ASTM E644-11(2019)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E644 − 11 (Reapproved 2019)
Standard Test Methods for
Testing Industrial Resistance Thermometers
This standard is issued under the fixed designation E644; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 These test methods cover the principles, apparatus, and
E1Specification for ASTM Liquid-in-Glass Thermometers
procedures for calibration and testing of industrial resistance
E77Test Method for Inspection and Verification of Ther-
thermometers.
mometers
1.2 These test methods cover the tests for insulation
E230/E230MSpecification for Temperature-Electromotive
resistance, calibration, immersion error, pressure effects, ther-
Force (emf) Tables for Standardized Thermocouples
mal response time, vibration effect, mechanical shock, self-
E344Terminology Relating to Thermometry and Hydrom-
heating effect, stability, thermoelectric effect, humidity, ther-
etry
mal hysteresis, thermal shock, and end seal integrity.
E563Practice for Preparation and Use of an Ice-Point Bath
as a Reference Temperature
1.3 These test methods are not necessarily intended for,
E1137/E1137MSpecification for Industrial Platinum Resis-
recommended to be performed on, or appropriate for every
tance Thermometers
type of thermometer.The expected repeatability and reproduc-
E1502Guide for Use of Fixed-Point Cells for Reference
ibility of the results are tabulated in Appendix X4.
Temperatures
E1750Guide for Use of Water Triple Point Cells
1.4 These test methods, when specified in a procurement
E1751/E1751MGuideforTemperatureElectromotiveForce
document, shall govern the method of testing the resistance
(emf) Tables for Non-Letter Designated Thermocouple
thermometer.
Combinations
1.5 Thermometer performance specifications, acceptance
E2251Specification for Liquid-in-Glass ASTM Thermom-
limits, and sampling methods are not covered in these test
eters with Low-Hazard Precision Liquids
methods; they should be specified separately in the procure- 3
2.2 Military Standard:
ment document.
MIL-STD-202Test Methods for Electronic and Electrical
Component Parts
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions of Terms Specific to This Standard:
priate safety, health, and environmental practices and deter-
3.1.1 ThedefinitionsgiveninTerminologyE344shallapply
mine the applicability of regulatory limitations prior to use.
to these test methods.
Specific precautionary statements are given in 5, 6, 8, 16, and
3.1.2 bath gradient error, n—the error caused by tempera-
ture differences in the working space of the bath. (The bath or
1.7 This international standard was developed in accor-
temperatureequalizingblocksshouldbeexploredtodetermine
dance with internationally recognized principles on standard-
the work areas in which the temperature gradients are insig-
ization established in the Decision on Principles for the
nificant.)
Development of International Standards, Guides and Recom-
3.1.3 connecting wire error, n—the error caused by uncom-
mendations issued by the World Trade Organization Technical
pensated connecting wire resistance. (Although the connecting
Barriers to Trade (TBT) Committee.
wire is part of the measurement circuit, most of it is not at the
1 2
These test methods are under the jurisdiction of ASTM Committee E20 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
TemperatureMeasurementandarethedirectresponsibilityofSubcommitteeE20.03 contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
on Resistance Thermometers. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Nov. 1, 2019. Published November 2019. Originally the ASTM website.
approved in 1978. Last previous edition approved in 2011 as E644–11. DOI: Available from Superintendent of Documents, U.S. Government Printing
10.1520/E0644-11R19. Office, Washington, DC 20234.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E644 − 11 (2019)
temperature that is being determined. Thermometers are avail- PROCEDURES
able in two-, three-, and four-wire configurations. There is no
5. Insulation Resistance Test
satisfactory way to compensate for the wire resistance in the
measurement with a two-wire thermometer although the wire
5.1 Scope—Theinsulationresistancebetweenthethermom-
resistance can be compensated for in three and four-wire
eter element with its connecting wires and its external shield,
thermometers.) case or means for mounting, should be sufficient to prevent
significant electrical shunting or ground loop current in the
3.1.4 immersion error, n—an error caused by the heat
measurement circuit, or any circuit failure if the excitation
conduction or radiation, or both, between the resistance ther-
sourceisgrounded.Thistestassumesthatthethermometerhas
mometerelementandtheenvironmentexternaltothemeasure-
a metallic or other electrically conductive sheath or housing.
ment system, because of insufficient immersion length and
The most probable factors that contribute to insulation failure
thermal contact of the thermometer with the medium under
are contamination, typically from moisture, and mechanical
measurement.
breakdownduetophysicaldamagetothedevice.Mostceramic
3.1.5 interchangeability, n—the extent to which the ther-
oxideinsulationabsorbsmoisture.Thismoistureisexpectedto
mometer matches a resistance-temperature relationship. (The
migrate inside the thermometer, depending upon the tempera-
verification of interchangeability can be accomplished only by ture condition of use, and to cause variations in the insulation
calibration. The deviations at the temperature limits and the
resistance. Test conditions for insulation resistance should
maximum deviation from the established resistance- therefore approximate the most severe conditions of probable
temperature relationship shall be specified.)
