Our dataloggers monitors 2 switch closure relays on one of our instruments. In the past, we accomplished this by wiring one end of each switch to the datalogger's 12V unswitched port, and the other end to a SE port. The SE ports were outfitted with voltage dividers.
However, at one site, the voltage dividers were not available, so we connected the switch to the 5V output instead of 12V. We wired the other end of the switch into a SE port as before. When the circuit is open, we're seeing 1-4 volts coming in instead of something about 0.
Could we be causing this problem by the lack of a voltage divider, or are there other things causing this problem?
thanks
You would need a pull down resistor to drop the voltage on the SE channel when a voltage source isn't connected. A common value used for a pull down is 100kOhm. Voltage dividers contain a pull down resistor, which is why you didn't run into it before. The pull down resistor would go between the SE channel and ground.
I assume your P channels are already in use for other measurements. The P channels in switch closure mode have the necessary resistors installed internally.