ASTM E3186-19
(Guide)Standard Guide for Use and Testing of Dry-Block Temperature Calibrators
Standard Guide for Use and Testing of Dry-Block Temperature Calibrators
SIGNIFICANCE AND USE
5.1 This guide applies to temperature sources with controlled temperature solid blocks. They are known under various names such as dry-well calibrators, dry-block calibrators, and temperature block calibrators. They are typically comprised of solid block materials such as metal or ceramic, a temperature-regulating device, a control sensor, and some built-in indicator of temperature in a portable package. Dry-block calibrators are commonly used for calibration of industrial thermometers. These calibrators are commonly used in either two modes: (1) the direct mode in which the calibrator is used as the calibrated reference, or (2) comparison mode in which the calibrator is an isothermal temperature source for comparing thermometers under test to a separate calibrated reference thermometer. The uncertainty of these calibrations is dependent on which of these two modes is used and a variety of thermal properties of the specific dry-block designs.
5.2 A thermally uniform, stable, and accurate temperature zone for calibration may be achieved with given measurement uncertainty. Various thermal properties of dry-block calibrator blocks have been identified that shall be characterized and/or quantified to determine uncertainty of measurements and care taken during the calibration process to optimize results appropriately. Temperature stability has been long recognized as a variable to be characterized. Others include axial temperature uniformity, radial temperature uniformity, stem conduction, block loading, hysteresis, and controller accuracy. External factors that influence results include ambient temperature, drafts, and power fluctuations. Recognizing and testing these properties will greatly improve calibration results.
SCOPE
1.1 The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard.
1.2 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.3 This guide is intended for use with dry-block temperature calibrators without the use of fluids or thermal contact-enhancing media over a range of -100 °C to 1700 °C.
1.4 In this guide, the essential features of dry-block calibrators used for the purpose of thermometer calibration in either the direct or comparison mode are described. The direct mode is defined as using the dry-block calibrator as a standalone instrument with the control sensor and the calibrator display serving as the reference while the comparison mode uses an external sensor and ancillary measurement system as the reference.
1.5 Measurement practices to optimize the accuracy of a dry-block calibrator to obtain optimum results are proposed in this guide.
1.6 Tests that can be performed to define uncertainty limits and how they may be used in creating uncertainty budgets are proposed in this guide.
1.7 Dry-block calibrator accessories such as built-in reference thermometers, switch testing circuitry, computer communications, or current loops will not be discussed.
1.8 It is advised that liquid-in-glass thermometers not be used in dry-block calibrators, as using liquid-in-glass thermometers with a metal block may cause damage to the readout of the thermometer.
1.9 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.
General Information
- Status
- Published
- Publication Date
- 31-Oct-2019
- Technical Committee
- E20 - Temperature Measurement
- Drafting Committee
- E20.07 - Fundamentals in Thermometry
Relations
- Effective Date
- 01-Dec-2023
- Effective Date
- 01-Nov-2019
- Effective Date
- 01-Sep-2019
- Effective Date
- 01-Apr-2018
- Effective Date
- 01-Nov-2016
- Effective Date
- 01-May-2013
- Effective Date
- 01-May-2012
- Effective Date
- 01-May-2011
- Effective Date
- 01-Nov-2010
- Effective Date
- 01-Nov-2009
- Effective Date
- 15-Nov-2008
- Effective Date
- 01-May-2008
- Effective Date
- 01-Jun-2007
- Effective Date
- 01-Jun-2006
- Effective Date
- 01-May-2006
Overview
ASTM E3186-19 is a standard guide developed by ASTM International for the use and testing of dry-block temperature calibrators. These calibrators, often referred to as dry-well calibrators, dry-block calibrators, or temperature block calibrators, are essential tools in industrial settings for calibrating various types of thermometers without the use of fluids or thermal contact-enhancing media. The guide outlines best practices for using these devices over a wide temperature range from -100 °C to 1700 °C, ensuring accurate, reliable, and reproducible temperature measurements in industries that rely on precise thermal control.
