TS–022 Using a weighing instrument for trade below the approved minimum capacity

Scope

This document sets out Trading Standards policy on using a weighing instrument below the minimum capacity, as stated in the Certificate of Approval and on the identification plate.

Reference documents

Policy

The minimum capacity for a weighing instrument is specified in the Certificate of Approval for the instrument. When the instrument is in use for trade, the identification (legends) plate will also state the minimum capacity.

According to OIML G15:

“Minimum limit for weighing (Min)

A related problem is the minimum value of the mass for which a machine can be used without giving raise to excessive relative weighing errors, i.e. at loads which are small compared to the maximum capacity of the machine.

This is a difficult problem to solve in practice since for the same type of construction, the absolute error generally increases with the capacity of the machine. A retail dealer can in fact not be expected to have a full range of weighing machines with varying capacities but will use one which covers the complete range of his usual sales. Thus, it happens frequently that the weighing machine is used with rather low loads compared to its maximum capacity.”

Trading Standards policy is that if a weighing instrument is used for direct weighing below its stated minimum capacity or above maximum capacity, the owner of the equipment does so it at their own risk; as it would not comply the Certificate of Approval for that instrument.

Tip Icon Blue2 NOTE

This policy is not applicable in the following situations:

  • For the determination of tare weight, where the value of the tare weight is less than the stated minimum capacity, and
  • Where two weighings are greater than minimum capacity but the derived mathematical weight value can be less than the stated minimum capacity of the weighing instrument.

Examples:

  1. A checkout weighing instrument with a verification scale interval of 2 g and a minimum capacity of 40 g may be used to ‘tare off’ a tray or bag of 15 g.
  2. A car and a trailer with rubbish are weighed at a refuse station on a weighbridge with a verification scale interval of 20 kg and minimum capacity of 400 kg. The gross weight of the car and trailer with rubbish is 1580 kg, the rubbish is dumped and the car and the trailer weighs 1380 kg. The difference between weighings is 200 kg, though this weight is less than the stated minimum capacity of the weighbridge it is still acceptable because all weighings took place with weight values greater than the approved minimum capacity.

Trade Measurement — Technical Policy

Policy number:TS - 022
Effective date: April 2017
Version number: 2
Policy name: Using a weighing instrument for trade below the approved minimum capacity
Reviewed by: Davis White, Legal Metrology Advisor and Senior Trading Standards Officer
Approved by: Phil Sorrell, Team Leader Compliance and Inspection