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ROC800-Series Instruction Manual
4-16
Input/Output Modules
Revised Jul-14
Figure 4-14. Discrete Output Relay Module Field Wiring
4.9 Resistance Temperature Detector (RTD) Input Modules
The Resistance Temperature Detector (RTD) module monitors the
temperature signal from an RTD source. The module can accommodate
input from a two-, three-, or four-wire RTD source.
The active element of an RTD probe is a precision, temperature-
dependent resistor made from a platinum alloy. The resistor has a
predictable positive temperature coefficient, meaning its resistance
increases with temperature. The RTD input module works by supplying
a small consistent current to the RTD probe and measuring the voltage
drop across it. Based on the voltage curve of the RTD, the ROC800
firmware converts the signal to temperature.
The RTD input module monitors the temperature signal from a
resistance temperature detector (RTD) sensor or probe. A two-channel
16-bit RTD module is available. The RTD module isolation includes the
power supply connections.
The RTD modules draw power for the active circuitry from lines on the
backplane.
It may be more convenient to perform calibration before connecting the
field wiring. However, if the field wiring between the ROC800 and the
RTD probe is long enough to add a significant resistance, then perform
calibration in a manner that considers this.
Connecting the RTD
Wiring
Temperature can be input through the Resistance Temperature
Detector (RTD) probe and circuitry. An RTD temperature probe
mounts directly to the piping using a thermowell. Protect RTD wires
either by a metal sheath or by conduit connected to a liquid-tight
conduit fitting. The RTD wires connect to the four screw terminals on
CONTROL
Vs
CONTROL
Vs
EXTERNALLY POWERED
DISCRETE DEVICE
+
-
-
+
SELF- POWERED
DISCRETE DEVICE
-
+
+
-
-
-
-
+
+
+
-
CH 1
CH 2
CH 3
CH 4
CH 5
-
Y
DO
RELA
5 CHAN
DOC0509A
RS
RS
LATCHING RELAY
NOTE: S = SET
R = RESET