Calibration Weights for precision value

Posted on

Calibration Weights

Re: Hanger and slotted Weights for Torsional stiffness set up Bigger size cycloids

From: Moses David Francis Samuel <fmosesdavid@eppinger-gears.com> on Fri, 02 Sep 2022 17:26:56 Add to address bookTo: You | See Details

Hello Mr. Singhania ,

Good day , Just today I have received the Orders slotted weights and hangers .

I was not in a comfortable position till I open the packages, even with your confident communication due to my worst experience with other suppliers.

On opening the package I was extremely satisfied , as the packaging , the marking , painting finish and the quality was 100% beyond expectation .

Really appreciate the workmanship and you kept you word in maintaining Quality at its best .

Much impressed and looking forward for more business with you. I would love to recommend you to fellow industry people.

Regards / Mit freundlichen Grüßen

Moses David F

Asst.Manager Gearbox Assembly

Eppinger Tooling Asia Pvt Ltd

SF No 345/2A-2B ,Kondampatty Village ,

KinathuKadavu,Pollachi Taluk,

Coimbatore 641202

Tel :         +91 4259-201148

Mobile : +91 73977 85848

Mail:        fmosesdavid@eppinger-gears.com

 Web:       www.eppinger.de

Calibration Weights for Scales & Balances

Posted on

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.

FAQ’s on Test Weights

1. What are calibration weights for balances?

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.

Calibration Weights

Posted on

Dear Sir/Madam,

I am proud to be linked with you.


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

Long term relation is our objective.

Kind regards,


Surendra Singhania

Shanker Wire Products Industries

DEOGHAR – 814112  (Jharkhand) INDIA

Mob: +91 9386142223

E.mail swpi@rediffmail.com

Calibration and verification: Two procedures having comparable objectives and results

Posted on

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

Abstract

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

Introduction

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

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

1 Calibration

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

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

2 Verification and error limits in legal metrology

2.1 Verification

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

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

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

2.2 Maximum permissible errors on verification and in service

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

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

3 Relationship between legally prescribed error limits and uncertainty

3.1 General

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

3.2 Relationship upon verification

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

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

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

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

4 Uncertainty contribution of verified instruments

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

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

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

5 System comparison

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

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

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

References

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

OIML BULLETINVOLUMEXLII •NUMBER1 •JANUARY2001

Calibrated Weights

Posted on

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

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

Vehicle for the verification of truck scales

Posted on

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

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

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

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

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

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

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

• Remote-controlled hydraulic crane;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Rear view of the trailer
H D Weights

Fig. 5 Rear view of the trailer

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

Unloading a 1 t block weight
High Denominational Weights

Fig. 6 Unloading a 1 t block weight

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

Moving standard weights to special spots on the weighbridge
Standard Weights

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

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

Forklift pulled up by a winch
H D Weights

Fig. 8 Forklift pulled up by a winch

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

Car driving up
H D Weights

Fig. 9 Car driving up

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

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

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

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

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

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

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

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

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

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

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

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

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

Why Calibration and adjustment are two separate things?

Posted on

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 our Calibrated Test Weights follow the link: http://www.weights-swpi.com/contact/