Laboratory manual for the evaluation of non-automatic weighing devices

Part 2, section 6—Agreement of registration

Table of contents


Reference

Section 18 of the Specifications Relating to Non Automatic Weighing Devices (1998)

Schedule II of the Weights and Measures Act

6.0 Agreement of registration – Generalities

Devices may be calibrated in one unit and use internal calculations to convert from that unit to other units. All indications in different units must be in agreement with each other at all times. Conversion factors can be found in Schedule II of the Weights and Measures Act.

LG-6.01 Test for the agreement of registrations

Purpose

The purpose of this test is to establish the accuracy and reliability of communication among all means of indication and registration of a device. The means of indication and registration include primary and secondary indications, printers, computers and other recording means.

Application

This test is applicable when a device is equipped with two or more means of registration that register in the same units of measurement (i.e., primary indicator, secondary indicator, printer, etc.). The test applies to mechanical analogue devices and electronic digital indicating devices. If the device (or weight indicator) can be interfaced to a printer, a compatible printer must be attached to the device for the test.

The following test must be performed for each unit of measurement that the device can display.

Test procedure
  1. Zero the device.
  2. Verify the agreement between indications and registrations at zero load (or the minimum load that can be printed).
  3. Apply a load to the load receiving element and print.
  4. By 1d steps, increase the load on the load receiving element by 10d, noting the registrations (including the printouts) at each step.
  5. Repeat the test with different loads (e.g., close to zero load, at mid capacity, close to capacity).
  6. Verify the agreement of all indications and registrations, including the printouts.
Interpretation of results

Weight indications and registrations must agree within the limits prescribed by the Specifications. The device complies with the requirements when the quantities indicated and/or printed are in agreement within the following limits:

The agreement of registration requirements are applicable when indications and registrations of weight values are in the same weighing mode (net, gross or tare). Indicated and registered net weights must therefore agree, within the above limits, as must indicated and registered gross weights and indicated and registered tare weights. However, this requirement is not intended to apply when a device indicates a gross weight and prints a net weight, as is the case with some POS systems.

The indication of a gross weight and the printing of a net weight is acceptable on POS systems as well as weighing systems used in applications other than direct sales to the public.

Weight classifiers

The verification scale interval of a printing device (i.e., printer, computer) may be larger than the verification scale interval of the weight classifier to which it is interfaced. In addition to the "agreement of registration" test described above, a test at the turning points of price ranges is performed to ensure that in all circumstances packages are classified accurately.

Example:

Weight classifier 10 kg × 5 g

The scale interval of the printing device is 10 g

Price ranges: 0 - 30 g (Included) = $1.00

Greater than 30 g = $2.00

A weight of 40 g and a price of $2.00 (second price range) may not be printed before the weight classifier indicates 35 grams.

LG-6.02 Suitability of unit conversion

Purpose

To uncover registration errors resulting from an inadequate unit conversion mechanism. This type of error is found when a DUT internally calculates a mass indication in a unit of measurement prior to converting it, rounding it off and registering it in a different unit of measure.

Application

To all DUT capable of indicating in a metric and in a non‑metric unit of registration.

Test procedure
Part 1
  1. For each of the units of measurement in which the DUT is capable of registering, perform the two following steps.
  2. Set the DUT to register in the unit of measurement being verified.
  3. At least fourteen times, add a test load equal to e and each time, record the registration.
Part 2
  1. Apply at load and record the indication in the unit the device was calibrated in. Use the "small weights" method to determine the true weight as indicated by the device. Remove the "small weights" once the true weight has been determined.
  2. Set the device to all other units it is capable of displaying and record the indication for each.
  3. Repeat steps 1 and 2 for 3 more loads, spread throughout the range of the device.
Interpretation of the results

The DUT is deemed to meet the requirements if:

Example of non compliance
Applied load
(lb)
Internal metric reading
(kg)
Rounded to 0.05 kg
(kg)
Conversion to lb
(lb)
Indication in lb
(lb)
49.6 22.49817769 22.5 49.6040175 49.6
49.7 22.54353692 22.55 49.71424865 49.7
49.8 22.58889615 22.6 49.8244798 49.8
49.9 22.63425538 22.65 49.93471095 49.9
50 22.67961461 22.7 50.0449421 50
50.1 22.72497384 22.7 50.0449421 50 (error)
50.2 22.77033307 22.75 50.15517325 50.2
50.3 22.8156923 22.8 50.2654044 50.3
50.4 22.86105153 22.85 50.37563555 50.4
50.5 22.90641076 22.9 50.4858667 50.5
50.6 22.95176999 22.95 50.59609785 50.6
50.7 22.99712921 23 50.706329 50.7
50.8 23.04248844 23.05 50.81656015 50.8
50.9 23.08784767 23.1 50.9267913 50.9
51 23.1332069 23.15 51.03702245 51
51.1 23.17856613 23.2 51.1472536 51.1
51.2 23.22392536 23.2 51.1472536 51.1 (error)
51.3 23.26928459 23.25 51.25748475 51.3
51.4 23.31464382 23.3 51.3677159 51.4
51.5 23.36000305 23.35 51.47794705 51.5

Note: 1 Under section 39 of the Specifications, indicated and printed representations of net, gross and tare weights of a device must have the same value of verification interval e for any given load.

Note: 2 In the case of a secondary indicating element intended to duplicate, for the benefit of consumers, the information displayed by the operator's indicating element, the registration on both displays must be in the same graduation size and in the same unit of measurement. Furthermore, the printed registration intended for the consumers must be exactly as the indicated registration (e.g. same graduation size and same unit of measurement).

Note: 3 An indicating element and a printer used in conjunction must at least register in the same unit of measurement. Supplementary information in other units of measurement may be provided by the indicator and/or printer.

Note: 4 A device may display weight values in two units of measurement simultaneously.

Note: 5 All weight indications and registrations must be within tolerances.

Revision

Rev. 1 (March 2010)
  • Added second part to LG-6.02 to test for accuracy of conversion
  • Formatting change
Date modified: