Scale calibration is the technical process that determines the difference between the value displayed by a weighing system and a traceable reference weight. Properly performed calibration not only shows whether the value on the screen is correct; it also reveals in which load range the deviation occurs, the repeatability, and the behavior at corner loads.
In this guide, we explain the calibration steps that can be applied for platform scales, floor scales, truck scales, and industrial weighing systems; the difference from legal inspection, and how it should be included in the maintenance plan.
Is scale calibration the same as inspection?
No. Calibration compares the measurement result with a traceable reference and reports deviations. Adjustment is the modification of the indicator or system parameters to reduce allowable deviation. Legal inspection and stamping are the conformity procedures carried out by authorized organizations within the scope of relevant legislation. A calibration certificate alone does not replace legal inspection.
Why is a scale calibrated?
- To maintain the correct amount of raw material in production recipes
- To prevent material loss in shipments and commercial weighings
- To demonstrate measurement traceability in quality management systems
- To verify the system after the replacement of the load cell, indicator, or mechanical components
- Determine drift, wear, and environmental effects that occur over time
Preparation before calibration
The first step is to determine the scale’s capacity, division value, and intended use. Reference weights must be in a class suitable for the target accuracy, current, and traceable certificate. The scale should be empty, clean, and mechanically free; it should be checked that the platform does not rub against the chassis, ramp, or surrounding foreign objects.
After power is supplied, the warming-up time recommended by the manufacturer is waited. Cable connections, grounding, junction box, signs of moisture, and load cell feet are examined. In a truck scale, the presence of stones, mud, or ice between the approach ramps and the platform can affect the zero point.
How is scale calibration done step by step?
1. Zero check
The indicator is zeroed when the platform is completely empty. The return to zero is checked several times. If the value stays at a different point continuously after unloading, mechanical sticking, cable issues, humidity, or load cell zero balance should be investigated.
2. Repeatability test
The same reference load is applied to the same position at least three times. The results are expected to be close to each other. Large differences may indicate loose connections, insufficient floor rigidity, electrical interference, or a damaged load cell.
3. Linearity test
The load is gradually increased and then decreased at different points of capacity. Zero, medium capacity, and points near full capacity must be observed. At each point, the reference value, display value, and error are recorded. The difference between loading and unloading results provides information about hysteresis.
4. Corner and eccentric load test
On platforms using multiple load cells, the same load is applied to different corners of the platform. If one corner gives different results from the others, the corner adjustment in the junction box, cable resistance, mechanical load transfer, and the corresponding load cell are checked. Mechanical causes must be eliminated before making any adjustments.
5. Adjustment and verification
If the results are outside the acceptance limits, zero and span adjustments are made by the authorized technical personnel. After the adjustment, all tests are repeated from the beginning. However, an adjustment made to display only a single point correctly does not mean that the system is correct across the entire measurement range.
What should be the calibration period?
There is no single fixed period for each operation. The period is determined according to usage frequency, the load the scale is exposed to, environmental conditions, process risk, past calibration results, and the quality procedure. Systems that are used frequently or perform critical formulations should be checked more frequently. In addition to periodic calibration, interim verification is recommended under the following circumstances:
- When the load cell, indicator, or junction box is replaced
- When the scale is moved or work is done on the foundation/chassis
- When there is overload, impact, lightning, or flood
- When unexplained deviation is observed in the results
- When a system that has not been used for a long time is reactivated
Most common calibration errors
Using an inappropriate reference weight, reading the platform before full load transfer, not warming up the scale sufficiently, and checking only at a single point are common mistakes. In addition, making electronic adjustments without evaluating wind, vibration, temperature changes, and floor deflection can hide the problem.
What should be included in the calibration record?
Device identification, brand-model, serial number, capacity and division value; environmental conditions, certificate information of the references used, test points, measured errors, uncertainty, applied settings, and evaluation of results must be recorded. These records are important to observe trends in subsequent checks.
load cell calibration and system calibration
A load cell or weighing cell can be characterized alone in the laboratory; however, the accuracy of the scale in the field depends on the platform, mounting elements, cables, junction box, and weighing indicator should be evaluated together. Therefore, the component certificate does not replace field verification of the installed system.
Frequently Asked Questions
How long does scale calibration take?
The duration varies depending on the capacity, number of test points, preparation of reference weights, and the need for mechanical adjustments. A full-capacity truck scale cannot be completed in the same time as a small platform scale.
Can the scale be used during calibration?
No. For safe and traceable results, the scale must remain under control throughout the test and should be closed to process or vehicle traffic.
Is the label sufficient after calibration?
The label quickly shows the last inspection date; the actual technical evidence is the record that contains measurement results, references, and uncertainty.
Technical support for accurate planning
To determine control points suitable for your scale type, capacity, and process risk You can contact Kobastar. When correct equipment selection, mechanical control, and recorded verification are considered together, the reliability of the weighing system can be maintained.