1、Specifications and Tests forPotentiometric DisplacementTransducersReaffirmed 29 September 1995ISA37.121982 (R1995)Formerly ISAS37.121982 (R1995)STANDARDISA The Instrumentation,Systems, andAutomation Society TMCopyright 1982 by the Instrument Society of America. All rights reserved. Printed in the Un
2、itedStates of America. No part of this publication may be reproduced, stored in a retrieval system, ortransmitted in any form or by any means (electronic, mechanical, photocopying, recording, orotherwise), without the prior written permission of the publisher.ISA67 Alexander DriveP.O. Box 12277Resea
3、rch Triangle Park, North Carolina 27709ISA-37.12-1982 (R1995), Specifications and Tests for Potentiometric Displacement TransducersISBN 0-87664-359-4ISA-S37.12-1982 (R1995) 3PrefaceThis preface, as well as all footnotes and annexes, is included for informational purposes and is not a part of ISA-37.
4、12-1982 (R1995).This standard has been prepared as a part of the service of ISA toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and critic
5、isms and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P.O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; Fax: (919) 549-8288; E-mail: standardsisa.org.The ISA Standards and Practices Department is aware of the growing
6、need for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA Standards of incorporating suitable references to the SI (and th
7、e metric system) in their business and professional dealings with other countries. Towards this end, this Department will endeavor to introduce SI and acceptable metric units in all new and revised standards to the greatest extent possible. The Metric Practice Guide, which has been published by the
8、Institute of Electrical and Electronics Engineers as ANSI/IEEE Std. 268-1992, and future revisions, will be the reference guide for definitions, symbols, abbreviations, and conversion factors. Certain metric units that are part of the SI system are in common accepted pressure measurement that is con
9、vertible to kilopascals by multiplying by 100.It is the policy of ISA to encourage and welcome the participation of all concerned individuals and interests in the development of ISA standards, recommended practices, and technical reports. Participation in the ISA standards-making process by an indiv
10、idual in no way constitutes endorsement by the employer of that individual, of ISA, or of any of the standards which ISA develops.This standard is intended as a guide for technical personnel at user facilities as well as by manufacturers technical and sales personnel whose duties include specifying,
11、 testing, or showing performance characteristics of strain-gage linear Potentiometric Displacement Transducers. By basing users specifications as well as technical advertising and reference literature on this standard, or by referencing portions thereof, as applicable, a clear understanding of the u
12、sers needs or of the transducers performance capabilities, and of the methods used for evaluating or proving performance, will be provided. Adhering to the specification outline, terminology and procedures shown will not only result in simple, but also complete specifications; it will also reduce de
13、sign time, procurement lead time, and labor, as well as material costs. Of major importance will be the reduction of qualification tests resulting from use of a commonly accepted test procedure and uniform data presentation.The development of this standard was initiated as the result of a survey con
14、ducted in December 1960. A total of 240 questionnaires was sent out to transducer users and manufacturers. A strong majority indicated in their replies a need for transducer standardization. As potentiometric displacement transducers were one of the types shown to be most in need of standardization,
15、 a project subcommittee, SP37.12, Potentiometric Displacement Transducers, was formed under the cognizance of SP37, Transducers for Aerospace Testing, and a standard was drafted and reviewed extensively, and revised in 1976. The reviewers were selected from a broad cross-section of all industries an
16、d sciences in which transducers are applied for measuring purposes.4 ISA-S37.12-1982 (R1995)The following individuals served as members of the 1977 SP37.12 Subcommittee:NAME COMPANYR. Bronson, Chairman Lockheed Electronics Company, Inc.M. Brown Bourns, Inc.J. Kauker Binary ControlsK. Posey, PE URS/F
17、orest i.e., “percent Voltage Ratio*.“4.2.1 Range*Expressed as “_to_radians/millimetres (degrees/inches).“4.2.2 End points*Expressed as “_% _% and _% _% VR.“End Points shall be omitted where adequately defined using Error Band specifications.4.2.3 Full scale output*Expressed as “_% _% VR.“NOTE Full s
