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 temper
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