On our machine we have a couple of different 2-wire switches wired into T100MD888+ PLCs. One has problems and one works fine. Here are some specs:
Switch #1: Pressure switch (SMC part # PS1000)
Load voltage: 12-24 VDC (we're running at 24V)
Load current: 5-40 mA
Leakage current: < 1 mA
Internal voltage drop: < 5 V
On voltage measured at PLC input: 3 V
Off voltage measured at PLC input: 15.2 V
Switch #2: Proximity switch (SMC part # D-C73)
Load voltage: 24 VDC
Load current: 5-40 mA
Leakage current: not specified
Internal voltage drop: < 2.4 V
On voltage measured at PLC input: 1.6V
Off voltage measured at PLC input: 19.3V
Switch #1 is the one that doesn't work properly. If I power up the PLC and the switch is already on (i.e. air pressure is on) the PLC reads the input as on. If I turn down the pressure until the switch goes off, the input goes off as well (so far so good). However, if I now increase the air pressure until the switch turns on, the input doesn't turn back on again. The only way to get the PLC to read the input as on is to power up the PLC while the pressure is on.
I tried the two suggestions mentioned in
this thread but neither achieved anything.
I know this really isn't a TriPLC issue but I was hoping you might have some insight into this since you are more familiar with the design of your PLCs. Plus, you've been very helpful with questions like this in the past.