18、cale output shall be omitted where adequately defined using End Points or Error Band specifications.4.2.4 LinearityExpressed as “_ linearity shall be within _% VR with specified load impedance.“NOTE The linearity modifier shall be one of those defined in ISA-S37.1; namely end point, independent, lea
19、st squares, terminal, or theoretical slope. Linearity values are dependent on load impedance.*Defined in ISA-S37.1ISA-S37.12-1982 (R1995) 154.2.5 Hysteresis*Expressed as “_% VR.“Alternately, the concepts of 4.2.4 and 4.2.5 may be replaced by 4.2.6.4.2.6 Combined hysteresis* and linearity*Expressed a
20、s “combined hysteresis and linearity within _ % VR.“NOTE The linearity modifier shall be stated.4.2.7 Repeatability*Expressed as “within _% VR over a period of _hours.“Alternately, the concepts of 4.2.2, 4.2.3, 4.2.4, 4.2.5, and 4.2.7 may be replaced by 4.2.8.4.2.8 Static error band*Expressed as “ _
21、% VR as referred to _(curve)_.“The curve shall be stated as follows:NOTES1. End Point Line a straight line between end points2. Best Straight Line a line midway between the two parallel lines closest together and enclosing all output versus measured values3. Least Square Line a straight line for whi
22、ch the sum of the squares of the residuals is minimized4. Terminal line a straight line between 0 and 100 percent of both measurand and output5. Theoretical Slope a straight line between the theoretical end points6. Other curves shall be defined if specified; e.g., mean-output curve4.2.9 Resolution*
23、 (See also 4.3.1)Expressed as “average resolution within _% VR and maximum resolution within _% VR.“4.2.10 Frequency responseExpressed as “within _% from zero to _ Hz at a peak-to-peak amplitude of _% VR.“4.2.11 Operating temperature range*Expressed as “from _C to _C.“4.2.12 Temperature error*Expres
24、sed as “within _% VR per _C.“ Or “within _% VR over the operating temperature range.“*Defined in ISA-S37.1*Defined in 4.316 ISA-S37.12-1982 (R1995)Alternately, 4.2.12 may be replaced by 4.2.13.4.2.13 Temperature error band*Expressed as “within _% VR from the reference curve established for the Stati
25、c Error Band and over the operating temperature range.“4.2.14 Acceleration error*Expressed as “within _% VR per gnalong _axis at steady acceleration levels to _ gn.“NOTE The error shall be listed either for each of the three axes or for the axis with the largest error; i.e., most sensitive axis.Alte
26、rnately 4.2.14 may be replaced by 4.2.15.4.2.15 Acceleration error band*Expressed as “within _% VR from the reference curve established for the Static Error Band for steady accelerations up to _ gnalong _ axis.“NOTE The error band shall be listed either for each of the three axes or for the axis wit
27、h the largest error; i.e., most sensitive axis.4.2.16 Vibration error*Expressed as “within _% VR along _axis over the specified vibration program.“ Signal “dropout“ or discontinuities shall be noted.NOTE The error shall be listed either for each of the three axes or for the axis with the largest err
28、or; i.e., most sensitive axis; and the program shall be detailed, preferably by a graph.Alternately 4.2.16 may be replaced by 4.2.17.4.2.17 Vibration error bands*Expressed as “within _% VR along _axis from the reference curve established for the Static Error Band over the specified vibration program
29、.“NOTE The error band shall be listed either for each of the three axes or for the axis with the largest error; i.e., most sensitive axis, and the program shall be detailed, preferably by a graph.4.2.18 Mounting Error*Expressed as “within _% VR“ or “within the Static Error Band.“4.2.19 Loading error
30、*Expressed as “within _% VR“ or “within the Static Error Band at a load impedance of _ohms.“*Defined in ISA-S37.1*Defined in 4.3ISA-S37.12-1982 (R1995) 174.2.20 Cycling life*Expressed as “_cycles at one fourth of the designated maximum operating frequency of the transducers.“4.2.21 Other environment
31、al conditionsPertinent environmental conditions that shall not change transducer performance beyond certain limits shall be included along with the limits beyond which the transducer performance shall not change.Examples are as follows:a) Ambient Pressure*b) Shock Triaxialc) High Level Acoustic Exci
32、tationd) Humiditye) Salt Atmospheref) Nuclear Radiationg) Magnetic Fieldsh) Sand and Dusti) Total Immersion (and in what medium)j) Solar (or other) Heat Radiationk) Temperature Shockl) Electromagnetic Interference, generation, or susceptibilitym) Vibration Acceleration Triaxial4.2.22 Storage life*Ex
33、pressed as “_ months (years) without changing performance characteristics beyond their specified tolerances.“NOTE Environmental storage conditions shall be described in detail. Where performance characteristics require additional tolerances over the storage life they shall be specified.4.3 Additiona
