There are many topics on this already discussing the pitfalls of trying to implement momentary buttons in any scada platform. Instead of me regurgitating, best to just search
Because, with currently available components, there is no way to ensure the PLC gets its bit released (in a reasonably short bounded time, typically ~100ms) if:
The browser hard crashes while the button is pressed,
The browser encounters a javascript bug or sandbox violation while the button is pressed,
Some other javascript operation hogs the CPU(s) (charts for the win!), delaying recognition of the mouse release,
The websocket gets cut off between browser and gateway (for any reaso…
Momentary buttons are minefields when using any query-response communication protocol. Such buttons must send a message to turn on the target when pressed, then send a separate message to turn off the target when released. Put those messages close together and you risk the underlying driver’s optimization (and possible lack of write verification) stomping on one message or the other. And the non-zero risk of packet loss / comm link breakage between one and the next.
In the short term, the be…
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