Laboratory manual for the evaluation of non-automatic weighing devices

Part 2, section 22—Multi-interval devices and multiple range devices

Table of contents


Reference

Sections 3, 5, 6, 8, 9, 16, 31 to 33 of the Specifications Relating Non Automatic Weighing Devices (1998)

22.0 Multi-interval devices and multiple range devices—Generalities

This section provides additional guidelines for the examination and testing of multi-interval and multiple range devices.

Note: a weight indicator tested separately will be set and tested for a maximum number of intervals (nmax) and for a minimum value of verification scale interval (emin) across the range.

22.1 Multi-interval devices

Definition
Multi-interval device

means a device having one weighing range which is divided into partial weighing ranges each with different scale intervals, with the weighing range determined automatically according to the load applied (pre-determined ranges/intervals), both on increasing and decreasing loads.

Intervals and capacities

22.1.1 On a multi-interval device, the value of the verification scale interval of a particular range must be lower than the value of the verification scale interval of the next range (e1 < e2 < e3, etc.)

22.1.2 Each partial range of a multi-interval device must have the same value of scale interval for both increasing and decreasing loads. The verification scale interval e must equal the scale interval d.

22.1.3 Each partial range of a multi-interval device must have the number of scale intervals (n) required by Section 3 of the Non Automatic Weighing Devices Specifications.

Example Each range of a Class III device must have a minimum of 500 n and a maximum of 10 000 n. The number of scale intervals "n" for each weighing range is determined by dividing the scale capacity for each range by the verification scale interval "e" for each range. See the following illustration:

Table 1: Multi-interval example
Partial weighing range (capacity) e n Max ⁄ e
0 – 3 kg 1 g 3 000 3 000⁄1
3 – 6 kg 2 g 3 000 6 000⁄2
6 – 15 kg 5 g 3 000 15 000⁄5
Example of a device that would not satisfy the above section 22.1.3
Weighing ranges e n
First 0 – 1 kg 1 g 1 000
Second 1 – 5 kg 5 g 1 000
Third 5 – 8 kg 20 g 400
Example of a device that satisfies section 22.1.3
Weighing ranges e n
First 0 – 1 kg 1 g 1 000
Second 1 – 5 kg 2 g 2 500
Third 5 – 8 kg 5 g 1 600

22.1.4 It is recommended (OIML requirements) that the maximum capacity of a partial weighing range of a multi-interval device (except the last range) must satisfy the requirements of the following table:

OIML recommended partial range minimums
Class I II III IIII
Max i/e i+1 ≥ 50 000 ≥ 5 000 ≥ 500 ≥ 50
Tare features

22.1.5 The maximum tare value that may be entered shall not exceed Max 1.

22.1.6 Whenever gross and tare weights fall in different weighing ranges, the net weight must always be in mathematical agreement with the gross and tare weights that are displayed and recorded (simultaneously or in sequence) (gross = tare + net).

22.1.7 The tare value must be equal to the value of the displayed scale division for all methods of tare entry (dtare = d). An attempt to enter, in the first range of a multi-interval scale, a tare value that is not equal to d must be rejected or rounded off to the nearest scale interval.

Example A multi-interval scale has a 2 g interval in the first range and 5 g in the second range. A keyboard entry of 5 g in the first range must be either rounded to 4 or 6 g or rejected.

22.1.8 Weight values (Net or Gross) must always begin with the lowest weighing range on the device regardless of the amount of keyboard or platter tare that is taken. Example: a multi-interval scale has two ranges: first 0 – 2 kg by 2 g, and second 2 – 5 kg by 5 g. A platter tare of 1 kg is taken; the device indicates zero. Then, the device must indicate the net weight from 0 up to 2 kg in intervals of 2 g; and from 2 up to 4 kg, in intervals of 5 g.

22.1.9 When Gross, Tare and Net weights are indicated or printed, there shall be mathematical agreement in all circumstances. The tare value must be rounded off to permit mathematical agreement. Example: A multi-interval device has two ranges. The first range 0–2 kg by 2 g, and the second 2 – 5 by 5 g. A key board tare of 1.998 kg is entered (in 2 g divisions); a gross load of 2.115 (in 5 g divisions) is put on the platter. The net weight indicated must be either 0.116 kg or 0.118 kg (first range; rounded off to 2 g division). If the gross, net and tare weights are indicated, they must be as follows:

Accpetable 1.998 kg tare value rounding examples
  Gross Tare Net
Option 1 2.115 kg 1.999 kg 0.116 kg
Option 2 2.115 kg 1.997 kg 0.118 kg

22.1.10 A tare value entered in the lower range may be either rounded off to the nearest value of the interval of the higher range in which the weighing occurs, or kept unchanged. In the latter case, the net weight could possibly be displayed with an interval smaller than the interval of the range in which the weighing occurs. When a device displays or prints the gross, net and tare values, in all cases the mathematical equation "tare + net weight = gross weight" must be satisfied.

