[foxboro] Bad I/O vs. high/low alarming

Hi list,

We are undertaking an "alarm management" (well, at this stage, alarm 
elimination) project in one of my plants.  The question of why we need bad 
I/O (BAO) alarming when we have high and low alarms on an AIN block was 
raised.  Most of our bad I/O alarms are due to sensor/transmitter 
failures, which typically either open the loop or drive the signal high, 
so it is a valid question.


So I was trying to think of a situation where one might get a bad I/O 
alarm but not a high or low when both high and low are enabled.  We set 
LASTGV = 0 as a rule (why it defaults to 1 is beyond me), and card 
failures would show up in system management.  Any other scenarios I might 
have overlooked?  What is the general feeling on this topic?


Thanks,

Corey Clingo
BASF Corporation

 
 
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