Load cell question for the experts

[vic92]

Hello, I must first say that I think this is an excellent forum, I have found some usefull info in the past.(thanks)

The question I have today is about loadcells, I am working in my companys R&D department I am trying to set up a pair of load cells to measure tension. The load cells I am using are brand new. They are rated at 100 lbs each , 10vdc exc. and the are 3mv/v.

I have hooked up 1 l/c to a data aquisiton system I have which is currently meassuring the excitation voltage (10.0vdc) and the output (m/v). I am sure all my readings are correct, because I am using a calibrated multimeter for verification.

I do understand that @ 30mv I should have 100lbs of tension and @ 0 lbs I should have 0 mv or close to. I was told with no load there should be no more that .3 mv positive bias ( which is fine I am reading .08 - .15mv). One question is: does this change the scaling? is it not now 0-30mv? also when I hang a weight (calibrated 5.005lbs +/- .001 ) I get about 1.95 mv which doesn't seem right I think I should be getting about 1.5 mv.
I also tried hanging a 25 lb weight and got a reading of 8.59 mv. which should been closer to about 7.5 mv (according to my math) I am trying to figgure out why my numbers arent meshing, Does any 1 have any ideas?

 

[waht]

I'm not really familiar with this sensor, but you could try a few things. Plot the voltages vs weight, up to 100 lb if possible. See how the graph looks like, if it's a straight line that means the whole thing is offset by some constant voltage.

Also, you might want to vary the bias voltage, +/- 0.5 volts, see if the readings change.

It's also the possible the multimeter has a too high impedance, so you could try loading the sensor with maybe a 1K resistor, see if it affect the data. Or vice-versa, it's possible the multimeter represents a too low impedance and sucks out the bias voltage from the sensor. In that case you would need a to check it with a high impedance probe, maybe 10 Megaohm using an oscilloscope.

These are the things I would try first based on limited knowledge of the sensor.

hope that helps.

 

[ravenprp]

Hello, thank you for your kind words about the forum. We are happy to hear that you have found useful information here in the past.

In regards to your question about load cells, it seems like you have done a thorough job in setting up your equipment and verifying your readings. It is always important to use calibrated equipment for accurate measurements.

To answer your first question, the change in scaling (from 0-30mv to 0-100lbs) should not affect your readings. The scaling only affects the interpretation of the data, not the actual values being measured.

As for your readings not matching up with your calculations, there could be a few potential reasons for this. One possibility is that there may be slight errors in your equipment or setup that are causing discrepancies in the readings. Another possibility is that the load cells themselves may have a small margin of error in their measurements.

If you have access to multiple load cells, it may be helpful to try using a different one and compare the readings to see if they are consistent. If the issue persists, it may be worth consulting with an expert in load cells or reaching out to the manufacturer for further assistance.

Overall, it seems like you are on the right track and have a good understanding of how load cells should work. Keep troubleshooting and gathering data, and hopefully you will be able to pinpoint the issue and find a solution. Best of luck in your R&D project!