RDP Group S7TW User manual

RDP CUSTOMER DOCUMENT
Technical Manual
TRANSDUCER AMPLIFIER
TYPE S7TW
Doc. Ref CD1210Z
This manual applies to units of mod status 13 ONWARDS
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
2. INSTALLATION INSTRUCTIONS ..............................................................................5
2.1 EMC Requirements...............................................................................................5
2.2 Supply/Output Connections...................................................................................5
2.3 Transducer Connections.......................................................................................6
2.4 TM202 on RDP transducers..................................................................................7
3. CONTROLS................................................................................................................8
3.1 Coarse Zero Switch...............................................................................................8
3.2 Fine Zero Potentiometer .......................................................................................8
3.3Zero Input Switch..................................................................................................8
3.4 Span Switch (Coarse gain) ...................................................................................8
3.5 Fine Span Potentiometer ......................................................................................9
3.6 Filter Switch...........................................................................................................9
4. SETTING UP PROCEDURE. ...................................................................................10
4.1 Bipolar or Half-stroke Applications......................................................................10
4.2 Offset Stroke Applications...................................................................................10
5. SPECIFICATION......................................................................................................11
6. WARRANTY AND SERVICE....................................................................................12
Index of Figures
Fig. 1 General view of S7TW.........................................................................................5
Fig. 2 Connection for LVDT Transducers......................................................................6
Fig. 3 Connection Schematic.........................................................................................6
Fig. 4 Signal Cable Installation for Optimum EMC ........................................................7

3
1. INTRODUCTION
The S7TW is a two-wire, 4-20mA-output oscillator/demodulator for use with LVDT
transducers having suitable primary impedance. (Refer to sect 5).
Coarse and Fine controls for gain and zero (4mA) allow use with the full range of RDP
transducers and a filter switch allows selection of optimum bandwidth/noise. The
differential signal amplifier circuit allows the use of long transducer cables.
The two-wire supply/output system allows use with long cables from the supply/monitor
with a wide range of supply voltage and high noise immunity.
In order to meet the primary impedance requirements of the S7TW, some RDP
transducers are modified to TM202. Section 2.4 refers.
Note: The S7TW is not suitable for use with differential or half-bridge 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
The RoHS Directive 2011/65/EU
R D Garbett
Director
RDP Electronics Limited

5
2. INSTALLATION INSTRUCTIONS
2.1 EMC Requirements
For EMC compliance, good quality shielded cable should be used for connection to
this instrument. The shields of both transducer and 4-20mA loop cables should
be connected as shown in Fig. 4.
Note 1
Cable shields to be grounded at only one end - the instrument end.
Note 2
When the instrument is a small part of a large electrical installation,
ensure the cables to and from the instrument are segregated from
electrically noisy cables.
Note 3
Ensure cables to and from the instrument are routed away from
any obviously powerful sources of electrical noise, e.g. electric
motors, relays, solenoids.
Note 4
ESD precautions should be used when working on the instrument
circuit board with the lid removed. The user should ensure he is
"grounded" by use of a wrist strap or at least touching ground
before touching any component including wires, terminals or
switches.
Note 5
The body of the transducer and the S7TW case should be
grounded. If the transducer fixing attachments to not provide a
good ground, then a ground strap should be used.
2.2 Supply/Output Connections
The two wires from the supply/output monitor are connected to terminals 6 and 7.
Polarity of supply is irrelevant as a reverse polarity protection circuit automatically
energises the oscillator/demodulator with the correct polarity.
Fig. 1 General view of S7TW
SPAN
I
F
ZERO
1
2
3
4
5
6
7
EXCIT
SIGNAL
4-20mA
LVDT AMPLIFIER S7TW
TB1
Filter 8
Zero Input 7

6
2.3 Transducer Connections
Fig. 2 Connection for LVDT Transducers
Function
TB1 PIN
Excitation Hi
Excit 1
Excitation Lo
Excit 2
Signal Hi
Signal 3
Signal Lo
Signal 4
Shield
Gland shell
(see Fig. 4)
Some RDP LVDTs have a
BLACK wire. This must be
insulated.
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 signal high and signal low wires will correct this.
Fig. 3 Connection Schematic
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
Gland
Gland
S7TW Case
Terminal
s
Transducer
Connections
TB
1
0V
1
2
3
4
6
5
7
Supply / Output
V+
V-
(Optional)
AMPLIFIER PCB

