UniStream® PLC
Unitronics
11
4-wire
Wiring the Temperature Inputs
N
OTE
▪
Each input offers three modes: thermocouple, mV or RTD. You can set each input
independently. The mode is determined both by wiring and by the hardware
configuration within the software application.
In order to ensure that the temperature inputs operate correctly, connect the points RTn+
and RTn- of unused temperature inputs
together. Note that ‘
n
’
designates input number).
Thermocouple and mV
Thermocouple
mV
About Thermocouple Isolation
Although the temperature inputs are isolated from the bus and the controller's power-
supply port, they are neither isolated from each other nor from the analog inputs.
Therefore, temperature inputs isolation may be bypassed when using an exposed-junction
(non-isolated) thermocouple in conjunction with analog inputs or another exposed-junction
thermocouple, which can lead to flow of unwanted currents through the thermocouple
wires that might interfere with thermocouple voltage reading.
In order to maintain temperature inputs isolation when using one or more of the analog
inputs or when using more than one thermocouple, either:
▪
Use isolated-junction thermocouples, or, if you are not using the analog inputs, you may
use up to one exposed-junction thermocouple;
▪
Electrically isolate exposed-junction thermocouples from other electrically-conductive
parts of the system.
