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Potentiometer Input Modules
FEATURES
● INTERFACES TO POTENTIOMETERS UP TO 10,000 OHMS
● HIGH LEVEL VOLTAGE OUTPUTS
● 1500 VOLT TRANSFORMER ISOLATION
● ANSI/IEEE C37.90.1-1989 TRANSIENT PROTECTION
● INPUT PROTECTED TO 240VAC CONTINUOUS
● 160dB CMR
● 95dB NMR AT 60HZ, 90dB AT 50HZ
● MIX AND MATCH OM5 TYPES ON BACKPANEL
● CSA CERTIFIED, FM APPROVED, CE COMPLIANT
3-Wire
Potentiometer
+EXC
4
4
+In
3
3
–In
2
2
2-Wire
Slidewire
–EXC
1
Backpanel
Term Block
FIGURE 1. OM5-PT Block Diagram.
OM5-PT
4
LPF
Surge
6
Suppression
and
5
Protection
3
NC
1
–V
–V
NC
2
+V
Isolated
–V
Field-Side
Power
14
DESCRIPTION
Each OM5-PT Potentiometer input module provides a single channel of
potentiometer input which is filtered, isolated, amplified, and converted to a
high level analog voltage output (Figure 1). This voltage output is logic
switch controlled, which allows these modules to share a common analog
bus without the requirement of external multiplexers.
The OM5 modules are designed with a completely isolated computer side
circuit which can be floated to 50V from Power Common, pin 16. This
complete isolation means that no connection is required between I/O
Common and Power Common for proper operation of the output switch. If
desired, the output switch can be turned on continuously by simply
connecting pin 22, the Read-Enable pin to I/O Common, pin 19.
Excitation for the potentiometer is provided from the module by two matched
current sources. When using a three-wire potentiometer, this method allows
cancellation of the effects of lead resistances. The excitation currents are very
small (less than 1.0mA) which minimizes self-heating of the potentiometer.
Signal filtering is accomplished with a six-pole filter which provides 95dB of
normal-mode-rejection at 60Hz and 90dB at 50Hz. Two poles of this filter are
on the field side of the isolation barrier, and the other four are in the output
stage. After the initial field-side filtering, the input signal is chopped by a
proprietary chopper circuit. Isolation is provided by transformer coupling,
again using a proprietary technique to suppress transmission of common
mode spikes or surges. The module is powered from +5VDC, 5%.
A special input circuit provides protection against accidental connection of
power-line voltages up to 240VAC.
Isochopper™
LPF
Amplifier
Pat Pending
+V
–V
Isolated
Computer-Side
Power
Power
Oscillator
20
V
OUT
19
I/O Common
22
RD EN\
17
+5V
16
Power Common
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