We do have a problem in the company that is one PT connected to PlC which is mean 1 out of 1 in PLC system we do have the PAHH is 55 mbar and PALL 8 mbar with a timer of 15 sec for the PAHH the problem started when PAHH goes more than the set point which is 55 it reached up to 71 but due to timer doesn't trip . We force it and we checked everything nothing there . We replaced the transmitter problem still there the reading goes more than the 55 bar the range for transmitte is 0- 60 mbar . So we did loop check , aculaizing valve , wiring all are okay . What the possible causes for this ???
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Answer Posted / carl ellis
Although the post has lots of information, it isn't clear
exactly what the problem is.
I think the problem is that the PLC does not alarm when the
pressure exceeds (goes above) 55mbar. But I'm not sure.
Given this description: when PAHH (pressure alarm High High)
goes more than the set point which is 55 it reached up to 71
but due to timer doesn't trip . We force it and we checked
everything nothing there, let's suppose that the PLC is not
indicating an alarm state.
a) what should the PLC do at the alarm condition?
b) How is an alarm indicated? A digital output (DO) goes
high? A lamp is driven by a DO lights up?
c) What exactly does not work as it should?
If the PLC does not indicate an alarm, yet the indicated
pressure goes higher than a high alarm, the problem is NOT
the field transmitter, the problem is in the alarm setup or
alarm annunciation.
Troubleshooting depends on
- an explanation of exactly what should be happening
- an explanation of how you know it is not working; that is,
what the evidence is that it is not working.
Yes, the pressure went above 55mbar.
How do you know that?
The transmitter's local display?
A milliampmeter in the analog input circuit?
Did the alarm ever work? Or is this a new commissioning and
you're trying to get the alarm to work?
Carl Ellis
Measure First
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