Suppose a level measurement system is “stuck” at one measurement value of approximately 40% even when the process liquid level rises and falls between 20% and 80% of range (as indicated by the sight-glass):
Pneumatic Level Transmitter
Note: Pneumatic level transmitters were obsolete and no more found in industries.
An instrument technician removes the cover from the pneumatic transmitter and momentarily presses the baﬄe against the nozzle. The level indicator in the control room does not respond at all but remains ﬁxed at about 40%.
Identify the likelihood of each possible fault in this list shown in the below table – whether the fault is “probable” (worth considering as a cause of this system’s trouble) or is “unlikely” (either completely ruled out as a cause, or just not worth considering at this point in the diagnosis) – following the results of the technician’s test:
Identify the below list of faults probable or unlikely to occur.
- Plugged isolation valve
- Plugged equalizing valve
- Fill ﬂuid lost in “wet” leg
- Low supply air pressure
- Transmitter restrictor (oriﬁce) clogged
- Indicator pointer stuck
- Transmitter nozzle clogged
- 3-15 PSI signal tubing plugged
- Transmitter out of calibration
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Credits: Tony R. Kuphaldt