use and shall be specified as a minimum at a specific
temperature, humidity, pressure and test voltage. It is recom-
3.1.6 self-heating, n—the increase in the temperature of the
mended that insulation resistance be measured using forward
thermometerelementcausedbytheelectricpowerdissipatedin
and reversed polarity on applied dc voltages.The test methods
the element, the magnitude depending upon the thermometer
customarily applied with the test article at room temperature
current and heat conduction from the thermometer element to
may also be employed to determine the insulation resistance at
the surrounding medium.
temperatures up to the rated application temperature for the
3.1.7 self-heating error, n—the error caused by variations
resistance thermometer. This is intended to be a non-
from the calibration conditions in the self-heating of the
destructive test.
thermometer element at a given current, arising from the
5.1.1 The insulation resistance, as measured between the
variations in the heat conduction from the thermometer to the
lead wires and case, does not represent the shunt resistance in
surrounding medium.
parallel with the sensing element. Therefore, this test should
notbeusedtoestimatetemperaturemeasurementerrorscaused
3.1.8 thermoelectric effect error, n—the error caused by a
by inadequate insulation resistance across the sensing element.
thermalemfinthemeasurementcircuitasaresultofdissimilar
5.2 Apparatus:
metals and temperature gradients in the circuit.
5.2.1 Because the insulation resistance is to be measured in
conjunctionwithothertests,thethermometershallbemounted
4. Significance and Use
as required for these tests.
4.1 These test methods provide uniform methods for testing
5.2.2 Any equipment made for the purpose of insulation
industrial resistance thermometers so that a given tester may
resistance testing shall be capable of measuring a resistance of
expect to obtain the same value of a test result from making 10
at least 10 gigohms (10 Ω) at the specified test voltage.
successive measurements on the same test article within the
(Warning—Some instruments designed for insulation resis-
limits of repeatability given in Appendix X4. Independent
tancetestingarecapableofproducinglethalvoltages(100Vor
testers may also expect to obtain the same result from the
greater) at their measuring terminals. Such instruments should
testing of the same article within the limits of reproducibility
have warning labels and used only by supervised and well
given in Appendix X4.
trained personnel.)
4.2 These tests may be used to qualify platinum resistance
5.3 Measurement Procedure:
thermometersforuseinspecificapplicationstomeetaparticu-
5.3.1 Make check measurements on a reference resistor of
lar specification such as Specification E1137/E1137M,orto
10 gigohms (10 Ω). Check the measurement instrument to
evaluate relative merits of equivalent test articles supplied by
65% at the required minimum insulation resistance using a
one or more manufacturers, or to determine the limits of the
certifiedreferenceresistor.Theseresultsshouldaccompanythe
application of a particular design of thermometer.
test report on the platinum resistance thermometer (PRT). For
example: When testing a PRT with a specified 100 megohm
4.3 The expected repeatability and reproducibility of se-
(10 Ω) minimum insulation resistance, the meter should be
lected test methods are included in Appendix X4.
tested with a resistor that has a certified resistance of 100
4.4 Some non-destructive tests described in these test meth- megohms 65%.
ods may be applied to thermometers that can be subsequently
5.3.2 Make insulation resistance measurements between the
sold or used; other destructive tests may preclude the sale or connecting wires and the shield or case, (1) before the
use of the test article because of damage that the test may thermometer is subjected to the conditions of any concurrent
produce. test (calibration, pressure, vibration), (2) during the test, and
E644 − 11 (2019)
(3) immediately after the thermometer has returned to ambient pointprovidesacalibrationofthetestthermometeratonlyone
conditions. All measured values of insulation resistance for temperature defined by suitable equilibrium phases. The tem-
each test condition shall exceed the minimum specified value. perature is an intrinsic property of a properly specified equi-
5.3.3 Apply the specified measuring voltage between the libriumstateofasubstance,suchasthefreezingpointat1atm.
joined connecting wires and the thermometer sheath or be- Thetemperatureofsomefixed-pointdevicescanberepeatedto
tween circuits that are intended to be isolated. Take measure- 60.1 m°C or better.
ments with normal and reversed polarity and record the lower
6.3 Apparatus and Procedure:
reading. Take the reading within 10 s of voltage application.
6.3.1 Ice-Point Bath—The most widely used and simplest
Since only minimum values of insulation resistance are of
fixed point is the ice-point. The ice point (0 °C) may be
concern, measurement accuracy need only be sufficient to
realized with an error of less than 0.01 °C if properly prepared
ensure that the minimum requirement is met. Insulation resis-
andused.Significantlygreatererrorsmayberealizedifcertain
tance measurements made during vibration require a high
conditions exist. Users of this test method are referred to
speedindicatingdevice,suchasanoscilloscope,todetectrapid
Practice E563 which contains a more detailed discussion as to
transient changes in resistance.
the proper preparation and use of ice point baths.
