Selection of standard weights for calibration of weighing instruments

Selection of standard weights for calibration of weighing instruments

TEUVO LAMMI

The Finnish Association of Technology for Weighing, Helsinki, Finland

Abstract

This paper deals with the selection of standard weights or test loads for the calibration of single-interval weighing instruments. Four tables are given for the selection of weights of at most 50 kg. The tables contain information about the accuracy of the weights and the instruments to be calibrated. According to the accuracy of the instrument a table is chosen; with its aid the weights are selected so that their accuracy is appropriate in relation to that of the instrument.

1 Introduction

The weights dealt with here are those given in OIML Recommendations:

R 111, “Weights of classes E1, E2, F1, F2, M1, M2, M3” (1994) [1] or

R 47, “Standard weights for testing of high capacity weighing machines” (1979–1978) [2]

R 111 covers weights of at most 50 kg and R 47 those from 50 kg to 5000 kg. Their errors are measured in connection with either the calibration or the verification of the weights. In both these cases the following conditions are supposed to be met:

  1. The errors of the weights comply with the maximum permissible errors (mpe’s) given in the Recommenda- tions;
  • The measurement uncertainty of the error of each weight is a fractional part of the mpe of the weight (usually at most 1/3 ´ mpe). This uncertainty is the uncertainty of the weight.

A generally accepted principle for selecting the weights for calibrating an instrument is that the accuracy of the weights should be appropriate in relation to that of the instrument and the influence of the errors of the weights on the calibration results should be controlled.

One way to achieve this is to select the weights for each applied load so that the quotient of the error of the weights and a certain error of the instrument specified by its user (maximum tolerable error) is not greater than a chosen fraction.

Usually, the value of the fraction chosen is 1/3, but sometimes it is 1/6. The idea of using 1/6 is explained in 4.2.2.

The user can specify the maximum tolerable errors,

e.g. by giving maximum differences between the indications of the instrument and the corresponding true values, as determined by the weights. In other words, he gives limits for the errors of the instrument obtained by means of calibration, and his expectation is that the errors are within the limits, the maximum tolerable errors. This is dealt with in more detail in Section 2.

In Section 3 the general rules for selecting R 111 and R 47 weights for the calibration of instruments are given, though these have been dealt with previously in the author’s publication Calibration of Weighing Instruments and Uncertainty of Calibration [3]. However, the main subject of this paper is to select the weights of class E2 to M3 of R 111 (class E1 is not dealt with here) using the tables given at the end of Section 4.

2 Maximum tolerable errors (MTEs) of instruments

Suppose that the user of an instrument has selected an error f representing the accuracy of the instrument or the accuracy of weighing with it (compare f with e in OIML R 76-1, T.3.2.3, 2.2 and 3.5.1 [4]). f may equal the scale interval of the instrument or a multiple thereof (OIML R 76-1, T.3.2.2). With the aid of f the user can define the maximum tolerable errors (MTEs) of the instrument. The MTEs can be:

± f for all the loads, or

± 0.5 f or ± f for certain “small” loads but ± f or ± 2 f for the larger loads, or

± 0.5 f or ± f for “small” loads, ± f or ± 2 f for certain “medium” loads and ± 1.5 f or ± 3 f for larger loads.

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In the following the absolute values êMTEú of the MTEs are used. The cases:

1) êMTEú = 0.5 f, f & 1.5 f; 0.5 f & f, or only f and

2) êMTEú = f, 2 f & 3 f, or f & 2 f are dealt with separately.

The “small” and “medium” loads expressed in terms of f are defined in 4.3.

  • General rules for selecting the weights used for calibrating instruments

The quotient Max/f, where Max is the maximum weighing capacity of the instrument, plays an important role. It is used in the tables in Section 4 but also in one of the following rules based on the requirement of R 76-1, 3.7.1 concerning standard weights for the verifi- cation of instruments.

  • Verified weights
  • Weights of at most 50 kg (R 111)

The sum of the absolute values of the mpe’s (sum of

êmpe÷ ’s) of the weights shall not be greater than 1/3 or 1/6 of the êMTEú of the instrument for the applied load (1/3 is used in R 76-1).

  • Weights from 50 kg to 5000 kg (R 47)

For these weights, rule 3.1.1 with the fraction 1/3 can be considered to be met if Max/f of the instrument is equal to or less than the n marked on the weights.

  • Calibrated weights
  • Errors of the indications of the instrument are not corrected for the errors of the weights

The sum of the absolute values of the errors of the weights shall not be greater than 1/3 or 1/6 of the êMTEú of the instrument for the applied load. However, on the basis of condition 1) in “Introduction” this rule is replaced with rule 3.1.1 here.

  • Errors of the indications of the instrument are corrected for the errors of the weights

The sum of the absolute values of the uncertainties of the weights shall not be greater than 1/3 of the êMTEú of the instrument for the applied load. The fraction 1/6 is not used here for this case.

  • Rules 3.1.1 to 3.2.2 only approximately met

Sometimes it is reasonable to allow the previous rules to be met only approximately. For example, 3.1.1 with the fraction 1/3 is approximately met if the sum of the

êmpeú ’s of the weights exceeds the limit 1/3 ´ êMTEú and the quotient of the excess and the limit is less than or about 1/10 for the applied load. This is applied similarly to the other rules too.

  • Tables for selecting weights of class E2 to M3 (R 111) according to Max/f of the instrument
  • General
  • Scope

Tables 1, 2, 3 and 4 at the end of this section cover the selection of the weights of class E2 to M3 of R 111 according to Max/f of the instrument to be calibrated. The tables are compiled so that the weights selected with their aid meet rule 3.1.1 above without any further action, however, with the exception of the weights for instruments/balances with “very” high Max/f.

The weights dealt with here are normally verified weights, but under the practice of 3.2.1 calibrated weights may also be concerned. The weights for the balances with “very” high Max/f are calibrated weights of class E2 which meet rule 3.2.2, if applicable. This is one of the two procedures to be dealt with in the tables.

  • Differences between the tables

In Tables 1 and 2 the values of êMTEú are: 0.5 f, f & 1.5 f or 0.5 f & f, or only f, and in Tables 3 and 4: f, 2 f & 3 f or f & 2 f (if êMTEú only takes on the value f, Table 1 or 2 is referred to). The fraction is 1/3 in Tables 1 and 3 and 1/6 in Tables 2 and 4.

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  • Selection of a table, its use, groups 1), 2), 3) and 4) of the instruments and procedures

The table is selected according to êMTEú and the frac- tion 1/3 or 1/6. Then Max/f of the instrument/ balance is calculated and, following the instructions given in the tables, it is assigned to one of the following groups (compare the groups with the accuracy classes for instruments/balances in R 76-1, 3.1.1 and 3.2):

Group 1): Special balances (Max/f is unlimited, special accuracy)

Group 2): Laboratory or precision balances (Max/f

£ 100 000, high accuracy)

Group 3): Instruments for industrial weighing (Max/f

£ 10 000, medium accuracy)

Group 4): Instruments for industrial weighing (Max/f

£ 1 000, low accuracy)

On the basis of Max/f and the group of the instru- ment/balance the accuracy class of the weights, or the procedure to be applied (see 4.1.1), is obtained from the table chosen.

The procedures are:

  • “Apply 3.2.2” or “No calibration”. If Max/f is high enough, they are applied for some balances of Group 1).
  • “Apply 3.2.2” means that calibrated weights of class E2 are selected applying 3.2.2 and “No calibration” means that some balances are not calibrated with the weights dealt with here. The procedure “Apply 3.2.2” is used for Tables 1 and 3. It cannot be used for Tables 2 and 4 because the fraction is 1/6 for them. Due to this fraction rule 3.2.2 is excluded. Therefore, the procedure “No calibration” has to be used for Tables 2 and 4 instead of “Apply 3.2.2”. Note that the highest value of Max/f dealt with in the tables is 650 000. More information about the use of the tables is given in the text below each table.

If weights £ 50 g are selected, problems caused by these weights are explained in 4.4. The application of the tables to the selection of the weights for verification of instruments/balances is dealt with in 4.5.

The use of Tables 1, 2, 3 and 4 is illustrated in 4.2.1 to

4.2.4 by means of examples. In order to use the tables properly the “small” and “medium” loads for which the values of êMTEú are given in Section 2 should be defined. This is done in 4.3.

  • Table 1

This table is for êMTEú = 0.5 f, f & 1.5 f; 0.5 f & f or only f and for the fraction 1/3. Table A in 4.3 shows in which cases the values of êMTEú are used. According to Max/f and the group of the instrument/balance the accuracy class E2 to M3 of the weights (3.1.1 or 3.2.1) or the procedure “Apply 3.2.2” is obtained from Table 1.

Example 1: Group 4): Instruments for industrial weighing (Max/f £ 1 000, low accuracy)

  1. If Max/f £ 660, weights of class M3 are selected irres- pective of the possible values of êMTEú . (Consider an instrument with Max 6 600 g, f = 10 g and Max/f = 660. Let the weights for the Max load be 5 kg, 1 kg , 500 g and 100 g of class M3. Their êmpeï’s are 2.5 g, 0.5 g, 0.25 g and 0.05 g respectively.
    1. Let êMTEïassume the value f = 10 g for all the loads. For the Max load the sum of the êmpeï’s of the weights is Sêmpeï = (2.5 + 0.5 + 0.25 + 0.05) g = 3.3 g » 1/3 ´ êMTEï » 3.3 g.
    1. Let êMTEïassume the values 0.5 f = 5 g, f = 10 g & 1.5 f = 15 g so that êMTEï= 0.5 f is used for the loads a) from 0 to 50 f (the loads are expressed in terms of f), ïMTEï = f for the loads,
  2. > 50 f but £ 200 f and ïMTEï = 1.5 f for the loads, c) over 200 f to Max. Let us investigate the sums S êmpeï of the weights (the test loads) which can be used at the greatest loads of the ranges a), b) and c) respectively. For the greatest load of the range a)  Sïmpeï = 0.25 g < 1/3 ´ 0.5 f » 1.7 g, for that of

b) Sï mpe ï = 1 g < 1 / 3 ´ f » 3.3 g and for that of

c) Sïmpeï = 3.3 g < 1/3 ´ 1.5 f = 5 g).

b) If 660 < Max/f £ 1 000

  • and êMTEú takes on the values 0.5 f, f & 1.5 f, the class is M3
  • the class is M2 if êMTEú takes on the values 0.5 f & f or only f.

