Oil & Gas Industry Instruments

[atlas0821]

I am very new to the instrumentation side of the oil and gas industry. I hope this isn't a stupid question, but when specifying an instrument (i.e. PT, TT, LT, etc..), I must specify wheter the instrument should fail upscale or downscale. Now when looking at my set of P&IDs, is there something that should flag me that it is either upscale or downscale? I don't know much about the process side of things at this time but am learning. I am a new EE and just not sure about the upscale/downscale when spec'ing instruments.

I am not sure if this can be answered without knowing about the particular process, but maybe if you can give me things to look for that might indicate which direction to fail at, that would be great.

Also, if you guys know of any sites that are good for new Instrumentation people, I would greatly appreciate it! Thanks!

 

[ScottyUK]

It depends on what the signal is used for. If it is for indication only then it probably doesn't matter one way or the other. If it feeds into some control function then it may be very important because the fail state may be used by a PLC or DCS to recognise the failed condition and ensure the signal is either discarded if a redundant sensor is available or to ensure that the controller drives to a safe state. You can't just consider the instrument in isolation - you must look at the overall system.


----------------------------------

Sometimes I only open my mouth to swap feet...

 

[JLSeagull]

This requirement typically applies to thermocouple burnout. A thermocouple is a pair of disimilar wires connected that provide a millivolt signal corresponding to temperature. These are often inserted into hot or corrosive places even where thermowells are used. Some types such as iron constantan corrode easily and fail as an open circuit. This could correspond to a very low temperature. If too you may add heat. If the thermocouple is open, determine which is worse, to add heat or remove heat. This is how you begin the decision process.