5.4 The repeatability of the measurement’s value is ex- 6.3.2 Freezing Points—In addition to the ice-point bath, the
pected to be 65% and the reproducibility 610%. See freezing-point temperature of various substances can be used
Appendix X4 for the results of round robin testing used to as fixed points.The metal freezing point materials identified in
determine the repeatability and reproducibility of this test. Guide E1502 are those most commonly employed.
6.3.3 Triple Point of Water—The triple point of water is a
6. Thermometer Calibration
commonly used thermometric fixed point used for calibrating
thermometers. To accurately realize the triple point of water, a
6.1 Scope—This test method covers recommended ways of
triplepointofwatercellisused.Thiscellmustbepreparedand
calibrating industrial resistance thermometers. Methods com-
handled in a specific manner. The user is directed to Guide
mon to most calibrations will be described, but the test
E1750 for the preparation and use of water triple point cells.
methods presented do not usually test the thermometer under
6.3.4 Fluid Baths— Control the temperature of fluid baths
the actual conditions of use. The heat transfer conditions can
by adjusting the amount of heating or cooling while agitating
vary widely, depending upon the medium, immersion length,
the bath fluid. Determine the amount of heating or cooling by
rate of flow of the medium, etc. These and other conditions
the indication of a sensitive thermometer in the bath. Table 1
should be carefully evaluated before installing a thermometer
listssomeofthecommonbathmediaandtheirusefulrangesof
for calibration or for temperature measurement. A resistance
operating temperatures. The bath medium must be chemically
thermometercanbecalibratedbyusingthecomparisonmethod
stable at the operating temperatures and be inert to the bath
or the fixed-point method, or both.The calibration results may
container and the thermometer material. The bath temperature
be used to assess interchangeability, to establish a unique
must be stable with time and uniform over the working space
resistance-temperature relationship for the thermometer under
at the operating temperatures. To test the stability of the bath,
test,ortoverifyconformancetoastandard.Incalibrationtests,
insert a reference thermometer into the working space of the
care should be taken to minimize thermal shock to the
bath and record the temperature as a function of time. The
thermometer when inserting it into a heated or cooled
variations of the readings indicate the limit of stability of the
environment, or when withdrawing it from a furnace or heated
bath. To test the temperature uniformity of the bath, while
bath. Transitions should be made slowly, preheating or pre-
keeping the position of the first reference thermometer fixed in
coolingthethermometerwhenpossible.Thistestisintendedto
the working space of the bath, insert a second reference
be a non-destructive test. However, calibration of a thermom-
thermometer into various positions in the bath and determine
eter to a higher temperature than it has previously experienced
the temperature relative to that of the first reference thermom-
may change it’s calibration at lower temperatures. Resistances
eter. The variations indicate the degree of temperature unifor-
taken at ascending temperatures should be compared with
mity of the bath. A copper, aluminum, or other compatible
thosetakenatdescendingtemperaturestodetectanychangein
the thermometer’s characteristics (see Section 16, Thermal
TABLE 1 Fluid Bath Media and Typical Operating Temperature
Hysteresis).
Range
6.2 Calibration Methods:
Media Temperature Range, °C
6.2.1 Comparison Method—This method consists of mea- Halogen –150 to –70
(CH Comp. Mixtures)
suring the resistance of the test thermometer in an isothermal
A
Silicone Oils –100 to 315
medium, the temperature of which is determined by a cali- A
Light Mineral Oils –75 to 200
Water 0 to 100
brated reference thermometer.The reference thermometer may
A
DryFluids 75to850
be a thermocouple, a liquid-in-glass thermometer, a resistance
(Fluidized Particle Bed)
A ,B
thermometer, or another thermometer of sufficient accuracy
Molten Salts 200 to 620
A
Liquid Tin 315 to 540
that has been calibrated by an approved method.
A
6.2.2 Fixed-Point Method—This method consists of mea- Fluids above 100 °C may react violently if water or a wet object is immersed into
them.
suring the resistance of the thermometer at the temperature
B
Some freshly prepared salt baths may require removal of corrosive components.
defined by the equilibrium state between different phases of a
Some salts will etch glass.
pure substance or a mixture of pure substances. Each fixed
E644 − 11 (2019)
metallicblockimmersedcompletelyandsuspendedinthebath
fluid can be more stable and uniform in temperature than the
bath. Such an arrangement with wells for thermometers in the
block are suitable for calibrating thermometers. To determine
the qualification of the block for the work, follow the proce-
duredescribedaboveforfluidbaths.Thecalibrationprocedure
can be made convenient by controlling the bath temperature
using a standard thermometer or with a working thermometer
thathasbeencalibratedatthevariouscontrolpointsintermsof
a standard thermometer. (Warning—Fluids may be easily
ignitedabovetheirflashpoints.Fluidsabove100°Cmayerupt
violently if water or wet objects are placed in them. Care
should be taken when handling corrosive, toxic, or hazardous
liquids and vapors.)
