Calibration error when using a load cell in DAQ assistant

[ajack88]

Hi,

I am having a problem calibrating a load cell using DAQ assistant. The load cell is being read as a full bridge input through a NI 9237 module connected to a CompactDAQ chassis. I have input a calibration table in the DAQ assistant for the correct channel but this does not seem to translate over to the numeric indicator and chart on the front panel. The calibration ranges from 0 mV/V at 0 tonnes to 1.995 mV/V at 300 tonnes but the numeric indicator shows values of the order of 1500 tonnes when there is no load in the system. I can see in NI MAX that the mV/V reading is 0 (well, actually just noise of the order of 1x10-6 mV/V) so my front panel should be reading pretty much 0.

Has anyone had a similar problem before and found a solution? I have a few other inputs, all mA readings, that work perfectly well on the same VI and we have had good readings from these load cells using a different VI that was written by professional LabVIEW programmers, so I know that the hardware works. Any suggestions would be appreciated.

Thanks,

Adam

[edjones93]

Hello,

I am Ed from National Instruments Applications Engineering. I am happy to assist you with regards to your query as to the cDAQ readings you have been experiencing.

Firstly, from the description of the purpose of your calibration chart, I would rather recommend a custom scale than that of a calibration chart. I have linked a document below which walks through custom scales:

http://digital.ni.com/public.nsf/allkb/F7DAE47B4408A86F8625765700767FCD?OpenDocument

Secondly, I have a few questions to gain a greater context for my research:

1. Was this calibration chart created for a different module or circuitry setup?

2. Has anything happened to the system to change both the software or hardware setup?

I was also hoping you could attach your VI code so I may review the methodology and see whether the issue may lie here, since you have outlined this may not be a hardware issue this would be my next area to review.

I hope that this is helpful and you are successful in your application.

Best regards,

Ed