Scale calibration with certificate

Calibration means measuring how far a scale deviates and recording that in a certificate. That is what an auditor wants to see, and it is something different from verification. We calibrate scales and balances from a few milligrams up to 60,000 kg, at your site or in our workshop - even if you bought the instrument elsewhere.

What is calibration?

During a calibration, the technician places test weights of known mass on the scale and records what the instrument reads. The difference between the two is the deviation. This is done at several points across the weighing range, because a scale that is correct at 1 kg can have a different deviation at 30 kg.

Calibration in itself changes nothing about the scale: it measures and records. If the deviation is larger than you allow, the next step is adjustment - setting the instrument so that it weighs correctly again - after which we measure again. That is different from verification, the legal inspection for scales used to charge by weight in trade. The difference is explained in detail in verification or calibration.

When should you have a scale calibrated?

The law does not require calibration, but your quality system usually does. ISO 9001 requires that measuring equipment used to demonstrate the quality of your product is calibrated traceably; HACCP, GMP, BRC and IFS ask the same for the scales in your process. The auditor wants to see the certificate, and the date on which the next calibration is scheduled.

Apart from the fixed interval, a calibration is advisable:

• after the instrument has been relocated or moved;
• after it has been dropped, knocked or overloaded;
• after a repair or a replaced load cell;
• if your own check weight shows a deviation larger than the limit you have set;
• before you put a new scale into service for a critical weighing.

How often it is needed, and how to justify that interval, is explained in how often should a scale be calibrated.

How a calibration works

1. Request. You give us the make, type, weighing range and readability, and where the instrument is located. You get a price in advance.
2. Appointment. At your site, in our workshop, or you send the instrument in. If there are several scales at one location, we do them in the same round.
3. Preparation. The instrument and the test weights acclimatise to the environment; the scale is levelled and cleaned where necessary.
4. Measurement. The deviation at several load points up to the maximum, the repeatability with the same weight, and the eccentricity: the same weight in the corners and in the middle of the weighing platform.
5. Adjustment if needed. If the scale is outside tolerance, we adjust it and measure again. Both the before and after values go on the certificate.
6. Certificate. You receive the certificate with all measured values, the measurement uncertainty and the weights used.

What is on the calibration certificate?

A certificate that is useful to an auditor says more than "approved". Ours includes:

• the identification of the instrument: make, type, serial number, weighing range and readability, and where it is located;
• for each load point, the test weight, the reading and the deviation;
• the repeatability and the eccentricity;
• the measurement uncertainty for the measured values;
• the test weights used, with their class and their own calibration, so that the measurement is traceable;
• the conditions during the measurement, the date and who carried it out.

What these details mean and what to look for is explained in what a calibration certificate contains.

Calibrated to Euramet cg-18

We calibrate to Euramet cg-18, the European guideline for the calibration of non-automatic weighing instruments. This guideline sets out which measurements are included - linearity, repeatability, eccentricity - and how the measurement uncertainty is determined. That way you know not only how much the scale deviates, but also how certain that statement is.

If your auditor asks for a certificate under accreditation (ISO/IEC 17025), please mention this in your request. We will then tell you in advance what is possible in your case.

On site, in the workshop or sent in

A floor scale, a pallet scale or a weighbridge we calibrate where it stands. That has an advantage beyond convenience: the instrument is measured on its own floor, with the vibration, draughts and temperature it experiences there every day. For the heavy test weights we have our own transport.

An analytical balance or a fine precision balance we prefer to calibrate in the workshop, where the conditions are controlled. A bench scale can go either way; sending it in or having it collected is often quickest. We will tell you what makes sense in your case when you make your request.

From milligrams to 60,000 kg

The weighing range determines which test weights are needed. For an analytical balance reading to 0.1 mg, these are fine weights in the highest classes; for a 3,000 kg floor scale or a weighbridge, they are weights of hundreds of kilos at a time. We calibrate the entire range, from laboratory balances to weighbridges of 60,000 kg.

Calibrating test weights: Masslab

A calibration is only as good as the weights used for the measurement. Our own test weights, and those of our customers, are calibrated in our laboratory Masslab, in OIML classes E2 to M3. Masslab customers can view their certificates, with the measurement results and the measurement uncertainty, in the customer portal on masslab.nl, and can schedule a collection there themselves.

If you use your own check weights for interim checks, have them included in the same round.

