Load cell

[joebacks]

Does anyone knows this?

We have a problem of this load cell, because we test its output signal, it gave some 2Vdc reading instead of some millivolt range. What might be the cause of this load cell trouble? Is there any way on how to fix this?

thank you so much...

 

[SABorn]

How did you test it?
As it will give a voltage out normally around the 2 volt mark, but any changes in the voltage will be in the mV range either side of the 2 volt depending how the load is applied to the cell.

Google "strain gauges" as these are what the cells have stuck to the block of metal to measure the tiny flex in the metal, it will give you a much better understanding on how a load cell works.

Normally to test a cell you would use 4 resistors configured as a wheatstone bridge with somewhere around 470 ohm resistors.

If the cell has been over stressed then it is useless attempting a repair.

If the cell is still mounted in it original location then check for corrosion or rust under the cell, as i have had many that a small amount of rust can place enough pre stress on a cell to over load it before weight is applied.
We are talking a mere fraction of flex in the cell for maximum reading, and corrosion or rust under the cell can cause this very easy.

Pete.

 

[joebacks]

Thank you so much...


We supplied at its excitation of around 10VDC, and measured its output signal, but it read 2VDC without any load instead of some mVolts range.

 

[Reloadron]

Attached is a basic image of a strain gauge as it is used in a simple Wheatstone bridge for a load cell. If you read this link it pretty much covers things over several pages. Pretty good read on strain gauges and load cells.

As to your problem, my guess is that the load cell was damaged. You should be seeing millivolts from a typical load cell sans any amplifier. Load cells typically have a mV/V output based on excitation voltage. For example a 500 Lb (or 500 Kg) load cell may have a mV/V of 3 mV. That means under a full load the load cell with 10 volts of excitation would output 30 mV.

The only way you would see a voltage like 2 volts is if the cell is severely damaged or as was pointed out by SABorn, if there was corrosion or a conductive liquid that leaked into the cell on the bridge itself. Some load cells do have 6 pins to allow for sense lines on the excitation lines. You are sure you are applying the excitation correctly and measuring the output correctly at the right pins (location terminals). You don't mention a make and model of the load cell?

Ron