6.3.4.1 Water Baths—Water baths are satisfactory in the
temperature range between 0 and 100 °C (see Test Method
E77). Some baths are available that combine the basic ideas
shown in Test Method E77 with pumps so that the bath fluid
may be circulated to heat or cool an external bath. Many
commercially available baths have self-contained heaters,
cooling coils, stirrers, and temperature controllers.
6.3.4.2 Salt Baths—In the range of temperatures between
200 and 620 °C, salt baths are useful. A salt bath and
procedures for its use are described in Test Method E77. Salt
baths for calibrating thermometers are commercially available.
Some salt baths, designed primarily for heat treating metals
FIG. 1 Typical Vapor Bath
and other materials, may be useful for calibrating thermom-
eters. (Warning—Molten salt will react violently if water
comes in contact with it (see the warning statement in 6.3.4).
6.3.5 Dry Block Calibrations—At high temperatures a fur-
While some salts will etch glass, some freshly prepared salt
nace fitted with a large metal block, can be used in calibration.
baths may also require removal of corrosive components.)
Insert the test thermometer and the reference thermometer into
6.3.4.3 Refrigerated Baths—In the range of temperatures
wells in the block and make comparison calibrations. The
below ambient, baths may be cooled by mechanical refrigera-
method is particularly useful above 300 °C and is limited
tion or by cryogens.The choice of fluids for such baths will be
primarily by the temperature uniformity of the block and
influenced by the temperature range. Means should be incor-
conduction error of the test thermometer. Make sure that the
porated in the experimental design to avoid moisture conden-
thermometer wells are both sufficiently deep and close fitting
sation. There is some discussion on refrigerated bath fluids in
with the thermometers to make the conduction loss error
Test Method E77.(Warning—Some of these fluids are flam-
negligible.
mable at room temperature and some give off poisonous
6.4 Reference Thermometers—Reference thermometers
vapors. They must be handled with care and operating in a
must have a known calibration, a stated uncertainty over the
hooded area is recommended.)
temperature range, and must be suitable for the intended
6.3.4.4 VaporBaths—Avaporbathmaybeusedbelow0°C.
calibration application.
(While the method is usable to temperatures in excess of 100
6.4.1 Standard Platinum Resistance Thermometer (SPRT)—
°C, it is more convenient to employ other types of baths.) Fig.
SPRTs are the most accurate reference thermometers and are
1 shows a typical vapor bath. An isothermal block houses the
used in defining the ITS-90 from approximately -259 to
test thermometer and the standard thermometer. An electric
962°C.TheSPRTsensingelementismadefrompureplatinum
heater is wound on the surface of the block. Vaporizing a
and supported essentially strain-free. Because of the delicate
cryogen(usuallyliquidnitrogen)willenablethevaporstocool
construction,theSPRTiseasilydamagedbymechanicalshock
theblock.Applyafewmilliwattsofpowertotheblocktoraise
and must be handled carefully to retain its calibration.
its temperature to the desired value for the calibration. Usually
6.4.2 Secondary Reference Thermometers—Secondary Ref-
an electronic controller is used to stabilize the temperature of
erence Thermometers are specially manufactured industrial
the block. A stable power supply is required to provide a
platinum resistance thermometers that are subjected to special
constant boil-off rate of the cryogen. Depending on the size of
heat treating and calibration to establish their measurement
the block, the number of test thermometers, and the heat
conduction down the supports or connecting wires, radiation
and convection baffles may be required in the bath to maintain 4
Preston-Thomas, H., Metrologia 27, 3 (1990); Mangum, B. W., Journal of
the temperature of the block constant. Research NIST 95, 1990, p. 69.
E644 − 11 (2019)
uncertainty. These thermometers contain sensing element con- measurement instrumentation must be consistent with the
structions that are not as easily affected by handling as are specified temperature measurement uncertainty. This test is
SPRT’s. However, they also typically have higher measure- intended to be a non-destructive test.
ment uncertainties and narrower usage ranges than SPRT’s. 7.1.1 This test may not be applicable to thermometers with
6.4.3 Reference Thermocouples—Thermocouples listed in immersion lengths less than 51 mm (2 in).
TablesE230/E230MandGuideE1751/E1751Mthathavebeen
7.2 Apparatus:
calibrated on the ITS-90 may also be used as reference
7.2.1 Ice-Point Bath—See 6.3.1.
thermometers. Noble metal thermocouples are the most com-
7.2.2 Measurement Instrument—See 6.5.
monly used reference thermocouples due to their stability and
7.3 Procedure:
large usable temperature range.
7.3.1 Insert the test PRT into the ice-point bath until no
6.4.4 Reference Liquid-In-Glass Thermometers—AnASTM
further insertion causes significant change in output. This
precision thermometer as found in Specifications E1 or E2251
insertion may include the mounting flange, threads, etc. The
or a liquid-in-glass thermometers of similar accuracy may be
purpose of this requirement is to maximize heat transfer
used. The reference thermometer shall be calibrated per Test
betweentheupperpartofthethermometerandthebathsothat
Method E77.
the stem conduction error is negligible.
