1、Designation: D 5720 95 (Reapproved 2002)Standard Practice forStatic Calibration of Electronic Transducer-Based PressureMeasurement Systems for Geotechnical Purposes1This standard is issued under the fixed designation D 5720; the number immediately following the designation indicates the year oforigi
2、nal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the procedure for static calibrationof ele
3、ctronic transducer-based systems used to measure fluidpressures in laboratory or in field applications associated withgeotechnical testing.1.2 This practice is used to determine the accuracy ofelectronic transducer-based pressure measurement systemsover the full pressure range of the system or over
4、a specifiedoperating pressure range within the full pressure range.1.3 This practice may also be used to determine a relation-ship between pressure transducer system output and appliedpressure for use in converting from one value to the other(calibration curve). This relationship for electronic pres
5、suretransducer systems is usually linear and may be reduced to theform of a calibration factor or a linear calibration equation.1.4 The values stated in SI units are to be regarded as thestandard. The inch-pound units in parentheses are for informa-tion only.1.5 This standard does not purport to add
6、ress all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in Section
7、 7.2. Referenced Documents2.1 ANSI/ISA Standards:S37.1 (R1982) Electrical Transducer Nomenclature and Ter-minology2S37.3 (R1982) Specifications and Tests For Strain GagePressure Transducers2S37.6 (R1982) Specifications and Tests For PotentiometricPressure Transducers2S37.10 (R1982) Specifications an
8、d Tests For PiezoelectricPressure and Sound-pressure Transducers23. Terminology3.1 Terms marked with “(ANSI, ISA-S37.1)” are takendirectly from ANSI/ISA-S37.1 (R1982) and are included forthe convenience of the user.3.2 Definitions of Terms Specific to This Standard:3.2.1 absolute pressurepressure me
9、asured relative to zeropressure (vacuum) (ANSI, ISA-S37.1).3.2.2 accuracyratio of the error to the full-scale output orthe ratio of the error to the output, as specified, expressed inpercent (ANSI, ISA-S37.1).3.2.3 ambient conditionsconditions (pressure, tempera-ture, etc.) of the medium surrounding
10、 the case of the transducer(ANSI, ISA-S37.1).3.2.4 best straight lineline midway between the twoparallel straight lines closest together and enclosing all outputversus measurand values on a calibration curve (ANSI, ISA-S37.1).3.2.5 bondedpermanently attached over the length andwidth of the active el
11、ement (ANSI, ISA-S37.1).3.2.6 bourdon tubepressure-sensing element consisting ofa twisted or curved tube of non-circular cross section that tendsto be straightened by the application of internal pressure(ANSI, ISA-S37.1).3.2.7 calibrationtest during which known values of mea-surand are applied to th
12、e transducer and corresponding outputreadings are recorded under specified conditions (ANSI, ISA-S37.1).3.2.8 calibration curvegraphical representation of thecalibration record (ANSI, ISA-S37.1).3.2.9 calibration cycleapplication of known values ofmeasurand, and recording of corresponding output rea
13、dings,over the full (or specified portion of the) range of a transducerin an ascending and descending direction (ANSI, ISA-S37.1).3.2.10 calibration recordrecord (for example, table orgraph) of the measured relationship of the transducer output tothe applied measurand over the transducer range (ANSI
14、,ISA-S37.1).3.2.11 calibration traceabilityrelation of a transducercalibration, through a specified step-by-step process, to aninstrument or group of instruments calibrated by the NationalInstitute of Standards and Technology (ANSI, ISA-S37.1).1This practice is under the jurisdiction of ASTM Committ
15、ee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.95 on InformationRetrieval and Data Automation.Current edition approved April 15, 1995. Published June 1995.2Available from Instrument Society of America, P.O. Box 12277, ResearchTriangle Park, NC 27709.1Copyright ASTM Inter
16、national, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.12 capsulepressure-sensing element consisting of twometallic diaphragms joined around their peripheries (ANSI,ISA-S37.1).3.2.13 diaphragmsensing element consisting of a thin,usually circular, plate that
17、 is deformed by pressure differentialapplied across the plate (ANSI, ISA-S37.1).3.2.14 differential pressuredifference in pressure betweentwo points of measurement (ANSI, ISA-S37.1).3.2.15 end pointsoutputs at the specified upper and lowerlimits of the range (ANSI, ISA-S37.1).3.2.16 end-point linest
18、raight line between the end points(ANSI, ISA-S37.1).3.2.17 end point linearitylinearity referred to the end-point line (ANSI, ISA-S37.1).3.2.18 environmental conditionsspecified external condi-tions (shock, vibration, temperature, etc.) to which a transducermay be exposed during shipping, storage, h
19、andling, andoperation (ANSI, ISA-S37.1).3.2.19 erroralgebraic difference between the indicatedvalue and the true value of the measurand (ANSI, ISA-S37.1).3.2.20 excitationexternal electrical voltage or current, orboth, applied to a transducer for its proper operation (ANSI,ISA-S37.1).3.2.21 fluida s
20、ubstance, such as a liquid or gas, that iscapable of flowing and that changes its shape at a steady ratewhen acted upon by a force.3.2.22 full-scale outputalgebraic difference between theend points (ANSI, ISA-S37.1).3.2.23 gage pressurepressure measured relative to ambi-ent pressure (ANSI, ISA-S37.1
21、).3.2.24 hermetically sealedmanufacturing process bywhich a device is sealed and rendered airtight.3.2.25 hysteresismaximum difference in output, at anymeasurand value within the specified range, when the value isapproached first with increasing and then with decreasingmeasurand (ANSI, ISA-S37.1).3.
