Instrument control on the process flow diagram
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I used to work in piping, and I’ve only just started working with process engineering; I have many questions regarding the instrument controls shown on the process flow diagrams. In terms of temperature control, some systems use TIC while others use TRC – what is the difference? How should the instrument control symbols on a flowchart be represented? I’m referring to things like TT, TY, and so on – what symbols are needed for the same instrument control? Please give me more guidance!
For your reference, here are the functional indicators and graphic symbols for process measurement and control instruments according to HGT 20505-2000: http://bbs.hcbbs.com/viewthread.php?tid=120913&highlight=20505
TRC – Temperature recording control; TIC – Temperature indication control. There used to be a difference between the two: R is for recording, while I only provides indication without recording. Now there’s little difference between the two; they both basically come with a recording function. Just look at what each letter on the gauge represents and you’ll know. They are all included in the legend
It’s usually included on the homepage diagram of the general process; you can match it accordingly
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I’ll explain the issue related to automatic control for you. The letter codes are divided into a first letter and a subsequent letter. Take ‘T’ for example: if it is the first letter, it denotes temperature; if it is the subsequent letter, it indicates an output function related to transmission. For ‘R’, the first letter refers to nuclear radiation, while the subsequent letter signifies a reading function for recording data. As for ‘C’, the first letter represents conductivity, whereas the subsequent letter indicates an output function related to control. So you will quickly understand the reasoning behind it
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Generally, the first few pages of a PID contain some legend explanations; there is a separate page dedicated to instrument symbols, outlining the meaning of the letters used for instruments. There are explanations inside for the first letter and the subsequent letters. Match it to the corresponding one and that’s it. Regarding PID, I think it’s necessary to first study the *legend carefully.
It can be found in Chemical Instrumentation and Automation; you can also search for it on Baidu
On the first few pages of the PID, there is a legend for the instruments, which explains the meaning of the letters. It shows what the first letter represents and what the second letter represents; you’ll understand it once you take a look