what is your solution of non-calibrated important pressure switches which can caused trip?

there are three DP switches that cause trip of unit but operators can not calibrated them periodically, so they can cause trip. do you face this problem? what is your solution?

 

You have to be joking I cannot think of a process plant in the World that would suffer trips due to something as basic as a Pressure switch. From the fact that you cannot calibrate them I take it they must be sealed? Either get a type that can be calibrated or if it's that important get a high quality Pressure Transmitter(s) and configure signal into your control equipment.

 

With this information the only thing I can suggest you is to install transmitter and control the trip setpoint from the PLC or DCS

Regards,
JJRU

 

First of all, why can't they be calibrated on a periodic basis? What prevents their calibration? Access? Instrumentation? Knowledge or experience? Isn't this the real problem: The fact that they are "critical" to the process and can trip the process or machine should make them high-priority for periodic calibration.

And calibration is really a misnomer, as when devices and instruments are "calibrated" during maintenance outages or on some other periodic basis, they are really just being checked for proper operation. The as-found condition is noted, and if the adjustment/setting has not changed (drifted) then usually no "calibration" is performed.

It's been my experience that during periodic "calibrations" more devices are replaced because they don't work at all or can't be made to work than are actually adjusted. So, "calibration" is really just testing devices/instruments to be sure they are still operating as they should, making any necessary adjustment or replacing devices/instruments which have failed or can't be made to work as required. With present-day devices and instruments, drifting of setpoints and adjustments isn't as common as in the past, so unless these devices have short longevity and are being found to cause nuisance trips, it's not clear exactly what's prompting this question.

And devices which can cause trips of the machine of the process should have their proper operation verified fairly frequently.

If the problem is access, can the devices be relocated using additional tubing so the sensing ports on the process? If the problem is calibration devices, can they be rented? If the problem is inexperience or lack of knowledge with the devices, that can also be remedied.

A couple of respondents have suggested using a (differential) pressure transmitter. First, that would also require periodic "calibration", and using a single transmitter for tripping a machine or process also has drawbacks. We don't know if these DP switches are redundant or not, so you would need to analyze a proper substitution of the switches with one or more transmitters to ensure reliable operation.

But, I question if this question is being asked because of nuisance trips caused by these DP switches not being periodically checked ("calibrated") and failing prematurely or not providing proper protection, or if the originator is just trying to understand if other sites <b>allow</b> their "operators" to skip periodic checking ("calibration") of critical devices/instruments? Neither is really a good reason, is it?