1、BRITISH STANDARD BS 4151:1967 Method of evaluating Pneumatic valve positioners with input signal of 3 to 15 lbf/in 2(Gauge)BS4151:1967 This British Standard, having been approved by the InstrumentIndustry Standards Committee and endorsed by theChairman of the EngineeringDivisional Council, was publi
2、shed under the authorityof the General Councilon 22March1967 BSI 02-2000 The following BSI references relate to the work on this standard: Committee reference INE/13 Draft for comment D65/1750 ISBN 0 580 341372 Co-operating organizations The Instrument Industry Standards Committee, under whose super
3、vision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: British Clock and Watch Manufacturers Association British Electrical and Allied Manufacturers Association British Industrial Measuring and Con
4、trol Apparatus Manufacturers Association* British Iron and Steel Federation British Nautical Instrument Trade Association British Railways Board British Scientific Instrument Research Association* Council of British Manufacturers of Petroleum Equipment Electrical Research Association Electricity Cou
5、ncil, the Central Electricity Generating Board and the Area Boards in England and Wales* Electronic Engineering Association Engineering Equipment Users Association* Gauge and Tool Makers Association Institution of Chemical Engineers Institution of Electrical Engineers Institution of Heating and Vent
6、ilating Engineers Institution of Mechanical Engineers Institution of Production Engineers Iron and Steel Institute Meteorological Office Ministry of Defence, Army Department Ministry of Health National Coal Board National Physical Laboratory (Ministry of Technology) Oil Companies Materials Associati
7、on* Scientific Instrument Manufacturers Association* Society of Instrument Technology* Water Resources Board Water-tube Boilermakers Association The scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the commit
8、tee entrusted with the preparation of this British Standard: Ministry of Technology Amendments issued since publication Amd. No. Date CommentsBS4151:1967 BSI 02-2000 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 Terminology 1 3 General testing procedure 1 4 St
9、atic behaviour 2 5 Dynamic behaviour 6 6 Air flow 6 7 Other considerations 6 Figure 1 Dead zone, relationship of stem position to input signal 3 Figure 2 Relationship between amplitude and frequency 5 Figure 3 Flow characteristic of a valve positioner at an output of9lbf/in 2 7BS4151:1967 ii BSI 02-
10、2000 Foreword This standard makes reference to the following British Standards: BS 1523, Glossary of terms used in automatic controlling and regulating systems. BS 1780, Bourdon tube pressure and vacuum gauges. BS 2643, Glossary of terms relating to the performance of measuring instruments. This Bri
11、tish Standard has been prepared under the authority of the Instrument Industry Standards Committee as one of a series of standards dealing with the evaluation testing of process control instruments. One standard, already published, covers the testing of pneumatic transmitters BS3512:1962, “Method of
12、 evaluating the performance of pneumatic transmitters with3 to15lbf/in 2(gauge) output”; another one dealing with automatic controllers is nearing completion and further standards relating to electronic controllers and electronic transmitters are being prepared. No attempt has been made to provide a
13、 form of grading or classification of valve positioners tested in accordance with this document; instead, requirements are laid down for the evaluation testing of positioners coming under the scope of the standards title. The methods of testing for various parameters of instrument performance which
14、are detailed in this standard are intended for use by manufacturers in determining the performance of their equipment and by users or independent testing establishments in verifying manufacturers performance specifications. The specified conditions of test in this standard, e.g.the range of ambient
15、temperatures, barometric pressures, electricity supply voltages and frequency relate to those which commonly arise in normal conditions of use. Consequently the values given should be employed where no other values are specified. The test conditions are not necessarily sufficient for instruments spe
16、cifically designed for unusually arduous duties; conversely a restricted series of tests, eliminating or amending those in the standard which might be considered inappropriate, would serve adequately for instruments designed to perform within a more limited range of conditions. With principles of ev
17、aluation testing as enumerated above it will be appreciated that the closest collaboration should be maintained between evaluator and manufacturer. Due notice should be taken by the evaluating facility of the manufacturers specification for the equipment being tested, and the manufacturer should be