This standard establishes a framework for optimizing calibration accuracy, identifying and quantifying uncertainties, and establishing correct measurement practices. It is intended to support users in achieving improved temperature calibration results and in creating robust uncertainty budgets for their measurements.
Key Topics
- Types of Dry-Block Calibrators: Describes calibrators composed of solid block materials (metal or ceramic) containing temperature-regulating devices, control sensors, and built-in temperature indicators.
- Calibration Modes: Outlines two primary operational modes:
- Direct Mode: The calibrator’s built-in sensor and display serve as the reference.
- Comparison Mode: The calibrator acts as an isothermal temperature source, with a separate calibrated thermometer used as the reference.
- Measurement Uncertainty: Emphasizes factors influencing calibration uncertainty, such as:
- Axial and radial temperature uniformity
- Temperature stability
- Stem conduction
- Block loading effects
- Hysteresis and controller accuracy
- External Influences: Highlights the impact of ambient conditions (temperature, drafts, power fluctuations) on calibration results, underscoring the importance of proper testing and environmental control.
- Unacceptable Practices: Advises against using liquid-in-glass thermometers with dry-block calibrators, as this can damage the thermometer.
Applications
Dry-block temperature calibrators play a vital role in industries where precise thermal measurements are required. Common applications include:
- Industrial Thermometer Calibration: Used for verifying and adjusting resistance temperature detectors (RTDs), thermocouples, and other industrial temperature sensors.
- Quality Assurance in Manufacturing: Ensures that temperature measurement instruments used on production lines are calibrated to maintain product quality.
- Laboratory Calibration Services: Supports laboratories specializing in temperature calibration by providing a solid-state, dry environment free of fluid contamination risk.
- Process Control and Maintenance: Enables routine and on-site calibration of process instrumentation, contributing to equipment reliability and safety.
- Compliance with International Standards: Facilitates adherence to regulatory and industry calibration requirements.
Following the recommended procedures in ASTM E3186-19 helps organizations achieve greater measurement accuracy, minimize downtime due to improper calibration, and reduce the risk of product quality deviations.
Related Standards
Several standards and documents are referenced or complement ASTM E3186-19, including:
- ASTM E344: Terminology Relating to Thermometry and Hydrometry
- ASTM E644: Test Methods for Testing Industrial Resistance Thermometers
- JCGM 100:2008: Guide to the Expression of Uncertainty in Measurement (GUM)
- International Laboratory Accreditation Cooperation (ILAC) documents: For calibration and proficiency testing
- WTO TBT Principles: Ensuring this standard aligns with international best practices
Summary
ASTM E3186-19 provides essential guidelines for the reliable operation and testing of dry-block temperature calibrators, targeting enhanced calibration accuracy and uncertainty verification. By adhering to this standard, organizations across process industries, laboratories, and manufacturing can ensure their temperature measurement systems remain accurate, consistent, and compliant with global standards. The comprehensive approach to calibration modes, uncertainty analysis, and practical limitations makes this standard a key resource for professionals involved in temperature calibration and metrology.
Get Certified
Connect with accredited certification bodies for this standard
BSMI (Bureau of Standards, Metrology and Inspection)
Taiwan's standards and inspection authority.