6.5 Measurement Instruments—Several types of instru-
7.3.2 Use normal operating current (typically 1 mA) if
mentscanbeused.Theyincludeanaloganddigitalinstruments
specified. Otherwise, use an operating current which results in
and those that use resistance bridges, voltage comparison, or
no significant self-heating, Record the resistance of the test
current and potential methods.
PRT when equilibrium is reached.
6.5.1 AC and DC Bridges and Digital Multimeters—AC
7.3.3 Slowly withdraw the thermometer from the bath in
bridges, DC bridges and digital multimeters are becoming
smallincrementsuntiltheresistanceincreasesequivalenttothe
increasingly common due to their ease of use and their
specified measured uncertainty. Pause long enough after each
compatibility with computerized data acquisition systems.
incremental change in immersion depth to assure thermal
These instruments typically provide the user the option of a
equilibrium is reached.
digital display which can be set to provide readings in ohms,
NOTE 1—This depth of immersion in the bath as measured from the tip
millivolts or temperature. The operating current of these
of the sensor to the surface of the liquid level is the minimum immersion
instruments must be low enough that any self-heating of the
length for the test PRT.
thermometer is minimized (see Specification E1137/E1137M
7.4 Repeatability and Reproducibility (R & R)—For ther-
and Section 12).
mometers with specified measurement uncertainties of 0.01 to
6.5.2 Bridges—Thermometer resistance can be measured in
0.1 °C, the minimum immersion length test should be repeat-
several bridge configurations. (See Appendix X1 and
able to 65 mm and reproducible to 610 mm. See Appendix
AppendixX2.)Themeasurementaccuracycanbeimprovedby
X4 for the results of round robin testing to determine the
using bridges that compensate for the connecting wire resis-
repeatability and reproducibility of the test.
tance and spurious thermal emf. Bridges are recommended
where high accuracy (0.001%) and ease of operation are
8. Pressure Test
desired.
6.5.3 Potentiometers—The laboratory potentiometer can be
8.1 Scope—This test is intended to determine the suitability
used to measure the resistance of a four-wire resistance
of the resistance thermometer for operation at elevated pres-
thermometer by comparing the voltage drop across the ther-
sures. The resistance thermometer should be tested in a vessel
mometer element with that across a stable resistor of known
that has been completely filled with water. (Warning—Use
value when the same current is flowing through both. The
compressible media only with extreme care because of an
effect of spurious thermal emf should be eliminated by
inherent explosion hazard. The test apparatus must also be
averagingtworeadings,onetakenwithnormalcurrentandone
designedtowithstandhighertestpressuresthanthetestarticle.
with the current reversed.Atypical potentiometric circuit with
This test is intended to be non-destructive, unless the test
current reversing switches is described in Appendix X3.
article fails. If the test article passes the pressure test, it may
then be used in the process application.)
6.6 Repeatability and Reproducibility (R & R)—TheR&R
of the measurements shall be consistent with the specified
8.2 Apparatus:
calibration uncertainties. See Appendix X4 for the results of
8.2.1 Pressure Vessel—A sketch of a pressure-tight vessel
round robin testing to determine the repeatability and repro-
suitable for the test is shown in Fig. 2. The vessel shall be
ducibility of this test.
consistent with the pressure requirement.
8.2.2 Ice-Point Bath—See 6.3.1.
7. Minimum Immersion Length Test
8.2.3 Measurement Instruments—The bridge,
7.1 Scope—Minimumimmersionlengthshallbedetermined potentiometer, or electronic devices used to measure the
using the procedure described in 7.3. The user must relate this resistance should be similar to those described in 6.5.
test method to the particular thermometer application, that is, 8.2.4 Pressure Source—Ahand-operated hydraulic pump or
the medium, velocity, turbulence of the fluid, etc., in choosing other pumping device may be employed along with an indi-
the design and immersion length of the thermometer. The cating pressure gage. (Warning—Observe all the safety pre-
temperature stability of the test bath and the sensitivity of the cautions applicable for liquid under pressure.)
E644 − 11 (2019)
measurements. Remove the thermometer from the vessel and
examine for deformation or any other effects due to the
hydrostatic pressurization.
8.3.3 Qualification—The differences between the ice point
resistance of the thermometer at the test pressure and the
averageofthetwomeasurementsatatmosphericpressureshall
constitute the resistance thermometer’s pressure stability.
8.4 Repeatability and Reproducibility (R & R)—There is a
high probability that repetition of the pressure test on a
particularthermometer(repeatability)orit’ssubsequenttesting
by another tester (reproducibility) will provide the same
indication of the thermometer’s condition. The differences
(8.3.3) are significant if greater than the icepoint measurement
repeatability (see Table X4.1).
9. Thermal Response-Time Test
9.1 Scope—The thermal response time is the time required
forathermometertoreacttoastepchangeintemperature.The
response time is tested by rapidly transferring the thermometer
fromroomtemperaturetoaheatedbath,usuallywater,flowing
at a known velocity. The thermometer resistance is monitored
during the test to determine the time to reach a specified
fraction of the total temperature change.