22、2.25.1 DiscussionHysteresis is expressed in percent offull-scale output, during any one calibration cycle.3.2.26 least-squares linestraight line for which the sum ofthe squares of the residuals (deviations) is minimized (ANSI,ISA-S37.1).3.2.27 least squares linearitylinearity referred to theleast-sq
23、uares line (ANSI, ISA-S37.1).3.2.28 linearitycloseness of a calibration curve to a speci-fied straight line (ANSI, ISA-S37.1).3.2.28.1 DiscussionLinearity is expressed as the maxi-mum deviation of any calibration point from a specifiedstraight line, during any one calibration cycle. Linearity isexpr
24、essed in percent of full-scale output.3.2.29 measurandphysical quantity, property, or condi-tion that is measured (ANSI, ISA-S37.1).3.2.30 measured fluidfluid that comes in contact with thesensing element (ANSI, ISA-S37.1).3.2.31 normal atmospheric pressure101.325 kPa (14.696lbf/in.2); equivalent to
25、 the pressure exerted by the weight of acolumn of mercury 760 mm (29.92 in.) high at 0C (32F) ata point on the earth where the acceleration of gravity is 9.8066m/s2(32.1739 ft/s2).3.2.32 operating environmental conditionsenvironmentalconditions during exposure to which a transducer must performin so
26、me specified manner (ANSI, ISA-S37.1).3.2.33 outputelectrical or numerical quantity, producedby a transducer or measurement system, that is a function ofthe applied measurand.3.2.34 overloadmaximum magnitude of measurand thatcan be applied to a transducer without causing a change inperformance beyon
27、d specified tolerance (ANSI, ISA-S37.1).3.2.35 piezoelectricconverting a change of measurandinto a change in the electrostatic charge or voltage generated bycertain materials when mechanically stressed (ANSI, ISA-S37.1).3.2.36 piezoresistanceconverting a change of measurandinto a change in resistanc
28、e when mechanically stressed.3.2.37 potentiometricconverting a change of measurandinto a voltage-ratio change by a change in the position of amoveable contact on a resistance element across which exci-tation is applied (ANSI, ISA-S37.1).3.2.38 rangemeasurand values, over which a transduceris intende
29、d to measure, specified by their upper and lowerlimits (ANSI, ISA-S37.1).3.2.39 repeatabilityability of a transducer to reproduceoutput readings when the same measurand value is applied toit consecutively, under the same conditions, and in the samedirection (ANSI, ISA-S37.1).3.2.39.1 DiscussionRepea
30、tability is expressed as themaximum difference between output readings; it is expressedin percent of full-scale output. Two calibration cycles are usedto determine repeatability unless otherwise specified.3.2.40 room conditionsambient environmental condi-tions, under that transducers must commonly o
31、perate, that havebeen established as follows: (a) temperature: 25 6 10C (77 618F); (b) relative humidity: 90 % or less; and (c) barometricpressure: 986 10 kPa (29 6 3 in. Hg). Tolerances closer thanshown above are frequently specified for transducer calibrationand test environments (ANSI, ISA-S37.1)
32、.3.2.41 sealed gage pressurepressure measured relative tonormal atmospheric pressure that is sealed within the trans-ducer.3.2.42 sensing elementthat part of the transducer thatresponds directly to the measurand (ANSI, ISA-S37.1).3.2.43 static calibrationcalibration performed underroom conditions an
33、d in the absence of any vibration, shock, oracceleration (unless one of these is the measurand) (ANSI,ISA-S37.1).3.2.44 strain gageconverting a change of measurand intoa change in resistance due to strain (ANSI, ISA-S37.1).3.2.45 theoretical outputproduct of the applied pressureor vacuum and the rat
34、io of full-scale output to calibratedpressure range.3.2.46 transducerdevice that provides a usable output inresponse to a specified measurand (ANSI, ISA-S37.1).3.2.47 transduction elementelectrical portion of a trans-ducer in which the output originates (ANSI, ISA-S37.1).3.2.48 warm-up periodperiod
35、of time, starting with theapplication of excitation to the transducer, required to ensureD 57202that the transducer will perform within all specified tolerances(ANSI, ISA-S37.1).4. Summary of Practice4.1 A pressure transducer based measurement system (pres-sure transducer, readout system, power supp