Sponsored listings
Frequently Asked Questions
ASTM E3186-19 is a guide published by ASTM International. Its full title is "Standard Guide for Use and Testing of Dry-Block Temperature Calibrators". This standard covers: SIGNIFICANCE AND USE 5.1 This guide applies to temperature sources with controlled temperature solid blocks. They are known under various names such as dry-well calibrators, dry-block calibrators, and temperature block calibrators. They are typically comprised of solid block materials such as metal or ceramic, a temperature-regulating device, a control sensor, and some built-in indicator of temperature in a portable package. Dry-block calibrators are commonly used for calibration of industrial thermometers. These calibrators are commonly used in either two modes: (1) the direct mode in which the calibrator is used as the calibrated reference, or (2) comparison mode in which the calibrator is an isothermal temperature source for comparing thermometers under test to a separate calibrated reference thermometer. The uncertainty of these calibrations is dependent on which of these two modes is used and a variety of thermal properties of the specific dry-block designs. 5.2 A thermally uniform, stable, and accurate temperature zone for calibration may be achieved with given measurement uncertainty. Various thermal properties of dry-block calibrator blocks have been identified that shall be characterized and/or quantified to determine uncertainty of measurements and care taken during the calibration process to optimize results appropriately. Temperature stability has been long recognized as a variable to be characterized. Others include axial temperature uniformity, radial temperature uniformity, stem conduction, block loading, hysteresis, and controller accuracy. External factors that influence results include ambient temperature, drafts, and power fluctuations. Recognizing and testing these properties will greatly improve calibration results. SCOPE 1.1 The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard. 1.2 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.3 This guide is intended for use with dry-block temperature calibrators without the use of fluids or thermal contact-enhancing media over a range of -100 °C to 1700 °C. 1.4 In this guide, the essential features of dry-block calibrators used for the purpose of thermometer calibration in either the direct or comparison mode are described. The direct mode is defined as using the dry-block calibrator as a standalone instrument with the control sensor and the calibrator display serving as the reference while the comparison mode uses an external sensor and ancillary measurement system as the reference. 1.5 Measurement practices to optimize the accuracy of a dry-block calibrator to obtain optimum results are proposed in this guide. 1.6 Tests that can be performed to define uncertainty limits and how they may be used in creating uncertainty budgets are proposed in this guide. 1.7 Dry-block calibrator accessories such as built-in reference thermometers, switch testing circuitry, computer communications, or current loops will not be discussed. 1.8 It is advised that liquid-in-glass thermometers not be used in dry-block calibrators, as using liquid-in-glass thermometers with a metal block may cause damage to the readout of the thermometer. 1.9 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.
SIGNIFICANCE AND USE 5.1 This guide applies to temperature sources with controlled temperature solid blocks. They are known under various names such as dry-well calibrators, dry-block calibrators, and temperature block calibrators. They are typically comprised of solid block materials such as metal or ceramic, a temperature-regulating device, a control sensor, and some built-in indicator of temperature in a portable package. Dry-block calibrators are commonly used for calibration of industrial thermometers. These calibrators are commonly used in either two modes: (1) the direct mode in which the calibrator is used as the calibrated reference, or (2) comparison mode in which the calibrator is an isothermal temperature source for comparing thermometers under test to a separate calibrated reference thermometer. The uncertainty of these calibrations is dependent on which of these two modes is used and a variety of thermal properties of the specific dry-block designs. 5.2 A thermally uniform, stable, and accurate temperature zone for calibration may be achieved with given measurement uncertainty. Various thermal properties of dry-block calibrator blocks have been identified that shall be characterized and/or quantified to determine uncertainty of measurements and care taken during the calibration process to optimize results appropriately. Temperature stability has been long recognized as a variable to be characterized. Others include axial temperature uniformity, radial temperature uniformity, stem conduction, block loading, hysteresis, and controller accuracy. External factors that influence results include ambient temperature, drafts, and power fluctuations. Recognizing and testing these properties will greatly improve calibration results. SCOPE 1.1 The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard. 1.2 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.3 This guide is intended for use with dry-block temperature calibrators without the use of fluids or thermal contact-enhancing media over a range of -100 °C to 1700 °C. 1.4 In this guide, the essential features of dry-block calibrators used for the purpose of thermometer calibration in either the direct or comparison mode are described. The direct mode is defined as using the dry-block calibrator as a standalone instrument with the control sensor and the calibrator display serving as the reference while the comparison mode uses an external sensor and ancillary measurement system as the reference. 1.5 Measurement practices to optimize the accuracy of a dry-block calibrator to obtain optimum results are proposed in this guide. 1.6 Tests that can be performed to define uncertainty limits and how they may be used in creating uncertainty budgets are proposed in this guide. 1.7 Dry-block calibrator accessories such as built-in reference thermometers, switch testing circuitry, computer communications, or current loops will not be discussed. 1.8 It is advised that liquid-in-glass thermometers not be used in dry-block calibrators, as using liquid-in-glass thermometers with a metal block may cause damage to the readout of the thermometer. 1.9 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.
