SWPI‘s world-leading expertise in metrology extends to Calibration Weights or Test weights, weight sets. Our weight portfolio covers weights according to OIML from fifty micrograms to one ton in all accuracy classes. Our test weights are used all over the world, not only for testing balances but also as primary standards in mass laboratories.
Calibrating Scale: Premium-quality weights to satisfy stringent testing requirements
Calibrating scale testing requirements have become more complex, requiring that the scales survive years of use in rough industrial environments. Ensuring scale calibration is key to extremely accurate and efficient production using a fully calibrated scale. Test weights for scales are important tools for weighing scale calibration.
If a scale is not calibrated, it can significantly cost a company financially, and even worse, it can damage its reputation. SWPI’s calibration Weights are perfectly designed to support testing and calibration of industrial scales. With a strong engineering focus on safe and productive testing, cast-iron weights up to 1 ton is perfect for this application, satisfying even the most stringent testing requirements. These test weights are available in different shapes and accuracy classes to ensure proper scale calibration and scale recalibration.
Weights are predominantly needed for performance tests and routine testing of balances and scales. In metrological terminology, a distinction is made between reference weights or “mass standards” (to calibrate other weights) and certified weights. National regulations and international recommendations define the error limits of certified weights. Weights are classified into tolerance limits which are defined either by OIML or ASTM. The conventional weight value (and not the mass) is used as the nominal value of the weight. For a high level of accuracy, certified weights are calibrated and traceable back to primary standards, which are usually national standards maintained by a National Metrology Institute (NMI).
2. What are OIML and ASTM calibration weight classes?
Weight classes are separated according to the error limits that are classified either according to OIML (International Organization of Legal Metrology) or ASTM (American Society for Testing and Materials) declarations as follows.
The OIML weight
Class E1 weights are intended to ensure traceability between national mass standards and weights of class E2 and lower (i.e. F1 and F2). Class E1 weights or weight sets shall be accompanied by a calibration certificate.
Class E2 weights are intended for use in the initial verification of class F1 weights and for use with weighing instruments of accuracy class I. Class E2 weights or weight sets shall always be accompanied by a calibration certificate. They may be used as class E1 weights if they comply with the requirements for surface roughness and magnetic susceptibility and magnetization for class E1 weights (and their calibration certificate gives the appropriate data).
Class F1 weights are intended for use in the initial verification of class F2 weights and for use with weighing instruments of accuracy class I and class II.
Class F2 weights are intended for use in the initial verification of class M1 and possibly class M2 weights. They are also intended for use in important commercial transactions (e.g. precious metals and stones) on weighing instruments of accuracy class II.
Class M1 weights are intended for use in the initial verification of class M2 weights and for use with weighing instruments of accuracy class III.
Class M2 weights are intended for use in the initial verification of class M3 weights and for use in general commercial transactions and with weighing instruments of accuracy class III.
Class M3 weights are intended for use with weighing instruments of accuracy class IIII.
Classes M3 and M2-3 are lower accuracy weights of 50 kg to 5 000 kg and are intended for use with weighing instruments of accuracy class III.*
*The error in a weight used for the verification of a weighing instrument shall not exceed one third of the maximum permissible error (MPE) for an instrument. These values are listed in section 3.7.1 of OIML International Recommendation 76 Non-automatic Weighing Instruments (1992).
ASTM Weight
ASTM Class 0: Used as primary reference standards for calibrating other reference standards and weights.
ASTM Class 1: Can be used as a reference standard in calibrating other weights and is appropriate for calibrating high-precision analytical balances with a readability as low as 0.1 mg to 0.01 mg.
ASTM Class 2: Appropriate for calibrating high-precision top loading balances with a readability as low as 0.01 g to 0.001 g.
ASTM Class 3: Appropriate for calibrating balances with moderate precision with a readability as low as 0.1 g to 0.01 g.
ASTM Class 4: For calibration of semi-analytical balances and for student use.
NIST Class F: Primarily used to test commercial weighing devices by state and local weights-and-measures officials, device installers and service technicians.
3. Why should I use certified calibration weights?
ASTM class 0 and ultra-class as well as OIML class “E0” and E1 should be used for the highest level of precision i.e. mass standards (calibrating other weights), micro-balance testing and calibration, and critical weighing applications. ASTM classes 1 & 2 and OIML classes E2 & F1 should be used for precision applications i.e. analytical balance testing and calibration. ASTM classes 3 & 4 and OIML classes F1 & F2 are best suited to top-loading balance calibrations and testing and moderate precision applications (laboratory non-critical).
Note: If a balance or scale is calibrated, the weight set used and the class must be documented.
