVICE............................................................................ 12
TABLE OF FIGURES
Fig. 1 Connections.................................................................................................. 6
Fig. 2 Internal Controls........................................................................................... 6
Fig. 3a LVDT transducer connections................................................................... 7
Fig. 3b Half bridge (differential inductance) transducer connections. ................... 7
Fig 4. Excitation Frequency.................................................................................... 9
Fig 5. Master/Slave Connections............................................................................ 9

3
1. INTRODUCTION
The DR7AC is a single channel signal-conditioning unit for use with transducers requiring
AC excitation and synchronous demodulation, producing a DC output voltage or current.
The DR7AC incorporates a DC-DC converter ensuring that the output of the unit is
electrically isolated from the supply.
Units may be master-slaved in systems where carrier frequency beating is a problem.
The unit is housed in a DIN-rail mounting thermoplastic case with recessed screw-clamp
terminals for all connections and 25-turn front-panel-accessible span and zero
adjustments.
All other controls are internal including coarse gain and zero switches, a zero input switch
and jumper links for master/slave setting and excitation frequency setting.
The unit is suitable for use with the complete range of RDP LVDT transducers.

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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. 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 DR7AC end, although grounding
at both ends may reduce the effects of high frequency EMI.
2. When the DR7AC is a small part of a large electrical installation, ensure the cables
to and from the DR7AC are segregated from electrically noisy cables.
3. Ensure cables to and from the DR7AC are routed away from any obviously powerful
sources of electrical noise, e.g. electric motor, relays, solenoids.
4. ESD precautions should be used when working on the instrument with the lid
removed. The user should ensure he is "grounded" by use of an earthed wrist strap
or at least touching earth before touching any component including wires, terminals
or switches.
5. The transducer body should be grounded. Some transducers such as LVDTs, load
cells, etc. without an internal body-to-shield connection, require a separate earth.
This should preferably be connected to the instrument shield terminal or as near
(electrically) as possible to this point.
2.2 Unit Mounting
The DR7AC 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 in an ambient temperature up to
40C. Above this temperature, a gap of 15 mm should be left in between each unit.

6
2.3 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. Output common is internally
connected to Excitation Lo.
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 Lo
4
Signal Hi
5
Screen
6
Master
7
Slave
8
m/s comm
9
Volts Out
10
Common
11
Common
12
Current Out
13
Supply +
14
Supply -
15
Screen
16
N/C
2.4 Internal Controls
To access internal controls the front part of the DR7AC 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.
It will usually only be necessary to make changes to Gain and Zero controls.
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.
Jumper J1
Exc. Freq.
Jumper J3, Exc. Volt.
Jumper J2
Master/Slave
Location for
Bridge
Completion
Resistors
Coarse
Gain
Control
Coarse
Zero Control
& Zero Input
Switch

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Primary Input 1
(Excitation High)
Primary Input 2
(Excitation Low)
Secondary Output 1
(Signal High)
Secondary Output 2
(Signal Low)
PRIMARY
COIL
SECONDARY
COIL
Shield
Excitation High
Shield
Excitation Low
Signal High
2.5 Transducer connections (LVDT and half bridge)
Fig. 3a LVDT transducer connections.
See fig. 1 for pin designations.
Most RDP LVDT transducers also have a BLACK wire. This is not required with the
DR7AC amplifier and should be insulated and left unconnected.
If the above configuration does not give the required output phase (i.e. the output rises
for outward transducer movement instead of falling); reverse signal high and signal low
connections.
Fig. 3b Half bridge (differential inductance) transducer connections.
In addition to these connections, it is necessary to add two bridge completion resistors
to compensate for the fact that the transducer is only half bridge. For RDP transducers,
the resistors should be 1k Ohms, high stability. These should be mounted in R11 and
R12 locations, as shown in Fig. 2.
If when connected, the phase of the amplifier output is not as required (for example, an
inward moving armature causes a rising amplifier output when a falling output is
required) then reversing the excitation high and excitation low wires will correct this.

