ASTM D5720-95(2002)
(Practice)Standard Practice for Static Calibration of Electronic Transducer-Based Pressure Measurement Systems for Geotechnical Purposes
Standard Practice for Static Calibration of Electronic Transducer-Based Pressure Measurement Systems for Geotechnical Purposes
SIGNIFICANCE AND USE
Electronic transducer-based pressure measurement systems must be subjected to static calibration under room conditions to ensure reliable conversion from system output to pressure during use in laboratory or in field applications.
Transducer-based pressure measurement systems should be calibrated before initial use and at least quarterly thereafter and after any change in the electronic or mechanical configuration of a system.
Transducer-based pressure measurement systems should also be recalibrated if a component is dropped; overloaded; if ambient test conditions change significantly; or for any other significant changes in a system.
Static calibration is not appropriate for transducerbased systems used under operating environmental conditions involving vibration, shock, or acceleration.
SCOPE
1.1 This practice covers the procedure for static calibration of electronic transducer-based systems used to measure fluid pressures in laboratory or in field applications associated with geotechnical testing.
1.2 This practice is used to determine the accuracy of electronic transducer-based pressure measurement systems over the full pressure range of the system or over a specified operating pressure range within the full pressure range.
1.3 This practice may also be used to determine a relationship between pressure transducer system output and applied pressure for use in converting from one value to the other (calibration curve). This relationship for electronic pressure transducer systems is usually linear and may be reduced to the form of a calibration factor or a linear calibration equation.
1.4 The values stated in SI units are to be regarded as the standard. The inch-pound units in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 7.
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Standards Content (Sample)
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Designation:D5720–95 (Reapproved 2002)
Standard Practice for
Static Calibration of Electronic Transducer-Based Pressure
Measurement Systems for Geotechnical Purposes
This standard is issued under the fixed designation D5720; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope S37.10 (R1982) Specifications and Tests For Piezoelectric
Pressure and Sound-pressure Transducers
1.1 This practice covers the procedure for static calibration
of electronic transducer-based systems used to measure fluid
3. Terminology
pressures in laboratory or in field applications associated with
3.1 Terms marked with “(ANSI, ISA-S37.1)” are taken
geotechnical testing.
directly from ANSI/ISA-S37.1 (R1982) and are included for
1.2 This practice is used to determine the accuracy of
the convenience of the user.
electronic transducer-based pressure measurement systems
3.2 Definitions of Terms Specific to This Standard:
over the full pressure range of the system or over a specified
3.2.1 absolute pressure—pressure measured relative to zero
operating pressure range within the full pressure range.
pressure (vacuum) (ANSI, ISA-S37.1).
1.3 This practice may also be used to determine a relation-
3.2.2 accuracy—ratio of the error to the full-scale output or
ship between pressure transducer system output and applied
the ratio of the error to the output, as specified, expressed in
pressure for use in converting from one value to the other
percent (ANSI, ISA-S37.1).
(calibration curve). This relationship for electronic pressure
3.2.3 ambient conditions—conditions (pressure, tempera-
transducer systems is usually linear and may be reduced to the
ture,etc.)ofthemediumsurroundingthecaseofthetransducer
form of a calibration factor or a linear calibration equation.
(ANSI, ISA-S37.1).
1.4 The values stated in SI units are to be regarded as the
3.2.4 best straight line—line midway between the two
standard.The inch-pound units in parentheses are for informa-
parallel straight lines closest together and enclosing all output
tion only.
versus measurand values on a calibration curve (ANSI, ISA-
1.5 This standard does not purport to address all of the
S37.1).
safety concerns, if any, associated with its use. It is the
3.2.5 bonded—permanently attached over the length and
responsibility of the user of this standard to establish appro-
width of the active element (ANSI, ISA-S37.1).
priate safety and health practices and determine the applica-
3.2.6 bourdon tube—pressure-sensingelementconsistingof
bility of regulatory limitations prior to use. Specific precau-
atwistedorcurvedtubeofnon-circularcrosssectionthattends
tionary statements are given in Section 7.
to be straightened by the application of internal pressure
2. Referenced Documents (ANSI, ISA-S37.1).
3.2.7 calibration—test during which known values of mea-
2.1 ANSI/ISA Standards:
surand are applied to the transducer and corresponding output
S37.1 (R1982)ElectricalTransducerNomenclatureandTer-
readings are recorded under specified conditions (ANSI, ISA-
minology
S37.1).
