GE GFK-0787B user manual

8

Warning

In certain cases, removing the DC power source from an output block or blocks which are part of a 32-circuit 4-block output group, causes leakage currents through the output driver circuits of the powered down block(s). To ensure that these potential leakage currents do not adversly affect the output devices being controlled, the following installation instructions must be followed.

A.All 4 blocks in an output group must be powered from the same common power source. If redundant power supplies are to be used they should be diode ªoredº power supplies that provide a common power source for the 4 blocks in a group. Different output groups may use different power sources.

B.Power disconnects for the blocks in a group should be wired such that either a single disconnect powers down all 4 blocks simultaneously or each individual block is powered down by its own disconnect. An individual disconnect and/or fuse for each individual block provides the greatest flexibility in replacing a failed block without disturbing the controlled output devices.

C.Ideally the disconnect for a source block (IC660BBD024) should be wired in the DC± supply line and for a sink block (IC660BBD025) in the DC+ supply line.

D.A rectifier diode must be wired in parallel with each output load as shown in the diagram. This diode should have a minimum 1 Amp forward current rating and 75 volt to 100 volt PIV rating. This diode does not affect the ability of the system to do output autotesting of each output if configured to do so.

Caution

When a 32-circuit 4-block output group is wired according to the instructions above and a single block is powered down for maintenance purposes, the following normal procedures should be followed.

HA PLC Force Logon may be required as always when an output block has power restored to it to cause the output block to start accepting data from the PLC(s). It is not required if the current output data the PLC(s) is sending matches the output default states at the block. To execute a PLC Force Logon, turn on the GMR control bit %M12263 (FORCLOG ± Force Block(s) to Log on).

HAn I/O fault reset should executed after restoring power to a block in an ouput group. This is done by turning on the GMR control bit %M12258 (IORES ± Perform I/OFault Table Clear).

8-16	GeniustModular Redundancy Flexible Triple Modular Redundant (TMR) System	GFK-0787B
	User's Manual ± March 1995