RDP Group S7AC User manual

RDP CUSTOMER DOCUMENT
Technical Manual
TRANSDUCER AMPLIFIER
TYPE S7AC
Doc. Ref CD1244G
This manual applies to units of mod status 10 ONWARDS
BS EN ISO 9001
Certificate No. FM13141
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 Connections General.................................................................................... 6
2.3 Typical supply/output connections................................................................ 7
2.4 Transducer connections (LVDT and half bridge).......................................... 8
3. CONTROLS ..................................................................................................... 10
3.1 Voltage/Current Output............................................................................... 10
3.2 Coarse Gain Selection................................................................................ 10
3.3 Fine Gain.................................................................................................... 10
3.4 Coarse Zero................................................................................................ 11
3.5 Zero Input................................................................................................... 11
3.6 Fine Zero.................................................................................................... 11
3.7 Over-Range Indicator................................................................................. 11
3.8 Excitation Frequency.................................................................................. 11
3.9 Master/Slave............................................................................................... 11
4.0 SETTING UP PROCEDURES.......................................................................... 12
4.1 LVDT & Half Bridge (Differential Inductance) Transducers ........................ 12
5. SPECIFICATION.............................................................................................. 14
6WARRANTY AND SERVICE............................................................................ 16
TABLE OF FIGURES
Fig. 1 Control locations........................................................................................... 6
Fig. 2a LVDT transducer connections................................................................... 8
Fig. 2b Half bridge (differential inductance) transducer connections. ................... 8
Fig. 3 Signal Cable Installation for Optimum EMC ................................................. 9
Fig. 4 Maximum Output Voltage vs. Supply Voltage............................................. 13
Fig. 5 Maximum load resistance for 20mA output vs. Supply Voltage.................. 13

3
1. INTRODUCTION
The S7AC is a signal-conditioning unit for use with transducers requiring AC excitation and
synchronous demodulation, producing a DC output voltage or current. Units may be
master-slaved in systems where carrier frequency beating is a problem.
The unit is housed in a robust aluminium case with connections via glands, all sealed to
IP65 specification. All controls are internal with coarse range switches and fine adjustment
potentiometers for gain and zero setting. Other controls include a zero-input switch, over-
range indicator and pins to which resisters can be fitted for half-bridge operation.
The unit is suitable for use with the complete range of RDP LVDT transducers.

4
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

5
2. INSTALLATION INSTRUCTIONS
2.1 EMC Requirements
For full EMC compliance, only shielded multi-core cables should be used 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) SCN - for transducer cable
(b) GND - for supply/output cable
With units to Mod.7 onwards status, with metal glands, for optimum EMC the shields
should be terminated as shown in Fig.2 (b).
The metal case should be grounded. This would usually be achieved by the use of fixing
bolts through the case mounting holes into the (grounded metal) surface the S7AC is
mounted on.
NOTES:
1. Cable shields to be grounded at only one end - the S7AC end, although earthing at
both ends may reduce the effects of high frequency EMI.
2. When the S7AC is a small part of a large electrical installation, ensure the cables to
and from the S7AC are segregated from electrically noisy cables.
3. Ensure cables to and from the S7AC 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.