Example 2: Group 3): Instruments for industrial weighing (Max/f £ 10 000, medium accuracy)

If 2 200 < Max/f £ 3 300

  • and êMTEú takes on the values 0.5 f, f & 1.5 f, the class is M2
  • the class is M1 if êMTEú takes on the values 0.5 f & f or only f.

Example 3: Group 2): Laboratory or precision balances

(Max/f £ 100 000, high accuracy)

Max/f = 6 500 (also see 4.4)

  1. Consider a balance with Max 650 g and f = 0.1 g

– let êMTEú be 0.5 f = 0.05 g for loads £ 500 g and f = 0.1 g for > 500 g to 650 g. The quotient L/(0.5 f)

= 500/0.05 has to be compared with Max/f = 6 500. Because 500/0.05 > 6 500 (L/(0.5 f) > Max/f), class

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F2 has to be used. Note that M1 would be suitable for the load 650 g but not for 500 g. (For 650 g the sum of theïmpeï’s for weights of class M1 is (25 + 5 + 3) mg = 33 mg

» 1/3 ´ ïMTEï= 1/3 ´ 0.1 g » 33 mg but for 500 g it is 25 mg > 1/3 ´ ïMTEï = 1/3 ´ 0.05 g » 16.7 mg).

– M1 would be suitable if the choice of the values of

êMTEú were made so that êMTEú = 0.5 f is used for loads £ 300 g and ïMTEï= f for > 300 g to 650 g (thus L/(0.5 f) = 300 g/(0.5 f) < Max/f ), or if êMTEú

= f for all loads.

  • Consider a balance with Max 65 g and f = 10 mg. Obviously, the weights used are £ 50 g and they should be of class F2 irrespective of the possible values of êMTEú .

Example 4: Group 1): Special balances

(Max/f unlimited, special accuracy)

a) If 65 000 < Max/f £ 200 000 (also see 4.4)

  • and êMTEú assumes the possible values 0.5 f & f or only f, weights of class E2 are selected
    • exceptionally, if weights of £ 50 g are used, 170 000

< Max/f < 200 000 and f = 1 mg, calibrated weights of class E2 are selected applying 3.2.2, i.e., the procedure “Apply 3.2.2” is used. Such a balance might have Max 190 g, f = 1 mg, Max/f = 190 000. However, if f > 1 mg (e.g., Max 380 g, f = 2 mg, Max/f = 190 000), weights (3.1.1 or 3.2.1) of class E2 are used.

b) If 200 000 < Max/f £ 300 000 (also see 4.4)

  • and êMTEú = 0.5 f, f & 1.5 f, the class of the weights is E2. (Consider a balance with Max 290g, f = 1mg, Max/f = 290 000 and ïMTEï = 0.5 f, f & 1.5 f. Let the weights for the Max load be 200 g, 50 g and two of 20 g of class E2. The sum of their ïmpeï’s is (0.30 + 0.10 + 2 ´ 0.080) mg = 0.56 mg which exceeds 1/3 ´ ïMTEï = 1/3 ´ 1.5 mg = 0.5 mg by 0.06 mg. This excess is neglected (3.3) because 0.06 mg/0.5 mg is near to 1/10).
    • if êMTEú = 0.5 f & f or only f, calibrated weights of class E2 are selected applying 3.2.2, i.e., the pro- cedure “Apply 3.2.2” is used.
  • Table 2 and the idea of using the fraction 1/6

In this table êMTEú = 0.5 f, f & 1.5 f; 0.5 f & f or only f as in Table 1 but the fraction is 1/6. Table A in 4.3 shows in which cases the values of êMTEú are used. According to Max/f and the group of the instrument/balance the accuracy class E2 to M3 of the weights (3.1.1 or 3.2.1) or the procedure “No calibration” is obtained from Table 2.

  1. If the weights are within the mpe’s, as they should be, the sum of their êmpeú’s is £ 1/6 ´ êMTEú of the instrument/balance for the applied load. The sum reveals the influence of the errors of the weights on the calibration results.
  2. Suppose that due to wear and tear the weights are not within the mpe’s. However, if their errors can be estimated to be within the mpe’s multiplied by 2, the weights can conditionally be used for the calibration of instruments/balances. The sum of the doubled

êmpe÷’s of the weights is £ 1/3 ´ êMTEú . So the

influence of the errors of the weights on the calibration results is twice that in 1) and thus at most 1/3 ´ êMTEú . If this is accepted, the calibration with these weights can be regarded as correct.

  1. In case 2), the increase of the influence of the errors of the weights from £ 1/6 ´ êMTEú to £ 1/3 ´ êMTEú has to be accepted. In principle this is not difficult because £ 1/3 ´ êMTEú is a generally accepted in- fluence. Because the errors of the weights may exceed the limits of the mpe’s even by 100 %, the period of readjustment of the weights can be extended. This is a considerable advantage. From this angle there are reasons to apply the fraction 1/6.
  2. If the aim is to minimize the uncertainty of the calibration of instruments/balances, the influence of the errors of the weights should be kept as small as possible. £ 1/6 ´ êMTEú could be suitable. Therefore, the errors of the weights should strictly be within the mpe’s as in 1) and the fraction 1/6 should be applied.

Note 1: In R 111 mpe’s on initial verification (mpe’s in 1) above) and in service are given. The latter are twice the mpe’s on initial verification. The mpe’s in service can be used in situations similar to the following. Parties concerned by weighings with legally controlled instruments/balances (e.g., non-self- indicating instruments) in which balance (the position of equilibrium) is obtained with the aid of weights, want to check whether the weights used are “acceptable”. The weights were adjusted to be within the mpe’s on initial verification. Now the errors of the weights are acceptable if they are within the mpe’s in service. One could say that the mpe’s in service give the user of the instrument protection against complaints about the incorrectness of the results of the instrument as far as the weights are concerned.

Note 2: Notwithstanding 2) above the weights, the errors of which are within the mpe’s in service, are not for calibration, verification or testing of instruments/balances.

Example 5: Group 3): Instruments for industrial weighing (Max/f £ 10 000, medium accuracy)

If 1 100 < Max/f £ 3 300, the class is M irrespective of

When the weights of class E2 to M3 selected by

êMTEú .

1

(Consider an instrument with Max 6 000 g, f = 2 g,

means of Table 2 (with the fraction 1/6) are used for the calibration of instruments/balances, the consequences of their errors could be as follows.

Max/f = 3 000 and ïMTEï = f = 2 g for all the loads. Let the weights for the Max load be 5 kg and 1 kg of class M1. The sum of their

ïmpeï’s is (250 + 50) mg = 0.30 g < 1/6 ´ ïMTEï = 1/6 ´ 2 g » 0.33 g).

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Example 6: Group 2): Laboratory or precision balances (Max/f £ 100 000, high accuracy)

Max/f = 6 500 (6 000 < Max/f £ 11 000; also see 4.4)

  1. Consider a balance with Max 650 g and f = 0.1 g. Let

êMTEú be 0.5 f = 0.05 g for loads £ 500g and f = 0.1 g for > 500 g to 650 g. Weights of class F2 are selected.

  • Consider a balance with Max 65 g and f = 10 mg. Obviously, the weights used are £ 50 g and they should be of class F1 irrespective of the possible values of êMTEú .

Example 7: Group 1): Special balances

(Max/f unlimited, special accuracy)

If Max/f £ 60 000 (also see 4.4)

  • and the weights are > 50 g, calibration is per- formed with the weights of class E2
  • if the weights are £ 50 g and êMTEú = 0.5 f & f, calibration is not performed with the weights dealt with here, i.e., the procedure “No calibration” is used. However, calibration is performed with the weights £ 50 g of class E2 if êMTEú = f for all the loads.
  • Table 3

Table 3 is for êMTEú = f, 2 f & 3 f or f & 2 f and for the fraction 1/3. If êMTEú = f for all the loads, apply Table 1. Table B in 4.3 shows in which cases the values of êMTEú are used. According to Max/f and the group of the instrument/balance the accuracy class E2 to M3 of the weights (3.1.1 or 3.2.1) or the procedure “Apply 3.2.2” is obtained from Table 3.

Example 8: Group 2): Laboratory or precision balances (Max/f £ 100 000, high accuracy)

Max/f = 6 500 (also see 4.4)

  1. Consider a balance with Max 650 g and f = 0.1 g. Let

êMTEú be f = 0.1 g for loads £ 500 g and 2 f =0.2 g for

> 500 g to 650 g. Weights of class M1 are selected.

  • Consider a balance with Max 65g and f = 10 mg. Let

êMTEú be f = 10 mg for loads £ 50 g and 2 f = 20 mg for > 50 g to 65 g. Weights of class M1 are selected.

  • Table 4

Table 4 is for êMTEú = f, 2 f & 3 f or f & 2 f and for the fraction 1/6. If êMTEú = f for all the loads, apply Table 2. Table B in 4.3 shows in which cases the values of êMTEú are used. According to Max/f and the group of the

instrument/balance the accuracy class E2 to M3 of the weights (3.1.1 or 3.2.1) or the procedure “No calibra- tion” is obtained from Table 4.

The consequences of using the fraction 1/6 are the same as in 1) and 2) in 4.2.2.

Example 9: Group 2): Laboratory or precision balances (Max/f £ 100 000, high accuracy)

Max/f = 6 500 (also see 4.4)

  1. Consider a balance with Max 650 g and f = 0.1 g
    1. let êMTEú be f = 0.1 g for loads £ 500 g and 2 f =

0.2 g for > 500 g to 650 g. The class is F2 because L/f = 500 g/0.1 g = 5 000 > 3 000 (e.g. F2 is necessary for the load 500 g)

  • if êMTEú = f = 0.1 g for loads £ 300 g and 2 f = 0.2 g for >300 g to 650 g, then L/f = 300 g/0.1 g = 3 000. So weights of class M1 are selected.
  • Consider a balance with Max 65 g and f = 10 mg. Let

êMTEú be f = 10 mg for loads £ 50 g and 2 f = 20 mg for > 50 g to 65 g. Because the weights for this balance are £ 50 g their class is F2.