ASTM E3186-19 is classified under the following ICS (International Classification for Standards) categories: 17.200.20 - Temperature-measuring instruments. The ICS classification helps identify the subject area and facilitates finding related standards.
ASTM E3186-19 has the following relationships with other standards: It is inter standard links to ASTM E344-23, ASTM E644-11(2019), ASTM E344-19, ASTM E344-18, ASTM E344-16, ASTM E344-13, ASTM E344-12, ASTM E644-11, ASTM E344-10, ASTM E644-09, ASTM E344-08, ASTM E644-08, ASTM E344-07, ASTM E644-06, ASTM E344-06. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
ASTM E3186-19 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
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: E3186 − 19
Standard Guide for
Use and Testing of Dry-Block Temperature Calibrators
This standard is issued under the fixed designation E3186; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1.1 The values stated in SI units are to be regarded as the
Barriers to Trade (TBT) Committee.
standard. No other units of measurement are included in this
standard.
2. Referenced Documents
1.2 This standard does not purport to address all of the
2.1 ASTM Standards:
safety concerns, if any, associated with its use. It is the
E344 Terminology Relating to Thermometry and Hydrom-
responsibility of the user of this standard to establish appro-
etry
priate safety, health, and environmental practices and deter-
E644 Test Methods for Testing Industrial Resistance Ther-
mine the applicability of regulatory limitations prior to use.
mometers
1.3 This guide is intended for use with dry-block tempera-
ture calibrators without the use of fluids or thermal contact-
2.2 Other Documents:
enhancing media over a range of -100 °C to 1700 °C.
JCGM 100:2008 “Evaluation of Measurement Data – Guide
to the Expression of Uncertainty in Measurement”, BIPM,
1.4 In this guide, the essential features of dry-block calibra-
Severes, France, 2008.
tors used for the purpose of thermometer calibration in either
the direct or comparison mode are described. The direct mode
3. Terminology
is defined as using the dry-block calibrator as a standalone
instrument with the control sensor and the calibrator display
3.1 Definitions:
serving as the reference while the comparison mode uses an
3.1.1 The definitions given in Terminology E344 shall be
external sensor and ancillary measurement system as the
considered as applying to the terms used in this guide.
reference.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 axial temperature uniformity, n—temperature differ-
1.5 Measurement practices to optimize the accuracy of a
ences along the immersed length of the thermometer boring
dry-block calibrator to obtain optimum results are proposed in
under test.
this guide.
3.2.1.1 Discussion—Axial temperature uniformity is some-
1.6 Tests that can be performed to define uncertainty limits
times referred to as axial temperature homogeneity.
and how they may be used in creating uncertainty budgets are
3.2.2 block-loading error, n—temperature reading error as a
proposed in this guide.
result of temperature uniformity profile in the block changes
1.7 Dry-block calibrator accessories such as built-in refer-
with the number and size of thermometers in the block.
ence thermometers, switch testing circuitry, computer
3.2.3 boring, n—machined hole in the dry block that can
communications, or current loops will not be discussed.
accommodate various sizes of thermometers and removable
1.8 It is advised that liquid-in-glass thermometers not be
sleeves.