S37.3 (R1982) Specifications and Tests For Strain Gage
3.2.8 calibration curve—graphical representation of the
Pressure Transducers
calibration record (ANSI, ISA-S37.1).
S37.6 (R1982) Specifications and Tests For Potentiometric
3.2.9 calibration cycle—application of known values of
Pressure Transducers
measurand, and recording of corresponding output readings,
over the full (or specified portion of the) range of a transducer
in an ascending and descending direction (ANSI, ISA-S37.1).
This practice is under the jurisdiction of ASTM Committee D18 on Soil and
Rock and is the direct responsibility of Subcommittee D18.95 on Information
3.2.10 calibration record—record (for example, table or
Retrieval and Data Automation.
graph) of the measured relationship of the transducer output to
Current edition approved April 15, 1995. Published June 1995.
the applied measurand over the transducer range (ANSI,
Available from Instrument Society of America, P.O. Box 12277, Research
Triangle Park, NC 27709. ISA-S37.1).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5720–95 (2002)
3.2.11 calibration traceability—relation of a transducer 3.2.31 normal atmospheric pressure—101.325 kPa (14.696
calibration, through a specified step-by-step process, to an lbf/in. ); equivalent to the pressure exerted by the weight of a
instrument or group of instruments calibrated by the National column of mercury 760 mm (29.92 in.) high at 0°C (32°F) at
Institute of Standards and Technology (ANSI, ISA-S37.1). a point on the earth where the acceleration of gravity is 9.8066
2 2
m/s (32.1739 ft/s ).
3.2.12 capsule—pressure-sensingelementconsistingoftwo
3.2.32 operating environmental conditions—environmental
metallic diaphragms joined around their peripheries (ANSI,
ISA-S37.1). conditionsduringexposuretowhichatransducermustperform
in some specified manner (ANSI, ISA-S37.1).
3.2.13 diaphragm—sensing element consisting of a thin,
3.2.33 output—electrical or numerical quantity, produced
usually circular, plate that is deformed by pressure differential
by a transducer or measurement system, that is a function of
applied across the plate (ANSI, ISA-S37.1).
the applied measurand.
3.2.14 differential pressure—difference in pressure between
3.2.34 overload—maximum magnitude of measurand that
two points of measurement (ANSI, ISA-S37.1).
can be applied to a transducer without causing a change in
3.2.15 end points—outputs at the specified upper and lower
performance beyond specified tolerance (ANSI, ISA-S37.1).
limits of the range (ANSI, ISA-S37.1).
3.2.35 piezoelectric—converting a change of measurand
3.2.16 end-point line—straight line between the end points
intoachangeintheelectrostaticchargeorvoltagegeneratedby
(ANSI, ISA-S37.1).
certain materials when mechanically stressed (ANSI, ISA-
3.2.17 end point linearity—linearity referred to the end-
S37.1).
point line (ANSI, ISA-S37.1).
3.2.36 piezoresistance—converting a change of measurand
3.2.18 environmental conditions—specified external condi-
into a change in resistance when mechanically stressed.
tions(shock,vibration,temperature,etc.)towhichatransducer
3.2.37 potentiometric—converting a change of measurand
may be exposed during shipping, storage, handling, and
into a voltage-ratio change by a change in the position of a
operation (ANSI, ISA-S37.1).
moveable contact on a resistance element across which exci-
3.2.19 error—algebraic difference between the indicated
tation is applied (ANSI, ISA-S37.1).
value and the true value of the measurand (ANSI, ISA-S37.1).
