Adjustment – what for?
Why should meters be adjusted?

adjustment (of a measuring instrument)
Definition of adjustment according to the International Dictionary of Legal Metrology Terms (Central Office of Measures. Warsaw, 2015)
An activity aimed at bringing a measuring instrument to a state of operation corresponding to its intended use.
Adjustment may be automatic, semi-automatic or manual.
•    Automatic adjustment – a set of operations performed without operator's intervention, which aim is to bring a measuring instrument to a state of operation corresponding to its intended use.
•    Semi-automatic adjustment – a set of operations performed partially without operator's intervention, which aim is to bring a measuring instrument to a state of operation corresponding to its intended use.
•    Manual adjustment – a set of operations performed by an operator, which aim is to bring a measuring instrument to a state of operation corresponding to its intended use.

Note 1
Types of adjustment include:
•    zero adjustment of a measuring instrument,
•    shift adjustment,
•    range adjustment (sometimes called gain adjustment).

Note 2
The adjustment of a measuring instrument should not be confused with calibration, which is its prerequisite.

Note 3
After a measuring instrument has been adjusted, it usually has to be recalibrated.

Therefore, adjustment (tuning) of a measuring instrument is restoring its original condition as foreseen by its manufacturer. During calibration (comparison of indicated value with a standard), sometimes a measuring instrument shows errors that are not acceptable for making measurements with it (they are not within error tolerance limits in a given measurement range allowed by the manufacturer of a device). In such a situation, the meter needs adjusting.
The possibility of adjustment of the instrument depends on the means of parameters adjustment intended by its manufacturer. And it is the manufacturer of a given device who can perform it. Most often such actions are performed automatically, digitally, by connecting the meter to a computer. Because of the limitations and the knowledge of the measuring instrument, only the manufacturer of a given device is the most suitable entity to carry out this type of adjustment. SONEL S.A. is the only official authorised representative performing all services of repair and adjustment of Sonel measuring devices.
 

What are the reasons for adjustment?

Measuring instruments have a time drift. After a certain period, they may not meet the permissible error requirement stated by the manufacturer.

Why does this happen?

Among other things, due to ageing phenomena – e.g. of optics and transducer in lux meters. In a lux meter it should be noted that a photoelectric cell, which is a sensor, ages in time, therefore, it should be subjected to periodical metrological control (calibration) and if the readings are unacceptable, an adjustment and recalibration. Only a valid certificate of calibration of a lux meter confirms the device's proper working order and its compliance with the declared spectral and basic uncertainty levels. Each measuring device, due to its storage, frequency of use, electronics, age and other factors, requires periodical adjustment.
By the means of calibration (metrological control of a meter), indication errors are determined, which later on during measurement should be added in the form of corrections to measurement results. By knowing the corrections to the indication, it is possible to update the used measurement procedures.
It should be remembered that measuring instruments, especially those used for tests related to electric shock protection, require periodical adjustment. The person carrying out the measurements should have full confidence in the proper working order of the instrument. Measurements made with an inoperative meter may contribute to an incorrect assessment of the effectiveness of protection of human health or even life.
Example:
During the calibration, the metrologist showed that the indication of the meter deviates significantly from the manufacturer's assumptions indicated in the operation manual. It should be remembered that the calibration process consists of comparing the indication of a calibrated instrument with the indication of a reference instrument. The calibration instrument should be significantly more accurate than the calibrated instrument.
Calibration is a statement of the present condition and in the case of instrument indication abnormalities, it does not include adjustment/tuning of a given instrument resulting in the change of this condition.

When sending a meter for calibration, customers often assume that if the meter gives incorrect indications (exceeding the maximum boundary errors), calibration will also include free tuning/adjustment. This is not the case. The customer is always informed of any occurring abnormalities. The laboratory can offer the customer:

• adjustment (paid),

The process of adjustment itself is a complex activity and apart from the knowledge of construction and operation of the device, it requires a labour-intensive procedure. The calibration is carried out in points in accordance with the prepared and accepted laboratory procedure. It usually covers several points for a given measurement range. Adjustment/tuning is the process of adjustment of indications of a given measurement device – often in a dozen or so points for a given measurement range. At each point, the value should be checked and – if necessary – adjusted. Therefore, this process, if not fully automatic, requires precision and much more time. After the adjustment, the device is subjected to another calibration which will allow checking the correctness of its indications.

• issuance of the calibration certificate with indications as they are (exceeding permissible errors).

Let’s remember: A calibration certificate is only a statement of the metrological condition of the tested measuring instrument. The calibration certificate does not include the evaluation of the calibration result or the evaluation of particular measurements. The conformity assessment is performed only at the request of the customer. It is not determined whether the results indicated by the calibrated instrument are correct or incorrect. The decision whether an instrument is suitable for performing a certain measurement is always made by the person performing the measurement. The mere possession of a calibration certificate does not prove the metrological working order of a measuring instrument. Only proper interpretation of calibration results will allow concluding that the instrument meets its specification.

Is every meter subject to adjustment?

It depends on the technical possibilities of the laboratory that performs the adjustment of a device. SONEL S.A. is the only authorised unit repairing and adjusting Sonel devices. As the manufacturer, we have the necessary knowledge and experience to perform all repairs of our meters.

Is the adjustment paid for?

Yes, the adjustment is a separate service performed upon the Customer's request. It is a labour-intensive and properly designed process for each type of measurement equipment. Additionally, after the adjustment, the meter is subjected to the calibration process again.
From 1 January 2021, our Research and Calibration Laboratory SONEL S.A. introduces the service for lux meters only:
Adjustment in the price of calibration (carried out only if the lux meter requires it).
If during the calibration the metrologist notices that the indication of the lux meter exceeds the acceptable values, he/she will send the device to the service for adjustment. The customers will not be asked for their consent; they will only be informed that the lux meter required it. As a result, the whole process will go much faster and this is what everyone wants so that they get their meter – their working tool – in the shortest possible time.