6
2.2 Connections General
Transducer and supply/output connections are made via two screw-clamped terminal
blocks mounted on the circuit board adjacent to the two cable glands as shown in Fig.1.
To reverse output polarity, reverse Signal Hi/Signal Lo. With all supplies, voltage output is
between OUTPUT and COMMON, which is internally connected to Excitation Lo. For best
results, COMMON should be grounded. NEVER CONNECT COMMON TO V+ OR V-.
Note that when using single supply, the output common is referenced to approximately half
the supply voltage and should be monitored with a floating or differential input instrument
with sufficient common mode voltage range.
Current (4-20mA) output is between OUTPUT and V-.
WARNING: INCORRECT SUPPLY CONNECTION, e.g. CONNECTING SUPPLY WIRE
TO OUTPUT (O/P) MAY DAMAGE THE UNIT AND INVALIDATE THE WARRANTY.
Fig. 1 Control locations
The GND terminal is connected to the case
R39
Master/Slave Links
1
2
3
4
1
2
3
4
5
6
F. ZERO
F. GAIN
RV2
RV1
O/R
LED1
CONN1
CONN2
R38
SW1
SW2
A
B
SP5
SP3
EX HI
EX LO
SIG LO
SIG HI
SCN
A
B
C
C
B
A
SP4
GND
V+
COM
V-
OUT
M/S
R11
R12
ZERO
GAIN
B
A
SP1
Bridge Completion Resistors
Case Ground to Common
Over-range Indicator
V or mA Select

7
GROUND
V+
COM
V-
O/P
M/S
V+ (12 to 36V)
V- (0V)
±2V to ±10V
GROUND
V+
COM
V-
O/P
M/S
V+ (12 to 36V)
V- (0V)
4 to 20 mA
+
-
GROUND
V+
COM
V-
O/P
M/S
V+ (+6 to +18V)
(0V)
±2V to ±10V
V- (-6 to -18V)
GROUND
V+
COM
V-
O/P
M/S
+
-
V+ (+6 to +18V)
(0V)
V- (-6 to -18V)
4 to 20 mA
2.3 Typical supply/output connections
a) Voltage output, single supply (ensure SP1 is NOT linked, see fig. 1)
This arrangement should only be used if (c) is not possible.
If this arrangement is used, either the supply V- or the output common (or both)
must be fully floating. Failure to do this may result in damage to the amplifier that is
not covered by warranty.
b) Current output, single supply (ensure SP1 is NOT linked, see fig. 1)
c) Voltage output, dual supply
d) Current output, dual supply
This arrangement should only be used if (b) is not possible.
If this arrangement is used output common (V-) must be floating with respect to
supply 0V. Failure to do this may result in damage to the amplifier that is not
covered by warranty.
Note 1 In a) and b) the COM (common) terminal floats at 1/2 the supply voltage
Note 2 Ground is connected to the case

8
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
2.4 Transducer connections (LVDT and half bridge)
Fig. 2a LVDT transducer connections.
See fig. 1 (or amplifier PCB) for pin designations.
Most RDP LVDT transducers also have a BLACK wire. This is not required with the
S7AC 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. 2b 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. 1.
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.

9
Cable Cores
Trim
Rubber Seal
Cable Shield Double Back
Over Plastic Sleeve
Plastic Sleeve
Cable
Gland Cap
Plastic Sleeve
Metal Gland
Nut
Wall of
Instrument Case
Fig. 3 Signal Cable Installation for Optimum EMC
1
2
Insert the end of the cable, plus the plastic sleeve into the metal outer shell of the
gland. The bore of the gland is a tight fit onto the cable shield, giving the required
ground contact.
3
Fit gland cap and tighten

10
3. CONTROLS
(For locations, see Figure 1)
3.1 Voltage/Current Output
Solder link SP4 determines which output mode is available at the Output terminal 2 of the
supply/output connector. The unit is normally supplied linked for voltage output, i.e. SP4
A-C. For current output change the link to B-C.
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 S7AC 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
(Note 2)
1
1
X0.07 to x0.25
4V max (Note 1)
4V max (Note 1)
4V max (Note 1)
1+2
2
0.25 to 0.7
4V max (Note 1)
4V max (Note 1)
4V max (Note 1)
1+3
3
0.7 to 2.5
2-4V max (Note 1)
1.7 –4V max
(Note 1)
4V max (Note 1)
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
Note 1: For supply ±10V (or 20V) minimum.
Note 2: Refer to Fig.4 re: supply voltage range.
3.3 Fine Gain
A screwdriver-adjusted, 20-turn potentiometer providing a 4:1 adjustment of gain,
interpolating between the ranges set by the GAIN RANGE switch.

