DAQmx scaling clarification/help

[dennisa]

I've read a few topics on DAQmx scaling and I  think I understand how to use it. But I need a little guidance. I have a load cell connected to a NI-USB 9237. I would like to create a custom scale so the data/ouput is reported in grams. following thisknowlegde base article DAQmx Custom Scales in Measurement and Automation Explorer (MAX) for the NI 9237

The load cells calibration data is as follows

Excitation = 10vDC

Zero Offset =  0.00926989 Volts (.9269 mV/V)

FSO @ 70grams = 0.0292662 Volts (2.926 mV/V)

If I undestand this correctly my Map Scale Ranges Custom Scale would be set as follows

Units

Pre-Scaled = Volts

Scaled = gr

Pre-Scaled Values

Max = 0.0292662

Min = 0.00926969

Scaled Values

Max = 70

Min =0

[RavensFan]

What guidance do you need?  So far it seems like you have a good understanding of what to do.  Next step is to create a small VI to read the DAQ channel and start putting some real loads on the load cell and see if the VI gives you the readings you are expecting.

[dennisa]

Well, I've made a custom scale with the data in my first post. Problem is the vi I created does not give me the results I expect. When I get back to work in the morning I'll post the .vi I made to test my custom scale.

[jschwartz]

Hi Dennis,

Just to confirm, at zero load you expect 0.00926989 Volts and at full load, you expect 0.0292662 Volts?  If this is what you expect, you should be able to use these in the Map Ranges scale.  Does your scale look similar to the one below?  What values are you getting that are unexpected?

[dennisa]

For some reason the output was reading an offset of 15ish grams. I was able to work out the scaling and I ended up using a table as it generated more acurate results.

Thank for the help