Force Sensor Calibration Errors and How to Prevent Bad Data

A calibration can produce a neat certificate and still fail to represent the installed force measurement. Common causes include an unsuitable reference, off-axis loading, fixture friction, unrecorded preload, unstable temperature, wrong excitation, excessive filtering and data reduction mistakes. Calibration should test the measurement chain under defined conditions and state its uncertainty and limitations. When results are unexpected, preserve the as-found state and isolate mechanics, sensor, electronics and calculation before adjusting span.

Define the measurand and range

State compression, tension or torque-related force, sign, working interval and required uncertainty. Identify whether calibration covers a bare sensor, assembled fixture or complete machine. A factory mV/V result and an installed displayed force are different measurands with different error sources.

Use a suitable reference

Confirm traceability, range, resolution, uncertainty and current status of weights, proving device or reference transducer. Account for local gravity where mass standards create force and precision requires it. The reference uncertainty should be small enough to support the intended acceptance decision.

Align force correctly

Use approved loading surfaces, adapters and bearings to apply axial force without moment or side load. Inspect contact and fixture stiffness. In tension, control thread engagement and backlash. Misalignment can create repeatable bias that looks like a sensor scale error.

Control preload and sequence

Record tare, fixture weight and preload. Use increasing and decreasing points with adequate stabilization to reveal hysteresis and creep. Avoid repeatedly returning only to a software zero that hides mechanical residual force. Define dwell time and cycle count before collecting results.

Stabilize environment and electronics

Record temperature, warm-up, excitation, amplifier range, cable, filtering and sample method. Prevent vibration and electrical noise from dominating readings. Do not compare values collected with different filter or averaging settings without accounting for response and uncertainty.

Check calculations and units

Verify mV/V conversion, capacity, gain, sign, decimal scaling and engineering units. Preserve raw readings before regression or corrections. Review whether a forced-zero or two-point fit conceals nonlinearity. Independent calculation checks catch errors that repeated loading cannot reveal.

Investigate failures systematically

If results exceed limits, repeat reference checks and inspect mechanics before changing calibration. Compare zero, bridge resistance, insulation, excitation and raw signal. Change one factor at a time. Record invalid runs rather than deleting evidence that may reveal instability or drift.

Report usable evidence

Include equipment identity, serial number, method, standards, environment, fixtures, points, direction, raw and corrected results, uncertainty, acceptance rule and as-found/as-left status. State untested directions or ranges. Link the record to configuration and responsible approval.

Engineering checklist

Define bare-sensor versus system calibration.
Use a traceable, capable reference.
Control alignment and fixture friction.
Test loading and unloading sequences.
Record signal settings and raw data.
State uncertainty and limitations.

Frequently asked questions

Can a two-point calibration prove linearity?

No. It establishes scale at those points but may not reveal intermediate nonlinearity or hysteresis.

Should span be adjusted immediately after a failure?

No. Preserve evidence and rule out mechanical, reference and electrical causes first.

Why include unloading points?

They reveal hysteresis and return-to-zero behavior hidden by increasing loads alone.

Decision record

Record the selected architecture, operating cases, assumptions, accepted limits and responsible approver. Attach drawings, calculations, calibration evidence and unresolved deviations. Define which mechanical, process, electrical or software change requires reassessment. Include the expected inspection interval, spare strategy, fault response and location of recoverable configuration files. Assign an owner and closure date to every conditional acceptance. Review the record after representative service and compare actual faults, drift and maintenance findings with the original assumptions. A concise decision record protects the engineering basis when equipment, personnel or operating conditions change.

Need a project-specific review? Send load cases, drawings, environment, signal requirements and acceptance criteria through our contact page.