GE GFK-0787B user manual Recommendations

B

Recommendations

The following recommendations are given to improve the primary safety as described by the list:

'A program in the DCS that checks regularly that no discrepancies exist between the override command signals from the DCS and the override activated signals received by the DCS from the PLC.

'The use of the maintenance override function should be documented on the DCS and on the programming environment if connected. The printout should include:

h time stamp of begin and end.

h ID of the person who is activating the maintenance overrideÐmaintenance engineer or operator (if the information cannot be printed, it should be entered in the work-permit).

h tag name of the signal being overridden.

'The communication packages different from a type-approved MODBUS should include CRC, address check and check of the communication time frame.

'Lost communications should lead to a warning to the operator and maintenance engineer. After loss of communication a time delayed removal of the override should occur after a warning to the operator.

Sensors

hard-wired

switch

PLC

Safeguarding

Application Program

Maintenance Override Handling

(Application Program)

Actuators

Warning to

the Operator

serial line (e.g. Modbus)		serial line
	Distributed	Engineering
	Control System	Workstation
	(DCS)

Version History

	This version 2.2 supersedes the version 2.1 from 24. Jun 1994
GFK-0787B	Appendix B Maintenance Override	B-3