There’s one part of the PID diagram that I don’t understand; please give me some guidance
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I would like to ask everyone, what does the symbol inside the red circle in this picture represent? First is a temperature transmitter, and I don’t understand what those two things connected to it mean Is the diamond-shaped box a safety instrument, with AI analysis indicators? It means the temperature is extremely high, at 95 degrees – what should be done? I don’t see it connected to any control component either What is the functional difference between it and the temperature gauge next to it?
AI seems to be an alarm signal.
It is generally an interlock indicator; AI should be for entering interlock mode, while the one above is a DCS display
I think there’s something wrong with this way of representation. . . For the left side, if it’s an HH interlock, a TIA would be more appropriate for the diamond-shaped element in the middle; there are no issues with communication to the DCS for the upper part. The right side has high/low alarms, so a TIA is a good choice. As for the type of interlock to use, check the descriptions in NOTE4 to see what’s specified
There’s a built-in temperature sensor right there; why connect two? Can’t we use the one next to it for HH?
What I actually want to ask is: since this instrument isn’t connected to any control components, why not simply use the signal from the temperature sensor nearby to trigger an HH alarm? Later, I thought it might be because the pipeline was quite long ； The two gauges are located quite far apart.
Yes, on the piping layout diagram the distances might be quite large, and there are some things that PID cannot convey clearly
Generally, interlocking and control are separated; if what is present nearby is merely a temperature indicator, there is no problem with communication from the SIS to the DCS display. According to clause 6.1.6 of GB/T 50770, Design Code for Safety Instrumented Systems in Petrochemical Industries, measuring instruments and sampling points should be installed separately; I believe this is the reason for having two of them – the temperature change along the same pipeline is very small, so it’s not a matter of location.
As shown in the diagram: The temperature transmitter signal is sent to the PLC for alarm indication (which can be considered as a SIS), and then the temperature is displayed on the DCS; the action that takes place when the temperature reaches HH (95 degrees) is described in NOTE4. The system shown next to it is a conventional temperature control system.
The AI at the bottom indicates that it is sent to the interlock system, usually something like SIS. The 2719C above is displayed on the DCS system. In other words, transfer the SIS data to the DCS