Factory Calibration and Linearisation: How Dead-Zone Compensation Gets Written 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
Each sensor'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, temperature-drift curve and so on) 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 before and after calibration:
| Stage | Reading deviation | Notes |
|---|---|---|
| Raw reading | Includes individual error | Uncompensated |
| After calibration | Pressed inside the specification | Compensation parameters written |
Dead-zone compensation
The measuring dead zones at both ends (see measuring dead zones) cannot be linearised into the effective zone; the calibration process treats the dead-zone segments specially 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.
Practical tips for engineers
- Analog outputs are factory-calibrated slightly wider than the nominal stroke; after installation the machine must be recalibrated.
- Two-point method: Slope = actual displacement ÷ (stroke-end reading − zero reading); Datum = Slope × zero reading; machine position = (Slope × current reading) − Datum.
- Example: zero reading 0.2 V, reading after moving 98 mm is 9.5 V → Slope = 98÷(9.5−0.2) = 10.537, Datum = 10.537×0.2 = 2.106.
Frequently Asked Questions
Q: Is factory calibration done on every unit?
Yes. Individual differences are calibrated unit by unit, not as one parameter set per model.
Q: What does linearisation solve?
It corrects the non-linear deviation of the full-stroke reading from the ideal straight line, pressing it inside the stated specification.
Q: Is a site zero still needed after calibration?
Yes. The mechanical zero offset still has to be set once at installation.