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

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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.

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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 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.

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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

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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

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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
2.4 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.

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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

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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.