4. Why / how often do I need to recalibrate my test weights?
Accurately calibrated test weights are the basis of accurate weighing results. The accuracy of test weights becomes less reliable over time. This is the result of normal wear and tear caused by regular use, dirt and dust. Periodic recalibration of test weights at an accredited mass-calibration laboratory is essential to ensure ongoing traceability. At our accredited mass-calibration laboratories, we clean, calibrate, and adjust each weight and then document the results in a calibration certificate. Our calibration services cover the basic reporting of conventional mass correction, uncertainty and traceability information in accordance with ISO/IEC 17025 requirements.
The frequency with which to recalibrate your test weights depends on the criticality of the weighing process. Selecting the correct test weight and weight class and also provides recommendations on how often to recalibrate your test weights. All of this information is determined based on your specific processes and risks.
5. What are buoyancy artifacts?
Air density is usually calculated from relevant air parameters such as air temperature, pressure, humidity and CO2 concentration. An alternative method of determining air density may be applied by utilizing two specially designed buoyancy artifacts. Both artifacts are compared in vacuum and in air. By comparing the two artifacts of identical nominal weight, the large volume difference reflects the air buoyancy and therefore results in a highly accurate determination of air density. The buoyancy artifacts are mainly used for the M_one vacuum mass comparator.
6. Why is a silicon sphere used for specialized volume measurement?
Spheres are used because the volume can be determined according to the definition of volume by a length measurement. Silicon (Si) spheres have the same homogenous atomic structure as a perfect diamond without voids or dislocations, so the density is more accurate than other materials. This is why a silicon sphere with a homogenous atomic structure serves as a reference for specialized volume measurement.
7. What are heavy-capacity weights used for?
Mass comparators go up to a capacity of six tons. Industrial scales go up to several hundred tons. Heavy-capacity weights—typically those in the range of 100 kg, 200 kg, 500 kg, 1 t and 2 t are used for sensitivity, eccentricity, linearity and repeatability testing of these higher-capacity devices. Weights are less than 2 t due to the maximum lifting capability of machines, typically forklifts and cranes. However, these weights can be combined to reach the desired weight. Check out our range of heavy-capacity weights, Click here
Heavy-capacity weights must be transported in heavy-duty trucks and it is important to ensure trucks do not exceed their rated load limit due to safety and government regulations. Heavy-capacity weights are generally constructed of cast iron not stainless steel due to the cost.
8. What are calibrated test weights used for? Are they used to calibrate weight scale systems? Do you offer test weights for scales?
Calibration Weights are used in scale calibration. This is a process that ensures scale accuracy. Test weights for scales or precision weights are used to calibrate weight scale systems of various levels of accuracy depending on the use and requirements. Certified test weights or precision weights should be used in these processes to calibrate weight scale systems. It is important to ensure the test weights are calibrated test weights and that they are accurate to provide accurate calibration results. Check out our range of scale calibration weights, click here.
9. What is the weighing scale tolerance limit of any scale? Can all scales offer precision weights?
This is the required accuracy of the scale, and specifically the tolerance of inaccuracy allowed before it is out of tolerance and in need of a weigh scale calibration by certified calibration weights. A calibrated scale will operate at a higher level of accuracy and maintain tolerance better. For this reason, weight scale calibration with certified weights for keeping the weighing scale tolerance limit is key for accurate, calibrated scales and weigh scale calibration. Learn more about keeping your weighing scale tolerance limit in your weighing processes.
10. What are scale weights? Are they calibration weights for scales? Must they be certified weights?
Scale weights are weights for scale calibration. These weights for scale calibration may be certified weights. Generally, weights for scale calibration are certified. When calibrating scale procedures are performed, it is necessary to have calibration weights for scales. Weighing scale calibration with scale weights or test weights should be performed on a regular basis depending on use. Learn more about scale calibration weights and weigh scale calibration.
SWPI‘s world leading expertise in metrology extends to certified test weights, weight sets as well as calibration weights for scales. The weight portfolio covers scale weights according to OIML or ASTM from fifty micrograms to one ton in all accuracy classes. Our test weights are used all over the world, not only for testing balances but also as primary standards in mass laboratories. We invite you to learn more about our certified test weights and consider using them in your weighing scale calibration and weigh-scale calibration processes.
11. What are the differences between OIML classes?
The exact difference is explained in the OIML guideline, but at a basic level, E1 has the narrowest and M1 the highest tolerance limit, i.e. E1 is the most accurate.
12. Plus Tolerance
Weights are calibrated according to OIML maximum permissible errors (+/- in mg). If the result of the calibration is in the plus range, it means that the weight is heavier than the specified nominal value, but still within the tolerance. Since most weights lose weight over time due to wear, it is more likely that this weight will take longer to fall out of tolerance (maximum permissible error). Through our production processes, most of our weights are calibrated in the plus range.
13. How often do you need to re-calibrate your weights?
Depending on how often the weights are in use, weights should be re-calibrated every 1-2 years.
Selection of standard weights for calibration of weighing instruments
TEUVOLAMMI
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:
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.
OIML BULLETIN V OLUME XLIV • N UMBER 4 • O CTOBER 2003 5
technique
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.
