1769-IF8, Status Bit, do you use them?

Ken Moore

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May 2004
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Hi folks,
The 1769-IF8 has a ChannelStatus Bit, do you use it?
From my reading of the manual, this bit is set when the channel has one of many possible "bad" events, over/under, etc...

I was wondering if you use this bit to write a BAD value to your scaled Tag, something like -999, something way out of the normal scaled range.
 
I use it to throw an fault and stop the controlled process.


Depending on how your code is written what happens when the value goes to -999 could be disastrous
 
I don't deal with Compacts very much, but this is a new application and I saw the status bit in the manual when I was researching the RAW counts for scaling. The code can be written to handle the out of range value.
 
Some people use them in an input mapping AOI to clear the value and/or trigger a fault bit.
 
Haven't used a 1769, but it's never a bad idea to create an alarm with such status information. If using the corresponding input for control, it's good practice to consider acting on it to prevent losses.

Often, with continuous processes, I'd put a corresponding PID in manual with last output maintained along with annunciating an alarm. For a sequential or batch process, maybe go to a hold condition.

Many moons ago when I walked into the control room at the start of my day, a night shift operator came across the room, shook my hand, and thanked me for the above PID behavior when an instrument went open-circuit for some reason. A large distillation column would have otherwise been seriously upset and would have taken many hours to restabilize.
 
This card is the same for the CLX: 1756-IF8. I typically have specific faults based on each channel for the process and a single module fault which would aggregate all those bits into a single alarm typically named along the lines of "Main Pannel Chassis 1 Slot 7 Failure".
 

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