Watlow Series 945 High/Low Limit Control - Manual (Page 4)

4
WATLOW Series 945 High/Low Limit User's Manual
Input Wiring
Figure 5 -
2 or 3 wire RTD
Input Wiring.
4
5
6
4
5
6
RTD, 2 or 3 Wire
945A - 2 _ _ _ - _ 000
945A - 3 _ _ _ - _ 000
Jumper #5 to #6
for 2 Wire RTD
Figure 4 -
Thermocouple
Input Wiring.
Sensor Installation Guidelines
We suggest you mount the sensor at a location in your process or system
where it reads an average temperature. Choose a point that will adequately
represent the process temperature without being overly reactive.
For thermocouple inputs: Use an isolated or ungrounded thermocouple if an
external 4-20mA output device with a non-isolated circuit common is con-
nected. Extension wire must be of the same alloy as the thermocouple itself to
limit errors.
For RTD Inputs: There could be a +2
°
F input error for every 1
Ω
of lead length
resistance when using a 2 wire RTD. That resistance, when added to the RTD
element resistance, will result in erroneous input to the instrument. To over-
come this problem, use a three wire RTD sensor, which compensates for lead
length resistance. When extension wire is used for a three wire RTD, all wires
must have the same electrical resistance (i.e. same gauge, copper stranded).
For 0-5VDC or 4-20mA process inputs: The rL and rH settings scale the
display to match the measured range of the process signal. For 0-5VDC
process input, the impedance is 100K
Ω
. For 4-20mA process input, the
impedance is 249
Ω
.
Thermocouple Input
+
-
7
9
945A - 1 _ _ _ - _ 000
945A - 2 _ _ _ - _ 000
945A - 3 _ _ _ - _ 000