Is there any difference between PI and PGI in a PID diagram?
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Is there any difference between PI and PGI in a PID diagram? What about TI and TGI? What are the abbreviations for each of them?
G, as the subsequent letter, denotes a viewfinder or observation device, and generally refers to on-site indication. I is used as a subsequent letter to indicate display, and is generally applied in remote indication instruments. The accurate usage shall be based on the design legend (instructions).
PI--Pressure indicating instrument, visible on the DCS. PGI--On-site indicating pressure gauge; it does not involve a DCS, and is simply an on-site pointer-type pressure gauge.
Isn’t the normal remote transmitter signal transmitted using a PT? And if it’s done on-site, PG is sufficient; why add I as well?
Adding I is unnecessary. It does not meet the specification requirements.
Take a look at the functional indicators and graphic symbols for process measurement and control instruments in HG/T 20505-2014
The subsequent letter I denotes indication; it does not indicate where the indication takes place – whether on-site or in the control room – which depends on the graphic symbol； The subsequent letter G denotes observation or viewing; the original meaning of ‘observation’ is direct visual inspection, such as of pointers, color bands, or color columns. It also does not indicate where to observe or with what scope. However, direct visual observation from the control room, or the use of viewports, is clearly illogical; hence it implies on-site observation or the use of viewports.
That’s not correct; there are only two types of PI and PG. The former relates to the functions of the DCS control system, which can be seen on the DCS screens, while the latter represents the pressure transmitters used on-site. The latter is actually the pressure gauge on-site.