34、l terminology4.3.1 average resolution: The reciprocal of the total number of output steps over the unit range multiplied by 100 and expressed in percent VR.4.3.2 maximum excitation: The maximum allowable voltage (current) applied to the potentiometric element at Room Conditions while maintaining all
35、 other performance characteristics within their limits. (Note The excitation value is particularly associated with temperature.)*Defined in ISA-S37.118 ISA-S37.12-1982 (R1995)4.3.3 mounting effects: The effects (errors) introduced into transducer performance during installation caused by fastening o
36、f the unit or its mounting hardware or by irregularities of the surface on (or to) which the transducer is mounted.4.3.4 operating temperature range: The range in extremes of ambient temperature within which the transducer must perform to the requirements of the “Temperature Error“ or “Temperature E
37、rror Band.“ (See 4.2.12 and 4.2.13, respectively.)4.3.5 potentiometric element: The resistive part of the transduction element upon which the wiper (movable contact) slides and across which excitation is applied. It may be constructed of a continuous resistance or of small diameter wire wound on a f
38、orm (mandrel).4.3.6 wiper (movable contact): That portion of the potentiometric assembly which slides on the resistance element. It is connected to a terminal and provides an electrical output as a function of the shaft position relative to the body.4.3.7 dielectric withstand voltage: The ability of
39、 insulated portions of the transducer to withstand a specified overvoltage for a specified time without arcing or conduction above a specified current value across the insulation.4.3.8 tap: A connection to a potentiometric element along its length, frequently at the elements center for use in provid
40、ing bidirectional output.4.3.9 worst resolution: The magnitude of the largest of all output steps over the unit range expressed as percentage voltage ratio (%VR).4.3.10 shaft: The mechanical input element of the transducer.4.3.11 shaft position: An indication of the position of the wiper relative to
41、 a reference point.4.3.12 noise (refer to noise test circuit): Noise is any spurious variation in the electrical output, not present in the input. Noise is defined quantitatively in terms of an equivalent parasitic transient resistance appearing between the wiper and the resistance element while the
42、 input shaft is being moved.The Equivalent Noise Resistance is established independently of the functional characteristics, in the Noise test circuit. The wiper is required to be excited by a specified dc constant current source. The Noise test circuit output measuring system is an oscilloscope with
43、 defined frequency bandwidth or time constant. The magnitude of the Equivalent Noise Resistance is measured as ohms variation while the input shaft is moved at a specified speed and observed as peak-to-peak deflection on the oscilloscope.For example: if the constant current is one milliampere dc and
44、 the oscilloscope deflection is 100 millivolts peak-to-peak, then the Equivalent Noise Resistance is 100 ohms.NOTE Noise may be characterized as generally reproducible, exhibited as a local nonlinearity, or it may be the classical sporadic type. Manufacturing cleanliness and improved quality control
45、 on processing may significantly reduce noise problems.ISA-S37.12-1982 (R1995) 194.4 Supplemental performance characteristicsNOTE In critical applications these characteristics may be of potential use in the specifications of potentiometric displacement transducers. These characteristics are typical
46、ly “Qualification Test“ items; however, specific test procedures are not described in this standard.4.4.1 End stopsThe physical limits of motion provided by the transducer design which define the Total Travel of the Shaft.NOTE In order to protect the transducer from overload, the End Stops will norm
47、ally be placed beyond the maximum requirements for (desired) Mechanical Travel.4.4.2 End point, shaft positionThe shaft positions immediately before the first and after the last measurable change(s) in Output Ratio, after wiper continuity has been established, as the shaft moves in a specified direc
48、tion.4.4.3 End point, theoretical, shaft positionThe shaft positions corresponding to the ends of the Theoretical Electrical Travel as determined from the Index Point.The Index Point is a point of reference, fixing the relationship between a specified shaft position and the output percent VR. For ex
49、ample: In an ideal symmetrical range bidirectional potentiometric displacement transducer, zero position input should produce 50% VR output.4.4.4 End resistance, shaft positionThe resistance measured between the wiper terminal and end terminal with the shaft positioned at the corresponding End Point.4.4.5 Extended position, linear potentiometerThe condition
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