9.1.1 The thermal response time is a common thermometer
specification related to the thermal lag error that occurs during
dynamic temperature measurement. This method provides a
commonbaselineforcomparingtheresponsetimesofdifferent
thermometer designs. The response time test may also be used
as a diagnostic tool to verify the internal construction of the
thermometer,specificallythematerialsthatsupportthesensing
element.
9.1.2 This method is applicable for thermometers designed
for direct immersion in liquids. An alternative installation is
available for a limited class of thermometers designed for
surface measurement that have approximately flat profiles and
can be mounted within a diameter less than 20 mm.
FIG. 2 Pressure Test Vessel
9.1.3 The response time determined by this method corre-
spondstoaspecificheattransfercondition.Theresponsetimes
8.2.5 Insulation-Resistance Apparatus—Use the apparatus using other media, flow, or mounting conditions may vary
indicated in Section 5 to measure the insulation resistance.
significantlyfromthisvalue.Therefore,extrapolatingresultsto
actual field conditions is not recommended.
8.3 Procedure:
9.1.4 This method is applicable to measurements of re-
8.3.1 Installation—Mount the resistance thermometer in the
sponse time longer than 1 s using strip chart recorders, but has
pressure vessel (which has previously been filled with water)
beenusedsuccessfullytomeasureshorterresponsetimesusing
suchthatnoleakagewilloccur.Connectthepressuresourceto
digital data acquisition systems.
the vessel and attach the thermometer wires to the resistance
9.1.5 Apractical upper limit of fluid velocity in a water test
measuring instrument. Insert the pressure vessel into the
bath is about 1 m/s. At higher flow rates, fluid separation
ice-point bath and allow the resistance reading to stabilize at
(cavitation) may occur, resulting in significant response time
temperature.
variation.
8.3.2 Measurements—With an appropriate excitation cur-
rent and no hydrostatic pressure applied to the thermometer, 9.2 Apparatus:
allow the output to stabilize. Obtain a resistance measurement 9.2.1 Fluid Bath—A typical bath arrangement is shown in
at the ice point followed by an insulation-resistance test (see Fig. 3.The bath consists of a drum mounted on a vertical shaft
Sections5and6).Pressurizethevesseltowithin 610%ofthe driven by an adjustable speed motor. This provides a known
specifiedvalue.Afterthethermometerreadingsbecomesteady, and adjustable fluid velocity past the thermometer, which is
repeat the ice point resistance determination and the insulation heldinafixedpositioninthebathontheendofapivotedarm.
resistance test with the pressure applied to the thermometer. The arm, in its raised position, allows the thermometer to be
Reduce the vessel pressure to atmospheric pressure and repeat stabilized near room temperature before being plunged rapidly
the ice point and room temperature insulation resistance into the bath.Aswitch activated by the arm signals the start of
E644 − 11 (2019)
FIG. 4 Alternative Installation for Surface Mount Thermometers
FIG. 3 Typical Bath Arrangement
the timing period at the instant the thermometer enters the
9.3.2.2 Mount the thermometer to a piece of foil tape cut
fluid. Alternatively, in the case of a water bath, the electrical
approximatelytwotimesthepipediameter.Thetapeshallhave
contact between the metal sheath of the probe and the water
a soft aluminum backing, nominal 0.07 mm (0.003 in) thick,
can be sensed to initiate the timing period. The water bath
with acrylic adhesive in accordance with Federal Specification
temperature can be controlled with infrared lamps directed at
L-T-80 or equivalent. Carefully rub the tape to the entire
the inner walls of the water chamber; however, other heating
mounting surface of the thermometer to remove all air and
methods are possible.
wrinkles in the tape.
9.2.2 Measurement Instruments—Instruments that are com-
9.3.2.3 String the thermometer lead wires through the pipe
patible with the thermometer and that have an output suitable
and attach the tape and mounted thermometer to the cut end of
for a data recorder can be used to monitor the thermometer
the pipe. Position the tape so the mounted thermometer is
resistance. The excitation current to the thermometer must be
approximately centered in the pipe and not less than 1 mm
limited to avoid appreciable self-heating (see Section 12).
from the inner wall of the pipe. Trim excess tape and rub the
Power dissipation less than 3 mW is acceptable for most
remainingtapearoundtheendofthepipetoformawatertight
thermometers.
seal. The tape end closure shall be approximately flat and
9.2.3 Recorder—Astrip chart, x-y or oscilloscope recorder,
conform to the pipe contour.
or digital data acquisition system shall be used to record the
9.3.2.4 Test the thermometer assembly as a sheathed ther-
thermometer output versus time. The frequency response or
mometer. Perform the test within1hof mounting to minimize
sample rate shall not exceed the equivalent of ⁄20 the 63.2%
the influence of the adhesive bond relaxing.
response time of the thermometer under test.