6 OIML BULLETIN V OLUME XLIV • N UMBER 4 • O CTOBER 2003
technique
Selectionofatable,itsuse,groups1), 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.
Table1
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)
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.
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.
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,
> 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)
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
OIML BULLETIN V OLUME XLIV • N UMBER 4 • O CTOBER 2003 7
technique
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.
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.
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.
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.
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).
8 OIML BULLETIN V OLUME XLIV • N UMBER 4 • O CTOBER 2003
technique
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)
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.
Table3
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)
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.
Table4
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)
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. 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
OIML BULLETIN V OLUME XLIV • N UMBER 4 • O CTOBER 2003 9
technique
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
£ 50
only 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
> 200
0.5 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
> 200
f, 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.
10 OIML BULLETIN V OLUME XLIV • N UMBER 4 • O CTOBER 2003
technique
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:
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.
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(M1if 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(F1if 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
technique
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/f
Weights 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.
Apply 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.
F1 (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 £ 10 000
M1 (F2 if ïMTEï = 0.5 f & f or f)
3 300 < Max/f £ 6 600
M1
2 200 < Max/f £ 3 300
M2 (M1 if ïMTEï = 0.5 f & f or f)
Max/f £ 2 200
M2
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
technique
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/f
Weights 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 > 110 000
No calibration
60 000 < Max/f £ 110 000
E2 (No calibration if 1) )
Max/f £ 60 000
E2 (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 £ 100 000
E2
30 000 < Max/f £ 50 000
F1 (E2 if ïMTEï= 0.5 f & f or f)
11 000 < Max/f £ 30 000
F1
6 000 < Max/f £ 11 000
F2 (F1 if 1))
Max/f £ 6 000
F2 (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 £ 10 000
F2
3 300 < Max/f £ 5 000
M1 (F2 if ïMTEï = 0.5 f & f or f)
1 100 < Max/f £ 3 300
M1
Max/f £ 1 100
M2
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 £ 1 000
M2
330 < Max/f £ 500
M3 (M2 if ïMTEï = 0.5 f & f or f)
Max/f £ 330
M3
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
technique
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/f
Weights 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 £ 650 000
E2 (Apply 3.2.2 if ïMTEï= f & 2 f)
130 000 < Max/f £ 400 000
E2
65 000 < Max/f £ 130 000
F1 (E2 if 1)) Exception: F1 if 1) , Max/f = 70 000 or 105 000
and L = 50 000 f 2)
Max/f £ 65 000
F1
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 £ 100 000
F1
40 000 < Max/f £ 65 000
F2 (F1 if ïMTEï= f & 2 f)
13 000 < Max/f £ 40 000
F2
6 500 < Max/f £ 13 000
M1 (F2 if 1)) Exception: M1 if 1) , Max/f = 7 000 or 10 500
and L = 5 000 f 3)
Max/f £ 6 500
M1
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 £ 10 000
M1
4 400 < Max/f £ 6 600
M2 (M1 if ïMTEï= f & 2 f)
1 300 < Max/f £ 4 400
M2
Max/f £ 1 300
M3
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
technique
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/f
Weights 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 > 300 000
No calibration
200 000 < Max/f £ 300 000
E2 (No calibration if ôMTEô= f & 2 f )
65 000 < Max/f £ 200 000
E2 Exception: No calibration if 1), 170 000 < Max/f < 200 000 and
f = 1 mg (E2 if f > 1 mg)
Max/f £ 65 000
F1 (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.
F1 (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 £ 10 000
M1 (F2 if ôMTEô= f & 2 f)
3 300 < Max/f £ 6 600
M1
2 200 < Max/f £ 3 300
M2 (M1 if ôMTEô= f & 2 f)
Max/f £ 2 200
M2
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
technique
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
We, produce exclusively Cast Iron Weights since 1961. OIML appreciated our Weights in 1973. OIML recognized us as one of the supplier of Cast Iron Weights in their Guides (G 12 – Suppliers of verification equipment) published in Mars, 1987.
Manufacturing Cast Iron Weights as per OIML Recommendation is our specialty. We also manufacture as per design of buyer. Our range is 50g to 1000kg and 4-oz to 3000lb in all accuracy class.
We maintain quality of our products strictly as per International Standards with guaranteed accuracy. Our major production is being consumed by buyers from Germany, Canada, France, Australia, Netherlands, Belgium, U.K., Qatar, Dubai, South Africa, Ireland, Cyprus, Tanzania etc. etc.
Our Calibration Laboratory is accredited in accordance with ISO/IEC 17025:2017.
For our full activity you may see our url https://www.weights-swpi.com
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:
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);
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)
High Denominational Weights
Fig. 3 Unloading two rolling weights using a remote-controlled crane
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.
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).
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.
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.
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.
H D Weights
Fig. 9 Car driving up
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:
