1、BRITISH STANDARD BS 8422:2003 Force measurement Strain gauge load cell systems Calibration method ICS 17.100; 19.060 BS 8422:2003 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 October 2003 BSI 31 October 2003 The following BSI references
2、 relate to the work on this British Standard: Committee reference ISE/NFE/4/1 Draft for comment 03/309174 DC ISBN 0 580 42746 3 Committees responsible for this British Standard The preparation of this British Standard was entrusted by Technical Committee ISE/NFE/4, Mechanical testing of metals, to S
3、ubcommittee ISE/NFE/4/1, Uniaxial testing of metals, upon which the following bodies were represented: Association of Consulting Scientists British Civil Engineering Manufacturers Association British Non-ferrous Metals Federation British Society for Strain Measurement GAMBICA Association Ltd. Lloyds
4、 Register National Physical Laboratory QinetiQ Society of British Aerospace Companies Ltd. United Kingdom Accreditation Service United Kingdom Steel Association Co-opted members The following bodies were also represented in the drafting of the standard through Panel ISE/NFE/4/1/1, Strain gauge load
5、cells. Institute of Measurement and Control MIRA Ltd. Amendments issued since publication Amd No. Date CommentsBS 8422:2003 BSI 31 October 2003 i Contents page Committees responsible Inside front cover Foreword ii 1S c o p e 1 2 Normative references 1 3 Terms, definitions and symbols 1 4G e n e r a
6、l 4 5A p p a r a t u s 5 6 Preparation 5 7 Standard calibration 6 8 Supplementary calibration A Repeatability 7 9 Supplementary calibration B Hysteresis 7 10 Supplementary calibrations C Creep and D Creep recovery 7 11 Supplementary calibration E Overload effect 8 12 Supplementary calibration F Temp
7、erature sensitivity at zero force 9 13 Supplementary calibration G Temperature sensitivity at maximum calibration force 9 14 Supplementary calibration H Concentric inclined application of force 10 15 Supplementary calibration J Eccentric inclined application of force 13 16 Supplementary calibration
8、K Eccentric force effects 16 17 Supplementary calibration L Base-loading effects 18 18 Supplementary calibration M Zero force output stability 19 19 Supplementary calibration N Output stability at maximum calibration force 19 20 Supplementary calibration P Damp heat 19 21 Supplementary calibration Q
9、 Sealing 20 22 Supplementary calibration R Excitation voltage effects 20 23 Calibration certificate 20 Annex A (informative) Example of content of a calibration certificate 21 Annex B (informative) Uncertainty budget 28 Bibliography 31 Figure 1 Representation of creep and creep recovery measurement
10、8 Figure 2 Concentric inclined application of force 11 Figure 3 Eccentric inclined application of force 14 Figure 4 Eccentric application of force 17 Figure A.1 Example of content of a calibration certificate 21BS 8422:2003 ii BSI 31 October 2003 Foreword This British Standard has been prepared by S
11、ubcommittee ISE/NFE/4/1, under the direction of Technical Committee ISE/NFE/4. The initial draft of this standard was based on the Institute of Measurement and Control publication WGL9301 1, but the standard has evolved significantly since that time. Other standards and international recommendations
12、 exist for the calibration of load cells, but these are restricted to specific areas of load cell use. BS EN ISO 376 covers the calibration of force-proving instruments (including load cells) used for the verification of uniaxial testing machines, and the use of load cells classified to it is specif
13、ied by various machine calibration standards. In the legal metrology area, OIML R60 2 prescribes evaluation procedures for load cells used in the measurement of mass. This British Standard does not replace the existing documents but is intended for use in those areas of industrial weighing and force
14、 measurement in which the existing procedures are not applicable. It has been assumed in the preparation of this British Standard that the execution of its provisions will be entrusted to appropriately qualified and experienced people, for whose use it has been produced. WARNING. This British Standa
15、rd calls for the use of procedures (e.g. inclined and eccentric testing) that may be injurious to health if adequate precautions are not taken. It refers only to technical suitability and does not absolve the user from legal obligations relating to health and safety at any stage. This publication do
16、es not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages
17、i and ii, pages 1 to 31 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.BS 8422:2003 BSI 31 October 2003 1 1 Scope This British Standard describes a method of calibration for strain gauge load cell systems for use in various industria