Example A multi-interval scale has a 2 g interval from 0 to 2 kg, and 5 g from 2 kg to 10 kg. A tare of 12 g is entered in the first range and the gross weight is 2 500 g (second range). The scale may display either 2 488 g (tare stored as 12 g) or 2 490 g (rounded off to 10 g).

Note:

Marking

22.1.11 The capacity and verification scale interval must be conspicuously marked near the weight display (See section 1.1.6, 1.1.7 and 1.1.8 of this manual).

Performance

Clarification

22.2 Multiple range devices

Definition
Multiple range device

means a device having two or more weighing ranges with different maximum capacities and different scale intervals for the same load receptor, each range extending from zero to its maximum capacity (two or more devices in one). The selection of the range may be manual or automatic.

Number of intervals and capacity

22.2.1 Each range of a multiple range device must have the number of scale intervals (n) as required by section 3 of the Non Automatic Weighing Devices Specifications.

22.2.2 For each range, e must equal d.

Zero setting feature

22.2.3 The zero setting feature in any weighing range must also be effective in the greater weighing ranges, if switching to a greater weighing range is possible while the device is loaded. The deviation from zero must be no more than 0.25 e. This is applicable to manual selection or automatic changing of weighing ranges.

Selection of the weighing range

22.2.4

  1. Manual selection of the weighing ranges is allowed from a smaller to a greater weighing range at any load;
  2. It is allowed from a greater to a smaller weighing range when there is no load on the platter, and the indication is zero or at a negative net value. The tare operation must be cancelled and zero must be set to ± 0.25 e1, both automatically.

22.2.5

  1. Automatic changeover of the weighing range is allowed from a smaller to the following greater weighing range when the load exceeds the maximum gross weight of the range being operated;
  2. It is allowed from a greater to a smaller weighing range when there is no load on the platter and the indication is zero or at a negative net value; the tare operation must be cancelled and zero must be set to ± 0.25 e1, both automatically.
Tare features

22.2.6 The tare value may only be transferred from one weighing range to another one with a larger verification scale interval.

22.2.7 The tare operation shall be effective also in the greater weighing range, if switching to a greater weighing range is possible when the device is loaded.

22.2.8 The tare value must be equal to the value of the displayed scale division for all methods of tare entry (dtare = d). An attempt to enter, in the lower range of a multiple range scale, a tare value that is not equal to d must be rejected or rounded off to the nearest scale interval.

Example A scale has a 2 g interval in the first range and 5 g in the second range. A keyboard entry of 5 g in the first range must be either rounded to 4 or 6 g or rejected.

22.2.9 A tare value entered in the lower range must be rounded off to the nearest interval of the higher range in which the net weighing occurs.

Example An automatic multiple range scale has a 2 g interval from 0 to 2 kg (lower range), and 5 g from 0 kg to 10 kg (higher range). A tare of 13 g is entered in the lower range and the gross weight is 2 500 g (second range). The tare value must be rounded to 15 g and the scale must display 2 485 g (rounded off to 15 g).

Note:

22.2.10 In all cases, the mathematical equation tare + net must = gross (indicated and printed).

Indication of the range in use

22.2.11 The range in which the device operates shall automatically and clearly be indicated for both the operator and the consumers.

Clarification If a scale has a decimal point and a different number of decimal places in each weighing range, the position of the decimal point and the number of digits following is an adequate definition of the weighing range in use. If the weighing range does not utilize a decimal point and differing numbers of decimal places (e.g. scale division are 20, 50 and 100 lb), another method must be provided to indicate the weighing range in use. A display of the capacity by division with an annunciator located near the weight display such as the following is acceptable:

Range in use

Range 1
20 × 0.005 kg
Range 2
5 × 0.002 kg
Marking

22.2.12 Each weighing capacity by division must be clearly indicated near the weight display. If the manufacturer chooses to indicate which weighing range is in operation using the method recommended above (with annunciator), no other marking of capacity by division is required.

Performance

Clarification

Revision

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