please I'm going to make a presentation about strain gauges and the part of calibration is difficult to me now i found and know the method but i don't know the exact purpose of strain calibration

 

Because the variation among strain gauges that are supposed to be alike is pretty large. I used to make strain gauges as part of my machine maintenance duties in the clean room. These were hand assembled units built to pretty precise tolerances, which is to say, calibration is a must.

Nothing in electronics is exactly alike. 1% Resistors are considered pretty precise, but precision equipment is even more so. All instrumentation requires calibration, always.

 

I agree completely with Bill's advice and would add that for real confidence in your measurements, it is important to add controls. The difference between calibration and controls can lead to a lengthy discussion, which is probably unnecessary here. Suffice it to say that calibration will often include testing several known objects to show and to adjust both linearity and accuracy. A control may be just one or two objects to show that the calibration has not changed.

Regards, John

 

thanks Bill so that's for knowing the maximum errors on it yes

 

I agree completely with Bill's advice and would add that for real confidence in your measurements, it is important to add controls. The difference between calibration and controls can lead to a lengthy discussion, which is probably unnecessary here. Suffice it to say that calibration will often include testing several known objects to show and to adjust both linearity and accuracy. A control may be just one or two objects to show that the calibration has not changed.

Regards, John

yes so before i use it i make voltage and temperature calibration and take my Precautions from errors

 

yes so before i use it i make voltage and temperature calibration and take my Precautions from errors

The output is linear with weight (mass) on the load cell : I follows, y= mx+b in Algebra terms. You need to calibrate the zero point (b) so it reads zero at zero load. Then you need to calibrate the gain (m) so the output follows the desired voltage change per kilogram of mass change.

You can adjust b and m every time the temperature changes or, you can use a second load cell in your reference (b) that is 90-degrees to the working cell. That is, it will not detect the mass change but will be the same temp as the working cell and (mostly) cancel any temperature error.

 

Note the difference between good circuit design and strain gauge calibration.

The actual physical characteristics of all components are subject to statistical variation over a range of values.
Good circuit design ensures that, as far as possible it should not make any difference to the circuit action whatever the value of the component parameter, so long as it is within range.

For instance feedback and other design techniques make the actual gain of a transistor unimportant for the circuit to perform its design purpose.
So a manufacturer can make insert a transistor straight out of the stock into a circuit board without having to calibrate each and every board he makes.
( This was once done before better design techniques)

However for certain components this cannot be done.
Examples include many transducers or sensors such as temperature sensors and strain gauges.