18、invited to comment upon the results. It is hoped that the introduction of standard evaluation tests will result in improved process control equipment. An indirect result should be an improvement in the content and form of specifications and trade literature; standardized presentation of manufacturer
19、s claims for instrument performance would enable a better assessment of products to be made by users and should ultimately benefit both user and manufacturing interests. With this in mind it is the intention to supplement the series of British Standards for evaluating process control equipment with
20、a standard layout for the presentation of performance data and test results. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself conf
21、er immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to8 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on
22、 the inside front cover.BS4151:1967 BSI 02-2000 1 1 Scope This standard specifies tests designed to determine the performance of pneumatic valve positioners which accept input signals of3lbf/in 2to15lbf/in 2 . NOTEThroughout this British Standard the term “valve operator” is used; alternative and eq
23、ually appropriate terms used within industry are “valve motor” and “valve actuator”. Although some valve positioners may be tested without being fitted to a valve operator, there are some positioners which form an integral part of the operator and these cannot be separately tested. The method of eva
24、luation described in this standard therefore specifies the use of a valve operator in all cases since this allows a ready comparison to be made between different types. The operator may be a spring-opposed or double-acting diaphragm or piston. 2 Terminology Terms used in the standard are in accordan
25、ce with BS2643 1)and BS1523 2) . For the purposes of this standard the following terms and definitions have been adopted: 2.1 Dead zone 2.1.1 forward path dead zone the largest change in input signal that can be effected without causing a detectable change in valve stem position 2.1.2 feedback path
26、dead zone the largest change in stem position that can occur without causing feedback 2.2 gain the ratio of change in valve operator pressure to change in input pressure when the stem is not allowed to move. In the case of a double-acting operator, it is the ratio of the change in pressure differenc
27、e between the two sides to the change in input pressure without position feedback 3 General testing procedure 3.1 For testing, valve positioners should be fitted to a valve operator acceptable for the purpose by the manufacturer of the positioner. 3.2 The valve operator should, where applicable, be
28、of a size and rating that gives a stem movement of2in for a change in operator pressure from3lbf/in 2to15lbf/in 2 . If a stem movement of2in cannot be achieved, the nearest value to this should be used. If necessary an alternative operator should be used to allow the positioner to be tested with its
29、 maximum recommended output pressure. Where a manufacturer specifies an operator pressure other than3lbf/in 2to15lbf/in 2then the specified range should be used. Valve positioners fitted with cams should be tested with input/output characteristics which are nominally linear. 3.3 The positioner and o
30、perator should be mounted on a test rig which shall be designed to make it possible to: 1) Carry out tests with variable, measurable friction on the stem. The friction may be measured, for example, by determining the force required to initiate stem movement when the operator pressure is constant. 2)
31、 Put different plug masses on the end of the stem. 3) Measure the stem position with an average error of less than0.20% and a repeatability of0.1% of the stroke of the valve. 4) Transmit the stem movement over a restricted range with a sensitivity of0.10% of the stroke and a response speed which all
32、ows the signal to follow the fastest motion of the valve without significant attenuation or lag. 5) For integrally mounted assemblies only, lock the stem at three positions so that its movement is less than0.1% of the span for maximum change in operator pressure (see4.5 Note). 3.4 All tests should b
33、e done with covers in position. 3.5 Test gauges to BS1780 3)should be used for pressure measurement. 3.6 Except where otherwise stated, the tests should be carried out under vibration-free conditions and between15 C and20 C. 3.7 The air supply pressure should be maintained to within 1% of the value
34、specified by the manufacturer and should not be subject to short term fluctuations. The supply of air should be such that it does not impair the dynamic performance of the equipment under test. 1) BS2643, “Glossary of terms relating to the performance of measuring instruments”. 2) BS1523, “Glossary
