PID diagram
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As shown in the diagram, it is the high liquid level interlock cut-off valve for the storage tanks in the tank farm. Is this a DCS interlock or an SIS interlock? How can these two types of interlocks be distinguished quickly? What does AS mean in the diagram? Thank you, experts
AS should be Air Source~~which means the source of air~~
Standard HG/T 20505-2014 specifies in detail that adding “Z” after a variable letter denotes the initiating variable and actuator of the SIS system.
The SIS diagram is very simple and clear; it shows the logical relationships； The DCS diagram is more visual and comprehensive.
There seems to be an error in the diagram; Z should represent the SIS system, but the legend for the SIS system should be a diamond symbol.
It’s either Z or SIS when seen; the valve position feedback is indicated by Z.
That’s right! What is the H right in front of Key?
Nothing crucial. Although no legend symbols were visible, LSA continued to show something that resembled I-16010; it should be an INTERLOCK function, rather than a TRIP function related to SIS interlocks. HZSO/HZSC are valve position switches, and the valve in question is XV16005. In summary, the overall naming rules for instrument tags are not well-defined; the LIMITSWITCHes for valves should also use the initial letter of the large valve – X, such as XZSO/XZSC – to correspond to XV. Whatever H represents, it is unlikely to affect whether this interlock is a DCS interlock or an SIS interlock. Either use I-16010 and Z-16010 to distinguish them, or use circles or diamond shapes within the boxes for differentiation; using initials is not very effective.