One of my NCD PR16-9-5 “2-Channel General Purpose SPDT Relay Shields” with an embedded Particle Electron microprocessor is misbehaving.
Firmware on the Electron responds to continuity across the first set of input terminals on the relay board (continuity occurs when a float switch in a water tank closes a circuit). The application has been running reliably for a couple of years, turning on a pump to fill the tank when the float switch’s contacts close at a pre-set low water level and turning the pump off when those contacts open, i.e. when the tank is full.
Recently the Electron’s firmware stopped notifying the pump that it needs to stop, i.e. when continuity has been lost because the float switch’s contacts opened. Consequently, the pump keeps running and the tank overflows.
I have verified with a meter that, indeed, there is no continuity across the input terminals when the water reaches its prescribe level (the float switch is working). The firmware on the Electron has not been touched in years and it does reliably turn the pump on when the contacts close. Clearly, something has failed and I suspect it’s the NCD board.
Can anyone suggest a course of action to better diagnose or resolve this issue? Replace the board? Move the wires from the float to a different pair of input terminals (and modify the code appropriately, of course)? Maybe look harder at the Electron rather than the relay board?