  • Values of êMTEú for Tables 1, 2, 3 and 4

The following auxiliary tables A and B give the values of

êMTEú which are to be used when selecting weights for the calibration of instruments/balances with the aid of Tables 1, 2, 3 and 4. Table A (for Tables 1 and 2) and B (for Tables 3 and 4) are patterned on the model of R 76-1, 3.5.1.

Definition 1: “Small” loads for an instrument/ balance (expressed in terms of f) are those less than or equal to some chosen load which is not greater than 50 000 f, 5 000 f, 500 f

or 50 f for groups 1), 2), 3) or 4) res- pectively. For example, for a balance of group 2) the “small” loads can be from 0 to 5 000 f or from 0 to a load less than 5 000 f, say, 3 000 f. 5 000 f or 3 000 f is the greatest “small” load L.

Example 10: If Max of a balance of group 2) equals 15 000 f, then Max/f = 15 000 and thus

< 20 000. If the greatest “small” load L is 3 000 f, then according to Table A êMTEú is 0.5 f for the loads from 0 to 3 000 f and f for the loads over 3 000 f to Max. êMTEú can also be chosen to be only f from 0 to Max.

Definition 2: “Medium” loads for an instrument/ balance (expressed in terms of f) are those

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Table A The values of êMTE ê = 0.5 f, f & 1.5 f, or 0.5 f & f, or only f in relation to Max/f and the group of an instrument/balance for Tables 1 and 2 (the groups are defined in 4.1.3)

Max/f of an instrument/balance in: Group 1)                          Group 2)                        Group 3)                         Group 4)  êMTE ê
£ 50 000£ 5 000£ 500£ 50only f 1)
£ 200 000 2)£ 20 000 2)£ 2 000 2)£ 200 2)0.5 f & f, or only f 3)
> 200 000> 20 000> 2 000> 2000.5 f, f &1.5 f, or 0.5 f & f, or only f 4)

1) from 0 to the greatest “small” load L (see Definition 1). In this case L = Max for the instrument/balance.

2) but greater than L/f in the same group.

3) 0.5 f for the “small” loads and f for larger loads, or only f for all the loads (see Example 10).

4) 0.5 f for the “small” loads, f for the “medium” loads (see Definition 2) and 1.5 f for the larger loads but êMTE ê can also be chosen to be 0.5 f for the “small” loads and f for larger loads, or only f for all the loads.

Table B The values of êMTE ê = f, 2 f & 3 f, or f & 2 f in relation to Max/f and the group of an instrument/balance for Tables 3 and 4 (the groups are defined in 4.1.3). (If for an instrument/ balance êMTE ê = f for all the loads, then according to 4.2.3 and 4.2.4 Table 1 or 2 is used instead of Table 3 or 4 respectively.)

Max/f of an instrument/balance in: Group 1)                          Group 2)                        Group 3)                         Group 4)  êMTE ê
£ 200 000 1)£ 20 000 1)£ 2 000 1)£ 200 1)f & 2 f 2)
> 200 000> 20 000> 2 000> 200f, 2 f & 3 f, or f & 2 f 3)

1) but greater than L/f in the same group (L = the greatest “small” load, see Definition 1).

2) f for the “small” loads and 2 f for larger loads.

3) f for the “small” loads, 2 f for the “medium” loads (Definition 2) and 3 f for the larger loads but êMTE ê can also be chosen to be f for the “small” loads and 2 f for larger loads (see Example 11 below).

greater than the greatest “small” load L but not greater than 200 000 f, 20 000 f,

2 000 f or 200 f for groups 1), 2), 3) or 4) respectively. For example, if the “small” loads for an instrument of group 3) are from 0 to 300 f, the “medium” loads are in the interval over 300 f to 2 000 f. Note: The lower limit of the “medium” loads is not predetermined because it depends on the choice of the greatest “small” load L. However, the corresponding upper limit is. It takes on the values 200 000 f to 200 f in the different groups respectively.

Example 11: If Max of an instrument of group 3) equals 2 500 f, then Max/f = 2 500 and thus

> 2 000. Let the greatest “small” load L be 400 f. According to Table B êMTEú is f for the loads from 0 to 400 f, 2 f for the “medium” loads over 400 f to 2 000 f and

3 f for the loads over 2 000 f to Max.

êMTEú can also be chosen to be f from 0 to 400 f and 2 f for the loads over 400 f to Max = 2 500 f.

  • Weights of nominal values £ 50 g

There are problems when selecting weights for balances in group 1) or 2), especially if weights of £ 50 g are to be used for the Max load.

In order to explain the nature of the problems consider Max 65 kg and Max 65 g balances both in group

1) with Max/f = 65 000. For the Max 65 kg balance the sum of the êmpeú ’s of class F1 weights of > 50 g is slightly below the limit 1/3 ´ êMTEú for the Max load (3.1.1), but for the Max 65 g balance the corresponding sum of the class F1 weights of £ 50 g exceeds the limit.

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In the tables the above problem is solved by giving two accuracy classes for some balances in group 1) or 2). One class is for weights > 50 g for balances with certain Max/f ’s and “large” Max loads (e.g: F1, Max/f = 65 000, Max 65 kg,), and the other for weights £ 50 g for balances with the same Max/f ’s as above and “small” Max loads respectively (e.g.: E2, Max/f = 65 000, Max 65 g).

Note: For a “large” Max load, e.g. 650 g there is no problem with a single weight of £ 50 g (i.e., weights of > 50 g are dominating) but for a “small” Max load, e.g. Max near to 100 g there may be.

In the column “Instruments/balances” of the tables several intervals of the values of Max/f are given. When using only weights > 50 g for balances of group 1) and 2) the upper limits of the intervals could be higher than those given in the tables. For example, in Table 1 the upper limits 20 000 (6 500 < Max/f £ 20 000) and 300 000

(200 000 < Max/f £ 300 000) could be raised to 22 000 and 330 000 respectively. But if weights £ 50 g were selected using the tables with the higher limits, their accuracy would not be suitable in all cases. Since weights £ 50 g are important for the calibration of the balances in question the limits have not been raised. As a result of this weights > 50 g selected using the tables may sometimes be more accurate than necessary.

  • Use of the tables to select weights for verification of instruments/balances

Table 1 or 2 ( êMTEú = 0.5 f, f &1.5 f; 0.5 f & f, or f) can be applied to select the weights for the verification of instruments/balances. Then “ f ” is replaced with “e”, “MTE” with “MPE”(maximum permissible error for instruments/balances), the “groups 1), 2), 3) and 4)” of the instruments/balances with the “accuracy classes I, II, III and IIII” respectively and “calibration” with “verifica- tion”. If in Table 1 or 2:

  1. only one accuracy class of weights is given for instruments/balances with a certain n = Max/e, then the correct class is obtained from the tables without any further action.
  2. two accuracy classes of weights are given for instruments/balances with a certain n = Max/e, then to choose the right class the OIML requirements in R 76-1, 3.2 and 3.5.1 have to be taken into account. This is elucidated in the following.

4.5.1 ÷ MPE÷ = 0.5 e, e & 1.5 e

For certain instruments/balances in Table 1 and 2 the accuracy classes of the weights are given in the form

e.g.: M2 (M1 if ï MTEï = 0.5 f & f or f) or F2 (F1 if ï MTEï = 0.5 f & f or f).

Use the replacements for êMTEú , f and groups 1) to 4) as given above. These accuracy classes are for instruments/balances with n = Max/e > 200 000 in class I, n > 20 000 in class II, n > 2 000 in class III or n > 200 in class IIII. Thus the values of the ÷MPE÷ ’s to be applied are 0.5 e, e & 1.5 e. According to the informa- tion on the use of the tables (given in the text below the tables) the accuracy class of the weights given first (M2 or F2 in the above examples) is used. The second accuracy class given in parentheses is to be ignored because the condition “if÷ MPE÷ = 0.5 e & e or e” is not in accordance with the OIML requirements for the instruments/balances in question.

4.5.2 ÷ MPE÷ = 0.5 e & e

For some balances in Table 1 and 2 there are accuracy classes of the weights in the form e.g.: M1 (F2 if 1). F2 if

ï MTEï = 0.5 f & f and L/(0.5 f) > Max/f …), F2 (F1 if 1))

or E2 (No calibration if 1) and ïMTEï= 0.5 f & f ). 1) refers to the use of weights of £ 50 g. Use the replacements for

êMTEú, f, groups 1) to 4) and calibration. This concerns class I balances with n = Max/e £ 200 000 but n > 50 000 and class II balances with n £ 20 000 but n > 5 000. The values of the êMPEú ’s to be applied are 0.5 e & e. Accuracy classes of the weights similar to those in the above examples, and in advice under the heading “Exception” in Table 1, can be used. However, one has to check that only those instructions in the tables are followed which are or lead to results which are compatible with the OIML requirements (also see 4.5.4).

4.5.3 ÷ MPE÷ = 0.5 e

In the case where êMPEú = 0.5 e is used for all the loads (e.g., n = Max/e = 50 000 and e ³ 1 mg for class I balances or n = 5 000 and e ³ 0.1 g for class II balances), Table 1 or 2 is exceptionally applied so that the weights are chosen according to Max/f where f = 0.5 e.

4.5.4 Restriction concerning balances of class II

The sections of Tables 1 and 2 which are intended for class II balances (originally intended for group 2) balances) can be used for the selection of weights only if for the balances e ³ 10 mg. So if 1 mg £ e £ 5 mg (R 76-1, 3.2) for class II balances with êMPEú ’s of 0.5 e & e, or only 0.5 e, the weights cannot be obtained correctly from the tables in all cases.

