This Code of Practice is intended to cover non-automatic weighing instruments. However, the Code may also be used for certain types of automatic weighing instruments where it is possible to calibrate the equipment in a static or non-automatic weighing mode. Where an instrument may be used in both automatic and non-automatic weighing modes, the provisions of this code apply only for the non-automatic weighing mode and a Calibration Certificate issued in these cases will only be valid for the non-automatic weighing mode. In such cases, additional testing will be required to determine the accuracy of the instrument when it is operating in its automatic mode.
The Code applies to all non-automatic weighing instruments regardless of Class. However, the majority of Class I instruments are used in applications where the calibration requirements are laid down by UKAS or by the Good Laboratory Practice (GLP) Guides. In other instances, the manufacturers specify calibration procedures and requirements. In these instances, a calibration carried out which complies with those requirements and Calibration Certificates that are issued in accordance with those requirements are regarded as being in conformance with this Code.
It is expected that calibrations performed in accordance with this Code of Practice will satisfy the requirements both of customers and third party assessment bodies enabling users of the weighing equipment to show compliance with the appropriate requirements of the ISO 9000 series of standards.
The Code recognises that many weighing instruments are only used for weighings which are less than the maximum weighing capacity. In such cases, the customer may request that the calibration should be carried out over the normal “working” range of the instrument; in which case the recommendation is that the calibration is carried out over the normal working range plus 5% - 10% (e.g. a 1500 kg capacity instrument, used only for weighings up to 1000 kg may be calibrated up to 1050 kg - working range of 1000 kg +5%).
Where the weighing instrument is used for a legally controlled purpose it will need to meet the requirements of all relevant legislation Nothing in this Code should be taken as overriding that legislation. UKWF members are expected to act in accordance with the legislation at all times and when legally controlled weighing equipment is outside the tolerances specified in that legislation or does not comply with the legislation in some other way, they will draw their customers attention to that fact. Customers are reminded that they have an obligation to comply with the Weights and Measures legislation, which cannot contractually be passed on to the calibrating organisation.
UKWF members are expected to work in compliance with Health and Safety legislation and to work in a safe manner; customers are reminded that responsibility for the Health and Safety of contractors working on their premises is as much theirs as the contractors'.
The Code does not recommend a specific frequency period for calibration, as each customer's operating circumstances are unique. The frequency of calibration should be based on the usage of the instrument, the risks associated with inaccurate performance and calibration history.
This Code was drawn up in consultation with LACORS (the Local Authority Co-ordinating body on Trading Standards) being an original contributor, CTSI (The Chartered Trading Standards Institute) and IMC (The Institute of Measurement and Control).
For a detailed technical explanation of the calibration process and the theory of calibration control, readers are recommended to refer to the Institute of Measurement and Control publication "A Code of Practice for the Calibration of Industrial Process Weighing Systems", WGC0496, reviewed and re-issued in 2011. A copy of this document can be found on the UKWF website.