by R OIML · Cited by 2 — Continuous totalizing automatic weighing instrument (belt weigher) A belt weigher that is installed with a conveyor belt designed to operate at a.
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Continuous totalizing automatic weighing instruments(belt weighers) Part 1: Metrological and technical requirements – Tests Instruments de pesage totalisateurs continus ‹ fonctionnement automatique(peseuses sur bande) Partie 1: Exigences m”trologiques et techniques – Essais OIMLR50-1 Edition 1997 (E)Organisation Internationale de M”trologie L”gale INTERNATIONAL RECOMMENDATION
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CONTENTSForeword ..3 Terminology (terms and definitions) .4 1General 11 1.1Scope 1.2Application 1.3Terminology 2Metrological requirements 11 2.1Accuracy classes 2.2Maximum permissible errors 2.3Minimum value of minimum totalized load ( Smin)2.4Minimum flowrate (Q min)2.5Simulation tests 2.6In-situ tests 3Technical requirements ..15 3.1Suitability for use 3.2Security of operation 3.3Totalization indicating and printing devices 3.4Out-of-range indication 3.5Zero-setting device 3.6Displacement transducer 3.7Belt weighers inclusive of conveyor 3.8Installation conditions 3.9Ancillary devices 3.10Sealing 3.11Descriptive markings 3.12Verification marks 4Requirements for electronic belt weighers ..20 4.1General requirements 4.2Application 4.3Acting upon a significant fault 4.4Switch-on procedure 4.5Functional requirements 4.6Examination and tests 5Metrological controls 23 5.1Pattern evaluation 5.2Initial verification and in-service inspection 6Test methods 26 6.1Simulation tests 6.2In-situ tests, control method Annex ATest procedures for continuous totalizing automatic weighing instruments .27 A.1Documentation A.2Comparing construction with documentation A.3Initial examination A.4General A.5Test program A.6Performance tests during pattern evaluation A.7Influence factors during pattern evaluation A.8Disturbances during pattern evaluation A.9Metrological characteristics A.10In-situ tests A.11In-situ material tests Bibliography 50 Ð 2Ð
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FOREWORDThe International Organization of Legal Metrology (OIML) is a worldwide, intergovernmental organizationwhose primary aim is to harmonize the regulations and metrological controls applied by the national metrological services, or related organizations, of its Member States.The two main categories of OIML publications are:1)International Recommendations (OIML R), which are model regulations that establish the metrologicalcharacteristics required of certain measuring instruments and which specify methods and equipment for checking their conformity; the OIML Member States shall implement these Recommendations to the greatest possible extent;2)International Documents (OIML D), which are informative in nature and intended to improve the work of themetrological services.OIML Draft Recommendations and Documents are developed by technical committees or subcommittees whichare formed by the Member States. Certain international and regional institutions also participate on a consultation basis.Cooperative agreements are established between OIML and certain institutions, such as ISO and IEC, with theobjective of avoiding contradictory requirements; consequently, manufacturers and users of measuring instruments, test laboratories, etc. may apply simultaneously OIML publications and those of other institutions.International Recommendations and International Documents are published in French (F) and English(E) and are subject to periodic revision.OIML publications may be obtained from the OrganizationÕs headquarters: Bureau International de M”trologie L”gale11, rue Turgot – 75009 Paris – France Telephone: 33 (0)1 48 78 12 82 and 42 85 27 11 Fax: 33 (0)1 42 82 17 27This publication – reference OIML R 50-1, edition 1997 (E) – was developed by the OIML subcommitteeTC9/SC2 Automatic weighing instruments. It was sanctioned by the International Conference of Legal Metrology in1996 and supersedes the previous edition dated 1994.Ð 3Ð ** *
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TERMINOLOGY(terms and definitions)The terminology used in this Recommendation conforms to the International Vocabu- lary of Basic and General Terms in Metrology (VIM – 1993 edition) and to the Vocabulary of legal Metrology (VML – 1978 edition). In addition, for the purposes of this Recom-mendation, the following definitions apply. T.1General definitions T.1.1Weighing instrument A measuring instrument that serves to determine the mass of a load by usingthe action of gravity. According to its method of operation, a weighing instrument is classified asautomatic or nonautomatic.T.1.2Automatic weighing instrument An instrument that weighs without the intervention of an operator and followsa predetermined program of automatic processes characteristic of the instru- ment.T.1.3Continuous totalizing automatic weighing instrument (belt weigher) An automatic weighing instrument for continuously weighing a bulk producton a conveyor belt, without systematic subdivision of the mass and without interrupting the movement of the conveyor belt.T.1.4Electronic instrument An instrument equipped with electronic devices.T.1.5Control method The method used to determine the mass of the product used as the test loadduring material tests. This will generally involve the use of a weighing instru- ment, referred to as the control instrument.T.2Classification T.2.1Type of load receptor T.2.1.1Weigh table A load receptor that includes only part of a conveyor. T.2.1.2Inclusive of conveyor A load receptor that includes an entire conveyor. Ð 4Ð
