2. INSTALLATION ELECTRICAL
2-15
TWO WIRE RTD LEAD COMPENSATION:
An example of how to add lead compensation to a two wire RTD may be seen in Figure
2-23.
Figure 2-23 2 WIRE RTD LEAD COMPENSATION
The compensation lead L2 would be added and it would compensate for the Hot (L1) and the Return (L3) assuming they are all of equal
length and gauge. To compensate for leads RL1 and RL2 a resistor, Rcomp, equal to the resistance of RL1 or RL2 could be added to
the compensation lead though in many cases this is unnecessary.
GROUNDING OF RTDs:
If it is required to ground one lead of the RTDs, this can be done at either the SR469 or at the motor. Ground-
ing should
not
be done in both places as it could cause a circulating current to flow. Only RTD Return leads may be grounded.
When grounding at the SR469, only one Return lead need be grounded as all are hardwired together internally. No error will be intro-
duced into the RTD reading by grounding in this manner.
If the RTD Return leads are tied together and grounded at the motor, only one RTD Return lead can be run back to the SR469. See
Figure 2-24 for wiring example. Running more than one RTD Return lead back will cause significant errors as two or more parallel paths
for the return current have been created. Use of this wiring scheme will cause errors in readings equivalent to that in the ‘Reduced RTD
Lead Number Application’.
Figure 2-24 RTD ALTERNATE GROUNDING
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