3.2.38 range—measurand values, over which a transducer
3.2.20 excitation—external electrical voltage or current, or
is intended to measure, specified by their upper and lower
both, applied to a transducer for its proper operation (ANSI,
limits (ANSI, ISA-S37.1).
ISA-S37.1).
3.2.39 repeatability—ability of a transducer to reproduce
3.2.21 fluid—a substance, such as a liquid or gas, that is
output readings when the same measurand value is applied to
capable of flowing and that changes its shape at a steady rate
it consecutively, under the same conditions, and in the same
when acted upon by a force.
direction (ANSI, ISA-S37.1).
3.2.22 full-scale output—algebraic difference between the
3.2.39.1 Discussion—Repeatability is expressed as the
end points (ANSI, ISA-S37.1).
maximum difference between output readings; it is expressed
3.2.23 gage pressure—pressure measured relative to ambi-
in percent of full-scale output. Two calibration cycles are used
ent pressure (ANSI, ISA-S37.1).
to determine repeatability unless otherwise specified.
3.2.24 hermetically sealed—manufacturing process by
3.2.40 room conditions—ambient environmental condi-
which a device is sealed and rendered airtight.
tions,underthattransducersmustcommonlyoperate,thathave
3.2.25 hysteresis—maximum difference in output, at any
beenestablishedasfollows:(a)temperature:25 610°C(77 6
measurand value within the specified range, when the value is
18°F); (b) relative humidity: 90% or less; and (c) barometric
approached first with increasing and then with decreasing
pressure: 986 10 kPa (29 6 3 in. Hg). Tolerances closer than
measurand (ANSI, ISA-S37.1).
shownabovearefrequentlyspecifiedfortransducercalibration
3.2.25.1 Discussion—Hysteresis is expressed in percent of
and test environments (ANSI, ISA-S37.1).
full-scale output, during any one calibration cycle.
3.2.41 sealed gage pressure—pressure measured relative to
3.2.26 least-squares line—straightlineforwhichthesumof
normal atmospheric pressure that is sealed within the trans-
the squares of the residuals (deviations) is minimized (ANSI,
ducer.
ISA-S37.1).
3.2.42 sensing element—that part of the transducer that
3.2.27 least squares linearity—linearity referred to the
responds directly to the measurand (ANSI, ISA-S37.1).
least-squares line (ANSI, ISA-S37.1).
3.2.43 static calibration—calibration performed under
3.2.28 linearity—closenessofacalibrationcurvetoaspeci-
room conditions and in the absence of any vibration, shock, or
fied straight line (ANSI, ISA-S37.1).
acceleration (unless one of these is the measurand) (ANSI,
3.2.28.1 Discussion—Linearity is expressed as the maxi- ISA-S37.1).
mum deviation of any calibration point from a specified
3.2.44 strain gage—converting a change of measurand into
straight line, during any one calibration cycle. Linearity is
a change in resistance due to strain (ANSI, ISA-S37.1).
expressed in percent of full-scale output.
3.2.45 theoretical output—product of the applied pressure
3.2.29 measurand—physical quantity, property, or condi- or vacuum and the ratio of full-scale output to calibrated
tion that is measured (ANSI, ISA-S37.1). pressure range.
3.2.30 measured fluid—fluid that comes in contact with the 3.2.46 transducer—device that provides a usable output in
sensing element (ANSI, ISA-S37.1). response to a specified measurand (ANSI, ISA-S37.1).
