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Force sensor calibration errors should be investigated before anyone changes the zero or span. A press that reads high at every test point needs a different investigation from one that reads correctly on loading but not on unloading. Keep the original readings, fixture arrangement and instrument settings: an adjustment can hide the symptom without removing its cause.
Read the error pattern before changing the calibration
Record the reference force and indicated force at several points through the working range. Calculate indication error as indicated force minus reference force, using the same units. Take readings in both increasing and decreasing load sequences where the equipment and approved method permit. A single full-scale point cannot show what happens between zero and maximum load.
| Observed pattern | Possible explanation | Next check |
|---|---|---|
| Offset | A similar force difference at several points | Check fixture preload, stored tare and the unloaded reference condition before resetting zero. |
| Scale error | Error grows approximately with applied force | Compare sensitivity, excitation, units and amplifier scaling with the identified sensor and reference. |
| Direction effect | Different readings at the same force on loading and unloading | Investigate friction, backlash, seating and hysteresis; do not fit one correction to conceal both curves. |
| Time effect | Indication changes while reference force is held | Record dwell time, temperature and both instruments together to distinguish reference drift from the test chain. |
| Step or plateau | A sudden jump or a reading that stops increasing | Inspect contact changes, mechanical stops, input overload and numerical clipping before repeating the load. |
These patterns suggest tests; they do not identify a failed component by themselves. For example, a sticking guide can create a repeatable direction-dependent error even when the load cell is healthy. Repeat a suspect point with the same setup before changing one variable, then record whether the pattern changes.
Force sensor calibration errors caused by configuration
The MV-LC0190 product data distinguish the 1 kg version, rated at 0.5 ±0.1 mV/V, from the 5, 20 and 50 kg versions, rated at 1.0 ±0.2 mV/V. Entering one nominal sensitivity for every capacity is therefore wrong. Use the supplied unit-specific calibration result where available; a catalogue tolerance is not a substitute for that result.
Check the force units throughout the chain. A capacity described in kilograms does not make a force reading in newtons numerically interchangeable with mass. When mass standards apply the reference force, the method must account for gravity and any other corrections needed at the required uncertainty. Avoid adding precision to the conversion that the reference method cannot support.
Save the raw bridge reading or instrument input value alongside the displayed engineering value when the equipment permits it. If the input follows the reference but the displayed value does not, investigate scaling and software. If both are wrong, examine the sensor, fixture, excitation and reference before editing a conversion factor.
Define what the calibration actually covers
A bare-sensor calibration and a machine-level check answer different questions. The first describes a transducer under its calibration conditions. The second includes mounting, force transmission, cables, conditioning and the selected readout. For product acceptance on a machine, identify the exact value used by the acceptance logic, not just the value visible on a nearby display.
Use the installed fixtures when they are part of the intended measurement. Confirm that the reference is in the same force path and that no guide, stop or contact carries load around it. Do not assume that two sensors positioned at different points in a moving mechanism must measure the same force; friction and inertia may separate those forces.
Set the loading direction, preload, stabilization criterion, dwell and filtering before collecting the comparison data. If the method changes midway, separate the runs. The installed load-cell calibration guide covers preparation and records for the wider commissioning procedure.
Decide whether the evidence supports acceptance
The display increment is the step between adjacent displayed values. Measurement resolution concerns the smallest force change that produces a discernible response under the test conditions; noise or friction may limit it. Neither value is calibration uncertainty. The reference certificate, repeatability, alignment, temperature, loading procedure and readout all contribute to the result. A finely divided display cannot compensate for an unsuitable reference or an unstable fixture.
Agree the allowable error and how measurement uncertainty affects the pass/fail decision before testing. If a result is close to the acceptance limit, the indicated difference alone may not justify a pass. Record the decision rule and any restricted range rather than silently widening the tolerance after seeing the data.
After an authorized repair or adjustment, retain both the as-found and as-left results. Where the as-found condition could have affected earlier production decisions, the equipment owner should assess the affected period and records. Recalibration does not retrospectively prove that those measurements were acceptable.
Calibration troubleshooting questions
Q1. Can I correct the problem with a two-point adjustment?
Only after the cause is understood and the method allows that adjustment. Two points can set zero and scale but cannot demonstrate intermediate linearity, return-to-zero behavior or loading-direction effects. Verify additional working points after the adjustment.
Q2. Why does the result change after removing and reinstalling the cell?
Contact position, thread engagement, preload or alignment may have changed. Compare the installation with the approved drawing and repeat the relevant checks. A stored calibration factor should not be accepted unchanged merely because the sensor serial number is the same.
Q3. Does a successful static check prove a press can capture a short force peak?
No. A static check does not establish the response of the sensor, conditioner, filter and recording chain during a fast event. Test that measurement separately under representative timing conditions; the MV-LC0190 data cited here do not establish a dynamic bandwidth.
Q4. What should accompany a request for calibration assistance?
Provide the sensor model and capacity, fixture photograph, reference identification, loading sequence, raw comparison results, units and instrument settings. Include whether the failure appeared before or after a mechanical or software change. Send these through the METRAVON enquiry page so the discussion can start with the observed error rather than a replacement guess.
Summary
Preserve the failed result, classify its pattern and check the complete measurement arrangement before adjusting it. Acceptance requires a defined working range, suitable reference and agreed treatment of uncertainty. A corrected display alone is not evidence that the original cause has been removed.
