Q. What is a “Virtual Measurement”?

A. Materials testing software uses two types of measurements to provide resuts or input for result calculations; physical measurements and virtual measurements.

A physical measurement is measurement data that is provided directly from a transducer that is monitoring the specimen, such as a load cell or an extensometer. A virtual measurement is measurement data that is provided as the result of a calculation. The inputs to the calculation can be one or more physical measurements, user-entered values, or previously calculated results.

A simple example of a virtual measurement is tensile stress, which is calculated as load (a physical measurement provided by the load cell) divided by the cross-sectional area of the specimen (usually a user-entered value).

A commonly overlooked virtual measurement is corrected extension, which adjusts values of crosshead or actuator extension to correct for compliance, or elastic stretch, of the testing instrument and load string components. Corrected extension is calculated as extension (a physical measurement provided by an encoder or LVDT) adjusted by a value taken from a compliance data file.