7
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. 4 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
2.4 TM202 on RDP transducers.
Some RDP transducers as standard have input impedance that is too low for use with the
S7TW. To correct this, a modification is available (TM202) for these transducers. The
modification code will be indicated on the transducer BUT if more than one modification is
applied to the transducer, the code may not be TM202. In this case, contact the factory.
List of RDP transducers requiring TM202.
D5/25, D5/25H, D5/25K, D525HK
D5/2000, ACT2000, ACW2000 (with any armature configuration)
D5/4000, ACT4000, ACW4000 (with any armature configuration)
D5/15000, ACT15000, ACW15000 with any armature configuration)
D5/18500, ACT18500, ACW18500 (with any armature configuration)

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3. CONTROLS
Please refer also to Fig. 1 for locations. The locations of all controls are also shown
on the legend plate mounted on the PCB.
3.1 Coarse Zero Switch
The toggles or levers 1 to 6 of an 8-way DIL switch are used to inject varying
amounts of offset into the output signal circuit. This, together with the Fine Zero
Potentiometer, allows aligning the 4mA output point to coincide with any desired
armature position. For example, an ACT1000 can be made to give a 4-20mA
output with a stroke of -0.5in. to +1in., etc.
The amount of offset for each lever setting is shown below:
Lever On
mA Output Shift (approx.)
1
-7
2
-5
3
-3
4
-2
5
+2
6
+3
3.2 Fine Zero Potentiometer
This control is used together with the coarse zero switch to set the 4mA output
level. Refer also to Section 3.1. Avoid applying excessive tightening force to the
locking nut.
3.3 Zero Input Switch
Toggle/lever 7 of the Zero Switch, when set to ON, zeroes the amplifier input signal
irrespective of the transducer position. This simulates the transducer mid-stroke
(zero output) signal and may be used to set the mid-range output level (e.g. 12mA)
or transducer mid-stroke position without disconnecting the transducer secondary.
3.4 Span Switch (Coarse gain)
This is an 8-toggle/lever DIL switch which, when used with the Fine Span control,
allows a 4-20mA output to be obtained with a wide range of transducer signals.
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.

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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 0.5 x range in mm
e.g. 0.046 x 0.5 x 50 = 1.15V
V/V at full-scale,
e.g. 2.3 V//V
Volt of output, per volt of
excitation, at full-scale
Sensitivity x 0.5
e.g. 2.3 x 0.5 = 1.15V
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 0.5 x
range in mm
e.g. (0.230/5) x 0.5 x 50=1.15V
The standard excitation of the S7TW is 0.5V for mod 6 onward, 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 1.15V would be correctly set as gain range 2.
The table below shows the V r.m.s. signals required for full
output with the Fine Span either at minimum or maximum:
Lever On
2 to 4
1
1 –2
2
0.7 –1
3
0.4 –0.7
None
0.25 –0.44
4
0.15 –0.25
5
0.1 –0.15
6
0.05 –1
7
0.03 –0.05
8
3.5 Fine Span Potentiometer
This control interpolates between the ranges of the Span switch. (Section 3.4).
Avoid applying excessive tightening force to the locking nut.
3.6 Filter Switch
Toggle/lever 8 of the "zero" DIL switch is used to select the bandwidth/noise
performance as shown in the specification:

10
4. SETTING UP PROCEDURE.
4.1 Bipolar or Half-stroke Applications
1. Connect the transducer and supply as shown in Section 2.
2. Select the relevant gain range by setting the Coarse Span switch as shown
in Section 3.4. Refer also to the transducer data to determine the input
signal.
3. Set Zero Input lever to ON, all other Zero levers to OFF.
4. Adjust Fine Zero potentiometer for 12mA output.
5. Reset Zero Input lever to OFF and adjust the transducer armature for 12mA
output. This determines the transducer centre stroke position.
6. Move the armature to the required full-scale position and adjust Fine Span
for 20mA output. (Note: primary or secondary connections may be reversed
to reverse the output polarity.)
7. Move the armature to the required zero position (an equal but opposite
displacement to that in step 6) and check the output is 4mA. Trim Fine Span
and zero if necessary for optimum linearity over the 4-20mA range.
4.2 Offset Stroke Applications
1. Carry out steps 1 to 5 in Section 4.1, then: -
2. Move the armature to the desired half-stroke position and use the Coarse
Zero switch to suppress the output to near 12mA (refer to Section 3.1). Trim
for exactly 12mA via Fine Zero.
3. Move the armature to the desired full-scale position and adjust Fine Span for
20mA output.
4. Repeat steps 2 and 3 for consistent results.
5. Move the armature to the desired 4mA position and check for 4mA output.