OIML BULLETIN    V OLUME XLIV • N UMBER 4 • O CTOBER 2003                                               11

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Table 1 Max/f and accuracy classes E2 to M3 of weights or procedure to be applied

  • ïMTEï of the instrument/balance takes on the values: 1) 0.5 f, f & 1.5 f or 2) 0.5 f & f or 3) only f (the values are chosen following the instructions in Table A in 4.3)
  • The fraction is 1/3 (the error of the weights shall not be greater than 1/3 ´ ïMTE÷ for the applied load)
Instruments/balances Max/fWeights Accuracy class or procedure
Group 1): Special balances (Max/f unlimited, special accuracy); f ³ 1 mg, e.g. f = 1 mg, 2 mg, 5 mg, 10 mg, 20 mg, etc. 
300 000 < Max/f £ 650 000 200 000 < Max/f £ 300 000 65 000 < Max/f £ 200 000   Max/f £ 65 000Apply 3.2.2 E2 (Apply 3.2.2 if ïMTEï = 0.5 f & f or f) E2 Exception: Apply 3.2.2 if 1), 170 000 < Max/f < 200 000 and f = 1 mg (E2 if f >1 mg) F1 (E2 if 1). E2 if ïMTEï = 0.5 f & f and L/(0.5 f ) > Max/f 2); L is the greatest “small” load (4.3) for which ïMTEï = 0.5 f)
Group 2): Laboratory or precision balances (Max/f £ 100 000, high accuracy); f ³ 10 mg, e.g., f = 10 mg, 20 mg, 50 mg or ³ 0.1 g. 
65 000 < Max/f £ 100 000 30 000 < Max/f £ 65 000 20 000 < Max/f £ 30 000 6 500 < Max/f £ 20 000   Max/f £ 6 500F1 (E2 if ïMTEï = 0.5 f & f or f) F1 F2 (F1 if ïMTEï = 0.5 f & f or f) F2 Exception: F1 if 1) , 17 000 < Max/f < 20 000 and f = 10 mg (F2 if f > 10 mg) M1 (F2 if 1). F2 if ïMTEï = 0.5 f & f and L/(0.5 f ) > Max/f 3); L is the greatest “small” load (4.3) for which ïMTEï= 0.5 f)
Group 3): Instruments for industrial weighing 
(Max/f £ 10 000, medium accuracy); 
f ³ 1 g, e.g., f = 2 g or 20 kg. 
6 600 < Max/f £ 10 000M1 (F2 if ïMTEï = 0.5 f & f or f)
3 300 < Max/f £ 6 600M1
2 200 < Max/f £ 3 300M2 (M1 if ïMTEï = 0.5 f & f or f)
Max/f £ 2 200M2
Group 4): Instruments for industrial weighing (Max/f £ 1 000, low accuracy); f ³ 5 g, e.g., f = 50 g or 50 kg. 660 < Max/f £ 1 000 Max/f £ 660      M3 (M2 if ïMTEï = 0.5 f & f or f) M3

1) Weights of £ 50 g are used (4.4).

2) F1 if L/(0.5 f) £ Max/f, or if ïMTEï = f for all the loads. Weights of > 50 g are used/dominating (4.4).

3) M1 if L/(0.5 f) £ Max/f, or if ïMTEï = f for all the loads. Weights of > 50 g are used/dominating (4.4).

In the column “Weights” the accuracy classes of the weights (3.1.1 or 3.2.1) and the procedure “Apply 3.2.2” (4.1.3) are given for the instruments/balances to be calibrated.

If there is only one accuracy class corresponding to a Max/f, it can be used irrespective of the values of êMTEú given in 1), 2) or 3) above. Frequently, another accuracy class along with conditions for its use is given in parentheses. This class must be applied if the conditions are met, e.g., if êMTEú = 0.5 f & f or f . Otherwise if êMTEú = 0.5 f, f & 1.5 f, the class given first is used.

This scheme is analogously applied to the case where the procedure “Apply 3.2.2” is used. For example, if only “Apply 3.2.2 ” is given, it is applied irrespective of the values of êMTEú .

Advice under the heading “Exception” is for certain special cases.

12          OIML BULLETIN    V OLUME XLIV • N UMBER 4 • O CTOBER 2003 

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Table 2 Max/f and accuracy classes E2 to M3 of weights or procedure to be applied

  • ïMTEï of the instrument/balance takes on the values: 1) 0.5 f, f & 1.5 f or 2) 0.5 f & f or 3) only f (the values are chosen following the instructions in Table A in 4.3)
  • The fraction is 1/6 (the error of the weights shall not be greater than 1/6 ´ ïMTE÷ for the applied load)
Instruments/balances Max/fWeights Accuracy class or procedure
Group 1): Special balances (Max/f unlimited, special accuracy); 
f ³ 1mg, e.g. f = 1 mg, 2 mg, 5 mg, 10 mg, 20 mg, etc. 
Max/f > 110 000No calibration
60 000 < Max/f £ 110 000E2 (No calibration if 1) )
Max/f £ 60 000E2 (No calibration if 1) and ïMTEï = 0.5 f & f 2) )
Group 2): Laboratory or precision balances 
(Max/f £ 100 000, high accuracy); 
f ³ 10 mg, e.g., f = 10 mg, 20 mg, 50 mg or ³ 0.1 g. 
50 000 < Max/f £ 100 000E2
30 000 < Max/f £ 50 000F1 (E2 if ïMTEï= 0.5 f & f or f)
11 000 < Max/f £ 30 000F1
6 000 < Max/f £ 11 000F2 (F1 if 1))
Max/f £ 6 000F2 (F1 if 1) and ïMTEï = 0.5 f & f 3) )
Group 3): Instruments for industrial weighing 
(Max/f £ 10 000, medium accuracy); 
f ³ 1 g, e.g., f = 2 g or 20 kg. 
5 000 < Max/f £ 10 000F2
3 300 < Max/f £ 5 000M1 (F2 if ïMTEï = 0.5 f & f or f)
1 100 < Max/f £ 3 300M1
Max/f £ 1 100M2
Group 4): Instruments for industrial weighing 
(Max/f £ 1 000, low accuracy); 
f ³ 5 g, e.g., f =50 g or 50 kg. 
500 < Max/f £ 1 000M2
330 < Max/f £ 500M3 (M2 if ïMTEï = 0.5 f & f or f)
Max/f £ 330M3

1) weights of £ 50 g are used (4.4).

2) E2 if 1) and ïMTEï= f for all the loads or if weights of > 50 g are used/dominating (4.4).

3) F2 if 1) and ïMTEï= f for all the loads or if weights of > 50 g are used/dominating (4.4).

In the column “Weights” the accuracy classes of the weights (3.1.1 or 3.2.1) and the procedure “No calibration” (4.1.3) are given for the instruments/ balances to be calibrated.

If there is only one accuracy class corresponding to a Max/f, it can be used irrespective of the values of êMTEú given in 1), 2) or 3) above. Sometimes, another accuracy class along with conditions for its use is given in parentheses. This class must be applied if the conditions are met, e.g., if 1) (if weights of £ 50 g are used). Otherwise if the weights are > 50 g, the class given first is used.

This scheme is analogously applied to the case where the procedure “No calibration” is used. For example, consider “E2 (No calibration if 1) )”. If the weights are £ 50 g, calibration is not performed with the weights dealt with here. Otherwise, if the weights are > 50 g, calibration is performed with weights of class E2.

OIML BULLETIN    V OLUME XLIV • N UMBER 4 • O CTOBER 2003                                               13

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Table 3 Max/f and accuracy classes E2 to M3 of weights or procedure to be applied

  • ïMTEï of the instrument/balance takes on the values: 1) f, 2 f & 3 f or 2) f & 2 f (the values are chosen following the instructions in Table B in 4.3). If ïMTEï = f for all the loads, apply Table 1
    • The fraction is 1/3 (the error of the weights shall not be greater than 1/3 ´ ïMTE÷ for the applied load)
Instruments/balances Max/fWeights Accuracy class or procedure
Group 1): Special balances 
(Max/f unlimited, special accuracy); 
f ³ 1 mg, e.g., f = 1 mg, 2 mg, 5 mg, 10 mg, 20 mg etc. 
400 000 < Max/f £ 650 000E2 (Apply 3.2.2 if ïMTEï= f & 2 f)
130 000 < Max/f £ 400 000E2
65 000 < Max/f £ 130 000F1 (E2 if 1)) Exception: F1 if 1) , Max/f = 70 000 or 105 000
 and L = 50 000 f 2)
Max/f £ 65 000F1
Group 2): Laboratory or precision balances 
(Max/f £ 100 000, high accuracy); 
f ³ 10 mg, e.g., f = 10 mg, 20 mg, 50 mg or f ³ 0.1 g. 
65 000 < Max/f £ 100 000F1
40 000 < Max/f £ 65 000F2 (F1 if ïMTEï= f & 2 f)
13 000 < Max/f £ 40 000F2
6 500 < Max/f £ 13 000M1 (F2 if 1)) Exception: M1 if 1) , Max/f = 7 000 or 10 500
 and L = 5 000 f 3)
Max/f £ 6 500M1
Group 3): Instruments for industrial weighing 
(Max/f £ 10 000, medium accuracy); 
f ³ 1 g, e.g., f = 2 g or 20 kg. 
6 600 < Max/f £ 10 000M1
4 400 < Max/f £ 6 600M2 (M1 if ïMTEï= f & 2 f)
1 300 < Max/f £ 4 400M2
Max/f £ 1 300M3
Group 4): Instruments for industrial weighing (Max/f £ 1 000, low accuracy); f ³ 5 g, e.g., f = 50 g or 50 kg. Max/f £ 1 000    M3

1) weights of £ 50g are used (4.4).

2) L is the greatest “small” load for which ïMTE÷ = f (see Definition 1 in 4.3).

3) L is the greatest “small” load for which ïMTE÷ = f (see Definition 1 in 4.3).

In the column “Weights” the accuracy classes of the weights (3.1.1 or 3.2.1) and the procedure “Apply 3.2.2” (4.1.3) are given for the instruments/balances to be calibrated.

