Laboratory manual for the evaluation of non-automatic weighing devices

Part 2, section 3—Indication and registration—representation

Table of contents


Reference

Sections 3, 5, 6, 30 to 38 of the Specifications Relating to Non Automatic Weighing Devices (1998)

3.0 Indication and registration – Representation – Generalities

The Specifications require that devices be provided with indicating and recording elements appropriate in design and amount, and that indications and recorded representations be clear, definite, accurate and easily readable under normal conditions of use of the device. There are several requirements that must be satisfied to facilitate the reading and interpretation of displayed weight values, while other requirements address the proper operation of indicating and recording elements.

3.1 Value of "d" and "e"

3.1.1 The maximum and minimum number of scale intervals must comply with section 3 of the Specifications.

3.1.2 The value of "d" (and "e") must be equal to 1 × 10x, 2 × 10x or 5 × 10x of a legal unit of measurement (kilograms, grams, milligrams, pounds), where x is a negative or positive whole number, or zero.

Clarification: if "e" … "d" then "e" must be equal to 1 × 10x of a legal unit of measurement, where x is a negative or positive whole number, or zero.

3.1.3 The value of "d" (and "e") of analogue indicating devices may be equal to ½n of a pound, ounce or any other Canadian whole units, where n is a positive whole number (1/2, 1/4, 1/8, 1/16, 1/32 pound, ounce).

3.1.4 For Class III, III HD and IIII devices, for multi-interval devices and multiple range devices, "e" must equal "d".

3.1.5 On Class I or II devices, other than a multiple range or multi-interval device, "d" may be smaller than "e"; "e" must be the value of the scale division immediately preceding the auxiliary reading means.

Clarification: if "e" ≠ "d" then "d" must be located to the right of the decimal point. This means that some division sizes for "e" are not allowed when "e" ≠ "d". For example, a device with e = 1 g and d =100 mg may not display, for a 300.1 gram weight, 300 [100] mg, but it may display 300[.1] g, with the auxiliary indicating element after the decimal point.

The values of "e" and "d" are also limited by the rule d < e <= 10d.

3.1.6 On a digital indicating device, if "e" is different from "d", "d" must be clearly differentiated from the other figures.

Acceptable solutions

  1. The last digit ("d") may be shaded.
  2. The last digit ("d") may appear in brackets.
  3. The last digit ("d") may be smaller and set apart.

3.2 Legible, readable and non ambiguous

3.2.1 Indications and registrations of weights, prices, etc. must be designed and located so that reading the results is reliable, easy and unambiguous.

3.2.2 Digits must be uniform in size, shape and character (except if "e" … "d").

3.2.3 Any indication of function or condition may not be represented in a manner that interferes with the interpretation of weight. For example, a "+" or "-" sign used as an over/under indication may not be placed adjacent to a weight value.

3.2.4 Except for postal scales, digital weight values must be in a single unit of measure across the weighing range. For any one indication of weight, only one unit of measure may be used.

3.2.5 Subordinate indications and recorded representations are appropriately designated or portrayed. A decimal point or a comma must be used to set apart decimal sub‑multiples of the unit.

3.2.6 A digital device must display at least one digit to the left of the decimal point or comma, and all the digits to the right of the decimal point or comma. If a decimal point or comma is not used, at least one active decade plus any constant (fixed) zeros must be displayed. All decades to the right of a decimal point or comma must be active (no fixed zero).

Clarification:

Table 1: Minimum zero indication examples
Capacity Minimum zero indication
25 × 0.01 lb 0.00 lb
5000 × 1 lb 0
100 000 × 20 lb 00 lb * The last digit is a fixed zero

3.2.7 Displayed and printed values of gross, tare and net must be in the same units.

3.3 Video display terminal

3.3.1 If an indicator or a video display terminal provides the primary or the only weight indication for the scale when in the weighing mode, the weight display must be a continuous live display, in an area dedicated to the weight display, and clearly distinguished and separated from other information on the display.

3.4 Analogue representation – dials, beams, poises, etc.

3.4.1 Scale marks (length, width and spacing) and indicators (pointers) must be designed and assembled so that reading the weighing results is easy and unambiguous. The overall inaccuracy of reading shall not exceed 0.2 e (OIML R 76-1 section 4.2.1).

The following are recommended minimum design requirements to ensure accuracy of reading, and overall accuracy of the device (compliance to 3.4.1).

Scale marks

3.4.1.1 Scale marks must consist of lines (graduations) of equal thickness; the width or thickness of the lines must be constant, not less than 0.2 mm and not larger than the space between the lines.

3.4.1.2 Lines must vary in length to facilitate readings. The length of the shortest lines must be equal or longer than the width of the clear space between the lines.

3.4.1.3 The distance between the main scale marks must be uniform to ensure a linear indication across the scale.

3.4.1.4 The clear space between lines must be at least 0.75 mm.

Numbering

3.4.1.5 The scale interval of numbering must be constant and should not be greater than 25 times the scale interval of the device.

3.4.1.6 If the scale is projected on a screen, at least two numbered scale marks should appear in the projected zone.

3.4.1.7 The height and width of the numbers (real or apparent) should be proportional to the scale marks and so that the reading of the weighing results is easy and unambiguous.

Indicator (pointer)

3.4.1.8 The width of the pointer must not exceed the width of the graduation lines and the width of the clear space between weight graduations.

3.4.1.9 The portion of the pointer that extends along the length of graduation lines and that may be brought into coincidence with the lines must be of the same width.

3.4.1.10 The length of the pointer must be such that the tip is at least level with the middle of the shortest scale mark. If the pointer and the scale marks are in the same plane, the distance between the tip of the pointer and the end of the graduation lines must not exceed 1 mm.

3.4.1.11 Parallax effects must be reduced to the practical minimum. The clearance between the pointer and the scale marks should in no case exceed 1.5 mm.

Weighbeams

3.4.1.12 The scale marks (graduations) must consist of lines of equal thickness. The distance between graduations should not be less than 2 mm so that the normal machinery tolerances for notches or scale marks do not cause errors in the weighing results exceeding 0.2 e.

3.4.1.13 Graduation should be perpendicular to the beam.

3.4.1.14 The normal balance position of a weighbeam must be horizontal; the weighbeam must have equal travel above and below the horizontal. The total travel distance between trig loops and between other limiting stops near the weighbeam must be sufficient to ensure accurate reading. The following minimum distances are recommended:

Table 2: Recommended minimum travel distances
Distance from the weighbeam fulcrum to the limiting stops (centimetres) Minimum travel between the limiting stops (millimetres)
30 or less 10
>30 to 50 13
>50 to 100 18
more than 100 23

3.4.1.15 A shoulder or a stop shall be provided on each weighbeam bar to prevent a poise from traveling and remaining back of the zero graduation.

Poises

3.4.1.16 No part of a poise (including the locking screw) shall be readily detachable. The adjusting material in a poise must be securely enclosed and firmly fixed in position and must not be in contact with the weighbeam. There must be no cavity that could accidentally hold foreign bodies.

3.4.1.17 A sliding poise, other than a hanging poise, on a notched weighbeam bar must have a pawl that will seat the poise in a definite and correct position in the notches, wherever in the notch the pawl is placed, and hold it there firmly and without appreciable movement.

3.4.1.18 Sliding poises must be provided with an indicating component. The indicating component of a poise must be sharply defined and the reading edge shall be parallel to the graduation lines.

Counterpoise weights

3.4.1.19 Counterpoise weights shall comply with the requirements prescribed by sections 20, 72, 73, 77, 78 and 79 of the Weights and Measures Regulations.

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