Magnetostrictive Displacement Sensor Calibration: Writing Dead-Zone Compensation into Firmware

Factory calibration is the process of writing each magnetostrictive displacement sensor's individual differences into firmware; linearisation compensation then corrects the deviation of the full-stroke reading from the ideal straight line (including dead-zone handling). These two steps are what put the stated non-linearity inside the specification, rather than relying on theoretical design alone.

What calibration does

Calibration is done per unit, not as one parameter set per model. Each unit's waveguide length, speed of sound and electronics-head delay differ slightly. At despatch, "true position vs. measured reading" is taken at several standard position points, and that unit's unique compensation parameters — zero offset, span coefficient and temperature-drift curve — are calculated and written to the electronics-head memory.

Linearisation: correcting non-linearity

The raw reading deviates from the ideal straight line; linearisation uses fitting and look-up tables to press the full-stroke deviation inside the stated non-linearity. For the definition and reading of non-linearity see the three accuracy terms. An illustrative comparison of the raw reading against the calibrated reading before and after pressing into spec:

Dead-zone compensation

The measuring dead zones at both ends (see measuring dead zones) cannot be linearised into the active range; the calibration process treats the dead-zone segments specially in firmware so that readings inside the effective range stay continuous and stable.

Engineering meaning

• Factory calibration is done on each unit, not "one parameter set per model";
• Calibration solves the sensor's individual deviation; the mechanical zero offset still has to be set once at installation (see zero-calibration steps);
• Methods for synchronised calibration of several sensors are in synchronised calibration of multiple sensors.

Overall installation and commissioning is in installation in practice; the relationship between calibration and accuracy figures is recapped in resolution, repeatability and non-linearity. Factory calibration sets the sensor's own accuracy; the whole chain still inherits the error of the PLC analog input card, so a coarse card caps practical accuracy well before the sensor itself.