Load cells

[NavArcJim]

I'm looking for guidance on the acceptable scale range of a load cell or Dynamometer when used for load testing.
for example for some torque wrenches, torquing is only accurate to values between 20% and 90% of the scale range.

is there any guidance for load cells / dynamometers? Is there a specification or technical instruction that backs that up?

thanks

 

[CoryPad]

They vary greatly. For example, new force cells from Instron are guaranteed to be linear, repeatable, and lacking hysteresis (within < 1%) from < 1% to 100% of full force, while force cells from other sources are much worse.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[JR97]

NavArcJim
Your load cell should be calibrated below and above where you intend to use it. Load cells definitely lose some linearity on the low end of the scale.

One thing to watch out for - manufacturers all spec their equipment accuracy as %full scale. That defines the potential error. At the low end, the error can be a much higher %. In other words, the accuracy they sell is % scale while what you need is % reading.

What we do is establish what % error we can stand (typically 1%) and apply that percentage at each calibration point. The result is the bottom end of the readout usually does not meet the criteria.

A rule of thumb I use is 20 - 100% of full scale.