18、l weighing and force measurement applications. NOTE The technical procedures covered in this British Standard are split into one “standard calibration” (Clause 7), which determines the basic response of the system in terms of non-linearity and reproducibility, and a number of “supplementary calibrat
19、ions” (Clause 8 to Clause 22), each of which determines the response of the system to one specific input factor. It is envisaged that load cell systems calibrated in accordance with this standard will normally undergo the standard calibration, possibly together with a number of supplementary calibra
20、tions, but a system may also be calibrated solely in accordance with one or more of the supplementary calibrations. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated refe
21、rences, the latest edition of the referenced document (including any amendments) applies. NOTE These are relevant only to supplementary calibrations P and Q. BS EN 60068-2-30:1999 (IEC 60068-2-30:1980), Environmental testing Part 2-30: Test methods Test Db and guidance: damp heat, cyclic (12 + 12 ho
22、ur cycle). BS EN 60068-3-4 (IEC 60068-3-4), Environmental testing Part 3-4: Guidance Damp heat tests. BS EN 60529, Specification for degrees of protection provided by enclosures (IP code). 3 Terms, definitions and symbols 3.1 Terms and definitions For the purposes of this British Standard, the follo
23、wing terms apply. 3.1.1 axial force force applied along the principal axis of a load cell NOTE See Figure 2, Figure 3 and Figure 4. 3.1.2 calibration 3.1.2.1 standard calibration procedure to determine the performance of a load cell system in terms of non-linearity and reproducibility 3.1.2.2 supple
24、mentary calibration procedure to determine system response to a particular input factor, other than those responses determined in the standard calibration 3.1.3 calibration forces 3.1.3.1 maximum calibration force maximum force applied during calibration 3.1.3.2 minimum calibration force minimum for
25、ce applied during calibration 3.1.4 compensated temperature range range of temperature over which a load cell meets its stated specificationBS 8422:2003 2 BSI 31 October 2003 3.1.5 creep change in output which occurs with time while a load cell is subjected to constant force and with all environment
26、al conditions and other variables remaining constant NOTE See Figure 1. 3.1.6 creep recovery change in output which occurs with time after the force applied to a load cell has been removed, with all the environmental conditions and other variables remaining constant NOTE See Figure 1. 3.1.7 deflecti
27、ons 3.1.7.1 deflection difference between the load cell system output under force and the output at zero force 3.1.7.2 maximum deflection difference between the load cell system output at maximum calibration force and the output at zero force 3.1.7.3 maximum mechanical deflection displacement along
28、the principal axis (3.1.18) for a change of force from zero to maximum calibration force 3.1.8 eccentric force force applied parallel to the principal axis (3.1.18) at a specified orientation and eccentricity NOTE See Figure 4. 3.1.9 excitation voltages 3.1.9.1 excitation voltages voltage applied at
29、 the input terminals of a load cell 3.1.9.2 maximum excitation voltage excitation voltage above which a load cell cannot be continuously operated without degradation of its performance 3.1.9.3 recommended excitation voltage excitation voltage or range of voltages at which a load cell can be continuo
30、usly operated and meet its stated specification 3.1.10 hysteresis difference between measurements of load cell deflection for the same applied force, one measurement being obtained by increasing the force from zero, the other by decreasing the force from the maximum calibration forceBS 8422:2003 BSI
31、 31 October 2003 3 3.1.11 inclined forces 3.1.11.1 concentric inclined force force applied through the principal axis (3.1.18) at the point of force application but inclined at an angle and at a defined direction with respect to the principal axis NOTE See Figure 2. 3.1.11.2 eccentric inclined force
32、 force applied eccentric to the principal axis (3.1.18) at the point of force application and inclined at an angle at a defined direction with respect to the principal axis NOTE See Figure 3. 3.1.12 load cell device which, when mechanically loaded and electrically energized, produces an electrical s
33、ignal, derived from electrical resistance strain gauges, which is a function of the applied force 3.1.13 load cell system load cell together with its associated fittings and instrumentation 3.1.14 loading surface surface of a suitably shaped loading pad used to permit the application of force to a l
34、oad cell 3.1.15 non-linearity maximum deviation of measured deflections, obtained for increasing forces only, from a best fit polynomial, calculated using the method of least squares NOTE This covers any degree of polynomial, including straight line fits. 3.1.16 output stability maximum change in lo
