Loadcell readngs help please.

[Morcego]

Hi
I have the following setup:
Loadcell 20Kg 3mv/v
Excitation 5V (full scale is 15mv)
Load cell outputs to INA125P
Ina125P is providing the excitation voltage and is configured for a gain around 333 to give full scale at 5v (15mv x 333 = 4.99V).
I have 2 calibrated weights 0,459Kg and 1,150 kg

I got the following readings (fluke multimeter)

No weight

At load cell terminals At INA125 output

No weight 110 uV 70,7 mV

0,459kg 460 uV 165,4 mV

1,150kg 970 uV 353.3mV

1.609kg 1.32 mV 479 mV

This does not make sense to me. Specially at the Ina125 output.

Should I use some kind of linearization formula ?

thanks in advance for any help.

M.






At the

 

[melone]

Looks pretty linear to me (R2 = 0.9966).....

 

[Skogsgurra]

Yes. Really not bad. No linearization should be needed. But you have a zero offset that shouldn't be there. Are you sure that the load is zero when no weights applied? Also, are you using the negative supply lead as a zero reference? Make sure that your wiring is exactly as in the INA125 appnote. Also, the gain is more than 333 - so there might be something wrong with your resistor selection.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Morcego]

Thanks.

In fact the offset is strange. But the connections are exactly the ones in INA125 datasheet. The load is zero. I have the load cell in my bench.



melone: What do you mean by R2=0.9966 ?

Thanks

M.

 

[Skogsgurra]

OK, then. Add a trimmer to take the offset away. There may be some imperfection in the foil or the glueing causing the offset.

R2 probably means the regression coefficient. Your .9966 is not bad - but also not very good. It is OK, I would say.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[whycliffrussell]

what is the deadweight on your loadcell?

 

[obg]

There is an offset on the INA25 that does not correspond to the load cell off-set. In order to make sense of the INA output you must determine this value. The load cell o/p is good when zero corrected. Check out for the commomn mode values on the INA125 I seem to remember an issue with this.

OBG