Bad Voltages

[USC Nuc Engr]

I'm currently using LabView to run gas flow meters for our research.  This has been working fine for a year, but all of the sudden one of the channels is giving a higher voltage than what I am setting it at.  When I set the output voltage to 0, it won't read any less than .3V.  I've changed the flow controller to another channel and it's working properly.  We also run a pneumatic valve (on/off) as a safety precaution in case of the flow controller breaking and not being able to shut the gasses off.  This pneumatic valve is couple to the same gas and is now always receiving an ON signal when the program is running.  Any ideas?

[LV_Pro]

The obvious answer is that your voltage source (you don't mention what it is) is faulty. Of course if there has been ANY hardware or software changes that is the first suspect. Can you set the voltage, does it change at all? Any changes to software, drivers, etc.?

[USC Nuc Engr]

Sorry I didn't have the part numbers when I posted this a bit ago.  From our computer we have a USB connection into a NI cDAQ-9172 Legacy NI CompactDAQ Chassis with 7 NI control modules (9211, 9263x2, 9205, 9481x2 and 9265).  All of the modules are acting properly except for NI 9205.  We have five flow controllers connected to this module in Ach0/8, 1/9, 2/10, 3/11 and 4/12.  There have been no changes to any hardware or to the LabView set-up in over a year.  However, a couple weeks ago the voltage output in Ach 2/10 won't go to anything below .3 Volts.  It works properly in the range of ~1.5 - 5V but no longer below 1.5V.

[USC Nuc Engr]

The NI 9481 modules are used to turn on/off pneumatic valves that were placed in-line before the air flow controllers as a secondary way to cut off the gas flow.  The 9211 and 9265 were set up to measure the temperature gauge and I'm not sure what else (as we have some devices that have since been removed).  The NI 9263 and 9205 are the only modules that are connected to the Air Flow Meters.  (Celerity TN260 & MKS Mass-Flo)

[billko]

I have to go with the consensus and vote for "hardware issue."