Finally had a chance to test the limit switches tonight. Wired the first one up to the DAQ and didn’t get a signal. Wired the second one up with the same result. Figured maybe the connections were bad in the connector, since I didn’t have the special tools to push the wires into the sockets. Checked continuity with a meter and pushed them in some more just to be sure. Reviewed the limit switch documentation and verified all the wires were in the right positions. Everything looked good. Wired one back up to the DAQ, still no signal. Started wondering what to try next. Reviewed the limit switch documentation again, and noticed the sample circuits have a pull up resistor between the voltage source and the signal. Added a 1K resistor to the circuit, and everything started working great. The sensor is actually much more sensitive than advertised. On a flat black surface (my computer keyboard) it works as advertised 2-20mm. On any white or reflective surface (envelope, etc.) the range is actually between 2 and 3 inches depending on the surface. I will have to test them on the actual surface they will be used with, but I expect to be able to mount them directly to the shelf. Originally I expected to need some spacer blocks to get them closer to the surface, but it will be much easier to mount them if that is not necessary.
Other good news – I found out the sbRIO board has been repaired (finally) and has been shipped to me. I should have it early next week. That means I will have my choice of RIO chassis to work with.