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

Evaluation by Zwiebel

Slotted Weights with Hanger

Slotted Weights are used in a variety of applications such as pressure, torque, and tensile strength testing. … Several Cast Iron Slotted Weights may be used together to build up from a minimum weight to a maximum test load. The hanger weight selected should be able to accommodate the total load needed.

Slotted Weights are made of high quality cast iron and are used with Hanger. Slotted Weights are calibrated so that we know the mass value.

Slotted Weights are also manufactured in Newton mass value.

To know more please visit http://www.slotterweight.com

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 Products Industries (SWPI) 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:

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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 {\displaystyle m} $m$ represents the mass of the object undergoing an acceleration a {\displaystyle a} $a$ . As a result, the newton may be defined in terms of kilograms ( kg {\displaystyle {\text{kg}}} ${\text{kg}}$ ), metres ( m {\displaystyle {\text{m}}} ${\text{m}}$ ), and seconds ( s {\displaystyle {\text{s}}} ${\text{s}}$ ) as 1 N = 1 kg ⋅ m s 2 . {\displaystyle 1 {\text{N}}=1\ {\frac {{\text{kg}}\cdot {\text{m}}}{{\text{s}}^{2}}}.} $1\ {\text{N}}=1\ {\frac {{\text{kg}}\cdot {\text{m}}}{{\text{s}}^{2}}}.$

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

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);

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)

Fig. 3 Unloading two rolling weights using a remote-controlled crane 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. 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). 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. 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. 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. Fig. 9 Car driving up 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. WOLFHARD GÖGGE and DETLEF SCHEIDT, Verification Authority of Rhineland-Palatinate, Bad Kreuznach, Germany For your requirements of High Denominational Weights, you may contact: www.weights-swpi.com

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.

Why Calibration and adjustment are two separate things?

We calibrate a weighing device to understand how it behaves but we adjust the device to change its behavior. So to change the behavior of something firstly, we need to find how it is behaving by calibration and then we can adjust the same. It is important to find the device’s behavior before making any changes to its behavior. Therefore, it is reasonable and common to calibrate a weighing device without adjusting it.

A relationship is developed between a known value (standard) and a measured value by the help of calibration.

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.

For all units of measurement, there are some standards established as the basis for a particular unit. In the context of weighing devices, standard come in the form of Test Weights. The Test Weight is only classified as checking equipment if it has relevant proof of accuracy. The Test Weight has a certified value and the weighing device is supposed to indicate a value of Test Weight once it is placed upon the weighing device’s receptor. This is how we understand the behavior of the weighing device by calibration using Test Weight of certified value.

We find a relationship between the certified value of Test Weight and the value indicated by the weighing device and finally we can also make analysis on the behavioral aspects of the weighing device.

Selection of appropriate Test Weight is very necessary for your balance. A balance can never be more accurate than the Test Weight used to adjust it, it depends on its tolerance. Accuracy of the Test Weight should correspond to the readout of the balance, rather than something better. SWPI’s Cast Iron Test Weights are intended for use in the Verification or Calibration of Weights and for use with weighing instruments of medium accuracy class or ordinary class. They are manufactured from high quality cast iron and are free of cracks and pit.

The proper selection of an appropriate Test Weights involve knowing their proper permissible error limit, which are already set according to the OIML standards according to their class. Test Weights manufacturing as per OIML Recommendation R-111 is our specialty. Shanker Wire Products Industries (SWPI) manufactures exclusively Test Weights since 1961.

The surface quality of the Test Weights also plays an important role in the calibration of the balance. The bottom surface of Test Weight should be perfectly levelled so that it touches the receptor in its totality. SWPI’s Test Weight are well known for its Test Weight with satisfactory surface quality which ensures the accurate calibration of the weighing device.

Adjustment is not calibration. You can calibrate a measurement device without adjusting it. Calibration is developing an understanding of a measurement device. Calibration should include the determination of the measurement uncertainty to enhance the understanding of the measuring device.

To enquire about Calibration Test Weights follow the link:

http://www.slotterweight.com/contact/

OIML Systems

Basic and MAA Certificates registered 2015.12–2016.02

Information: www.oiml.org section “OIML Systems”

The OIML Basic Certificate System The OIML Basic Certificate System for Measuring Instruments was introduced in 1991 to facilitate administrative procedures and lower the costs associated with the international trade of measuring instruments subject to legal requirements. The System, which was initially called “OIML Certificate System”, is now called the “OIML Basic Certificate System”. The aim is for “OIML Basic Certificates of Conformity” to be clearly distinguished from “OIML MAA Certificates”. The System provides the possibility for manufacturers to obtain an OIML Basic Certificate and an OIML Basic Evaluation Report (called “Test Report” in the appropriate OIML Recommendations) indicating that a given instrument type complies with the requirements of the relevant OIML International Recommendation. An OIML Recommendation can automatically be included within the System as soon as all the parts – including the Evaluation Report Format – have been published. Consequently, OIML Issuing Authorities may issue OIML Certificates for the relevant category from the date on which the Evaluation Report Format was published; this date is now given in the column entitled “Uploaded” on the Publications Page. Other information on the System, particularly concerning the rules and conditions for the application, issue, and use of OIML Certificates, maybe found in OIML Publication B 3 OIML Basic Certificate System for OIML Type Evaluation of Measuring Instruments (Edition 2011) which may be downloaded from the Publications page of the OIML web site.

Magazine: “Weights & The Society” Volume: 06 & Issue No.: 1

Magazine: Weights & The Society

(Volume: 06 & Issue No.: 1)

Published by Shanker Wire Products Industries

GOLDEN JUBILEE CELEBRATIONS OF METRIC SYSTEM IN INDIA

“Legal Metrology – Achievements of India and what it can offer to others.”

Article by:

Sri P.A Krishnamurthy,

Former Director, Legal Metrology, Government of India.

INTRODUCTION:

The field of ‘Legal Metrology’ or Weights and Measures’ as is known in the common parlance, is the field where measurements are regulated by Government laws for the benefit of all stakeholders. The main object of such regulation is to ensure standardized procedures for calibration acceptable to all stakeholders, transparency in the whole procedure, and accountability of the measurement results.

THE LAWS OF LEGAL METROLOGY IN INDIA:

Regulation of Weights and Measures were implemented in the early stages of post-independence through the Standards of Weights and Measures Act, 1956, and the standards of Weights and Measures Enforcement Acts of the States and Union Territories. These Acts required the adoption of the metric systems in basic units of mass, length, and volume units in commercial transactions and ensuring verification of certain basic commercial weights and measures weighing and measuring instruments used in mass, length, and volume. The specification of the commercial weights and measures were prepared by the Metric Committee of the then Indian Standards Institution (BIS) and notified in the form of Rules under the Enforcement Act. The metrication and regulation of such rudimentary weights and measures were achieved fairly well by the dedicated enforcement agency throughout the county and in the process, fairly uniform procedures for the regulation of these measuring instruments were achieved with regard to the licensing policy of their manufacture, sale, and repair. Continue reading

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