Siemens SIWAREX WL200 Series Operating Instructions Manual page 14

Description
3.2 Design and principle of operation
Principle of operation
The basic component in each case is a special type of spring body. The application of force
elastically deforms the spring body. The ohmic resistance of the strain gauges changes as a
result.
Figure 3-2
For each load cell, at least four strain gauges are connected together as a complete
Wheatstone bridge. The stretched or compressed strain gauges are connected in such a
manner that the positive or negative resistance changes are summed to produce an overall
imbalance of the bridge.
The supply voltage is applied across one diagonal of the bridge and, in the case of the six-
wire connection method, also the sensor voltage SENSE. The measured voltage is tapped
across the other diagonal.
For a constant supply voltage EXC, therefore, the measured voltage SIG changes
proportionally to the introduced load. In practice, load cells contain additional resistors for
temperature compensation and for zero-signal and characteristic-value compensation.
Depending on their type and the requirements, these resistors can be arranged at the input
or output of the load cell.
Figure 3-3
14
Principle of operation, based on the example of a loaded bending beam load cell
The principle of a Wheatstone bridge
Operating Instructions, 07/2016, A5E02199611B-03
SIWAREX WL200