Could the expert take a look and see if there are any issues with the PID diagram?
Thread Content
There are a few unclear points here: what does the label “I” in the diamond mean? If it is a linked signal, what is the difference between it and pisa1201-1?
The pneumatic control valves shown in the figure include pneumatic diaphragm control valves and pneumatic cylinder valves. The dashed line represents the control signal; is the control signal an electrical signal? Is it still a gas signal? No distinction is made. The signal is likely an electrical signal, so how can it act directly on a pneumatic valve? I is a logical value, indicating that a certain actuator is controlled by this logical value. But how were TICA-1301b and YL-2201-1 given to I? TICA-1301b has no communication signal (no S), and YL-2201-1 also has no communication signal (no S). What does this ‘I’ mean? ? This diagram is a bit messy and hard to understand.
This is the preliminary design of a certain plant. Is the level of detail insufficient? If it’s meant to be at the level of construction drawings, then TICA-1301b should normally control TV1301-1b; YL2201-1 indicates that the motor is running, while FIB (it should be FIA) controls FV1301-2b. These are all part of the DCS system. Meanwhile, TICA-1301b sends signals to the SIS system, where upper limit settings are used to control TV, FV, and YL to shut down. This is the SIS system. Is this how it should be understood? And how should it be depicted?
This post was last edited by Ku Liang Zhi Le on 2021-4-28 at 12:10. It’s easy to understand if it’s a preliminary design; the P&ID diagrams in such designs are merely illustrative. According to the legend symbols, a diamond shape with a box around it represents an SIS system, while a circle with a box around it denotes a DCS system (PBCS, that is, the Basic Process Control System). ), FIB should be FIC, as it clearly has a control function (its output is sent to the control valve). If it is FIA, then it indicates a flow indication alarm rather than control, which would not explain why its output is sent to the control valve. During detailed design, the SIS function should be sent to the solenoid valve to switch the gas circuit; therefore, a three-way solenoid valve should be added to the control valve.
Check the home page – the gauge function symbol; this graphic symbol is commonly used in SIS interlocks.
According to the diagram, “I” is a sequential logic signal; its source and operating principle need to be checked in other relevant drawings； PISA1201-1 is a controller, labeled as “SIS system interlock”.
I think the I in the diamond represents only a DCS chain, not an SIS chain. The source of the signal needs to be checked in other drawings; signal lines can be drawn on the same drawing, while in different drawings they are represented by a diamond symbol I. However, generally it is necessary to label them with numbers using I, so that it can be determined where the signal comes from and where it is going. For specific details, you can refer to the drawing methods in HG/T20505.
It should be related to the operation of PISA1201-1; when PT1201-1 is activated, the corresponding devices listed in Table I should also operate simultaneously. The I for TE1302B should be marked on TB1301-1.