What does the content in the red box represent? Also, what do I and L mean?
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This post was last edited by Catalyzing a Grain on 2018-12-11 at 21:59. I’m seeking advice from experts.
It seems to be a choice between remote and local modes; the traffic is to be controlled via DCS interlock or in conjunction with the local PLC interlock
PLC interlock and DCS interlock
The notation here is a symbol for interlock logic systems, indicating that under emergency interlock conditions, the DCS system can interlock to shut off that flow control valve. However, this drawing method is likely quite old; in the latest standard HGT 20505-2014 \"Functional Indicators and Graphic Symbols for Process Measurement and Control Instruments\", it is required that interlock logic symbols be represented by solid diamonds, with the text \"I\" indicated within the diamond” ； When there are many local interlock logic circuits, the interlock logic circuits should be numbered
I stands for display, while L indicates centralized control or local control
I learned that there’s also this way of expressing it
To interlock the control valve, isn’t it sufficient to add a solenoid valve to the control valve itself, with the interlock signal going to this solenoid valve to close the valve directly? I’ve really never seen this kind of representation before. .
Yes, both the control signal for this regulating valve and the interlock shutdown signal require solenoid valves; accurately, two solenoid valves should be used. The representation here isn’t very clear. Moreover, the SIL level for the control of this entire system is relatively low. Generally, valves that are involved in process control should be equipped with separate emergency interlocks, but it depends on the unified regulations set by their project
Doesn’t it mean interlock?
Inside the red box is an interlock input signal, which represents the result of the interlock action; as for I and L, they denote interlock