35、ad cell system output, either at zero force or at maximum calibration force, over an extended period of time, with all the environmental conditions and other variables remaining constant 3.1.17 pre-load maximum calibration force applied prior to calibration 3.1.18 principal axis axis along which a l
36、oad cell is designed to be loaded NOTE See Figure 2, Figure 3 and Figure 4. 3.1.19 repeatability measure of agreement between the results of successive measurements of deflection for repeated applications of the same calibration force from zero, with all the environmental conditions and other variab
37、les remaining constant 3.1.20 reproducibility measure of agreement between the results of successive measurements of deflection for repeated applications of the same calibration force from zero, with the load cell rotated about its principal axis between each successive force applicationsBS 8422:200
38、3 4 BSI 31 October 2003 3.1.21 side force force acting at a 90 angle to the principal axis of a load cell on the specified loading surface and in a defined direction 3.1.22 supply voltage voltage used to energize a load cell system 3.1.23 warm-up period period of time during which a load cell system
39、 achieves and maintains a specified level of stability of its zero load output reading, with all environmental conditions and other variables remaining constant 3.1.24 zero force output output reading from a load cell at a stated excitation voltage and at zero force NOTE This is obtained with the ap
40、propriate loading fittings located in the normal calibration position. 3.2 Symbols NOTE Symbols that are used only in Annex B are defined separately in that annex. 1) 4 General 4.1 Calibration methods The standard calibration specified in Clause 7, and the supplementary calibrations specified in Cla
41、use 8 to Clause 22, shall be carried out only if requested by the customer. 4.2 Identification of connection details All connection details for the load cell and any associated indicator shall be clearly identified and shall be recorded on the calibration certificate (see Clause 23). 4.3 Laboratory
42、reference standards The reference standards used by the laboratory shall be traceable to the SI system of units with a combined uncertainty appropriate to the customers requirements. 1) The units of deflection will be those of the indicator, which will not necessarily be millivolts per volt (mV/V).
43、d 1 mean deflection at maximum calibration force with concentric inclined application of force, in millivolts per volt (mV/V) 1) d 2 mean deflection at maximum calibration force with eccentric inclined application of force, in millivolts per volt (mV/V) 1) d 3 mean deflection at maximum calibration
44、force with eccentric application of force, in millivolts per volt (mV/V) 1) d max maximum deflection with concentric application force along the principal axis, in millivolts per volt (mV/V) 1) E eccentricity, in millimetres (mm) NOTE This is the distance between the loading axis of the applied forc
45、e, at the point of force application, and the principal axis of the load cell. e 1 effect of concentric inclined application of force, as a percentage of d max(%) e 2 effect of eccentric inclined application of force, as a percentage of d max(%) e 3 effect of eccentric application of force, as a per
46、centage of d max (%)BS 8422:2003 BSI 31 October 2003 5 4.4 Environmental conditions The calibration of the load cell shall be made at a temperature within the range 18 C to 28 C, unless otherwise specified within the relevant procedure or by the customer. To ensure stable conditions, the load cell s
47、ystem shall be kept at this temperature until thermal stability is achieved before the commencement of the calibration. NOTE A temperature within the range 18 C to 28 C is normally used, but the customer may specify a different temperature if required for a specific application. The temperature of t
48、he load cell shall be recorded and shall be maintained to within a range of 2 C for each calibration performed. If the temperature is kept within this range for all calibrations, the overall range shall be recorded on the calibration certificate (see Clause 23). If this is not the case, the temperat
49、ure range for each individual calibration shall be recorded separately on the calibration certificate. 4.5 Zero force output The zero force output of the load cell shall be measured before and after each calibration and the maximum and minimum values for each loading mode shall be recorded on the calibration certificate (see Clause 23). 4.6 Deflection NOTE This applies to both the standard calibration and the supplementary calibrations. If the
