Watlow 942 Series - Chapter 2; Input Wiring

9
Install and Wire, Chapter 2 WATLOW Series 942 User's Manual
Input Wiring
Figure 9 -
2 or 3 wire RTD
Input Wiring.
Figure 8 -
Thermocouple
Input Wiring.
Long lead lengths create electrical resistance. There will be approximately +2°C input error
for every 1Ω of lead length resistance, when using a two wire RTD. The resistance, when
added to the resistance of the RTD element, will result in erroneous input to the instrument.
To overcome 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 three extension wires
must have the same electrical resistance. (i.e. same gauge, copper stranded).
RTD, 2 or 3 Wire
Model # 942A -
2 _ _ _ - _ 000 942A - 3 _ _ _ - _ 000
Thermocouple Input
Model # 942A -
1 _ _ _ - _ 000 942A - 3 _ _ _ - _ 000
942A -
2 _ _ _ - _ 000 942A - 4 _ _ _ - _ 000
+
-
7
9
You must use an isolated or ungrounded thermocouple, if an external device with a non-
isolated circuit common is connected to the 4-20mA or 0 - 5VDC output.
Extension wire for thermocouples must be of the same alloy as the thermocouple itself to
limit errors.
4
5
6
4
5
6
Jumper #5 to #6
for 2-Wire RTD