9.3.3 Equipment Preparation—Stabilize the bath at the
9.3 Procedure: specified temperature. Rotate the bath to provide the specified
9.3.1 Thermometer Installation—Mount the thermometer in fluid velocity (for water, the fluid velocity is typically 1 m/s).
asuitablefixtureonthepivotedarmsothethermometercanbe Adjustthespanandzerothecontrolsoftherecordertoprovide
immersedtoatleastitsminimumimmersionlengthinthebath a convenient chart width, using resistors in place of the
(see Section 7). thermometer to simulate both ambient and bath temperatures.
9.3.2 Alternative Installation for Surface Mount The temperature corresponding to the specified percentage of
Thermometers—Thermometers designed for surface tempera- the temperature difference may be simulated in a like manner,
turemeasurementmaybemountedtofoiltapeasshowninFig. and a line corresponding to this temperature drawn on the
4. The response times obtained using this installation are recorder chart.
slowerthandirectimmersionbutbetterrepresentasurfaceheat 9.3.4 Measurement—Stabilize the thermometer in its raised
transfer condition. position,atambienttemperature,thenrapidlyimmerseitinthe
9.3.2.1 Prepare the sample holder from low conductivity fluidbath.Thetimesweepisautomaticallystartedattheinstant
plastic pipe with an outside diameter less than 30 mm. For thethermometerentersthebath,andtherecordingiscontinued
1 3
example, standard PVC ⁄2 in. or ⁄4 in. Schedule 40 pipe meets until the thermometer has reached the specified change in
this requirement. temperature. Make at least three measurements on each
E644 − 11 (2019)
thermometer, and verify the response times agree within the (2)All evaluation sweeps shall cover the entire frequency
specified repeatability. spectrum specified.
(3)Sweeprateofthefrequencyshallnotexceedoneoctave
9.4 Repeatability and Reproducibility (R & R)—TheR&R
per minute, so that all resonances can fully respond.
of 63.2% thermal response times, for step changes from the
(4)A sufficient number of accelerometers or multiple
ambient temperatures to baths at 70 °C, are expected to be
sweeps shall be utilized so that information is obtained at the
65%and 610%,respectively,withthermometersofresponse
specimen mounting area in all three major orthogonal axes.
times of 1 to 30 s (see Appendix X4 for the results of round
Continuous records shall be made for each sweep. Resonant
robin testing to determine the repeatability and reproducibility
peak levels and frequencies shall be measured.
of this test).
(5)Acontrolaccelerometershallbeplacedonthefixtureas
10. Vibration Test close to the test specimen mounting point as possible.
10.2.3.2 Vibrationfixturetestrunsshallbemadeasfollows:
10.1 Scope—In industrial applications, resistance thermom-
(1)Using the conditions described above (10.2.1, 10.2.2,
eters are subject to significant vibratory motion. In this test the
and 10.2.3) and the test levels and frequencies specified by the
performance characteristics of thermometers are examined
user, perform a vibration sweep on each of the three major
both during and after being subjected to specified limits of
orthogonal axes of the fixture.
vibration.Thefollowingmethoddescribessine-wavevibration
(2)Make a continuous record of the monitoring acceler-
equipment, fixtures, fixture evaluation, procedures and accep-
ometer output.
tance criteria. The actual test duration, vibration levels, fre-
(3)Note resonant frequencies and amplitudes.
quency spectrum and performance requirements are to be
specified by the user. All tests and evaluations shall be (4)Relocate monitoring accelerometers as necessary to
completely define the vibration fixture vibration response
performed at a temperature of 25 6 10 °C unless otherwise
specified. This test may affect the characteristics of the test around the specimen mounting plane.
article in a manner not immediately apparent from resistance-
10.2.4 Each vibration fixture, when evaluated according to
temperature measurements made after the test. If the test
the above requirements, shall meet the following minimum
articles are to be sold or used after vibration test, additional
standards:
qualification tests may be needed to observe possible intermit-
10.2.4.1 Sinusoidal transmissibility shall be such that the
tent temperature indication.
vibration input in the axis of applied vibration of the specimen
10.2 Apparatus: mountingpointshallbewithin 63dBofthatspecifiedoverthe
10.2.1 Vibration Driver—A driver shall be used that is
entire frequency band, and
capable of producing sinusoidal motion in the acceleration
10.2.4.2 Sinusoidal cross-talk (vibration input in either axis
ranges and frequencies specified. The driver shall have the
orthogonal to the axis of applied vibration at the specimen
following minimal capabilities:
mounting point) shall not exceed the input.
10.2.1.1 Adequate force to drive the vibration fixture and
10.3 Procedure:
the test specimen to the double amplitude (peak-to-peak
displacement) and acceleration (g-level) specified. 10.3.1 Installations:
10.2.1.2 The ability to sweep logarithmically the specified
10.3.1.1 Attach the resistance thermometer to the vibration
frequency spectrum at specified rates (not to exceed 1 octave/
fixture in a manner which simulates as closely as possible the
min).
mounting method to be used in service. The thermometer
10.2.1.3 The ability to control vibration amplitude and
signal cable shall be clamped to the fixture at a point no more
acceleration (g-level) to 610% of the specified level.
than 51 mm (2 in.) from the cable end closure if not secured
10.2.1.4 The ability to control the frequency to 62%.
otherwise.