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Ð 5Ð T.2.2Belt speed control T.2.2.1Single speed belt weigher A belt weigher that is installed with a conveyor belt designed to operate at asingle speed, designated in this Recommendation as the nominal speed.T.2.2.2Variable speed belt weigher A belt weigher that is installed with a conveyor belt designed to operate at morethan one speed.T.3Construction Note:In this Recommendation the term ÒdeviceÓ is applied to any part which uses any means to perform one or more specific functions.T.3.1Load receptor The part of the belt weigher intended to receive the load.T.3.2Belt conveyor The equipment for conveying the product by means of a belt resting on rollersturning about their axis.T.3.2.1Carrying rollers The rollers by means of which the conveyor belt is supported on a fixed frame.T.3.2.2Weighing rollers The rollers by means of which the conveyor belt is supported on the load recep-tor. T.3.3Electronic parts T.3.3.1Electronic device A device employing electronic sub-assemblies and performing a specific func-tion. An electronic device is usually manufactured as a separate unit and is cap- able of being independently tested.Note:An electronic device, as defined above, may be a complete weighinginstrument (for example: counter scale) or part of a weighing instrument (for example: printer, indicator). T.3.3.2Electronic sub-assembly A part of an electronic device, employing electronic components and having arecognizable function of its own.T.3.3.3Electronic component The smallest physical entity that uses electron or hole conduction in semi-conductors, gases or in a vacuum.
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Ð 6Ð T.3.4Weighing unit The part of a belt weigher providing information on the mass of the load to bemeasured.T.3.5Displacement transducer A device on the conveyor providing information either corresponding to thedisplacement of a defined length of the belt or proportional to the speed of the belt.T.3.5.1Displacement sensing device The part of the displacement transducer that is in permanent contact with thebelt or integral with a non-drive pulley. T.3.6Totalization device A device that uses information supplied by the weighing unit and the displace-ment transducer to do either:¥an addition of partial loads, or ¥an integration of the product of the load per unit length and the speed of the belt.T.3.7Totalization indicating device A device that receives information from the totalization device and indicatesthe mass of the loads conveyed.T.3.7.1General totalization indicating device A device that indicates the overall total of the mass of all the loads conveyed.T.3.7.2Partial totalization indicating device A device that indicates the mass of the loads conveyed over a limited period.T.3.7.3Supplementary totalization indicating device An indicating device with a scale interval greater than that of the general total-ization indicating device and intended to indicate the mass of the loads con- veyed over a fairly long period of operation.T.3.8Ancillary devices T.3.8.1Zero-setting device A device enabling zero totalization to be obtained over a whole number ofrevolutions of the empty conveyor belt.T.3.8.1.1Nonautomatic zero-setting device A zero-setting device that requires observation and adjustment by the operator. T.3.8.1.2Semi-automatic zero-setting device A zero-setting device that operates automatically following a manual commandor indicates the value of the adjustment required.T.3.8.1.3Automatic zero-setting device A zero-setting device that operates automatically without the intervention ofthe operator after the belt has been operating empty.
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Ð 8Ð T.4.2Weigh length (L) [ not applicable to belt weighers inclusive of conveyor]The distance between the two imaginary lines at the half distance between theaxes of the end weighing rollers and the axes of the nearest carrying rollers.When there is only one weighing roller, the weigh length is equal to half the distance between the axes of the nearest carrying rollers on either side of the weighing roller. T.4.3Weighing cycle [ applicable only to belt weighers whose method of operation is byaddition]The group of operations relating to each addition of information on the load atthe end of which the totalization device returns to its initial position or state for the first time.T.4.4Maximum capacity (Max) The maximum instantaneous net load that the weighing unit is intended toweigh on the portion of the conveyor belt representing the weigh length.T.4.5Flowrate T.4.5.1Maximum flowrate (Q max)The flowrate obtained with the maximum capacity of the weighing unit and themaximum speed of the belt.T.4.5.2Minimum flowrate (Q min)The flowrate above which the weighing results comply with the requirementsof this Recommendation.T.4.6Minimum totalized load ( Smin)The quantity, in units of mass, below which a totalization may be subject to excessive relative errors.T.4.7Maximum load per unit length of the belt The quotient of the maximum capacity of the weighing unit and the weighlength.T.4.8Control value The value, in units of mass, that is indicated by the totalization indicatingdevice when a known additional mass has been simulated or deposited on the load receptor with the empty belt running for a prescribed number of complete revolutions.T.4.9Warm-up time The time between the moment that power is applied to a belt weigher and themoment that the belt weigher is capable of complying with the requirements.
