The Measuring Instruments (Non-Prescribed Instruments) Regulations 2006

Automatic gravimetric filling instruments

47.—(1) In addition to the requirements set out in paragraphs 44 and 45, the following specific requirements shall apply in relation to automatic gravimetric filling instruments.

(2) Accuracy classes

(a) The manufacturer shall specify both the reference accuracy class Ref(x), and the operational accuracy class(es) X(x).

(b) An instrument type is designated a reference accuracy class Ref(x), corresponding to the best possible accuracy for instruments of the type. After installation, individual automatic gravimetric filling instruments are designed for one or more operational accuracy classes, X(x), having taken account of the specific products to be weighed. The class designation factor (x) shall be ≤, and in the form 1 × 10^k, 2 × 10^k or 5 × 10^k where k is a negative whole number or zero.

(c) The reference accuracy class, Ref(x) is applicable for static loads.

(d) For the operational accuracy class X(x), X is a regime relating accuracy to load weight and (x) is a multiplier for the limits of error specified for class X(1) in sub-paragraph 3(b)

(3) MPE

(a) Static weighing error

(i) For static loads under rated operating conditions, the MPE for reference accuracy class Ref(x), shall be 0.312 of the maximum permissible deviation of each fill from the average: as specified in Table 11; multiplied by the class designation factor (x).

(ii) For instruments where the fill may be made up from more than one load (e.g. cumulative or selective combination weighers) the MPE for static loads shall be the accuracy required for the fill as specified in sub-paragraph (3)(b) (i.e. not the sum of the maximum permissible deviation for the individual loads).

(b) Deviation from average fill

Table 11

Value of the mass of the fills (m) in grams	Maximum permissible deviation of each fill from the average for class X(1)
m ≤ 50	7.2%
50 < m ≤ 100	3.6 grams
100 < m ≤ 200	3.6 %
200 < m ≤ 300	7.2 grams
300 < m ≤ 500	2.4 %
500 < m ≤ 1 000	12 grams
1 000 < m ≤ 10 000	1.2 %
10 000 < m ≤ 15 000	120 grams
15 000 < m	0.8 %
Note: The calculated deviation of each fill from the average may be adjusted to take account of the effect of material particle size

(c) Error relative to pre-set value (setting errors)

• For automatic gravimetric filling instruments where it is possible to pre-set a fill weight, the maximum difference between the pre-set value and the average mass of the fills shall not exceed 0.312 of the maximum permissible deviation of each fill from the average, as specified in Table 11.

(4) Performance Under Influence Factor and Electromagnetic Disturbance

(a) The MPE due to influence factors shall be as specified in sub-paragraph (3)(a).

(b) The critical change value due to a disturbance is a change of the static weight indication equal to the MPE as specified in sub-paragraph (3)(a) calculated for the rated minimum fill, or a change that would give equivalent effect on the fill in the case of instruments where the fill consists of multiple loads. The calculated critical change value shall be rounded to the next higher scale interval (d).

(c) The manufacturer shall specify the value of the rated minimum fill.