D5720–95 (2002)
3.2.47 transduction element—electrical portion of a trans- measured fluid and a transduction element that modifies the
ducer in which the output originates (ANSI, ISA-S37.1). signal from the sensing element to produce an output. The
3.2.48 warm-up period—period of time, starting with the materials used in the sensing element must be compatible with
application of excitation to the transducer, required to ensure the measured fluid. Some parts of the transducer may be
that the transducer will perform within all specified tolerances hermetically sealed if those parts are sensitive to and may be
(ANSI, ISA-S37.1). exposed to moisture. Pressure connectors must be threaded
with appropriate fittings to attach the transducer to standard
4. Summary of Practice
pipe fittings, or to other appropriate leakproof fittings. The
4.1 Apressure transducer based measurement system (pres- output cable must be securely fastened to the body of the
sure transducer, readout system, power supply, and signal
transducer.Asimpleschematicofagenericpressuretransducer
conditioner), pressure standard, and appropriate controllers, is shown in Fig. 1.
regulators, and valves are connected to pressure or vacuum
6.2.1 Sensing Elements—A wide variety of sensing ele-
sources, or both.
ments are used in pressure transducers. The most common
4.2 Pressure or vacuum is applied in predetermined inter-
elements are diaphragms, capsules, bourdon tubes, and piezo-
valsoverthefullrange(oraspecifiedportionofthefullrange)
electric crystals. The function of the sensing element is to
of the pressure measurement system.
produce a measurable response to applied pressure. The
4.3 Thepressuremeasurementsystemoutputiscomparedat
response may be sensed directly on the element or a separate
each pressure or vacuum interval to the applied pressure or
sensor may be used to detect element response.
vacuum as indicated by the pressure standard.
6.2.2 Diaphragms—Diaphragms are usually plates, disks,
4.4 The error in pressure measurement system output is
or wafers of stainless steel, silicon, crystal, or ceramic that
calculated for each pressure or vacuum interval over the
deflect when subjected to pressure. Deflection of the dia-
calibrated range.
phragm is detected by sensors.
4.5 From error, the accuracy of the pressure measurement
6.2.2.1 Strain-Gaged Diaphragms—Themostcommondia-
system is computed and a determination is made to accept or
phragmdeflectionsensoristhestraingage.Straingagescanbe
reject the pressure measurement system.
bondedtothediaphragmorimbeddedinthediaphragm.Terms
4.6 From a calibration curve, a relationship between system
typically used to describe these sensors are bonded foil strain
output and applied pressure may be determined.
gages, bonded semiconductor strain gages, sputtered thin film
strain gages, diffused semiconductor strain gages, molecularly
5. Significance and Use
diffused strain gages, piezoresistive strain gages, or silicon
5.1 Electronic transducer-based pressure measurement sys-
chips.
tems must be subjected to static calibration under room
6.2.2.2 Mechanically Linked Diaphragms— Mechanically
conditions to ensure reliable conversion from system output to
linked diaphragms use sensors which are physically separate
pressure during use in laboratory or in field applications.
from the diaphragm.Awide variety of sensors are used in this
5.2 Transducer-basedpressuremeasurementsystemsshould
style element. Sensors may include cantilever beams or
be calibrated before initial use and at least quarterly thereafter
bridges, linear displacement transducers (LDT), potentiom-
and after any change in the electronic or mechanical configu-
eters, or vibrating wires. Beams and bridges are typically
ration of a system.
strain-gaged sensors and terms such as semiconductor strain-
5.3 Transducer-basedpressuremeasurementsystemsshould
gage sensing beam and sputtered strain-gage bridge are used
also be recalibrated if a component is dropped; overloaded; if
with these devices. The LVDT, LDT, and potentiometer trans-
ambient test conditions change significantly; or for any other
ducers use a rod or a rod-sweeper assembly attached to a
significant changes in a system.
diaphragmtosensedeflection.Vibratingwiretransducersusea
5.4 Static calibration is not appropriate for transducerbased
tensioned wire that is attached to the diaphragm and deflection
systems used under operating environmental conditions in-
ofthediaphragmcausesachangeinthefrequencyofvibration
volving vibration, shoc
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