ASTM E644-98
(Test Method)Standard Test Methods for Testing Industrial Resistance Thermometers
Standard Test Methods for Testing Industrial Resistance Thermometers
SCOPE
1.1 These test methods describe the principles, apparatus, and procedures for calibration and testing of resistance thermometers.
1.2 These test methods cover definitions of terms and tests for insulation resistance, interchangeability, calibration, immersion error, pressure effects, thermal response time, vibration effect, mechanical shock, self-heating effect, stability, thermoelectric effect, humidity, and thermal hysteresis.
1.3 This series of tests is not necessarily intended nor recommended to be performed on every thermometer. Not all the tests are appropriate for all types of thermometers. The expected limits of results are given in the test procedures and also tabulated in Appendix X4.
1.4 The test methods, when specified in a procurement document, shall govern the method of testing the resistance thermometer and the accuracy of the tests.
1.5 Thermometer performance specifications, acceptance limits, and sampling methods are not covered in these test methods; they should be specified separately in the procurement document.
1.6 This standard does not purport to address all of the safety problems, 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 6.3.2, 6.3.5, and 8.1.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 644 – 98
Standard Test Methods for
Testing Industrial Resistance Thermometers
This standard is issued under the fixed designation E 644; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope E 563 Practice for Preparation and Use of Freezing Point
Reference Baths
1.1 These test methods describe the principles, apparatus,
E 1137 Specification Industrial Platinum Resistance Ther-
and procedures for calibration and testing of industrial resis-
mometers
tance thermometers.
E 1502 Guide for Use of Freezing–Point Cells for Refer-
1.2 These test methods cover the tests for insulation resis-
ence Temperatures
tance, calibration, immersion error, pressure effects, thermal
E 1750 Guide for Use of Water Triple Point Cells
response time, vibration effect, mechanical shock, self-heating
E 1751 Guide to Temperature Electromotive Force (EMF)
effect, stability, thermoelectric effect, humidity, and thermal
Tables for Non-Letter Designated Thermocouple Combi-
hysteresis.
nations
1.3 These test methods are not necessarily intended for,
2.2 Military Standard:
recommended to be performed on, or appropriate for every
MIL-STD-202 Test Methods for Electronic and Electrical
type of thermometer. The expected repeatability and reproduc-
Component Parts
ibility of the results are tabulated in Appendix X4.
1.4 These test methods, when specified in a procurement
3. Terminology
document, shall govern the method of testing the resistance
3.1 Definitions:
thermometer.
3.1.1 The definitions given in Terminology E 344 shall
1.5 Thermometer performance specifications, acceptance
apply to these test methods.
limits, and sampling methods are not covered in these test
methods; they should be specified separately in the procure-
4. Significance and Use
ment document.
4.1 These test methods provide uniform methods for testing
1.6 This standard does not purport to address all of the
industrial resistance thermometers so that a given tester may
safety concerns, if any, associated with its use. It is the
expect to obtain the same value of a test result from making
responsibility of the user of this standard to establish appro-
successive measurements on the same test article within the
priate safety and health practices and determine the applica-
limits of repeatability given in Appendix X4. Independent
bility of regulatory limitations prior to use. Specific precau-
testers may also expect to obtain the same result from the
tionary statements are given in 6.3.2, 6.3.5, and 8.1.
testing of the same article within the limits of reproducibility
given in Appendix X4.
2. Referenced Documents
4.2 These tests may be used to qualify platinum resistance
2.1 ASTM Standards:
thermometers for use in specific applications to meet a particu-
E 77 Test Method for the Inspection and Verification of
2 lar specification such as Specification E 1137, or to evaluate
Thermometers
relative merits of equivalent test articles supplied by one or
E 230 Temperature-Electromotive Force (EMF) Tables for
2 more manufacturers, or to determine the limits of the applica-
Standardized Thermocouples
tion of a particular design of thermometer.
E 344 Terminology Relating to Thermometry and Hydrom-
2 4.3 The expected repeatability and reproducibility of se-
etry
lected test methods are included in Appendix X4.
4.4 Some non-destructive tests described in these test meth-
ods may be applied to thermometers that can be subsequently
These test methods are under the jurisdiction of ASTM Committee E20 on
Temperature Measurement and are the direct responsibility of Subcommittee E20.03
on Resistance Thermometers.