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Ð 9Ð T.5Errors T.5.1Error (of indication) The value, in units of mass, of the difference between two readings from a totalization indicating device on a belt weigher, minus the (conventional) true value of the mass relating to those readings. [Adapted from VIM 5.20].T.5.2Intrinsic error The error of a belt weigher, determined under reference conditions. [ VIM 5.24].T.5.3Initial intrinsic error The intrinsic error of a belt weigher as determined prior to performance testsand durability evaluations.T.5.4Fault The difference between the error of indication and the intrinsic error of a belt weigher. Note:Principally, a fault is the result of an undesired change of data contained in or flowing through an electronic instrument.T.5.5Significant fault A fault greater than the absolute value of the appropriate maximum permiss-ible error for influence factor tests for a load equal to the minimum totalized load (Smin) for the designated class of the belt weigher. A significant fault does not include:¥faults that result from simultaneous and mutually independent causes in the belt weigher or in its checking facility, ¥faults that imply the impossibility of performing any measurement, ¥transitory faults that are momentary variations in the indications which can- not be interpreted, memorized or transmitted as a measurement result,¥faults that are so serious they will inevitably be noticed by those interested in the measurement.T.6Influences and reference conditions T.6.1Influence quantity A quantity that is not the measurand but that affects the value of the meas- urand or the indication of the belt weigher. [ Adapted from VIM 2.7].T.6.1.1Influence factor An influence quantity having a value within the specified rated operating condi-tions of the belt weigher. T.6.1.2Disturbance An influence quantity having a value within the limits specified in this Recom-mendation but outside the rated operating conditions of the belt weigher.
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Ð 10Ð T.6.2Rated operating conditions The conditions of use, giving the ranges of the measurand and of the influencequantities for which the metrological characteristics are intended to lie within the maximum permissible errors specified in this Recommendation. [Adaptedfrom VIM 5.5].T.6.3Reference conditions A set of specified values of influence factors fixed to ensure a valid intercom-parison of measurement results. [Adapted from VIM 5.7].T.7Tests T.7.1Material test A test carried out on a complete belt weigher using the type of material that itis intended to weigh.T.7.2Simulation test A test carried out with standard weights on a test unit consisting of a completebelt weigher without the belt conveyor. T.7.3Performance test A test to verify whether the equipment under test (EUT) is capable of accomp-lishing its intended functions.T.7.4Durability test A test to verify whether the EUT is capable of maintaining its performancecharacteristics over a period of use.
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Ð 11Ð CONTINUOUS TOTALIZING AUTOMATIC WEIGHING INSTRUMENTS(BELT WEIGHERS) 1General 1.1Scope This International Recommendation specifies the metrological and technical re-quirements for continuous totalizing automatic weighing instruments of the belt conveyor type, hereinafter referred to as Òbelt weighersÓ, that are subject to national metrological control.It is intended to provide standardized requirements and test procedures for evaluat-ing metrological and technical characteristics in a uniform and traceable way. 1.2Application This Recommendation applies to: ¥belt weighers that determine the mass of a product in bulk by using the action of gravity on that product;¥belt weighers that are intended for use with single speed belt conveyors and belt weighers that are intended for use with variable speed belt conveyors.1.3Terminology The terminology given in pages 4-10 shall be considered as a part of this Recom-mendation.2Metrological requirements 2.1Accuracy classes Belt weighers are divided into three accuracy classes as follows:0.5 1 22.2Maximum permissible errors Maximum permissible errors apply to loads equal to or greater than the minimumtotalized load (Smin).2.2.1Maximum permissible errors for automatic weighing The maximum permissible errors for each accuracy class, positive or negative, arethe appropriate values in Table 1 rounded to the nearest totalization scale interval (d).
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