11
V+
COM
V-
OUT
M/S
M/S
M/S
M/S
Slaves
MASTER
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.
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
A screwdriver-adjusted, 20-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 Frequency
Units are normally supplied with 5kHz excitation. Other excitation frequencies are
possible, but must be ordered with instrument.
Note: If the frequency is reduced then output noise (ripple) will increase, e.g. for 2.5kHz,
15mV; and 1kHz, 900mV peak to peak.
3.9 Master/Slave
The module may be configured as a master oscillator or slave oscillator via solder links
SP3 and SP5.
For Master oscillator link SP3 B-C and SP5 A-B.
For Slave units, link SP3 A-C and remove SP5.
Link the M/S terminal of the supply/output connector of all modules as shown below:
Normally, units are supplied as masters with SP3 linked B-C and SP5 linked A-B, although
for a stand-alone unit, SP3 is not essential.
NOTE! If mixing new
(Mod 10 and
onwards) units with
old units, the new
version must always
be the master. New
units will not work as
slaves to old ones. If
in doubt, contact
RDP.

12
4.0 SETTING UP PROCEDURES
4.1 LVDT & Half Bridge (Differential Inductance) Transducers
4.1.1 Determine the transducer output from the manufacturer's data sheet and set the
Coarse Gain control as shown in Sections 3 and 4.
4.1.2 Connect the transducer to the 5-way connector as detailed in Section 2. Switch ON
power and allow a 15-minute warm-up period (for maximum accuracy).
4.1.3 Press the ZERO/INPUT switch and adjust the ZERO controls for zero output as
shown in Section 3. (For 4-20mA outputs, "zero output" = 12mA). Release the switch.
4.1.4 Adjust the transducer armature for zero output (12mA). The FINE ZERO control
may be used to obtain an absolute zero indication if the armature adjustment is too coarse.
Now proceed with either 4.15 or 4.16 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. 0.200 inches for a D5/200
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 0.4 inches for a D5/200 transducer, then the zero controls are used to
"back-off" the signal equivalent to 0.200 inches, then:-
(a) Set up as in 4.1.5, i.e. ±5V output for ±0.2 inches using a D5/200.
(b) Move the armature by exactly 0.200 inches (for a D5/200 transducer) and then
adjust the ZERO controls to back off this signal to zero (or 4mA). Now move the
armature back 0.400 inches 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.

13
Total Supply (V+ to V-) Voltage in Volts
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
2
4
10
6
8
1
3
9
5
7
Output Voltage (Volts)
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
100
200
500
300
400
Maximum Load Resistance (Ohms)
Total Supply (V+ to V-) Voltage in Volts
Fig. 4 Maximum Output Voltage vs. Supply Voltage
Fig. 5 Maximum load resistance for 20mA output vs. Supply Voltage

14
5. SPECIFICATION
Supply
±6 to ±18V dc or 12 to +36V dc at 50mA typical
Voltage Output –dual supply
±4±10V into 2k} Refer to
single supply
±4V to ±10V into 10k} Fig.4
Regulation
0.5mV/V typical
Current Output- both supplies
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.
Regulation
1µA/V typical
Oscillator Output
1V rms. at 5kHz standard. 25mA maximum.
Oscillator Temperature Coefficient
0.005%/°c typical
Demodulation
Synchronous
Amplifier Gain
x.07 to x500 in 8 ranges with fine control interpolation
Zero Range
±5V minimum
Linearity
0.1% 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 500Hz (flat)
Noise -Voltage Output
Current Output
5mV peak to peak typical
10µA peak to peak 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
98 x 64 x 34 mm (3.9 x 2.5 x 1.5 inches)
Weight
260 g (0.57 lb)
Gland Cable Diameter
Seals
3 to 6.5 mm (0.12 to 0.26 inches)
IP65 specification

15
Notes

16
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.