Laboratory manual for the evaluation of non-automatic weighing devices
Part 2, section 22—Multi-interval devices and multiple range devices
Table of contents
- 22.0 Multi-interval devices and multiple range devices—Generalities
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
- 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:
|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|
|First 0 – 1 kg||1 g||1 000|
|Second 1 – 5 kg||5 g||1 000|
|Third 5 – 8 kg||20 g||400|
|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:
|Max i/e i+1||≥ 50 000||≥ 5 000||≥ 500||≥ 50|
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:
|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).
- OIML: tare must be rounded off R76-1, section 4.7.1)
- U.S.: tare must be either rounded up or kept unchanged (Pub 14 page 1-44)
The rounding off of the tare value is the method preferred by Measurement Canada. MC may allow only this method sometime in the future.
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).
- For any test performed on a multi-interval scale, the tolerance is a function of the verification scale interval e of the range corresponding to the test load used.
- The smallest value of the verification scale interval applies to the tests to determine the maximum value of AZSM, the maximum permissible error for the return to zero test and for the creep-return to zero test, etc. The motion detection requirement must be satisfied for each partial range. The shift test must be performed at one-half of the capacity of each partial weighing range.
- temperature effect on no load: the tolerance (one verification scale interval⁄ 5°) applies to the smallest verification scale interval.
- time (half hour creep/return to zero): The deviation on returning to zero as soon the indication has stabilized, after the removal of any load which has remained on the device for half hour, shall not exceed 0.5 e1.
- Devices equipped with keyboard or platter tare must meet the tolerances for net loads for any tare taken up to the maximum tare capacity.
22.2 Multiple range devices
- 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
- Manual selection of the weighing ranges is allowed from a smaller to a greater weighing range at any load;
- 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.
- 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;
- 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.
22.2.6 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).
- OIML: tare transferred only from the lowest to the largest range and rounded off to the scale interval (R76-1, section 4.7.1).
- U.S.: tare transfer only from the lowest to the largest range and must be rounded up (Publication 14, page 1–46)
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
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.
- Each weighing range of a multiple range scale is considered to be an individual scale and must be evaluated accordingly.
- temperature effect on no load. The tolerance (one verification scale interval/ 5°) applies to the smallest verification scale interval.
- time (half hour creep/return to zero). The deviation on returning to zero from Max1 shall not exceed 0.5 e1. The deviation on returning to zero from Maxi shall not exceed 0.5 ei. Furthermore, after returning to zero from any load greater than Max1, and immediately after switching to the lowest weighing range (manually or automatically), the indication near zero must not vary by more than e1 during the following 5 minutes.
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