Navigation:  Tutorials > Measurement tutorials > Strain measurement > DEWESoft 7.0  data acquisition, processing, analyzing and storage software Quarter bridge setup

Let's take a look at a quarter bridge setup in DEWESoft using DAQP-BRIDGE-A. A single strain gage is attached to the tuning fork. From the specification, we can see that the resistance of the strain gage is 120 Ohms and the gage factor k is 2,07. When selecting strain gages, we can typically choose from 120 or 350 Ohms. 120 Ohms gages will have less power consumption and less heating, while 350 Ohms will have large signals and therefore work better with longer cables.

 

With this information, we can set the quarter bridge with 120 Ohms as the input type. This means that the single bridge will be the real gage, while other three gages will be internal precision resistors. Now, the input scaling is in mV/V .

We can freely select the Excitation voltage . A higher excitation voltage will increase the signals, and therefore reduce the noise. This will also cause more gage self-heating and will increase the power consumption. All strain gages has a certain limit for excitation voltage, so check this prior to connecting the sensor not to burn it. Higher excitation voltages are therefore recommended for longer lines. The next step is to enter the k factor and Bridge factor from the specification. Since this is only a quarter bridge, we can enter the bridge factor as 1.

 

The scaling changes from uV/V to um/m. We can now enter the range in units of relative deformation.

 

We have the tuning fork connected with three wire connection. The three wire connection allows us to cancel out the effect of wire resistance. Especially with long cables, the wire can significantly reduce the sensitivity of the gage. The third wire combined with the shunt calibration allows us to measure this resistance and correct this error.

The shunt calibration can be used to measure and correct the resistance in this case. We need to choose the Bridge cal scaling and click the Compensate button . Shunt calibration takes a while since it has to set several configurations and measure back the results. After that, the wire resistance measurement shows in the drawing, the Corr(ection). factor is shown and, if possible, the Excitation voltage level is raised to still meet the required sensitivity of the gage.

As the last step, we set the Lowpass filter of the amplifier to 5 kHz to be able to see the tuning fork natural frequency, which is 440 Hz (A4 tone).