A.2 POWER FOR DO OPERATION
If the 24 V dc supply of the controller is not already fully loaded (24 V dc, 80 mA maximum, net of
internal controller requirements), it can be used as a source of power for a DO; otherwise, a sepa-
rate, external 24 v dc supply must be used. In the upper circuit illustration of Figure A-2, the +24 V
is obtained from TB1 screw lugs 1 or 4 (TB1-1 or TB1-4) of the controller standard rear terminal
board. In the lower circuit illustration of Figure A-2, the dc electromechanical relay is actuated by
an external power source when the power common path is closed by the DO.
Figure A-2. Power For DO Operation
A.3 DO WITH SOLID STATE RELAY
Figure A-3 shows a DO used to control a solid state relay. Power from the controller rear terminal
board 24V dc screw lug TB1-1 or TB1-4 is through a resistor which is added to the circuit to limit
the current flow and to establish the voltage across the relay when the DO switch is open.
Figure A-3. DO with Solid State Relay
Appendix A. Discrete Output DOs
A-2
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