Current edition approved June 10, 1998. Published February 1999. Originally Discontinued; see 1996 Annual Book of ASTM Standards, Vol 14.03.
published as E 644-78. Last previous edition E 644-91. Available from Superintendent of Documents, U.S. Government Printing
Annual Book of ASTM Standards, Vol 14.03. Office, Washington, DC 20234.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 644
sold or used; other destructive tests may preclude the sale or mometer is subjected to the conditions of any concurrent test
use of the test article because of damage that the test may (calibration, pressure, vibration), (2) during the test, and (3)
produce. immediately after the thermometer has returned to ambient
conditions. All measured values of insulation resistance for
PROCEDURES
each test condition shall exceed the minimum specified value.
5.3.3 Apply the specified measuring voltage between the
5. Insulation Resistance Test
joined connecting wires and the thermometer sheath or be-
5.1 Scope—The insulation resistance between the thermom-
tween circuits that are intended to be isolated. Take measure-
eter element with its connecting wires and its external shield,
ments with normal and reversed polarity and record the lower
case or means for mounting, should be sufficient to prevent
reading. Take the reading within 10 s of voltage application.
significant electrical shunting or ground loop current in the
Since only minimum values of insulation resistance are of
measurement circuit, or any circuit failure if the excitation
concern, measurement accuracy need only be sufficient to
source is grounded. This test assumes that the thermometer has
ensure that the minimum requirement is met. Insulation resis-
a metallic or other electrically conductive sheath or housing.
tance measurements made during vibration require a high
The most probable factors that contribute to insulation failure
speed indicating device, such as an oscilloscope, to detect rapid
are contamination, typically from moisture, and mechanical
transient changes in resistance.
breakdown due to physical damage to the device. Most ceramic
5.4 The repeatability of the measurement’s value is ex-
oxide insulation absorbs moisture. This moisture is expected to
pected to be 65 % and the reproducibility 610 %. See
migrate inside the thermometer, depending upon the tempera-
Appendix X4 for the results of round robin testing used to
ture condition of use, and to cause variations in the insulation
determine the repeatability and reproducibility of this test.
resistance. Test conditions for insulation resistance should
therefore approximate the most severe conditions of probable
6. Thermometer Calibration
use and shall be specified as a minimum at a specific
6.1 Scope—This test method covers recommended ways of
temperature, humidity, pressure and test voltage. It is recom-
calibrating industrial resistance thermometers. Methods com-
mended that insulation resistance be measured using forward
mon to most calibrations will be described, but the test
and reversed polarity on applied dc voltages. The test methods
methods presented do not usually test the thermometer under
customarily applied with the test article at room temperature
the actual conditions of use. The heat transfer conditions can
may also be employed to determine the insulation resistance at
vary widely, depending upon the medium, immersion length,
temperatures up to the rated application temperature for the
rate of flow of the medium, etc. These and other conditions
resistance thermometer. This is intended to be a non-
should be carefully evaluated before installing a thermometer
destructive test.
for calibration or for temperature measurement. A resistance
5.1.1 The insulation resistance, as measured between the
thermometer can be calibrated by using the comparison method
lead wires and case, does not represent the shunt resistance in
or the fixed-point method, or both. The calibration results may
parallel with the sensing element. Therefore, this test should
be used to assess interchangeability, to establish a unique
not be used to estimate temperature measurement errors caused
resistance-temperature relationship for the thermometer under
by inadequate insulation resistance across the sensing element.
test, or to verify conformance to a standard. In calibration tests,
5.2 Apparatus:
care should be taken to minimize thermal shock to the
5.2.1 Because the insulation resistance is to be measured in
thermometer when inserting it into a heated or cooled environ-
conjunction with other tests, the thermometer shall be mounted
ment, or when withdrawing it from a furnace or heated bath.
as required for these tests.
