Output Relays - GE 469 Instruction Manual

3.2.10 Output Relays

3–22
469
Hot
Compensation
RTD Return
FIGURE 3–24: 2-Wire RTD Lead Compensation
The compensation lead L2 is added to compensate for Hot (L1) and Return (L3), assuming
they are all of equal length and gauge. To compensate for leads RL1 and RL2, a resistor
equal to the resistance of RL1 or RL2 could be added to the compensation lead, though in
many cases this is unnecessary.
RTD Grounding
Grounding of one lead of the RTDs is done at either the 469 or at the motor. Grounding
should not be done in both places as it could cause a circulating current. Only RTD Return
leads may be grounded. When grounding at the 469, only one Return lead need be
grounded as they are hard-wired together internally. No error is introduced 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 469. See the figure below for a wiring example. Running more
than one RTD Return lead to the 469 causes significant errors as two or more parallel
paths for the return current have been created. Use of this wiring scheme causes errors in
readings equivalent to that in the Reduced RTD Lead Number application described earlier.
469
Hot
Compensation
RTD Return
Compensation
Hot
Hot
Compensation
RTD Return
There are six (6) Form-C output relays (see Specifications on page 2–6 for details). Five of
the six relays are always non-failsafe; 6 SERVICE is always failsafe. As failsafe, the
6 SERVICE relay is normally energized and de-energizes when called upon to operate. It
also de-energizes when 469 control power is lost and will be in its operated state. All other
Motor Control
Terminal Box
L1
A1
Rcomp
L2
A2
L3
A3
Motor Control
Terminal Box
L1
A1
L2
A2
L3
A3
L4
A4
L5
A5
L6
A6
L7
A7
A8
No connection
FIGURE 3–25: RTD Alternate Grounding
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 3: INSTALLATION
Motor
RL1
+
RTD1
RL2
–
808719A1.CDR
Motor
+
RTD1
–
J1
–
RTD2
+
J2
+
RTD3
–
808720A2.CDR