This picture shows a general arrangement of strain measurement on a beam. The beam is instruments with strain gauges and displacement transducers (LVDTs) and these are connected to an interface rack which sends the data to a computer.
This picture shows detail of the interface rack on one of our mechanical test machines. We have a number of cards for the racks that can read strain gauges directly but in this instance we are using an external bridge circuit.
We have large numbers of Linear Variable Displacement Transducers
This is a “digital DEMEC” for measuring strain