Hello - I have a very basic question that is escaping myself and my colleagues. There seems to be a difference of opinion on how to correctly identify the following on a P&ID:
- A pressure transmitter is installed on a distillation tower.
- The transmitter is wired to a safety PLC and then to an on/off valve where it will close the valve on high pressure.
- Sidenote - the PLC also transmits this pressure signal to the DCS via ethernet so as to take advantage of the operators seeing an additional pressure reading.
My question is, does the symbol for the PLC contain the identifier "PC" as in pressure controller or "PSH" as in pressure switch - high?
In my mind, a switch is reserved for a sensing element with only discrete measurement capabilities. The switch then triggers a relay which manipulates a final element. In this case, we are using an analog instrument that triggers the final element similar to a switch but we are also using the full range of measurement of the instrument.
I can honestly see both ways. Any thoughts?
Thanks,
Jamie