M-23—Inspection of scales that are affected by differences in acceleration due to gravity

Category: Mass
Bulletin: M-23 (rev. 4a)
Issue Date: 2009-06-30
Effective Date: 2009-06-30
Supersedes: M-23 (rev. 3)


Table of contents


1.0 Purpose

The purpose of this bulletin is to establish the policy relating to the inspection of scales that are affected by differences in acceleration due to gravity.

2.0 Background

Most electronic scales do not measure mass directly, but instead, measure the relative amount of force that a mass imparts on a weighing element as a result of acceleration due to gravity (also called gravitational attraction). Acceleration due to gravity, however, varies throughout Canada and the differences are significant enough that a scale adjusted, inspected and certified in one part of the country can be outside the limits of error when shipped to and tested in another part of the country. This is of particular concern when scales are initially inspected at a factory and then shipped to end users across the country.

3.0 Application

Since January 1st, 2003, Notices of Approval for affected Class I and II scales state that these scales are highly subject to differences in acceleration due to gravity, that they require readjustment upon any relocation and that they must be marked to this effect.

Furthermore, all inspections of devices at the factory or any location other than the intended point of use are subject to the requirements of this bulletin.

4.0 Inspections conducted by Measurement Canada staff or an authorised service provider at a location other than the final end use destination

4.1 Scales that are not affected by differences in acceleration due to gravity and that are currently inspected at the factory, will continue to be inspected at the factory. This includes scales that determine weight by comparing two masses, such as mechanical beam scales, equal arm scales, mass comparators and most dial scales, since gravity will act equally on each mass.

4.2 Scales equipped with internal calibration weights that can automatically adjust the scale upon a simple operator command and that are currently initially inspected at the factory, will continue to be inspected at the factory.

However, it is imperative that the scale end-user be fully aware that the scale must be readjusted upon any relocation in order to ensure accurate measurement. These scales must therefore be clearly marked, and their documentation clearly reflect, that a readjustment must be performed at the point of use and after any relocation.

4.3 For all other scales not covered by sections 4.1 or 4.2 (this includes electronic scales that make force measurements by direct readings and "spring" scales), a gravity tolerance application has been developed. This calculator is intended to assist manufacturers, dealers and inspectors in determining whether or not scales can be inspected at a given location and then put into service at their final destination.

Manufacturers, dealers and inspectors can access the calculator, enter the scale accuracy class, Max and e, the desired inspection location (e.g. the factory) and the scale's final destination. Using acceptance limits of error, the calculator will determine the most stringent limit of error applicable to the scale, determine if the difference in acceleration due to gravity between the point of inspection and the point of use will cause the scale to exceed the limits of error and finally, indicate whether or not the scale can be inspected at the desired location.

Note: In the case of multi-interval or multiple range scales, Max and e must be entered for each weighing range and the calculator must indicate that inspection at the desired location is possible for each of the weighing ranges.

4.3.1 If the gravity calculator indicates that the scale can be inspected at the desired remote location (e.g. the factory), an inspector or accredited agency may do so and issue the inspection certificate to the scale end-user, specifying the location where the scale will be used.

4.3.2 Alternatively, if the company seeking the inspection has addressed the disposition of these scales within a documented separate action plan (non-accredited client) or an action plan included in the quality documentation (accredited client), the inspection may continue. Where there is no action plan or the quality documentation does not address the disposition of scales affected by acceleration due to gravity, the scale shall be marked "Not for Use in Trade until Inspected" and alternate inspection arrangements must be made.

4.3.2.1

An action plan, whether separate or contained within quality documentation, shall contain the following:

  1. a statement indicating that the company submitting the action plan will assume responsibility to ensure that the scale measures within prescribed limits of error at its final destination.
  2. a brief explanation of how 4.3.2.1 (a) will be achieved (e.g. biasing, testing with weights, etc.).
  3. the date when the action plan will come into force.
  4. the action plan must be signed by a senior official within the company.

