Force and displacement calibration

The top-loading scalepan TMAs require no calibration. Instruments fitted with the voice coil type motors will require calibration. Most instruments achieve this by applying one or more known masses (which can be accurately measured on a balance cahbrated by traceable standards) and nulling the displacement that occurs. This way the force required to rebalance the applied mass is obtained independently from the displacement measurement. The instrument measuring system will adjust the voltage or current applied to the coil, and when the displacement has been successfully nulled this value is equivalent to the force due to the applied mass. The value of force to current should be linear over the range of operation of the instrument. 

Displacement calibration is usually made by inserting known thickness samples, such as slip gauges, into a suitable fixture and noting the resultant displacement. A calibration can be created from these measurements. The displacement applied should be traceable to primary or secondary standards. LVDTs are usually linear over their range of operation and typically cover 1- to 5 mm with resolution to 0.1 xm or better, which is usually sufficient for most experiments. 

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