TS–026 Retrofitting a roller or conveyor system to an existing approved weighing instrument

This policy defines the procedure to be followed when retrofitting a roller or conveyor system (non- motorised) to an existing approved non-automatic weighing instrument. No variant approval application is required.

Reference documents


Where it is proposed to retro fit a roller or conveyor system to an existing approved non-automatic weighing instrument (NAWI), the roller or conveyor system may be fitted on top of the existing load receptor plate or directly on the load receiving frame (underneath the weighing platter). No significant alteration is allowed to be made to the structural design of the approved load receiving frame which otherwise could comprise the overall integrity of the structural strength.

In addition, the following conditions must be observed:

  1. The dimensions of the roller system must not exceed the approved load receptor size.
  2. Care should be taken to ensure that approach ramps (if any) do not interfere with the weighing platform.
  3. Maximum capacity of the existing load cell (Emax) must satisfy the below condition:

Emax ≥ Q x Max x R / N

  • Q = (Max + DL + IZSR + NUD + Additive Tare) / Max
    • Max = Maximum capacity of the instrument
    • DL = Dead Load of load receptor (includes the weight of load receptor frame, load receptor, proposed roller system and any other additional construction mounted on the load receptor).
    • IZSR = Initial Zero Setting Range
    • NUD** = Correction for non-uniform distributed load
  • R = 1 (for instrument without leverwork)
  • N = Number of load cells

The below is a exert from OIML R76 Part 1 Annex F Compatibility checking of modules of non-automatic weighing instruments F.1 Weighing instruments:

** The values for the non uniform distribution of the load generally might be assumed for typical constructions of weighing instruments when no other estimations are presented.

  • Weighting instruments (WIs) with lever work and one load cell, or WIs with load receptors which allow only minimal eccentric load application, WIs with one single point load cell: 0% of Max
    • eg hopper or funnel hopper with a symmetric arrangement of the load cells, but without shaker for material flow on the load receptor
  • Other conventional WIs: 20% of Max
  • Fork lift scales, over head track scales and weighbridges: 50% of Max
  • Multi-platform weighting machine:
    • fixed combination: 50% of Maxtotal
    • variable selection or combined: 50% of Maxsingle bridge

Trade Measurement — Technical Policy

Policy number: TS - 026
Effective date: April 2017
Version date: May 2017
Version number: 2
Policy name: Retrofitting a roller or conveyor system to an existing approved weighing instrument
Reviewed by: Davis White, Legal Metrology Advisor and Senior Trading Standards Officer
Approved by: Phil Sorrell, Team Leader Compliance and Inspection