36、ly, and signalconditioner), pressure standard, and appropriate controllers,regulators, and valves are connected to pressure or vacuumsources, or both.4.2 Pressure or vacuum is applied in predetermined inter-vals over the full range (or a specified portion of the full range)of the pressure measuremen
37、t system.4.3 The pressure measurement system output is compared ateach pressure or vacuum interval to the applied pressure orvacuum as indicated by the pressure standard.4.4 The error in pressure measurement system output iscalculated for each pressure or vacuum interval over thecalibrated range.4.5
38、 From error, the accuracy of the pressure measurementsystem is computed and a determination is made to accept orreject the pressure measurement system.4.6 From a calibration curve, a relationship between systemoutput and applied pressure may be determined.5. Significance and Use5.1 Electronic transd
39、ucer-based pressure measurement sys-tems must be subjected to static calibration under roomconditions to ensure reliable conversion from system output topressure during use in laboratory or in field applications.5.2 Transducer-based pressure measurement systems shouldbe calibrated before initial use
40、 and at least quarterly thereafterand after any change in the electronic or mechanical configu-ration of a system.5.3 Transducer-based pressure measurement systems shouldalso be recalibrated if a component is dropped; overloaded; ifambient test conditions change significantly; or for any othersignif
41、icant changes in a system.5.4 Static calibration is not appropriate for transducerbasedsystems used under operating environmental conditions in-volving vibration, shock, or acceleration.6. Apparatus6.1 Pressure Measurement SystemsElectronic transducer-based pressure measurement systems covered in th
42、is practicemay be either individual pressure transducers, as described in6.2, with independent power supplies, signal conditioners, andreadout systems or the systems may be self-contained instru-ments such as pressure meters or pressure monitors, as de-scribed in 6.7.3.1.6.2 Pressure TransducersPres
43、sure transducers usuallyconsist of a sensing element that is in contact with themeasured fluid and a transduction element that modifies thesignal from the sensing element to produce an output. Thematerials used in the sensing element must be compatible withthe measured fluid. Some parts of the trans
44、ducer may behermetically sealed if those parts are sensitive to and may beexposed to moisture. Pressure connectors must be threadedwith appropriate fittings to attach the transducer to standardpipe fittings, or to other appropriate leakproof fittings. Theoutput cable must be securely fastened to the
45、 body of thetransducer. A simple schematic of a generic pressure transduceris shown in Fig. 1.6.2.1 Sensing ElementsA wide variety of sensing ele-ments are used in pressure transducers. The most commonelements are diaphragms, capsules, bourdon tubes, and piezo-electric crystals. The function of the
46、sensing element is toproduce a measurable response to applied pressure. Theresponse may be sensed directly on the element or a separatesensor may be used to detect element response.6.2.2 DiaphragmsDiaphragms are usually plates, disks,or wafers of stainless steel, silicon, crystal, or ceramic thatdef
47、lect when subjected to pressure. Deflection of the dia-phragm is detected by sensors.6.2.2.1 Strain-Gaged DiaphragmsThe most common dia-phragm deflection sensor is the strain gage. Strain gages can bebonded to the diaphragm or imbedded in the diaphragm. Termstypically used to describe these sensors
48、are bonded foil straingages, bonded semiconductor strain gages, sputtered thin filmstrain gages, diffused semiconductor strain gages, molecularlydiffused strain gages, piezoresistive strain gages, or siliconchips.6.2.2.2 Mechanically Linked Diaphragms Mechanicallylinked diaphragms use sensors which
49、are physically separatefrom the diaphragm. A wide variety of sensors are used in thisstyle element. Sensors may include cantilever beams orbridges, linear displacement transducers (LDT), potentiom-eters, or vibrating wires. Beams and bridges are typicallystrain-gaged sensors and terms such as semiconductor strain-gage sensing beam and sputtered strain-gage bridge are usedwith these devices. The LVDT, LDT, and potentiometer trans-ducers use a rod or a rod-sweeper assembly attached to adiaphragm to sense deflection. Vibrating wire
