Proximity Probe Postivie Movement (with 9242 card, 9068 or 9058 cRIO)

[Mayberry]

If a proximity probe driver is providing an output voltage of 0VDC to (-)24VDC and I want to ensure the 9242 can see the shaft movement towards the probe as being a positive movement would I connect the OUT terminal of the proximity probe to the (+) or the (-) of the 9242 card?

The driver is a gap voltage reading driver, NOT a 4-20mA driver. 

I have been told that the AI0- terminal of the 9242 has a 50 ohm impedance whereas the AI0(+) does not (I can't find this documented anywhere). 

I have also been told that even if the polarity is NOT wired correctly that the resulting waveform would just represent the opposite of what we desired (we want the shaft movement towards the probe to show as being a positive movement).

The end goal is to view the data in INSIGHTCM and when the shaft moves towards the probe the OUT of the driver becomes closer to 0VDC (becomes less negative) and this is represented as an upward movement on a graph. 

Should the OUT of the driver be connect to the +  or - of the 9242 card? 

[AndyClegg]

Not sure about the compatibility of that specific IO module, but we're just doing an application with a 0 to -20V proximity sensor and are using an 9221 IO module and have done a preliminary test with a probe connected and seems to work. I expect yours will be the same, but the 0 to -20V output is what is generated by a signal conditioning unit that goes between the actual probe itself and the IO module, so you need to look at the specs of the signal conditioning unit not the probe itself.

Hope this helps

[Mayberry]

Thanks Andy, to clarify your 0 to -20V output is wired to the 9221 in what order? The 0 to -20V signal is going to the + or - terminal of the 9221 card? 

[AndyClegg]

Just checked with the guy who is doing this and the IO module being used is actually an NI-9229 (I was looking at an early list of IO modules)

The NI-9229 module has differential analogue inputs, rather than single ended analogue inputs refernced to COM / Neutral as found on the 9221 and the 9242.