Monitor PLC Remotely

[cwood3]

I have a compressor station that is equipped with a "Station PLC" that runs everything. There is also a remote field office that monitors several of the station parameters via SCADA. In other words, an operator can be at the field office and look at a screen that displays the current compressor discharge pressure. At the station, there is a pressure transmitter located on the discharge piping. It sends it's signal to the Station PLC. The Station PLC sends the signal to the field office via SCADA. The field can only monitor, nothing else.

So...on the P&ID, the PT is a bubble on the piping, with a line going to a square box with a diamond/single horizontal line (indicating PLC at station panel). To indicate that this signal is also available for monitoring at the field office, do I merely make the single horizontal line in the diamond a double line?.....double line with text "Field Office"?.....or another symbol altogether?....and what type line to indicate the link?

I am not an instrument engineer.

Thanks all.

 

[lacajun]

Based on my experience, I would stick pretty closely to ISA symbology. Drop the horizontal line in the diamond/square box to indicate it is field mounted. Run a software signal link from that to another square box/triangle with a line through it for the office location, if that's the primary location.

You could put Field Office next to the symbol for the SCADA in the office. You may want to put SCADA text next to it to eliminate confusion in the future. However, your loop sheets and plan drawings should clear up the text issues on the P&ID's. I'm not a fan of cluttering up P&ID's for stuff like that. It isn't wrong just unnecessary. Double lines are for auxiliary locations normally accessible to an operator.

If your SCADA is PC based, the correct symbol is a hexagon, with a horizontal line through it and no square surrounding it.

Pamela K. Quillin, P.E.
Quillin Engineering, LLC