Changing input level range on scxi-1121

[TopKid]

Hi,

My setup is as follows. PXI-6070E <> SCXI-1000 <> SCXI-1121 <> SCXI-1328.

My end goal is to be able to measure temperatures in excess of 300 degrees Celcius with a K type

thermocouple. I attempted to do this with my setup but was returned an error from my DAQmx Create Channel(AI_temp-thermocouple).vi

when I set the maximum level as 400 degrees Celcius. From my calculations I figured that 400 degrees celcuis with a K type thermocouple

should give me approximately  16.4mV. I have my gain setting on the SCXI as 1000. However, I also changed my overall gain setting on both the SCXI-1121(hardware jumpers) and in MAX all the way down to 10 but still got the error I mentioned above. My understanding is that the gain on the SCXI-1121 just needs to be below 500 to accomodate my setup. Also, the PXI-6070E seems to be able to handle any input up to +/- 10V.

Please advise where I am mistaken here. Where do I make the adjustment to allow my thermocouple to measure beyond 350 degrees C.

Is the problem the 6070E or the SCXI-1121?

Thanks a bunch.

Ruz

[TheWoost]

Hi Ruz,

I configured a similar setup to yours in LabVIEW, and was able to set the maximum temperature value to 400 degrees only when the programmable gain on the SCXI-1121 was 250 or less.  The maximum value that is allowed by the DAQmx Create Channel(AI_temp-thermocouple).vi is a calculation based upon the type of thermocouple, gain setting on the hardware, input voltage range of the communicator DAQ board, and degree scale.  What are the specifics of the error message that you receive when you set the gain down to 10?  Copying and pasting the error message would be helpful.  Are you selecting the proper scale when configuring the DAQmx Create Channel function?  If you create the temperature task in Measurement and Automation Explorer instead of LabVIEW, do you get the same results?

Regards,
Andrew W
National Instruments

[TopKid]

Hmm. the message I get is Error # 200077 "Requested value is not a supported value for this property." when I set the gain to 250. Same error I got when I put the gain all the way down to 10.

Did you use the simulated device or the real hardware? Also, is there a way to adjust the input voltage range on the DAQ communicator board? I am using the PXI-6070E and have not

seen a way to adjust this when doing a thermocouple measurement.

Any ideas?

[TheWoost]

Hi Ruz,

I tested with the simulated devices, but there should be no difference in the behavior when selecting configurations in software.  Do you get differing behavior if testing this with simulated devices?  Have you verified that the jumper settings on your SCXI-1121 match those that you set in MAX?  Please refer to page 2-8 of the SCXI-1121 User Manual here for more detailed information on the proper input channel jumper settings.

Because the thermocouple acquisition task is set up using the analog input channel on the SCXI-1121, all allowable settings in the task are based off of this device.  Manually changing properties on the PXI-6070E is only possible if it is the device specifically set up for the task.

Regards,
Andrew W
National Instruments