8
3. CONTROLS
(For locations, see Figure 2)
3.1 Voltage/Current Output
Voltage output is available between pins 9 & 10 (common). Current output is available
between pins 12 and 11 (common). Pins 10 and 11 are internally connected.
3.2 Coarse Gain Selection
Typically, transducer manufacturers' data sheets or calibration certificates will give a figure
allowing the full-scale output to be calculated. Possible formats for this are as follows; the
examples assume a transducer range of ±50mm.
Sensitivity format
Explanation
To convert to F.S. output
mV/V/mm
e.g. 46mV/V/mm
Millivolts of output, per volt of
excitation, per mm of travel
Sensitivity x 1 x range in mm
e.g. 0.046 x 1 x 50 = 2.3V
V/V at full-scale,
e.g. 2.3 V//V
Volt of output, per volt of
excitation, at full-scale
Sensitivity x 1
e.g. 2.3 x 1 = 2.3V
mV/mm at a specified
excitation voltage.
E.g. 230mV/mm at 5V exc.
Millivolts of output, per mm of
travel, given a specified
excitation voltage.
(Sensitivity / specified excitation
voltage) x 1 x range in mm
e.g. (0.230/5) x 1 x 50=2.3V
The standard excitation of the DR7AC is 1V, as used in the calculations above.
The following table shows the band of transducer full-scale output voltages appropriate to
each of the 8 Gain Range Settings. For example, a transducer with a full-scale output of
2.3V would be correctly set as gain range 3.
An 4-way toggle switch, SW1, sets the overall gain in the ranges shown below:
SW1
toggles
ON
Gain
Range
Gain Range
(Approximate)
Recommended Input
For ±5V O/P
For 4-20mA O/P
For ±10V O/P
1
1
X0.07 to 0.25
4V max
4V max
4V max
1+2
2
0.25 to 0.7
4V max
4V max
4V max
1+3
3
0.7 to 2.5
2-4V max
1.7-4V max
4V max
1+4
4
2 to 6
0.8-2.5
0.7-2
1.6-4V max
NONE
5
5 to 20
0.3-1
0.22-0.8
0.6-2
2
6
17 to 50
0.1-0.3
0.07-0.25
0.2-0.6
3
7
50 to 170
0.03-0.1
0.02-0.08
0.06-0.2
4
8
170 to 500
0.01-0.03
-
0.02-0.06
3.3 Fine Gain (On front panel, labelled GAIN)
A screwdriver-adjusted, 25-turn potentiometer providing a 4:1 adjustment of gain,
interpolating between the ranges set by the GAIN RANGE switch.
3.4 Coarse Zero
A 5-way toggle switch, SW2, (toggle 6 –see section 3.5) provides output zero shifts of
about 1V per step (with Fine Gain at minimum –up to 4V at maximum). When used with
FINE ZERO will suppress any output (up to 5V) to zero. All toggles OFF is normal, ie no
suppression applied. Switching toggle 1 ON with toggles 3, 4 or 5 will suppress positive
outputs. Switching toggle 2 ON with toggles 3, 4 or 5 will suppress negative outputs. The
suppression increases when toggles 3, 4 or 5 are switched ON.

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3.5 Zero Input
SW2 toggle 6 which, when switched to ON, zero’s the signal, input voltage to the amplifier
irrespective of transducer position. This enables a true amplifier zero to be realised.
3.6 Fine Zero (On front panel, labelled ZERO)
A screwdriver-adjusted, 25-turn potentiometer allowing adjustment of output zero by ±1V
to ±4V depending on Fine Gain setting. Used with 3.3 will provide up to 100%
suppression.
3.7 Over-Range Indicator
A red lamp that indicates when the demodulator input exceeds the linear range.
3.8 Excitation Voltage
Units are normally supplied with 1V excitation. This can be changed to 3V by changing J3
to B-C.
3.9 Excitation Frequency
Fig 4. Excitation Frequency
3kHz
5kHz (Factory setting)
If necessary, excitation
frequency can be changed
by moving J1 as shown.
Figure 2 shows the location
of J1.
Other excitation frequencies
are available if stated when
ordering.
3.10 Master/Slave
The unit may be configured as a master oscillator or slave oscillator by the setting of J2.
For Master oscillator (Factory Default) link J2 B-C
For Slave units link J2 A-D
Link terminal 6 on the MASTER unit with terminal 7 on the SLAVES and link terminal 8 on
all units as shown below:
Fig 5. Master/Slave Connections
SLAVE (S)
MASTER
5
6
7
8
5
6
7
8
5
6
7
8
5
6
7
8
See Fig 2 for the
location of J2

