In all commercial applications where product is sold by weight, it is a legal requirement that weighing equipment must be verified as ‘legal for trade’. In summary, this means that the equipment (from an individual scale to a complete pre-pack line) has undergone a stringent set of tests to ensure it is sufficiently accurate and fit for purpose.
The following list provides examples* of typical applications where a legal-for-trade scale might be required:
This certification can only be given by a weights and measures inspector or an ‘approved qualifier’. An appropriate approved body must evaluate the design and operation of the equipment to ensure that it conforms to the published guidelines/ requirements. It is also an offence to have, or use, seriously incorrect equipment or to alter equipment that is incorrect after it has been stamped. If a trade approved unit undergoes any alteration or repair, it will require re-verification to ensure that the approval remains valid.
Weights and measures authorities around the world are responsible for controlling legal for trade equipment and related legislation. Most countries globally (outside of the USA) have adopted International Organization of Legal Metrology (OIML) requirements for weighing equipment. OIML has developed a set of international guidelines relating to the manufacture and use of weighing and measuring instruments for legal metrology applications.
In the US, requirements for legal for trade weighing equipment are laid out in Handbook 44 (Specific Tolerances and Other Technical Requirements for Weighing and Measuring Devices).
Equipment is certified under the National Type Evaluation Program (NTEP) which is developed through cooperation between the National Conference on Weights and Measures (NCWM) and the Weights and Measure division of the National Institute for Standards and Technology (NIST). NTEP is a process for the testing and evaluation of weighing equipment and critical components to ensure their compliance with Handbook 44.
According to NTEP, the term ‘used for trade’ refers to devices that are used for selling, purchasing, exchanging, custody transfer, or establishing the cost for services or hire on the basis of a measurement.
By NTEPs terms, a ‘device’ is a weighing or measuring instrument. The term also refers to major elements such as indicators, weighing elements and volume registers.
In Canada, approval for trade is governed by standards and testing by Industry Canada under Measurement Canada's approval process. Measurement Canada approval is required even if the product is NTEP certified.
Please click here to see more about recent changes to Measurement Canada's Weights and Measures Regulations
Countries within the EC are generally required to adopt the harmonised European Directives for CE compliance, including those relating to “prescribed weighing instruments”.
In the EC weighing instruments are split into two categories; Automatic Weighing Instruments (AWI) and Non-Automatic Weighing Instruments (NAWI). The main difference between the two being that a NAWI requires the intervention of an operator during the weighing process to adjust the quantity of material being weighed. NAWIs are certified under the EC Non-Automatic Weighing Instruments Directive, while most AWIs fall within the remit of the EC Measuring Instruments (MID) directive.
In the UK , Automatic checkweighers are not prescribed and do not have to be verified before they can be used for average weight, the owner of the instrument must always be able to show however that they are suitable for their use. The law relating to the average weight of packages os the responsibility of the local weights and measures department working under NMO guidelines. The rationale for regulating equipment is that the accuracy of quantity for a large number of individual transactions can be guaranteed by ensuring the accuracy of the equipment making the measure. This is normally applicable to pre-pack lines.
*Disclaimer: This document is intended to provide a basic introduction, it is by no means an exhaustive explanation of the regulations and should not be used as such. Those needing to fully understand the how the law impacts upon their business should refer to the links outlined in the ‘useful links’ section of the site, or speak to one of our sales representatives.