The DEGRAD output indicates that a critical class 4 error exists in the system or the auto-shutdown latch has not been cleared. Repair action should be taken in a timely manner whenever critical errors are reported. If the system is degraded, redundancy has been lost and a failure on the remaining functional side of the system will cause a system failure. Whenever the system is degraded, the following actions take place:

1. The DEGRAD output is set to TRUE.

2. Error code SSC 27, EC 20 (FB logic has disabled system switchovers) is reported indicating the switchovers based on error counts are disabled.

3. Error code SSC 30, EC 06 (QUADLOG ACM/CCM Shut Down module outputs) is reported for SD controller if AUTOSD is enabled.

So without getting too deep into this it seems that if the DEGRAD output is TRUE, the RSCALRM bit 10 would also be TRUE, HOWEVER there MAY be scenarios where the opposite could occur, RSCALRM bit 10 might be TRUE but DEGRAD is FALSE.

If you need to know for sure, I would contact Siemens Technical Support, however if it were me I'd follow the recommendations in the QUADLOG Safety Manual and stick to using the TOT_IOSD to trip my shutdown logic: http://support.automation.siemens.com/WW/view/en/23447258

Regards,
RJP