used in dry-block calibrators, as using liquid-in-glass ther-
3.2.3.1 Discussion—These are also referred to as wells.
mometers with a metal block may cause damage to the readout
3.2.4 hysteresis, n—property of a device or instrument
of the thermometer.
whereby it gives different output values in relation to its input
1.9 This international standard was developed in accor-
values depending upon the directional sequence in which the
dance with internationally recognized principles on standard-
thermal input values have been applied.
ization established in the Decision on Principles for the
1 2
This test method is under the jurisdiction of ASTM Committee E20 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Temperature Measurement and is the direct responsibility of Subcommittee E20.07 contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
on Fundamentals in Thermometry. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Nov. 1, 2019. Published December 2019. DOI: the ASTM website.
10.1520/E3186-19. Availible for download from http://www.bipm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3186 − 19
3.2.4.1 Discussion—In practice hysteresis it is typically uncertaintyofthesecalibrationsisdependentonwhichofthese
defined as the absolute value of the difference between the two modes is used and a variety of thermal properties of the
temperatures at the same set point arrived at from the two specific dry-block designs.
directions. Hysteresis is typically largest at the midpoint
5.2 A thermally uniform, stable, and accurate temperature
between maximum and minimum temperature scans.
zone for calibration may be achieved with given measurement
3.2.5 measurement zone, n—zone in the thermal boring
uncertainty. Various thermal properties of dry-block calibrator
corresponding to the location of the sensitive element of the
blocks have been identified that shall be characterized and/or
temperature probe.
quantified to determine uncertainty of measurements and care
3.2.5.1 Discussion—The zone may be long enough to cover
taken during the calibration process to optimize results appro-
a range of typical sensors calibrated or used as reference
priately. Temperature stability has been long recognized as a
thermometers.
variable to be characterized. Others include axial temperature
uniformity, radial temperature uniformity, stem conduction,
3.2.6 radial temperature uniformity, n—temperature differ-
block loading, hysteresis, and controller accuracy. External
ences between borings in the isothermal block or a removable
factors that influence results include ambient temperature,
sleeve that is inserted into the block.
drafts, and power fluctuations. Recognizing and testing these
3.2.6.1 Discussion—Radialtemperatureuniformityissome-
properties will greatly improve calibration results.
times referred to as temperature differences between the
borings.
6. Apparatus
3.2.7 sleeves, n—removable inserts that can be inserted into
6.1 A dry-block calibrator system is a controlled tempera-
dry block borings to improve thermal contact and reduce
ture system typically comprised of solid block materials such
thermal gradient errors.
as metal or ceramic, a temperature-regulating device, a control
3.2.7.1 Discussion—Theymayalsobereferredtoasadapter
sensor, and some built-in indicator of temperature in a portable
sleeves.
package. When used in comparison mode, the system also
3.2.7.2 Discussion—Sleeves may be made of metal or
includes a calibrated reference thermometer.
ceramic.
6.2 An example of a dry-block calibrator is shown in Fig. 1.
3.2.8 stem conduction, n—errors created as a result of heat
This is an example of a system that is operating in the
conducting up the thermometer stem.
comparison mode, as the reference thermometer is providing
3.2.8.1 Discussion—This is largely a property of the ther-
traceability to the SI.The key features shown in this figure will
mometer itself but is influenced by the immersion depth
be discussed throughout this standard. The term UUT refers to
available on the thermometer and the clearance between the
the unit under test.
thermometer and the boring.
3.2.8.2 Discussion—It is also known as conduction error. 6.3 The mechanical design of the dry-block calibrator and
the materials used in the construction determine the limits of
3.2.9 temperature stability, n—temperature variations in the
the working temperature range as well as the overall stability
block as a result of the temperature control function.
and uniformity of the dry-block calibrator system. A poorly
3.2.9.1 Discussion—Stability can also be influenced by
designed calibrator will not provide the desired level of
external changes in ambient temperature, drafts, and line
uncertainty needed for precision calibration. However, the
voltage fluctuations.
performance of a marginal unit may be improved to acceptable
levels of uncertainty by the use of sleeves to improve thermal
4. Summary of Practice
contact and reduce errors due to radiation or convection.
