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Eliminating vibration effects from the output signal of a loadcell?

Eliminating vibration effects from the output signal of a loadcell?

Eliminating vibration effects from the output signal of a loadcell?

(OP)
As you know loadcells generally work in an environment with lots of mechanical vibration. So the output signal of the loadcell also vibrates very much. Averaging the output slows the output very much. Can we eliminate / filter out this vibration from the output signal wihout a much loss of the response rate? Thanks in advance.

RE: Eliminating vibration effects from the output signal of a loadcell?

The vibrations are superimposed on the usually much slower load variation signal. They are also, usually, symmetrical with regard to the baseline (load signal).

We have used a rather crude technique where we look for the local maxima and minima and then create a new signal that is the average of these.

The technique works quite well and has the advantage that it adapts itself to vibration level, is fast (no filter time constant) and is totally transparent when vibrations are non-existant.

It is only when vibration saturates the load cell or its electronics that you have to watch out for false readings. The check for saturation can be easily built into the algorithm.

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Eliminating vibration effects from the output signal of a loadcell?

(OP)
Thanks good idea. But what if the vibrations are not symmetrical then does it still work? Also at what rate do you convert the signals?  

RE: Eliminating vibration effects from the output signal of a loadcell?

You are right. If they are not symmetrical, you will get an error. But you can easily check that with an oscilloscope. We use around 3 kSa/s. That is our standard sampling rate for low-frequency and process signals.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Eliminating vibration effects from the output signal of a loadcell?

At a trade show, Sartorius had an agitated batch mixer bouncing and thumping, and I couldn't believe it when the guy put a 50g weight on the top of the vessel and the indicated weight immediately responded showing an increase of 50g.  Clearly, zero averaging on the output.  

The explanation was that the mounting jig reduced non-vertical forces to zero to eliminate the effects of agitator perturbations that typically forces the use of signal averaging that severely damps the response of the weight signal.  

I don't know if the same is true for higher frequency vibrations, but if beating the existing vibes with other vibes doesn't work, you might want to call the mechatronics division of Sartorius.   

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