If there is only one accuracy class corresponding to a Max/f, it can be used irrespective of the values of êMTEú given in 1) or 2) above. Sometimes, another accuracy class along with conditions for its use is given in parentheses. This class must be applied if the conditions are met, e.g., if êMTEú = f & 2 f. Otherwise if êMTEú = f, 2 f & 3 f, the class given first is used.

This scheme is analogously applied to the case where the procedure “Apply 3.2.2” is used. For example, consider “E2 (Apply 3.2.2 if êMTEú = f &2 f )”. If êMTEú = f & 2 f , calibrated weights of class E2 are used applying 3.2.2. Otherwise, if êMTEú = f, 2 f & 3 f, weights (3.1.1 or 3.2.1) of class E2 are used.

Advice under the heading “Exception” is for certain special cases.

14          OIML BULLETIN    V OLUME XLIV • N UMBER 4 • O CTOBER 2003 

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Table 4 Max/f and accuracy classes E2 to M3 of weights or procedure to be applied

  • ïMTEïof the instrument/balance takes on the values: 1) f, 2 f & 3 f or 2) f & 2 f (the values are chosen following the instructions in Table B in 4.3). If ïMTEï = f for all the loads, apply Table 2
  • The fraction is 1/6 (the error of the weights shall not be greater than 1/6 ´ ïMTE÷ for the applied load)
Instruments/balances Max/fWeights Accuracy class or procedure
Group 1): Special balances 
(Max/f unlimited, special accuracy); 
f ³ 1mg, e.g. f = 1 mg, 2 mg, 5 mg, 10 mg, 20 mg etc. 
Max/f > 300 000No calibration
200 000 < Max/f £ 300 000E2 (No calibration if ôMTEô= f & 2 f )
65 000 < Max/f £ 200 000E2 Exception: No calibration if 1), 170 000 < Max/f < 200 000 and
 f = 1 mg (E2 if f > 1 mg)
Max/f £ 65 000F1 (E2 if 1). E2 if L/f > 30 000 2); L is the greatest “small” load
 (4.3) for whichôMTEô = f)
Group 2): Laboratory or precision balances (Max/f £ 100 000, high accuracy); f ³ 10 mg, e.g., f = 10 mg, 20 mg, 50 mg or ³ 0.1 g. 
65 000 < Max/f £ 100 000 30 000 < Max/f £ 65 000 20 000 < Max/f £ 30 000 6 500 < Max/f £ 20 000   Max/f £ 6 500F1 (E2 ifôMTEô= f & 2 f) F1 F2 (F1 if ôMTEô= f & 2 f) F2 Exception: F1 if 1), 17 000< Max/f < 20 000 and f = 10 mg (F2 if f > 10 mg) M1 (F2 if 1). F2 if L/f > 3 000 3); L is the greatest “small” load (4.3) for whichôMTEô = f)
Group 3): Instruments for industrial weighing 
(Max/f £ 10 000, medium accuracy); 
f ³ 1 g, e.g., f = 2 g or 20 kg. 
6 600 < Max/f £ 10 000M1 (F2 if ôMTEô= f & 2 f)
3 300 < Max/f £ 6 600M1
2 200 < Max/f £ 3 300M2 (M1 if ôMTEô= f & 2 f)
Max/f £ 2 200M2
Group 4): Instruments for industrial weighing (Max/f £ 1 000, low accuracy); f ³ 5 g, e.g., f = 50 g or 50 kg. 660 < Max/f £ 1 000 Max/f £ 660    M3 (M2 if ôMTEô= f & 2 f) M3

1) weights of £ 50g are used (4.4).

2) F1 if L/f £ 30 000. Weights of > 50 g are used/dominating (4.4).

3) M1 if L/f £ 3 000. Weights of > 50 g are used/dominating (4.4).

In the column “Weights” the accuracy classes of the weights (3.1.1 or 3.2.1) and the procedure “No calibration” (4.1.3) are given for the instruments/ balances to be calibrated.

If there is only one accuracy class corresponding to a Max/f, it can be used irrespective of the values of êMTEú given in 1) or 2) above. Frequently, another accuracy class along with conditions for its use is given in parentheses. This class must be applied if the conditions are met, e.g., if L/f > 3 000 (a balance in group 2) with Max/f £ 6 500). Otherwise if L/f £ 3 000, the class M1 given first is used.

This scheme is analogously applied to the case where the procedure “No calibration” is used. For example consider “E2 (No calibration if

êMTEú = f & 2 f)”. If êMTEú = f & 2 f, calibration is not performed with the weights dealt with here. Otherwise, if êMTEú = f, 2 f & 3 f, calibration is performed with weights of class E2.

Advice under the heading “Exception” is for certain special cases.

OIML BULLETIN    V OLUME XLIV • N UMBER 4 • O CTOBER 2003                                               15

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References

  • OIML Recommendation R 111, Weights of classes E1, E2, F1, F2, M1, M2, M3 (1994)
  • OIML Recommendation R 47 Standard weights for testing of high capacity weighing machines (1979-1978)
  • T. Lammi: Calibration of Weighing Instruments and Uncertainty of Calibration. OIML Bulletin Volume XLII,

Number 4, October 2001

  • OIML Recommendation R 76-1, Nonautomatic weighing instruments. Part 1: Metrological and technical requirements – Tests (1992)

16       OIML BULLETIN    V OLUME XLIV • N UMBER 4 • O CTOBER 2003 

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Calibration and verification: Two procedures having comparable objectives and results

KLAUS-DIETERSOMMER, Landesamt für Mess- und Eichwesen Thüringen (LMET), GermanySAMUELE. CHAPPELL, Consultant, Formerly of theNational Institute of Standards and Technology(NIST), USAMANFREDKOCHSIEK, Physikalisch-TechnischeBundesanstalt (PTB), Germany

Abstract

The most important actions required to ensure the correct indication of measuring instruments are: Kin industrial metrology, regular calibration of the measuring instruments according to the implemented quality systems; and Kin legal metrology, periodic verification or conformity testing of the instruments according to legal regulations. Both actions are strongly inter-related and are pre-dominantly based on the same measuring procedures. Historically, however, these actions have been established with separate rules, metrological infrastructures and activities. This paper, therefore, addresses the differences, common bases and the relationship between calibration and verification. In particular, the relationships between legally prescribed error limits and uncertainty and the uncertainty contribution of verified measuring instruments are discussed.

Introduction

The correctness of measurements and measuring instruments is one of the most important prerequisites for the assurance of the quality and quantity of products and services, and the accuracy of the instruments must be consistent with their intended use.

In compliance with the ISO 9000 standard series and the ISO/IEC 17025 standard, traceability of measuring and test equipment to the realization of SI units must be guaranteed by an unbroken chain of comparison measurements to allow the necessary statements about their metrological quality. The most important actions to ensure the correct indication of measuring instruments are: Kin industrial metrology: regular calibration of the measuring instruments according to the implemented quality systems; and Kin legal metrology: periodic verification or conformity testing of the measuring instruments according to legal regulations. Both actions are closely related and are mostly based on the same measuring procedures. Historically, however, these actions have been established with separate rules and metrological infra-structures and activities. Verification has become a principal part of legal metrology systems and calibration is widely used in quality assurance and industrial metrology – accreditation bodies prefer calibration as a primary action to provide proof of the correctness of the indication of measuring instruments. As a result, today it must be acknowledged that there is a lack of reciprocal understanding of the identical metrological nature of these activities between the different communities of users. In particular, their specific concerns are insufficiently understood, and there is widespread incomprehension concerning the relation-ship of error limits and uncertainty of measurement. For instance, the use of legally verified instruments within the framework of quality management some times presents problems since only the MPEs for the instruments are provided, without the measurement uncertainties being explicitly given.

1 Calibration

Usually, calibration is carried out in order to provide a quantitative statement about the correctness of the measurement results of a measuring instrument. For economic reasons, laboratories strive for broad recognition of their calibration and measurement results. Confidence in results, therefore, is achieved through both establishing the traceability and providing the un-certainty of the measurement results. According to the VIM [1], calibration may be defined as a “set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values realized by standards”. This means that the calibration shows how the nominal value of a material or the indication of an instrument relates to the conventional true values of the measurand. The conventional true value is realized by a traceable reference standard [1]. According to this definition, calibration does not necessarily contain any actions of adjustment or maintenance of the instrument to be calibrated. Figures 1 and 2 show examples of calibration by means of the comparison method, i.e. by comparison of the indication of the instrument under test, and the corresponding indication of appropriate standards respectively. Calibration certificates for measuring instruments give the measurement deviation, or correction, and the uncertainty of measurement. Only this combination characterizes the quality of the relation of the measurement result to the appropriate (SI) unit. Figure 3illustrates the meaning of a (single) calibration result as it is typically presented. The uncertainty of measurement is a parameter, associated with the result of measurement, that characterizes the (possible) dispersion of the values that could reasonably be attributed to the measurand [1]. In other words, uncertainty is a measure of the in completeness of knowledge about the measurand. It is determined according to unified rules [2, 3] and is usually stated for a coverage probability of 95 %. Its value, together with the determined measurement error, is valid at the moment of calibration and under the relevant calibration conditions. If a recently calibrated measuring instrument is used under the same conditions as during the calibration, the measurand Y may be reduced to the following parts: Y = XS+ δX(1)where XS represents the corrected indication of the calibrated instrument. δX may be the combination of all other (unknown) measurement deviations due to imperfections in the measuring procedure. Thus, it follows that the associated standard uncertainty of the measurement carried out by means of a calibrated instrument is:u2(y) = u2(xs) + u2(δx)(2)

This means that the calibration uncertainty u(xs) of a newly calibrated instrument enters directly into the total uncertainty of the measurement u(y) as an (inde-pendent) contribution. When the calibrated instrument is used in a different environment, the measurement uncertainty determined by the calibration laboratory will often be exceeded if the instrument is susceptible to environmental influences. A problem can also arise if the instrument’s performance is degraded after prolonged use. Furthermore, the stated uncertainty of measurement can be considered as being related to national standards only for certificates issued by laboratories that have demonstrated their competence beyond reasonable doubt. Such laboratories are normally well recognized by their customers. In other cases, for example, when working standard calibration certificates are used, reference to the national standards cannot be taken for granted and the user must be satisfied as to the proper traceability – or take other actions. Sometimes, calibration certificates give a conformity statement, i.e. a statement of compliance with given specifications or requirements. In these cases, according to the EA document EA-3/02 [4], the obtained measurement result, extended by the associated uncertainty, must not exceed the specified tolerance or limit. Figure 4 illustrates this approach.

