Questions regarding flowcharts
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As shown in the figure, a stop valve with position feedback feeds into the PLC. Then, what do those two three-way stop valves above, along with that arrow and the letters S/ND, mean? I couldn’t find any explanation for them in the description at the beginning of the flowchart. What is the function of these two valves?
The two on top are solenoid valves. :D
DE: normally energized – excited under normal conditions, powered on. NDE: normally de-energized – not excited under normal conditions, powered off. For the operating principles of these two solenoids, refer to this post: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1476191
According to the design specifications, when high security is required by the system, redundant solenoids should adopt an \"or\" logic structure； When the system requires high availability, redundant solenoids should adopt an \"AND\" logic structure. In the diagram, S represents the solenoid valve, and NDE means permanently energized excitation. The arrow indicates the direction of exhaust during power loss. This is a 2-position 3-way solenoid valve; it operates based on a logical relationship – the interlock function will only be activated when both solenoid valves lose power. High availability is required.
NDE: normally de-energized – it is not energized under normal conditions and is not charged. If that’s the case, it isn’t \"fail-safe,\" which suggests there is a problem with the design.
The pneumatic cut-off valve in the diagram is quite critical; it requires redundant control via two solenoids, as well as feedback signals regarding its position. The two solenoids share one DO signal. However, the air circuit design in the diagram is unreasonable; if the solenoid valve has three ports: input, output, and exhaust! Therefore, the air outlet of the upper solenoid valve should be connected to the exhaust port of the lower solenoid valve, while the bypass parallel air pipe should be connected to the input port of the lower solenoid valve. In this way, any electromagnetic failure will not cause the valve to move to a faulty position.
I would like to ask what IA at the top means
Don’t you know this? Initial letters of instrument air in English
s represents the solenoid valve; the arrows indicate the flow direction of the air flow. NDE: normal de-energized. The two solenoid valves provide protection against faults in the air flow circuit.