10.2.2 Vibration Fixtures—Theserequirementsestablishthe
10.3.1.2 Mount a control accelerometer adjacent to the
minimum standards for vibration fixtures. In general the intent
mounting point of the thermometer.
is to provide a fixture which most nearly simulates the test
10.3.1.3 Locate a monitoring accelerometer on the test
article’s conditions of service.
specimen, usually near the resistance thermometer element.
10.2.2.1 Material—Magnesium, aluminum, or other materi-
This location may vary when subsequent testing proves that
als with high internal damping factors.
other portions of the thermometer are more sensitive to
10.2.2.2 Fabrication methods in order of preference:
vibration. Continuously record the output of the monitoring
(1)Cast, then machined to desired dimensions.
accelerometer. Ensure that the monitoring accelerometer has a
(2)Machined from solid stock.
small mass relative to that of the test specimen. On very small
(3)Welded assembly.
thermometers,orduringvibrationtestingathightemperatures,
(4)Bolted assembly.
the use of a monitoring accelerometer may not be possible.
10.2.3 Vibration-Fixture Evaluation :
10.3.2 Resonant Search:
10.2.3.1 The following conditions shall exist for fixture
10.3.2.1 Sweepthroughthespecifiedfrequencyspectrumat
evaluations:
(1)Allfixturesshallbeevaluatedwitheitheraprototypeor aboutapproximatelyonefourththespecifieddoubleamplitude
adummyspecimeninplace.Thisdummyshallbedynamically and acceleration. Sweep rate is to be logarithmic and is not to
equivalent to and mounted in the same way as the specimen. exceed 1 octave/min.
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10.3.2.2 During this sweep, note all resonant frequencies 11. Mechanical Shock Test
where the response (displacement of the resonating thermom-
11.1 Scope—Mechanical shock may occur during shipping
eter divided by the displacement of the vibration fixture) is
andhandlingorasaresultofsurgesinprocessequipment.This
greater than two. Resonances with a response less than two
test simulates the mechanical shock conditions that an indus-
shall be ignored.
trial thermometer is expected to withstand, using commercial
10.3.2.3 In addition to the monitoring accelerometer de-
test equipment capable of producing a shock pulse of repro-
scribed in 10.3.1, resonant frequencies may also be observed
ducible duration and acceleration.This test may be destructive
aurally or visually, with strobe lights, microscopes, etc.
and may affect the characteristics of the test article which
should be qualified after the shock tests for stability during
10.3.2.4 Repeat the resonant search in the remaining two
thermal cycles.
major orthogonal axes.
10.3.2.5 Remove any monitoring accelerometers used. 11.2 Apparatus:
11.2.1 Shock Test Table—A variable-drop-height table, de-
10.3.3 Resonance Dwell:
signed to meet MIL-STD 202 (Method 213B) condition or
10.3.3.1 Select the four most significant resonant frequen-
equal is used to yield a half sine acceleration pulse of known
cies of each axis, if any, noted in 10.3.2. The end usage, such
time duration and peak acceleration. The test carriage is
as known vibration in the actual thermometer field location,
releasedforafreefalldrop,stoppedbyimpactonasteelspring
should be considered.
and arrested on rebound. Additional weights are used to
NOTE2—Theresonantfrequencieschosenmaynotnecessarilybethose compensate for the test article to obtain the required pulse
with the largest resonance responses. Vibration test and product design
duration and peak acceleration. Other methods may also be
personnel may choose other frequencies that may be actually more
used.
destructive to the test specimen. End usage, such as known vibrations, or
11.2.2 Monitoring Equipment—An accelerometer and a
lack of vibrations, in the actual thermometer field locations, should be
triggered dual trace oscilloscope with a frequency response of
considered.
2000 Hz or greater shall be used for calibration of the shock
10.3.3.2 Vibrate at one of the resonant frequencies at the
pulse and for monitoring the test unit. The oscilloscope
level and duration specified by the user.
sensitivityshallbesufficienttoallowdetectionofashockpulse
10.3.3.3 Proceed to one of the remaining resonant frequen-
deviation greater than 10% of the required value.
cies and repeat 10.3.3.2.
11.3 Procedure:
10.3.3.4 Continue until the selected resonance frequencies
11.3.1 The vibration fixture of 10.2.2 less test unit shall be
on all axes have been tested.
installed on the shock machine carriage with additional weight
10.3.4 Cycling Vibration—After the resonance dwell vibra-
addedequaltothatofthetestunitplusweightsforestablishing
tion test described in 10.3.3 is finished, perform the cycling
the desired shock pulse.At least one test drop shall be made to
vibration as follows:
verify acceleration and pulse duration prior to installing the
10.3.4.1 Adjust the vibration equipment to sweep the speci- thermometer. Test acceleration shall be within 610% of
specified g-level and repeatabi
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