Grounding a noisy load cell
Grounding a noisy load cell
(OP)
I have a 25000 pound (15V max) load cell that is supplied by a battery pack/converter which puts out 12.22 VDC. The load cell is read via DAQ board by laptop. The issue I am having is that the noise level (without any load) is approximately 1mV which according to what I have calibrated with compression machines is about 1000 pounds/mV. How can this be? Granted the load cell came with a spec sheet calibrated at 10 VDC the initial reading without any load shouldn't be that high. Do I need to ground the DAQ board or the battery pack? Also any ideas as to where all this noise is coming from with the load cell?





RE: Grounding a noisy load cell
RE: Grounding a noisy load cell
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Grounding a noisy load cell
-AK2DM
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RE: Grounding a noisy load cell
RE: Grounding a noisy load cell
There is a world of difference in what you might be able to achieve between trying make measurements using a 8 bit single-ended A/D converter in a inexpensive USB stick, verses a 24 bit National Instruments computer acquisition A/D with differential channel inputs and front-end programmable gain. What you are calling noise may be the wrong equipment.
Reading a load cell or other strain gauge/piezo resistive sensor where the full scale output is only a few millivolts is not straight forward. Usually a load cell will be connected to a low pass filter, probably a differential amplifier, and then to a sigma-delta type of A/D converter. Additional filter may be performed in the A/D or software.
RE: Grounding a noisy load cell
RE: Grounding a noisy load cell
A GF of 2 means that full scale output is 0.2% of your excitation voltage. So a noise source doesn't have to be particularly large to destroy your signal.
All is not lost though - there are plenty of circuits designed to cope with this kind of sensitivity. There's power supply filtering, Wheatstone bridge arrangements, signal conditioning, shielding, and data acquisition amplification to consider. It is definitely not just a matter of grounding or not - in fact in this case a floating differential measurement is probably best. You need to look at your measuring circuit in detail. Does the load cell spec sheet have any application recommendations? The fact that the calibration is at 10Vdc is not relevant - the cell was just be a little more sensitive at 12.22Vdc.
RE: Grounding a noisy load cell
RE: Grounding a noisy load cell