2 Verification and error limits in legal metrology

2.1 Verification

Verification of the conformity of measuring instruments is a method of testing covered by legal regulations. It is a part of a process of legal metrological control that in many economies requires type evaluation and approval

of some models of instruments subject to legal regulations as a first step. Figure 5 shows the typical test sequence over the lifetime of a measuring instrument subject to legal regulations. Type evaluation is usually more stringent than verification. It includes testing the instrument’s performance when subjected to environmental influence factors in order to determine whether the specified error limits for the instrument at rated or foreseeable in situoperating conditions are met [5].The basic elements of verification are [5]:K qualitative tests, e.g. for the state of the instrument(which is essentially an inspection); and K quantitative metrological tests. The aim of the quantitative metrological tests is to determine the errors with the associated uncertainty of measurement (cf. 1) at prescribed testing values. These tests are carried out according to well-established and harmonized testing procedures [5].

Following the definition of calibration, as given in 1,the quantitative metrological tests may be considered a calibration. This means that an instrument’s assurance of metrological conformity involves both verification and calibration, and the measuring equipment necessary to determine conformity during verification might be the same as that used for calibration, e.g. as shown in Figs. 1 and 2.The results of the verification tests are then evaluated to ensure that the legal requirements are being met(see 2.2). Provided that this assessment of conformity leads to the instrument being accepted, a verification mark should be fixed to it and a verification certificate may be issued. Figure 6 illustrates these elements of verification. According to the above definitions and explanations, Table 1 compares the primary goals and the actions of calibration and verification.

2.2 Maximum permissible errors on verification and in service

In many economies with developed legal metrology systems, two kinds of error limits have been defined: K the maximum permissible errors (MPEs) on verification; and K the maximum permissible errors (MPEs) in service. The latter is normally twice the first. MPEs on verification equal “MPEs on testing” that are valid at the time of verification. For the measuring instrument user, the MPEs in service are the error limits that are legally relevant. This approach is explained and illustrated in detail in 4.3 of [5].

The values of the error limits are related to the intended use of the respective kind of instrument and determined by the state of the art of measurement technology.

3 Relationship between legally prescribed error limits and uncertainty

3.1 General

If a measuring instrument is tested for conformity with a given specification or with a requirement with regard to the error limits, this test consists of comparisons of measurements with those resulting from use of a physical standard or calibrated standard instrument. The uncertainty of measurement inherent in the measurement process then inevitably leads to an uncertainty of decision of conformity. Figure 7 (taken from the standard ISO 14253-1) [6] makes this problem quite clear: between the conformance zones and the upper and lower non-conformance zones there is in each case an uncertainty zone whose width corresponds approximately to twice the expanded uncertainty of measurement at the 95 % probability level. The uncertainty comprises contributions of the standard(s) used and the instrument under test as well as contributions that are related to the measuring procedure and to the in-complete knowledge about the existing environmental conditions (cf. 3).Because of the uncertainty of measurement, measurement results affected by measurement deviations lying within the range of the uncertainty zones cannot definitely be regarded as being, or not being, in conformity with the given tolerance requirement.

3.2 Relationship upon verification

In practice, measuring instruments are considered to comply with the legal requirements for error limits if: K the absolute value of the measurement deviations is smaller than or equal to the absolute value of the legally prescribed MPEs on verification when the testis performed under prescribed test conditions; and K the expanded uncertainty of measurement of the previous quantitative metrological test (cf. 2.1), for a coverage probability of 95 %, is small compared with the legally prescribed error limits. The expanded measurement uncertainty at the 95 %probability level, U0.95, is usually considered to be small enough if the following relationship is fulfilled:U0.95≤1–3⋅MPEV(3)

where MPEV is the absolute value of the MPE on verification. Umaxis, therefore, the maximum acceptable value of the expanded measurement uncertainty of the quantitative test. The criteria for the assessment of compliance are illustrated in Fig. 8 (cf.[5]): cases a, b, c and d comply with the requirements of the verification regulations, whereas cases e and f will be rejected. Values in all cases, including their uncertainty of measurement, lie within the tolerances fixed by the MPEs in service. Consequently, the MPE on verification of a newly verified measuring instrument will in the worst case be exceeded by 33 %. However, as the legally prescribed MPEs in service are valid for the instrument users, there is, therefore, negligible risk in the sense that no measured value under verification – even if the measurement uncertainty is taken into account – will be outside this tolerance band. So far, the MPEs on verification may be seen as supporting the conclusion that an instrument would be in conformity with required MPEs in service (MPES) taking into consideration the above-mentioned influences. The advantages of this verification system are that it is practical in terms of legal enforcement, and – due to the widened tolerance band in service [MPES–; MPES+]- it is potentially tolerant of external influences and of drifts in indication over the legally fixed validity periods. Verification validity only expires early in cases of un-authorized manipulations and damage that could reduce the accuracy of the instrument.

3.3 Relationship upon testing of working standards In legal metrology, working standards are the standards that are used routinely to verify measuring instruments. In several economies, some of the working standards used in legal metrology must be tested or verified according to special regulations. The MPEs of such working standards depend on their intended use. In general, they should be significantly lower than the expanded uncertainties that are required by equation(3).

Usually, a working standard, e.g. mass (weight) [7], is considered to comply with the respective requirements for legal error limits if the difference between its indication, or measured value, and the corresponding value realized by a reference standard is equal to or less than the difference between the prescribed error limits, MPEws, and the expanded uncertainty of measurement,U0.95:|Iws– xs| ≤MPEws– U0.95(4) where: Iws= the indication of the working standard under test;andxs= the value provided by a reference standard. In practice, this means that with respect to measurement deviations, a tolerance band is defined that is significantly reduced when compared with the range between the legally prescribed error limits[MPEws–;MPEws+] (see Fig. 4). The magnitude of this tolerance band may be described by the interval [MPEws–+ U; MPEws+– U].This approach is consistent with the prescribed procedures for statements of conformity on calibration certificates (cf. 1 and [4]).

4 Uncertainty contribution of verified instruments

In practice, it is often necessary or desirable to deter-mine the uncertainty of measurements that are carried out by means of legally verified measuring instruments. If only the positive statement of conformity with the legal requirements is known, for example in the case of verified instruments without a certificate, the uncertainty of measurements for such instruments can be derived only from the information available about the prescribed error limits (on verification and in service)and about the related uncertainty budgets according to the requirements established in 2.2 and 3.2.On the assumption that no further information is available, according to the principle of maximum entropy, the following treatment is justified: K The range of values between the MPEs on verification can be assumed to be equally probable. K Due to uncertainty in measurement, the probability that indications of verified instruments are actually beyond the acceptance limits of the respective verification declines in proportion to the increase in distance from these limits. A trapezoidal probability

distribution according to Fig. 9 can, therefore, reflect adequately the probable dispersion of the deviation of verified measuring instruments. K Immediately after verification, the indications of measuring instruments may exceed the MPEs on verification by the maximum value of the expanded uncertainty of measurements at most. K After prolonged use and under varying environmental conditions, it can be assumed that the expanded measurement uncertainty, compared with its initial value, may have increased significantly. In particular, the following evaluation of the un-certainty contribution of verified instruments seems to be appropriate: a) Immediately after verification, the trapezoidal probability distribution of the errors according to plot (a)of Fig. 9 can be taken as a basis for the determination of the uncertainty contribution of the instruments. The following may, therefore, be assumed for this standard uncertainty contribution uINSTR[2]:uINSTR= a⋅ (1 + β2) / 6 ≈0.7 ⋅MPEV(5)where a= 1.33–⋅MPEVand β= 3 / 4.MPEVis the absolute value of the MPEs on verification.

b) After prolonged use and under varying environ-mental conditions, it can be assumed that, in the worst case, the measurement error extended by the measurement uncertainty will reach the values of the MPEs in service. The resulting trapezoidal distribution could more or less be represented by plot (b)of Fig. 9. In this case, the following may be assumed for the standard uncertainty contribution [2]:uINSTR= a⋅ (1 + β2) / 6 ≈0.9 ⋅MPEV(6) where: a= 2 ⋅MPEVandβ= 1 / 2

5 System comparison

Table 2 shows a comparison between verification and calibration, which is partially based on Volkmann [8].In conclusion, verification offers assurance of correct measurements by a measuring instrument according to its intended use especially for those instruments that

require type evaluation and approval. It is based on technical procedures equivalent to those used in calibration and provides confidence in the correctness of indications of verified instruments although no expert knowledge by the instrument’s user is required. Verification, therefore, may be considered a strong tool in both legal metrology and quality assurance when large numbers of measuring instruments are involved. In particular, it excels as a simple means by which enforcement can be realized, and because the user is only affected by the MPEs in service, it provides a high degree of confidence over a long time period.

One disadvantage in verification is that the influence of uncertainty on a decision of conformity of a measuring instrument to specific requirements is not completely clear. In comparison, traditional calibration is considered an important basic procedure for legal metrology activities and also for fundamental measurement applications in scientific and industrial metrology. It is practically not limited as far as the measurement task is concerned, but does require sound expert knowledge on the part of the instrument’s user in carrying out and evaluating measurements.

