PID instrument symbol issue
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This post was last edited by dfr4dfr4 on 2019-9-17 08:32. There was a small project in the past; for its initial construction and expansion, different design firms were responsible for designing the PID control systems. The instrument symbols used in the diagrams to represent valves that control the flow rate of flow meters were actually different – which one is more accurate? What’s the difference between these two?
Please have the original poster take a look at the uploaded pictures; it seems to me that one is normal while the other one is rotating. Thank you!
Only one image can be seen; it’s the image labeled B, and it seems fine
It’s not showing fully; there are two images, one A and one B. Try merging them into one image:
I think either one is fine; as long as it’s expressed clearly
Figure A shows flow control implemented using DCS, while Figure B shows flow control implemented using PLC.
According to the requirements of the new standards HG/T20505-2014 and SH/T3101-2017, the diagram on the right side is incorrect. Because the box + diamond in the right diagram only represents the SIS system.
There are significant differences between the old version and the new version in Specification 20505
Figure B shows PLC control according to the old version