Separate action plans must be submitted for review to the gravimetric specialist in the region where the company resides. Action plans contained within quality documentation are subject to review during audits. All action plans shall be subject to follow up to ensure effectiveness and may be revoked if deemed ineffective. A listing of companies with documented separate action plans shall be maintained by the program officer responsible for gravimetric measurement.

4.3.2.2

Scales shall be certified for compliance at their point of testing (e.g. factory) and the certificate issued to the

end-user, if known. If the end-user is unknown, the certificate is issued to the factory (i.e. inspection site location).

4.3.2.3

Applying correction factors (biasing) may be used as a method to ensure a scale is accurate at the intended point of use. Scales may be altered after the inspection has been completed and reporting as required by section 41 of the Weights and Measures Regulations shall be submitted within 5 days to the nearest Measurement Canada district office. The decision to bias and responsibility for ensuring a biased device is accurate at its intended point of use will rest with the manufacturer or dealer, not Measurement Canada.

4.3.2.4

If the scale is to be sold to a distributor for resale, then either the original supplier or distributor or both may have an action plan. If the original supplier has an action plan but the distributor does not, then the suppliers action plan must address final disposition of the device to the end user location. However, if the distributor also has an action plan, the supplier may transfer this responsibility to the distributor who will then become responsible for final disposition of the device.

4.3.2.5

The requirements for inspection and reporting are summarized in the Inspection and Reporting Flowchart in Appendix 'A'.

Appendix A—Inspection and reporting flowchart

Inspection and reporting flowchart

Inspection and Reporting Flowchart
Description of Inspection and Reporting Flowchart

START

  • Scale affected by gravity?
    • No – Certificate issued to end user (if known) or (if unknown) to inspection site.
    • Yes
      • End user known?
        • Yes – On Site Inspection?
          • Yes – Certificate issued to end user
          • No – Gravity Calculator
            • Inspection May Proceed – Certificate issued to end user
            • Inspection May Not Proceed – Is the inspection authorized by an action plan?
              • No – Device must be marked "Not For Use in Trade Until Inspected" and must be inspected on-site (R28(2))
              • Yes – Certificate issued to end user (if known) or (if unknown) to inspection site location
                • Device Adjusted?
                  • No – END
                  • Yes – Report Required (W&M R40/41)
        • No – Inspection Authorized by Action Plan?
          • No – Device must be marked "Not For Use in Trade Until Inspected" and must be inspected on-site (R28(2))
          • Yes – Certificate issued to end user (if known) or (if unknown) to inspection site location
            • Device Adjusted?
              • No – END
              • Yes – Report Required (W&M R40/41)

5.0 Revision

The purpose of this revision is to:

  1. Remove the term calibrations from 3.0.
  2. Remove the requirement in the action plan, to report the final destination in writing to the nearest Measurement Canada District Office
  3. Add the Inspection and Reporting Flowchart (Appendix A) in 4.3.2.5.

The purpose of Revision 3 was to:

Remove section 4.3.2 and change minor wording in 4.3.1 and 4.3.2.1 (now 4.3.2) to ensure that an inspection may be completed for a company which holds a valid action plan, without requiring disclosure of the customer information. This is in order to ensure confidential customer information may stay protected if desired.

The purpose of Revision 2 was to:

  1. Change the "issued to" requirements to the end-user, in all cases where the end-user is known and an inspection is carried out.
  2. Clarify that Bulletin is applicable to all device inspections and calibrations performed at a location other than the final end use location.
  3. Clarify that action plans may be stand alone documents in the case of non-accredited companies or included in the quality documentation for accredited companies.
  4. Clarify responsibility for final disposition of the device.
  5. Remove extraneous information from Bulletin.

The purpose of revision 1 was to:

  1. Change the implementation date; and
  2. Clarify action plan and documentation requirements for the inspection of scales at accredited and non-accredited companies.
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