calibration problems with PhidgetBridge + Load cells

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calibration problems with PhidgetBridge + Load cells

Postby flow_ » Mon Dec 10, 2012 9:45 am

I am using
4x 3135-Micro Load Cell - CZL635
1x 1046-PhidgetBridge 4-Input

I started out with the formula from the WIKI site:
Expected Force or Weight = K * (Measured mV/V - Offset)

An average of 20 measurements give me following result:
(Faktor 10000)
CH0:{(Measured mV/V} = 41.2428421053
CH1:{(Measured mV/V} = 478.4056842105
CH2:{(Measured mV/V} = 470.7763333333
CH3:{(Measured mV/V} = 840.3097894737
This values are my offsets.

Next I calculate the "K" value by using a reference weight 1kg.
Here the first interesting thing happens I get a different value for K
For 1 channel I get a totally different value, the other 3 channels are pretty much the same.

Here my questions:
Is it normal that the measured signal values differ that much for the same sort of sensors?
As a consequence the K value has to be different for each sensor?

Thank's for help!


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Re: calibration problems with PhidgetBridge + Load cells

Postby burley » Mon Dec 10, 2012 3:30 pm

How different? It is expected that each load cell will require individual calibration but I would expect the part to part variance to be, ballpark, under 25%.

At the end of the day though it doesn't matter too much what sort of gain you need provided the sensors all report similar final measurements. Do you see consistent results from the sensors once calibrated at least?
Brian Burley
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