Tutorials > Measurement tutorials > Strain measurement

For full bridge sensor we will use a "home made" force sensor. The sensor is built from two xy strain gages, where one gage is oriented in the principal direction and another one in transverse direction. This sensor is therefore temperature compensated and has bending cancellation.

Let's do a step by step calibration of such a configuration. First of all we change the Input type to Full bridge and Balance sensor is performed. If the bridge zero is not successful, we should choose the highest possible Range, perform zero, then switch to the wanted range and perform zero again. Then we set the Lowpass filter . Since this example will measure more or less static measurements in a low region of the probe, the results can be enhanced by using a very low lowpass filter. In this case it is set to 10 Hz .

Full bridge channel setup - 1

Next we set the Strain scaling to used and set the k factor of the gages to 2 and the Bridge factor to 2.6 . The value of 2 is read from the strain gages data sheet. The value of 2.6 is a bridge factor from the table of bridge configurations. Now the input values are strain in um/m .

Full bridge channel setup - 2

Now we need to do the final Scaling by function since the force should be measured in N. Now it's time to do some calculations using following equations:

Stress = Force / Area and

Stress = E · Strain

Therefore the Force = Area · E · Strain. Given that the elastic modulus (Young's modulus) of steel is 210000 N/mm2 and the cross section of the sensor is 139 mm2 we get:

Force = 139 mm2 · 210000 N/mm2 · strain / 1E6 = 28 · strain

Factor 1E6 is there because the strain is measured in um/m and we need to have a scaling factor for this unit.

Full bridge channel setup - 3

Now we have the real data scaled in N. The last thing to do is to select the measurement Range based on the input . In this case the lowest range will be more than enough for the measurement.

The Short and Shunt button is for checking the strain gage. The Short is used to short the pins on the input and measure the bridge offset. The Shunt (which is also used in the shunt calibration routine) can be used to see if the bridge is reacting - so to check if the connections are working.