DT9829 Setup for Load Cell

[Todd]

I am having trouble configuring a load cell with the DT9829.  I have setup load cells on other data acquisition hardware without issues before.  I am having issue with the load cell either displaying 0 lbf or almost 10x the applied force.  I have also found the calibration function results in a different correction factor every time I run it.

I am using an Omega LDSH-15K, which has a transducer Rated Output of 3.002 mV/Vnominal.  I put 15,000 lbf in the box for transducer capacity.  The load cell is sitting on a bench, not mechanically attached to anything.

If I push on the load cell, it shows -8,000 lbf if I don't include offset nulling and shunt calibration.  When I include offset nulling and shut calibration, I get a different "gain" just about every time.  One time it worked and the output was reasonable.  I am not sure why the output of the 15,000 lbf load cell is so variable.  Any suggestions?

Thanks,

Todd

[Fausto]

Hello @Todd.

The OMEGA LSHD-15K load cell requires an excitation voltage of 10V.  Since the DT9829 can only provide an excitation voltage of 3V, you would need to provide the 10V from an external source.  Is that the case? 

The calibration procedure is documented in chapter 7 of the DT9829 User's Manual.

 https://www.mccdaq.com/PDFs/Manuals/UM9829.pdf

With a 10V excitation voltage source connected to the load cell, please reply with screen captures if the issue continues.

Regards,

Fausto

[Todd]

The Omega LSHD-15K load cell is ratiometric with a nominal gain of 3 mV/V excitation, so for an excitation voltage of 10VDC, the output will be 30mV at full scale of the load cell.  The QuickDAQ software has an input for the 3 mV/V value for the load cell setup.  The excitation voltage is 3VDC for the DT9829 module which would reduce the full scale output from 30mV to 9mV.

I think there is an issue with the QuickDAQ software when the Shunt Calibration is selected.  Sometimes the value gets applied and sometimes it doesn't. 

A different data Aquisition system I used recently completed the shunt calibration automatically vs installing a shunt resistor, so I assumed it was a similar feature for the DT9829, which was an incorrect assumption.  When I completed the shunt calibration several times without the resistor, I noticed the correction value would change drastically each time.  It would also be ideal if the correction factor had a limited range vs any calculated value.

When I tried not including the shunt calibration, I had the same issue.  I found that re-setting the channel type and starting over appeared to fix the issue.  Now the load cell reading is displaying 15-20 lbf when I push on it.

Regarding completing the calibration procedure in chapter 7, I just received a new DT9829 from the factory with a calibration sheet.  Does it still need to be calibrated, or should the factory calibration be good for 6 months to 1 year?

Thanks,

Todd

[Fausto]

@ToddThe factory calibration is good for a year.

[Todd]

Thanks for confirming there is no need to complete the calibration procedure per chapter 7, if the hardware is being used within the facotry calibration period.