35、of terms used in automatic controlling and regulating systems”. 3) BS1780, “Bourdon tube pressure and vacuum gauges”.BS4151:1967 2 BSI 02-2000 3.8 Unless otherwise stated, the stem static friction should be adjusted to correspond to10% of the thrust exerted by the diaphragm or piston due to the maxi
36、mum operator pressure change. 3.9 Where the gain of the positioner can be altered, it should be set at its maximum value. 3.10 Any mechanical stops should be adjusted so that they do not interfere with the movement over the range with which this standard is concerned. 3.11 When a full evaluation in
37、accordance with this standard is not required, those tests which are carried out should be performed, and the results reported, in accordance with the relevant parts of the standard. 4 Static behaviour 4.1 Accuracy. The valve positioner should be adjusted in accordance with the manufacturers instruc
38、tions so that when the input is changed from3lbf/in 2to15lbf/in 2the valve stem moves2in as nearly as is practicable. The input should then be slowly changed from2lbf/in 2to16lbf/in 2and then back to2lbf/in 2five times; the input pressure and valve stem position should be measured at intervals of1.5
39、lbf/in 2between3lbf/in 2and15lbf/in 2 , the same input values being used in each direction. The smoothness of the change should be such that no overshoot occurs, at any point, in the input signal to the valve positioner. From this test the following should be determined: 1) Average departure from li
40、nearity (including hysteresis and dead zone). The arithmetic mean of the deviation from linearity at each point of measurement separately for rising and falling inputs. The reference for linearity is defined as the straight line between the average of the ten positions of the stem corresponding to3l
41、bf/in 2input and the average of the ten positions of the stem corresponding to15lbf/in 2input. 2) Hysteresis (including dead zone). The algebraic difference between the two arithmetic means of the deviations from linearity found for the same input when approached from opposite directions, i.e.rising
42、 and falling. 3) Repeatability. The root mean square deviation of the groups of five corresponding readings, separated for rising and falling input pressure. The tests in1), 2) and3) should be repeated with the assembly adjusted as follows in turn: a) The stem moves2 in when the input pressure is va
43、ried from3lbf/in 2to9lbf/in 2 . b) The stem moves2 in when the input pressure is varied from9lbf/in 2to15lbf/in 2 . c) The positioner gain at its minimum value. d) Altered as necessary to permit the use of the maximum change in valve operator pressure recommended by the makers; adjusted so that this
44、 causes2 in stem movement for a change in input of3lbf/in 2to15lbf/in 2 . e) With friction increased to give approximately20% hysteresis in stem position with the valve positioner disconnected. 4.2 Dead zone. Dead zone should be measured at approximately4lbf/in 2and14lbf/in 2by the application of an
45、 input of triangular wave form of such a frequency that it can readily be followed by the valve stem. (This may be applied manually if desired, since the actual frequency is unimportant for the purpose of the test provided the above condition is satisfied.) The amplitude should then be reduced until
46、 the proportional part of the stem movement is reduced to zero. The input amplitude (peak to peak percentage of12lbf/in 2 ) is thus the dead zone of the forward path, and the amplitude of the stem movement (peak to peak percentage of the stroke) is the dead zone of the feedback path. The relationshi
47、p of the output signal is shown in Figure 1. 4.3 Constancy. Constancy should be assessed by determining the changes in the stem position relative to the base of the yoke corresponding to3lbf/in 2 , and in the stem travel for a change in input from3lbf/in 2to15lbf/in 2 , due to the following causes,
48、all other conditions meanwhile remaining constant. NOTEIn order to exclude the effects of hysteresis all measurements at any one point should be made with the input signal approaching from one direction. 4.3.1 Supply pressure variation. By measurement of the changes caused by a variation of 10% abou
49、t the normal supply pressure to the valve positioner. 4.3.2 Temperature variation. By measurement of the changes caused by a variation in temperature. Sufficient time should be allowed for stabilization at each temperature, and measurement should be taken at approximately20 C, 0 C, +20 C, +40 C; above this temperature, measurements should be taken at20degC intervals up to the manufacturers recommended maximum. In each case the maximum departure from linearity should be stated. NOTE 1The dewpoint of the supply air should be less than20 C at supply pressur
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