Transitions should be made slowly, preheating or pre-cooling
5.2.2 Any equipment made for the purpose of insulation
the thermometer when possible. This test is intended to be a
resistance testing shall be capable of measuring a resistance of
non-destructive test. However, calibration of a thermometer to
at least 10 gigohms (10 V) at the specified test voltage.
a higher temperature than it has previously experienced may
change it’s calibration at lower temperatures. Resistances taken
NOTE 1—Caution: Some instruments designed for insulation resis-
tance testing are capable of producing lethal voltages (100 volts or greater) at ascending temperatures should be compared with those
at their measuring terminals. Such instruments should have warning labels
taken at descending temperatures to detect any change in the
and used only by supervised and well trained personnel.
thermometer’s characteristics (see Section 16, Thermal Hys-
5.3 Measurement Procedure: teresis).
5.3.1 Make check measurements on a reference resistor of 6.2 Calibration Methods:
10 gigohms (10 V). Check the measurement instrument to6 6.2.1 Comparison Method—This method consists of mea-
5 % at the required minimum insulation resistance using a suring the resistance of the test thermometer in an isothermal
certified reference resistor. These results should accompany the medium, the temperature of which is determined by a cali-
test report on the platinum resistance thermometer (PRT). For brated reference thermometer. The reference thermometer may
example: When testing a PRT with a specified 100 megohm be a thermocouple, a liquid-in-glass thermometer, a resistance
(10 V) minimum insulation resistance, the meter should be thermometer, or another thermometer of sufficient accuracy
tested with a resistor that has a certified resistance of 100 that has been calibrated by an approved method.
megohms 65%. 6.2.2 Fixed-Point Method—This method consists of mea-
5.3.2 Make insulation resistance measurements between the suring the resistance of the thermometer at the temperature
connecting wires and the shield or case (1) before the ther- defined by the equilibrium state between different phases of a
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 644
pure substance or a mixture of pure substances. Each fixed at the operating temperatures. To test the stability of the bath,
point provides a calibration of the test thermometer at only one insert a reference thermometer into the working space of the
temperature defined by suitable equilibrium phases. The tem- bath and record the temperature as a function of time. The
perature is an intrinsic property of a properly specified equi- variations of the readings indicate the limit of stability of the
librium state of a substance, such as the freezing point at 1 atm. bath. To test the temperature uniformity of the bath, while
The temperature of some fixed-point devices can be repeated to keeping the position of the first reference thermometer fixed in
60.1 m°C or better. the working space of the bath, insert a second reference
6.3 Apparatus and Procedure: thermometer into various positions in the bath and determine
6.3.1 Ice-Point Bath— The most widely used and simplest the temperature relative to that of the first reference thermom-
fixed point is the ice-point. The ice point (0°C) may be realized eter. The variations indicate the degree of temperature unifor-
with an error of less than 0.01°C if properly prepared and used. mity of the bath. A copper, aluminum, or other compatible
Significantly greater errors may be realized if certain condi- metallic block immersed completely and suspended in the bath
tions exist. Users of this test method are referred to Practice fluid can be more stable and uniform in temperature than the
E 563 which contains a more detailed discussion as to the bath. Such an arrangement with wells for thermometers in the
proper preparation and use of ice point baths. block are suitable for calibrating thermometers. To determine
6.3.2 Freezing Points— In addition to the ice-point bath, the the qualification of the block for the work, follow the proce-
freezing-point temperature of various substances can be used dure described above for fluid baths. The calibration procedure
as fixed points. The metal freezing point materials identified in can be made convenient by controlling the bath temperature
Guide E 1502 are those most commonly employed. using a standard thermometer or with a working thermometer
6.3.3 Triple Point of Water—The triple point of water is a that has been calibrated at the various control points in terms of
commonly used thermometric fixed point used for calibrating a standard thermometer.
thermometers. To accurately realize the triple point of water, a
NOTE 2—Caution: Fluids may be easily ignited above their flash
triple point of water cell is used. This cell must be prepared and
points. Fluids above 100°C may erupt violently if water or wet objects are
handled in a specific manner. The user is directed to Guide
placed in them. Care should be taken when handling corrosive, toxic, or
E 1750 for the preparation and use of water triple point cells.
hazardous liquids and vapors.
6.3.4 Fluid Baths— Control the temperature of fluid baths
6.3.4.1 Water Baths— Water baths are satisfactory in the
by adjusting the amount of heating or cooling while agitating
temperature range between 0 and 100°C (see Test Method
the bath fluid. Determine the amount of heating or cooling by
E 77). Some baths are available that combine the basic ideas
the indication of a sensitive thermometer in the bath. Table 1
shown in Test Method E 77 with pumps so that the bath fluid
lists some of the common bath media and their useful ranges of
may be circulated to heat or cool an external bath. Many
operating temperatures. The bath medium mu
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.