4.1 This guide describes the practices and procedures that
6.4 Thermal insulation at the entrance to the boring may
will enable the user to evaluate various dry-block calibrator
influence both axial uniformity and stem conduction. This is
capabilities, test for and evaluate various uncertainties, and
due to the flow of heat in the block and the stem in the vertical
create a user-defined uncertainty budget.
direction. Axial temperature uniformity is discussed more in
depth in 8.6. Stem conduction is covered in 8.7.
5. Significance and Use
5.1 This guide applies to temperature sources with con- 6.5 Proper fit between the probe under test and the dry-
block borings is essential. Too loose of a fit means that there
trolledtemperaturesolidblocks.Theyareknownundervarious
names such as dry-well calibrators, dry-block calibrators, and will be poor thermal contact between the probe under test and
the dry- block. Too tight of a fit may mean the probe may get
temperature block calibrators. They are typically comprised of
solid block materials such as metal or ceramic, a temperature- either damaged or permanently stuck inside the dry block
boring. Great care must be used when selecting the proper size
regulating device, a control sensor, and some built-in indicator
of temperature in a portable package. Dry-block calibrators are boring for a specific probe.
commonly used for calibration of industrial thermometers.
7. Procedure
These calibrators are commonly used in either two modes: (1)
the direct mode in which the calibrator is used as the calibrated 7.1 Minimum Immersion Length:
reference, or (2) comparison mode in which the calibrator is an 7.1.1 The immersion length for a probe greatly influences
isothermal temperature source for comparing thermometers the stem conduction uncertainty. Stem conduction applies both
under test to a separate calibrated reference thermometer. The to the reference thermometer and the UUT. Tests shall be done
E3186 − 19
FIG. 1 Example of a Dry-block Calibrator System
for each family of probes that is used in the dry-block between the upper part of the thermometer and the bath so that
calibrator to determine a minimum immersion length and to the stem conduction error is negligible.
determine stem-conduction uncertainty. A family of sensors 7.1.2.2 Use normal operating current (typically 1 mA) if
may be distinguished by the outside diameter of the sheath, the specified. Otherwise, use an operating current which results in
sensor length, the sheath thickness and the materials used for no significant self-heating, Record the readout of the test
the sheath, insulators and lead wires. thermometer when equilibrium is reached.
7.1.2 Minimum Immersion Length Test: 7.1.2.3 Slowly withdraw the thermometer from the bath in
7.1.2.1 Insert the test thermometer into the ice-point bath small increments until the readout increases equivalent to the
until no further insertion causes significant change in output. specified measured uncertainty. Pause long enough after each
This insertion may include the mounting flange, threads, etc. incremental change in immersion depth to assure thermal
The purpose of this requirement is to maximize heat transfer equilibrium is reached.
E3186 − 19
7.1.2.4 The ice-point bath and dry well have different heat 8.5.1 Display resolution uncertainty is specific to the direct
transfer characteristics. The minimum immersion length deter- calibration scheme.This is the contribution due to quantization
mined using the E644 ice-bath method described above will error of the thermometer readout.
likely under estimate the length required for the dry-well. The
8.5.2 To calculate display resolution uncertainty, take the
ice-bath method is still useful as a relative measure. This is
display resolution and divide by two. This result has a
especially important for direct mode when the reference
rectangular distribution. Use standard practice to determine the
thermometer and UUT have different thermal cross sections.
expanded uncertainty of a rectangular distribution. For
example, if a thermometer has a display resolution of 0.1 °C,
8. Measurement Uncertainty
then the rectangular distribution is 60.05 °C and the expanded
uncertainty is 0.058 °C with a coverage factor of 2 (k=2).
