All of Epsilon’s strain gaged transducers employ a full Wheatstone bridge design. They are powered by an excitation voltage, typically between 5 and 10 VDC. The output of the extensometer is proportional to the excitation. For this reason the calibrated output is often expressed as mV/V value. An extensometer with a full scale span of 2.345 mV/V will have a full scale output of 23.450 mV if the excitation is 10V. This span data is provided by Epsilon on each extensometer test certificate.
All strain gaged sensors must be connected to some external electronics to provide readings. The electronics provide the excitation and normally amplifies the sensor’s output to a high level DC voltage. This resultant voltage is used for readout or control of the test machine. In digital systems the voltage output is converted via data acquisition hardware into engineering units of strain. In instances where a chart recorder or X-Y recorder is used, the output is set to easily yield a specified strain/cm on the graph.
When any new device like an extensometer is first used, the sensor must be calibrated with the electronics to ensure proper configuration. There are several ways to accomplish this. Generally the process is very straightforward. If your extensometer will be connected to an available strain channel in your test controller, Epsilon can normally supply the unit with the correct connector to plug directly in. For external data acquisition systems, a strain gaged signal conditioning module capable of providing the excitation is required. Often this is part of the data acquisition system. For systems that require high level inputs or for use with chart recorders and X-Y plotters, Epsilon offers optional signal conditioning electronics.