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4.0 SETTING UP PROCEDURES
4.1 LVDT & Half Bridge (Differential Inductance) Transducers
4.1.1 Determine the transducer full scale output from the manufacturer's data sheet and
set the Coarse Gain control as shown in Sections 3.
4.1.2 Connect the transducer to the 4-way connector as detailed in Section 2. Switch ON
power and allow a 15-minute warm-up period (for maximum accuracy).
4.1.3 Switch on the ZERO INPUT switch (SW2 toggle 6) and adjust the ZERO controls on
the DR7AC for either 0 volts or 12 mA output (depending on which output is being used).
Switch off the ZERO INPUT switch.
4.1.4 Adjust the transducer armature for either 0 volts or 12 mA output from the DR7AC.
The FINE ZERO control may be used to obtain an absolute zero indication if the armature
adjustment is too coarse.
Now proceed with either 4.1.5 or 4.1.6 according to application.
4.1.5 Bipolar Operation (e.g. ±5V or 4-20mA)
(a) Move the transducer armature by a precise amount (e.g. 5mm for a D6/05000
transducer) and adjust the FINE GAIN control for the desired output, e.g. 5V, or 20mA.
(b) Relocate the transducer armature at the centre of the stroke and check that the
output is zero. Re-adjust the FINE ZERO control if necessary.
Repeat (a) and (b) for consistent results.
(c) Move the armature to the full-scale position in the opposite direction and check for
example -5v or 4mA output.
4.1.6 Unipolar Operation (e.g. 0 to 10V)
If it is required that the transducer be used over its entire working range in the one
direction, e.g. 0 to 10mm for a D6/05000 transducer, then the zero controls are used to
"back-off" the signal equivalent to 5mm, then:-
(a) Set up as in 4.1.5, i.e. ±5V output for ±5mm using a D6/05000.
(b) Move the armature by exactly 5mm(for a D6/05000transducer) and then adjust the
ZERO controls to back off this signal to zero. Now move the armature back 10mm
and adjust the FINE GAIN control for the required output.
(c) Repeat (b) until consistent results are obtained. If, for any reason, the coarse gain
is changed, restart the whole procedure.

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5. SPECIFICATION
Supply
9 to 36 V DC 250 mA max (Isolated from output)
Voltage Output
±10V into 2k
Current Output-
4-20mA into 100/550max. Overload internally limited to
30mA max. This is an active output that should not be
connected to any external power supply as this will
damage unit.
Oscillator Output
1V rms. at 5kHz standard. 25mA maximum.
3Vrms and 3 kHz also available.
Oscillator Temperature Coefficient
0.005%/°c typical
Demodulation
Synchronous
Amplifier Gain
X0.07 to x500 in 8 ranges with fine control interpolation
Zero Range
±5V minimum
Linearity
0.05% of full scale
Input Resistance
130k ohm differential
Zero Stability Voltage Output
Current Output
0.002% of FS typical/°C (optimum at ±10V o/p)
0.005% of FS typical/°C
Gain Stability Voltage Output
Current Output
0.005% of FS typical/°C (optimum at ±10V o/p)
0.01% of FS typical /°C
Bandwidth
DC to 250Hz (flat)
Noise -Voltage Output
Current Output
Current Output
5mV RMS
20µA RMS typical
EMC Specification
When subjected to radiated electro-magnetic energy (as
EN61000-4-3) an additional error can occur at certain
frequencies:
Field Strength
Typical Maximum Error
10V/m
1.5%
3V/m
0.1%
Temperature Range
-10°C to +60°C
Dimensions
114.5 x 99 x 22.5 mm
Weight
125 g
Seals
IP20 specification

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6 WARRANTY AND SERVICE
WARRANTY.
R.D.P. Electronics products are warranted against defects in materials or workmanship.
This warranty applies for one year from the date of delivery. We will repair or replace
products that prove to be defective during the warranty period provided they are returned
to R.D.P. Electronics.
This warranty is in lieu of all other warranties, expressed or implied, including the implied
warranty of fitness for a particular purpose to the original purchaser or to any other person.
R.D.P. Electronics shall not be liable for consequential damages of any kind.
If the instrument is to be returned to R.D.P. Electronics for repair under warranty, it is
essential that the type and serial number be quoted, together with full details of any fault.
SERVICE.
We maintain comprehensive after-sales facilities and the instrument can, if necessary be
returned to our factory for servicing.
Equipment returned to us for servicing, other than under warranty, must be accompanied
by an official order as all repairs and investigations are subject to at least the minimum
charge prevailing at the date of return.
The type and serial number of the instrument should always be quoted, together with full
details of any fault and services required.
IMPORTANT NOTES.
1.No service work should be undertaken by the customer while the unit is under warranty
except with the authorisation of RDP Electronics.
2.If the instrument is to be returned to R.D.P. Electronics for repair, (including repair under
warranty) it is essential that it is suitably packed and that carriage is insured and prepaid.
R.D.P. Electronics can accept no liability whatsoever for damage sustained during transit.
3.It is regretted that the above warranty only covers repairs carried out at our factory.
Should the instrument have been incorporated into other equipment that requires our
engineers to perform the repair on site, a charge will be made for the engineer's time to
and from the site, plus any expenses incurred.
The aforementioned provisions do not extend the original warranty period of any product
that has been either repaired or replaced by R.D.P. Electronics.
THIS WARRANTY MAY BE NULL AND VOID SHOULD
THE CUSTOMER FAIL TO MEET OUR TERMS OF PAYMENT.