Calibrated from day one with a new scale

For 498 versions in our catalogue, you can order a calibration certificate together with the scale; you will see it with the product in the table of versions. The scale then arrives calibrated and your records start on the day of delivery. For floor, pallet and analytical scales, you can also order installation with on-site calibration as a service straight away.

Also for scales you bought elsewhere

Measuring and recording is possible for virtually any instrument, regardless of make or supplier. Adjustment is possible for most; for a verified instrument this also requires re-verification, which we arrange through the manufacturer for KERN, Adam, OHAUS, Baxtran and Gram. For another brand, we tell you in advance what can and cannot be done.

Between two calibrations: checking it yourself

A certificate tells you how the scale weighed on that day. What happens afterwards you will only see if you check it yourself: regularly place a check weight on the scale, sometimes on the edge of the weighing platform too, and note what it reads. That log shows at an audit that the instrument was in order between two calibrations. If it deviates, first have a look at why is my scale inaccurate.

Internal adjustment does not replace calibration

Many analytical and precision balances have a built-in adjustment weight: at the press of a button, or automatically when the temperature changes, the balance adjusts itself. That is convenient and keeps the balance sharp from day to day, but it is not a calibration. The internal weight is not itself traceably calibrated, and it checks only one point of the range.

A calibration with external test weights records what the balance does across the entire range, and at the same time checks whether the internal adjustment is still correct. For an audit, that certificate is what counts.

When is a deviation too large?

You decide that yourself, based on what you weigh. A certificate states how large the deviation and the measurement uncertainty are; whether that is good enough depends on the tolerance your process requires. Someone who has to dose a 5 g ingredient to within 0.1 g sets a different limit from someone checking one-tonne pallets. Record that limit in your quality system; you will then see straight away on the certificate whether the instrument complies.

If you have not yet set a limit, what accuracy and capacity do I need will help you on your way, and we are happy to advise during the calibration.

Calibration by sector

• Food - HACCP, BRC and IFS require calibrated scales for recipes, fill weights and checks for the e mark.
• Laboratory and pharmaceutical - GMP and internal procedures require short intervals and a certificate with measurement uncertainty, often per balance.
• Production and logistics - ISO 9001 requires that floor, pallet and counting scales used for shipping or receiving goods are demonstrably accurate.
• Healthcare - personal and baby scales used for medical decisions must be and remain reliable.

Which scales are used in each sector is shown under scales by sector.

After the calibration

You keep the certificate in your quality file; together with your own log of interim checks, it shows that the instrument was in order all year. We help you set the interval and keep track of when the next calibration is due.

Request calibration

Call +31 345 786 553, email sales@weegexperts.nl or use the form on this page. Useful to have to hand:

• make and type - a photo of the type plate is enough;
• the serial number and the weighing range;
• whether it carries an M mark;
• what you have noticed, or what you need;
• where the instrument is located, and whether it can be moved.

We will then tell you what can be done, what it costs and when it can be scheduled. Calibration often goes together with maintenance; the full overview is under scale services.

Frequently asked questions about calibration

Is calibration a legal requirement?

No. The law requires verification if you charge by weight in trade; calibration is required by your quality system, such as ISO 9001, HACCP, GMP, BRC or IFS. In practice, the auditor wants to see a valid certificate.

Is calibration the same as verification?

No. Calibration records how much a scale deviates. Verification is a legal inspection that is required if you charge by weight. A calibrated scale therefore cannot simply be used for trade.

How often should I have calibration done?

That is determined by your own quality system, not by law. Once a year is a common starting point; more often with heavy use, a demanding environment or critical weighings.

What happens if my scale deviates too much?

We adjust it and measure again; the before and after values both go on the certificate. If there is more to it, such as a damaged load cell, we tell you first with a price, and you decide.

Does the scale have to come to you?

Not necessarily. Floor scales, pallet scales and weighbridges we calibrate on site; fine balances we prefer to do in the workshop. Sending it in or having it collected is also possible.

What does a calibration cost?

That depends on the weighing range, the number of measuring points, where the instrument is located and how many scales are included in the same round. You get the price in advance.

Can I have a new scale supplied calibrated?

Yes, for 498 versions in our catalogue. You select the calibration certificate with the product; the scale then arrives calibrated.

Do you also calibrate scales of other brands?

Yes. Measuring and recording is possible for virtually any instrument. What can be done afterwards in terms of adjustment or re-verification depends on the brand; we tell you in advance.

Do you also calibrate test weights?

Yes, in our laboratory Masslab, in OIML classes E2 to M3. The certificates are then available in the Masslab customer portal.