How often a force gauge, dynamometer, load cell or load shackle should be calibrated is a question every auditor asks and to which no law gives a fixed answer. The interval comes from your own quality system and must be justified. In this article you can read which reference points standards offer, which factors make the interval shorter or longer and how you make a well-founded choice using the certificates from force calibration.
What do the standards say?
For most force measuring instruments there is no legal verification obligation; that does exist for scales used for trade. Quality standards such as ISO 9001 require measuring equipment to be calibrated at specified intervals and that you can justify those intervals. Some concrete reference points:
- ISO 376 sets the maximum validity of a calibration of reference force transducers at 26 months.
- ISO 7500-1 covers the verification of tensile and compression test benches; this is generally carried out annually.
- Manufacturers of dynamometers and crane scales usually recommend annual calibration.
- For lifting equipment there is also a periodic inspection of the lifting component itself; that is a separate assessment, not a calibration of the measurement.
A good starting point: 12 months
For a new or unknown instrument, an interval of twelve months is a sensible start. It matches most manufacturers' recommendations, fits into an annual audit cycle and after two calibrations already gives a first picture of the stability. Choose a shorter interval for:
- intensive or rough use, such as daily lifting, shock loads or outdoor use;
- measurements with direct consequences for safety, such as proof load tests and monitoring working loads;
- small tolerances relative to the accuracy of the instrument;
- an unknown or poor history, for example after purchasing used equipment.
When to recalibrate immediately?
Apart from the interval, there are events that make a new calibration necessary, regardless of the date on the certificate:
- Overloading, even briefly: the measuring body may be permanently deformed.
- A fall or knock to the transducer or indicator.
- Repair or replacement of cable, connector, amplifier or display, because the measuring chain then changes. See sensor or complete measuring chain.
- Deviating zero after unloading, or an indication that does not become stable.
- Moisture or corrosion on the transducer or connector.
- Long storage without use, especially for mechanical force gauges.
Extending the interval with justification
An interval may become longer if the history justifies it. To do this, compare the deviations on consecutive certificates at the same measuring points. If the change between two calibrations remains well within the tolerance you apply to the instrument, an extension to, for example, 18 or 24 months is defensible. Observe the hard limits from the standards, such as the 26 months of ISO 376, and record the justification in your measuring equipment register. A practical checklist can be found in measuring equipment management checklist.
Note: a stable deviation is not the same as a small deviation. A transducer that deviates by 0.3 % every year is predictable and can be perfectly usable with a correction. A transducer that deviates by 0.1 % one year and 0.4 % the next actually calls for a shorter interval.
Interim checks
Between two calibrations you can keep an eye on things yourself:
- a check load of known mass, for example a calibrated weight, for a dynamometer or crane scale;
- a fixed reference load in the installation, for a load cell in a press or dosing system;
- the shunt or cal function of the indicator as a check of electronics and cable, not as a calibration;
- a zero check after every use.
Record the results. They are not a replacement for the calibration, but they do show whether the instrument has changed in the meantime and strengthen the justification for your interval.
Guide values per type of instrument
As a starting point, always to be adapted to your own use and risk:
| Instrument | Usual interval | Point to note |
|---|---|---|
| Dynamometer or force gauge in lifting applications | 12 months | Matches the periodic inspection of lifting equipment; earlier after shock loading |
| Load shackle or load pin | 12 months | Mounting and pin wear; also check the zero after use |
| Load cell in a press, assembly line or dosing system | 12 months, 24 with a stable history | Calibrate as a complete measuring chain with its own indicator |
| Hydraulic jack or cylinder with force readout | 12 months | Recalibrate after every overhaul of seals or pressure gauge |
| Crane or hanging scale | 12 months | If used for trade, the legal verification obligation also applies, see scale verification |
| Reference transducer according to ISO 376 | 12 to 24 months, maximum 26 | Class lapses when the readout is changed |
Do you rarely use an instrument, for example only for an annual proof load test? Then schedule the calibration shortly before that use, so that the certificate is valid and recent at the time of the measurement.
Schedule it and get reminded
The biggest risk is not a wrong interval, but an expired certificate that nobody noticed. Record the next calibration date for each instrument and have yourself reminded in time. In the MASSLAB customer portal you can see the history and expiry date for each force measuring instrument and you automatically receive a reminder.
In summary
Start with an interval of twelve months, shorter for heavy use or safety-critical measurements, and only extend on the basis of a demonstrably stable history and within the limits of the standards. Recalibrate immediately after an overload, fall, repair or a deviating zero. Would you like to have your force gauge, dynamometer or load shackle calibrated? See the options at force calibration in tension and compression.