References

[1]International Vocabulary of Basic and General Termsin Metrology: BIPM, IEC, IFCC, ISO, IUPAC, IUPAP,OIML, 1993[2]Guide to the Expression of Uncertainty in Measure-ment(Corrected and reprinted 1995): BIPM, IEC,IFCC, ISO, IUPAC, IUPAP, OIML, page 101[3] EA-4/02, Expression of the Uncertainty of Measure-ment in Calibration, Ed. 1: European Cooperationfor Accreditation (EA), April 1997 (previously EAL-R2)[4] EA-3/02, The Expression of Uncertainty in Quanti-tative Testing, Ed. 1: European Cooperation forAccreditation (EA), August 1996 (previously EAL-G23)[5] Schulz, W.; Sommer, K.-D.: Uncertainty of Measure-ment and Error Limits in Legal Metrology: OIMLBulletin, October 1999, pp. 5–15[6] Geometrical Product Specification (GPS) –Inspection by measurement of workpieces andmeasuring equipment, Part 1: Decision rules forproving conformance or nonconformance withspecification, ISO 14253–1: 1998, InternationalOrganization for Standardization (ISO), Geneva,1998[7] OIML R 111 (1994): Weights of classes E1, E2, F1, F2,M1, M2, M3[8] Volkmann, Chr.: Messgeräte in der Qualitäts-sicherung geeicht oder kalibriert. AWA-PTB-Gespräch 1997, Braunschweig 1997[9] Klaus Weise, Wolfgang Wöger: Messunsicherheitund Messdatenauswertung. Verlag Weinheim, NewYork, Chichester, Singapore, Toronto: Wiley-VCH,1999

OIML BULLETINVOLUMEXLII •NUMBER1 •JANUARY2001

Calibrated Weights

Calibrated Weights are used almost exclusively for adjusting and testing – (calibration of electronic balances). We therefore call them Test weights as this is their purpose of use. Adjusting a balance means that you are intervening in the weighing system, to make sure that the display is set to show the correct nominal value. And Calibration, on the other hand you are testing whether the display is correct and documenting any deviation. Regular servicing is essential for ensuring that a balance or a weighting device performs with specification. Thus adjusting and calibration both requires test weights, which are also used with weighing instruments of all classes. These test weights are also need to be protected and finely coated thus to properly adjust and calibrate our weighing machines, weighing instruments and other weighing systems.

The International valid OIML Directive R111-2004 classifies test weights hierarchically into accuracy classes with E1 is the most accurate and M3 is the least accurate weight class. As the appropriate test weight is only classified as checking equipment if it has relevant proof of accuracy. The whole test weight range in OIML accuracy classes are E1,E2,F1,F2,M1,M2,M3. With E1 being the most accurate and M3 being the least accurate one.

Cast Iron Slotted Calibration Weights & Hangers – M1 Accuracy

The  hanger weight is a weight in itself, that also has its weight Calibrated so that the hanger can be used as part of the overall weight under test,  and will hold a number of Cast Iron slotted weights depending on its usable shaft lengths. The slotted weights are discs with slots in them and are designed to sit on the hanger. Several Cast Iron Slotted Weights may be used together to build up from a minimum weight to a maximum test load.

These weights are used to test force gauges, crane scales or other suspended weighing scales. Cast Iron Slotted Weights are primarily used to calibrate large capacity scales.

Shanker Wire Cast Iron Slotted Weights are manufactured from a high quality iron. The surface are free of cracks, pits and sharp edges. All surfaces are smooth and free of scratches, dents and pores. Weights are protected by a durable coat of paint to protect the casting from rusting.

The M1 Cast Iron slotted hanger weights (Newton Cast Iron Slotted Weights, Kilogram Cast Iron Slotted Weights)  are the most common hanger weights we sell and are suitable for testing and calibration in the 5 N / 500 g up to 200 N / 20 kg.

Cast Iron Slotted Weight Hangers:

Cast Iron Slotted Weights are typically used with a hanger that also has its weight calibrated so the hanger can be used as part of the overall weight under test. Weight hangers are available in a variety of lengths and weight capacities. Hangers are calibrated to a mass value, and also have a capacity of how much weight can be loaded onto them.

Calibration Weight Certification:

You will normally need a calibration certificate to satisfy, if the tests that you do are on equipment that can effect the quality of your product and you are audited by an outside organization. Our Calibration Laboratory is NABL accredited in accordance with the standard ISO/IEC 17025 : 2017, So you can be satisfied with the quality and accuracy of the Cast Iron Newton Slotted Weights and Hangers.

Construction and General Shape:

Cast Iron Slotted Weights have adjusting cavities. Each weight has its nominal value cast into the topside of the weight. Weights are protected by a durable coat of paint to protect the casting from rusting.

Click here to enquire about Cast Iron slotted Weights and Hanger:

https://www.slotterweight.com

Newton Weights

A newton is defined as 1 kg⋅m/s2 (it is a derived unit which is defined in terms of the SI base units). One newton is therefore the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force. The units “metre per second squared” can be understood as a change in velocity per time, i.e. an increase of velocity by 1 metre per second every second.

In 1946, Conférence Générale des Poids et Mesures (CGPM) Resolution 2 standardized the unit of force in the MKS system of units to be the amount needed to accelerate 1 kilogram of mass at the rate of 1 metre per second squared. In 1948, the 9th CGPM Resolution 7 adopted the name newton for this force. The MKS system then became the blueprint for today’s SI system of units. The newton thus became the standard unit of force in the International System of Units.

The newton is named after Isaac Newton. As with every SI unit named for a person, its symbol starts with an upper case letter (N), but when written in full it follows the rules for capitalisation of a common noun; i.e., “newton” becomes capitalised at the beginning of a sentence and in titles, but is otherwise in lower case.

In more formal terms, Newton’s second law of motion states that the force exerted on an object is directly proportional to the acceleration hence acquired by that object, namely: F = m a , {displaystyle F=ma,}

Where m represents mass of the object undergoing an acceleration a. As a result the Newton may defined in terms of kilograms as 1 N = 1 kg ⋅ m s 2

{displaystyle 1 {text{N}}=1 {frac {{text{kg}}cdot {text{m}}}{{text{s}}^{2}}}.}

Examples

At average gravity on Earth (conventionally, g = 9.80665 m/s2), a kilogram mass exerts a force of about 9.8 newtons. An average-sized apple exerts about one newton of force, which we measure as the apple’s weight. 1 N = 0.10197 kg × 9.80665 m/s2    (0.10197 kg = 101.97 g).

The weight of an average adult exerts a force of about 608 N. 608 N = 62 kg × 9.80665 m/s2 (where 62 kg is the world average adult mass).

To enquire about Newton Slotted Weights follow the link:

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Vehicle for the verification of truck scales

WOLFHARD GÖGGE and DETLEF SCHEIDT, Verification Authority of Rhineland-Palatinate, Bad Kreuznach, Germany

Rhineland-Palatinate, one of the 16 States of the Federal Republic of Germany (surface area about 20 000 km2 – population four million) has about 1 200 truck scales. This means that a large number of initial verifications and (at 3-yearly intervals) subsequent verifications have to be carried out. According to the corresponding European Union recommendations, the initial verification may be carried out by the manufacturer if a recognized quality management system is used, provided that the process is supervised by the Verification Authority.

Market surveillance, i.e. the question of how the truck scales will metrologically function over a long period of time, is carried out by the Verification Authority. One tool is subsequent verification every third year, using standard weights that have been tested by the Authority. However, the verification of truck scales requires the use of weights with large nominal values (between 100 kg and 1 000 kg) and in order to move such heavy weights, auxiliary equipment has to be installed on the truck.

In principle it is imaginable that platform weighing machines may be tested without weights using hydraulic load installations, though up to now nobody has developed such a system. Nowadays almost all balances are provided with electronic equipment that can be tested relatively easily in the Verification Authority laboratory. However, this cannot substitute a complete check with standard weights at the site of a truck scale. This means that for truck scales to be verified, weights will still have to be transported, moved and loaded on site in the future.

This article concerns a Rhineland-Palatinate Verification Authority vehicle that has been in service for some years (see article in the OIML Bulletin No. 114, March 1989) and which was completely modified about two years ago; meanwhile much experience has been gathered with this new verification vehicle. A normal truck can be used for the construction of a verification vehicle, but with the following special features incorporated:

• Small distance between axles, so that high loads can be moved even onto small weighbridges;

• High-powered engine, so that the vehicle can be driven on public roads without slowing down other traffic (despite its heavy weight);

• Remote-controlled hydraulic crane;

• Supports that can be raised by hydraulic jacks for safe operation of the crane;

• Additional hydraulic supports for lifting up the truck’s front axle, so that the necessary weights can be loaded even on very short weighbridges;

• The ratio of the standard weights compared to the weight of the truck when empty should be about 1:1. In this case the application of the substitution method according to OIML Recommendation R 76 is simple; and

• Removable top cover for easy unloading of the weights. For the verification vehicle in question (Fig. 1) all these aspects have been taken into account and therefore:

Verification vehicle. On the tractor: 25 rolling weights (500 kg each); on the trailer: 15 t block weights, forklift and passenger car

Fig. 1 Verification vehicle. On the tractor: 25 rolling weights (500 kg each);

on the trailer: 15 t block weights, forklift and passenger car

• The distance between axles is 4.55 m. Additional hydraulic supports are mounted behind the front wheels to lift up the front axle (Fig. 2);

Additional hydraulic support for lifting up the front axle
High Denominational Weights

Fig. 2 Additional hydraulic support for lifting up the front axle

• Engine power is 368 kW (500 bhp); and

• Maximum crane load (depending on the working radius) is between 1.6 t and 0.5 t for 3.6 m up to 8 m (Fig. 3)

Unloading two rolling weights using a remote-controlled crane
High Denominational Weights

Fig. 3 Unloading two rolling weights using a remote-controlled crane

Trailer: block weights beneath the passenger car and to the right and left of the forklift, which is standing on the loading area
High Denominational Weights

Fig. 4 Trailer: block weights beneath the passenger car and to the right and left of the forklift, which is standing on the loading area

The crane is operated by remote control, and the truck is equipped with supports which can be hydraulically drawn out when the crane is operating; the handling platform is equipped with an awning.

The loading area of the truck serves for the transport of weights of 12.5 t in the form of 500 kg cylindrical weights. The empty weight of the truck is also 12.5 t, therefore the maximum weight is 25 t.

