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

If you set BADOPT=3 it means you want to get an I/O BAD alarm when a HIGH or 
LOW Out of Range Alarm is raised.
This is normally used if you think that  it is not distinguishable when 
input signal is out of range and when it is BAD.
However, you can set the BADOPT option to a suitable value as per your 
desired BAD alarm strategy.

LASTGV is default to 1 because it holds the last good value of the input 
signal when it goes to BAD. This setting is very useful because it prevents 
the control loop from being disturbed.
If you are using input types other than FoxCom the individual input signal 
BAD will not be registered in SMDH. In this case the individual I/O failure 
will not cause an FBM failure alarm.

Rgds,
Ali Ahmed Zahidi
Pakistan Refinery Ltd.
Karachi, Pakistan.



----- Original Message ----- 
From: "Corey R Clingo" <corey.clingo@xxxxxxxx>
To: <foxboro@xxxxxxxxxxxxx>
Sent: Monday, June 12, 2006 7:16 PM
Subject: [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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