What is the best way to interface an open collector sensor output such as the output of this device to the NI9403?
https://www.pepperl-fuchs.com/australia/en/classid_9.htm?view=productdetails&prodid=7691
The device is being powered by a 18VDC supply.
What has thrown me is the fact that the sensor output whilst open collector, when not engaged is already measuring 18V even though I have no pullup on that output. I know I've missed something obvious here but it has been a long day!
Normally I would expect there to be a reference voltage on the DAQ that I would use to pull up the output via say a 10k resistor. But there is no reference voltage pin on the NI9403. Does that mean I need to supply a TTL level supply (5V), reference that to the same 0V as my 18V supply that is powering the sensor, then use the 5V supply to pull up the open collector output?
Or is there a more clever way using say a Zener diode to limit the output voltage to say 3.9V but still use the 18V supply for the pullup?
Cheers