In order to be able to perform the testing procedure as prescribed, the necessary rolling weights have to be manipulated on the bridge without the use of any mechanical device after they have been unloaded using the crane. However, it transpired that there are not enough auxiliary personnel able to move the heavy weights and that the latter involve a high accident risk when they start rolling unintentionally (in Germany two people were killed by rolling weights).

The former truck scales verification equipment was equipped with rolling weights only. To counter the aforementioned problems, the trailer has been modified to cater for the safe handling of rolling weights. However, the tractor itself is still equipped with rolling weights just in case this facility is required under special circumstances.

The trailer was custom-designed so that it can also be used for the verification of small weighbridges; for this purpose supports are mounted on the trailer directly behind the front axle so that the trailer fits on a weighbridge of 4.10 m in length. The trailer has a total weight of 30 t, of which 15 t are standard block weights of 200 kg, 500 kg and 1 000 kg (Fig. 4). Because of the supports on the tractor and trailer it is possible to verify weighbridges even with very short platforms, i.e. a total load of 55 t (Fig. 5) on a weighbridge of length 8.80 m and a load of 44 t on a weighbridge of length 5 m.

Rear view of the trailer
H D Weights

Fig. 5 Rear view of the trailer

Using block weights reduces the risk of accidents, but on the other hand the disadvantage is that they cannot be moved manually so this is done by a forklift with a loading capacity of 3 t. The forklift is used for loading and unloading the trailer (Fig. 6) as well as for positioning and removing weights on particular spots of the weighbridge according to the verification officer’s instructions (Fig. 7).

Unloading a 1 t block weight
High Denominational Weights

Fig. 6 Unloading a 1 t block weight

The forklift is stored along with the trailer and is operated by the driver of the verification vehicle – therefore external auxiliary personnel for moving the weights are no longer necessary.

Moving standard weights to special spots on the weighbridge
Standard Weights

Fig. 7 Moving standard weights to special spots on the weighbridge

When work with the forklift is finished, it is put back on the trailer using two ramp rails which can be moved up and down hydraulically. Since the forklift cannot mount such a steep ramp by itself, it is pulled up by an electric winch (Fig. 8). The remote control for this winch is operated by the driver of the forklift.

Forklift pulled up by a winch
H D Weights

Fig. 8 Forklift pulled up by a winch

On a rack above the block weights there is also space to store a small car (Fig. 4). This has the advantage that the verification vehicle, which due to its exceptionally high load of 55 t is only allowed to use public roads with special authorization, can directly drive from one operation to the next. For all other trips – for example to a verification office or back home – the driver uses this car. Consequently the verification vehicle itself is only used when absolutely necessary.

Car driving up
H D Weights

Fig. 9 Car driving up

Car in its final position on the trailer (beneath the car, winch for pulling up the forklift
Standard Weights

Fig. 10 Car in its final position on the trailer (beneath the car, winch for pulling up the forklift)

The car has to be small enough to fit on the trailer, and since most of the time it is only used by one person, this does not pose a problem. The car in question is a Fiat Cinquecento with 40 kW (55 bhp) which is able to mount the two ramp rails (Figs. 9 and 10).

If necessary, the driver may spend the night in the driver’s cab, which is quite comfortable. He can be reached at any time using a mobile phone.

The cylindrical and block weights on these vehicles are all standard weights and are tested and adjusted every six months by the Verification Authority. As permissible tolerances, the mpe in accordance with OIML R 47 is applied.

The running costs for the verification vehicle are 1 180 DM per day. If this is considered too high, the weights may be picked up at the Verification Office by the truck scale owner, who must ensure that he is equipped with a forklift, a crane and, of course, a truck to transport the weights. He must also use his own personnel to move and place them, and must later return them to the Verification Office.

The Rhineland-Palatinate Authority verification vehicle is fully booked throughout the year, except when repairs and maintenance work have to be carried out. The percentage of annual utilization is actually greater than 100 % since weighbridges are not only verified on weekdays but also on some weekends (on 23 Saturdays and Sundays in 1998). Weekend operation can be necessary because some companies cannot put their weighing instruments out of operation for a long time for maintenance and verification (on average 1.5 days) during the week. Therefore, they prefer to pay an extra charge for the weekend service.

A verification vehicle costs about 680 000 DM to purchase; annual income is about 290 000 DM less operating costs but including maintenance costs. This means that the vehicle costs are depreciated after approximately 8 years.

The verification vehicle (including the driver) is selffinancing – financial support is only necessary from the government for the initial capital – therefore outright purchasing is highly recommended.

The verification vehicle is also occasionally used for testing truck scales during the 3-year period. This is a chance to study the metrological behavior of road vehicle weighers during this period until the next subsequent verification is due.

Private companies own similar vehicles for testing truck scales and it is up to the owner of the truck scale whether he uses a privately operated vehicle or if he prefers the Verification Office one, but the periodical reverification itself is always carried out by an inspector of the Verification Authority.

For your requirements of High Denominational Standard Weights, you may contact:

https://www.weights-swpi.com/contact/

Metrication in Weighing & Measuring System in India

WEIGHTS play a vital role in the Society. Normally we use it to judge the cost of products while selling or buying. During the ancient period transactions of commodities were being made either through the “Exchange” or “Barter” system which failed to satisfy the need of a common man of the Society. It laid down the foundation of a system of weighment and measurement. But every social structure/Elaka (region) period gave rise to their own system throughout the whole world which could satisfy their local needs to some extent only but failed to cope up with inter-regional/ inter-state or international trade as the world was coming closer very fastly.

The French Scientists encouraged by the revolution; assigned themselves to the task of evolving a system using nature as model and natural phenomena as guide to discourage the national/regional susceptibilities, if any. The credit goes to Talleyrand, that in 1790, the French Constituent Assembly took the initiative and entrusted the uphill task of establishing a Weighing/Measuring unit/system which may have global acceptance.

After careful examination of various reports submitted by groups of leading scientists of that era, 1/10th million part of a quadrant of the earth’s meridian was adopted as the unit of length “The Metre”. The unit of mass was derived from this unit of length by defining a “Kilogram” as equal to the mass of water at its freezing point having a volume of a decimetre (1/10th of a metre) cube.

Based on the conclusions of aforesaid observations, two physical prototype Standards of Platinum one for ‘Metre’ and other for “Kilogram” were constructed and deposited in the Archives of the French Re public in 1799. Despite the fact that the “Metric System” was the most scientific and its fractions & multiples were based on decimal system, it could not get wide range acceptance by all the advanced countries due to their own socio-political reasons. Many learned scientists of France as well as other European Countries advocated and raised their voice in favour of a uniform measuring system based on “Metric System”, the system remain dormant for several years.

In 1870 the French Government took the initiative and organized a convention in Paris which was attended by 15 countries. In 1872 another convention was held with the participation of delegates from 30 countries, 11 of whom were from American continent. Finally on 20th May 1875 a “Convention du Metre” was signed by 18 countries. The signatory states not only bound themselves with the adoption of Metric system but agreed to form a permanent scientific body at Paris. Thus Bureau International des poidsetmeansures (BIPM) came into existence. So manifest were its advantages that by 1900 as many as 38 countries adopted this system in principle. This figure was doubled in the following fifty years.

Despite having all the positive aspect this “Metric System” could not be conceived and encouraged by the then “British Rulers” of India, rather they encouraged the “Zamindars” the local rulers to develop their own system of weighment and measurement. This was nothing but the famous “Divide & Rule” policy which kept these so called local rulers separate and discourage them coming on a common platform with a common uniform sense of understanding

But this phase could not last long. The interim Govt. adopted a resolution (Resolution No. 0-1-Std (4) 45 dt. 3rd Sept. 1946) which laid the foundation of National Standards Body. The purpose of this body was “to consider and recommend to Govt. of India National Standards for the measurement of length, weight, volume and energy”.

Indian Standard Institute started functioning in June 1947. Dr. Verman, the then Director of the Institute prepared a report in which he advised to adopt the Metric System and its fractions and multiples with Indian nomenclature. Just after independence a sample survey was con ducted which revealed that at least 150 different types of weight system were in use in different parts of the country Strange to note that most of these weights were having the same nomenclature but differ in actual weight markedly For example more than 100 types of “mounds” were in use ranging from 280 “tolas” to 8320 “tolas” a piece in Weight as compared to the standard mound of 3200 tolas. This system was traditional bound and not only exploiting the illiterate people but also encouraging the way to certain known malpractices. For instance, while buying the products from the producers they use the “Seer/mound” of higher weight value where as a lower weight value of Seer/mound were used while delivering these things to the consumers. In both the cases the powerful “Trader body” was benefited. It was felt by our national leaders that unless an uniform scientific system of weighment  & measurement is adopted the interest of the producers as well as consumers cannot be fully protected which was essential for the sound economic growth of the society and the country as a whole.

To implement the uphill task for introducing a systematic and uniform way of weighment and measurement, a Central Metric Committee was constituted under the chairmanship of Union Ministry of Commerce and Industry with several Central Govt. dept., State Govt. Scientists Technocrats, representatives from trade and industry as well as ordinary consumers as its members

After several meetings, marathon discussion and taking several aspects and arguments of different participants in consideration, the “Metric System” came into effect. A resolution was passed by both the houses of Parliament. On 28th December, 1956, it got consent of the President of India with the remarks that “An Uniform System of Weighing & Measuring in metric be introduced throughout all the states and union territories of India”

The Indian Standards Institute was entrusted to prepare the Standards of Weights & Measures & the Indian Weights & Measures Act 1956 was promulgated with the following preamble

i) To use an uniform system of Weights &Measures.

ii) To make greater order and efficiency in economic management like industrial production, trade and even in running a household.

ii) To fully protect the interest of producers and consumers.

iv) To develop trade with other countries of world.

v) To put the country on the map of matriculation in the world.

A sufficient number of enforcing officers were recruited and trained at ILM, as per provisions of the Act for better and uniform implementation of Metric system.

We are Manufacturer- Exporter of Standard Weights, Roller Weights, Cylindrical Weights, Slotted Weights, Test Weights ranging from 1 mg to 1000 kg in all accuracy classes.

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