8.1 Overview:
8.1.1 While it is beyond the scope of this document to
8.6 Axial Temperature Uniformity:
provide tests and methods to determine each element of the
8.6.1 These errors are the result of a gradient along the
uncertainty budget, the format shown here should provide a
length of the thermometer boring of the block or adapter
basic framework for uncertainty budget calculations. Any
sleeve. This temperature gradient will inadvertently cause
calculations of measurement uncertainty should follow local
different temperatures to be measured when calibrating ther-
uncertainty budget calculation guidelines such as the “Evalu-
mometers with different length sensors or immersion depths.
ation of Measurement Data – Guide to the Expression of
Thegreatesttemperaturedifferenceinthemeasurementzoneis
Uncertainty in Measurement.”
measured with a specifically designed thermometer using a
8.1.2 The uncertainties as presented in this guide are listed
readout with sufficient resolution and stability to provide the
in Tables X1.1 and X1.2. Application of these uncertainties to
desireddata.Measurementsaremadestartingwiththegradient
the direct calibration scheme is reported in Table X1.1.
thermometer immersed to the greatest depth of the boring and
Applicationoftheseuncertaintiestothecomparisoncalibration
withdrawing it in regular increments. Increments of 20 mm are
scheme is reported in Table X1.2
usually adequate. Immersion depths should be accurate to
1 mm. Each measurement should be taken when the block
8.2 Electronic Measurement:
temperature has settled reestablishing the temperature equilib-
8.2.1 This is the contribution in uncertainty caused by the
rium and stability within the boring. The immersion depths
thermometer readout and electrical noise in the system. It takes
measured should represent those anticipated to be covered by
into the account the noise from the readout, the noise from the
the sensitive lengths of the thermometers to be calibrated.
probes, and the calibration of the readout.
Some thermometers may have sensors nearly 60 mm in length.
8.2.2 For the direct calibration scheme, this uncertainty
Therefore, it is recommended to measure temperatures at the
applies only to the measurement of the UUT.
bottom or 0, 20, 40, and 60 mm then back to 0 mm to verify
8.2.3 For the comparison calibration scheme, this method
that the temperature in the boring has not drifted. Axial
applies to both the reference probe and the UUT. In other
uniformity is typically worse at the limits of the temperature
words, these two uncertainties shall be considered and com-
range. Measurements at the lower, midpoint, and upper end of
bined to estimate the electronic measurement uncertainty.
the calibrator’s temperature range are recommended. Heavily
8.3 Reference Thermometer Calibration Uncertainty and
loadingtheboringmayalsoinfluencetheuniformityadversely.
Reference Thermometer Drift Uncertainty:
Even more accurate results can be obtained by simultaneously
8.3.1 This uncertainty only applies to the comparison cali-
using a reference thermometer in addition to the gradient
bration scheme. This is the contribution of uncertainty caused
measurement thermometer. The reference thermometer re-
by the reference thermometry. This uncertainty has two com-
mains at the bottom of one boring while the gradient thermom-
ponents. The first comes from the thermometer’s uncertainty
eter is moved up and down in another boring. The difference
from its calibration. The second comes from the long-term
betweenthetworeadingswillprovidethedesiredgradientdata
stability of the reference probe. Drift of temperature sensors is
without the fluctuations caused by phenomena such as insta-
discussed more in 8.12.
bilities from the controller and drift. Refer to Fig. 2a. Sepa-
rately plotting the data from the average values referred to in
8.4 Dry-Block Calibration Uncertainty and dry-block drift
Fig.2aestablishesthegradientprofilecurve.Thiscurveshould
Uncertainty:
be smooth and regular. Poor fit is often the result of not
8.4.1 This uncertainty only applies to the direct calibration
compensating for instability of the block. Careful use of this
scheme. This is the contribution of uncertainty caused by the
second technique while making accurate immersion depth
dry block’s calibration. This uncertainty has two components.
measurements will provide smooth regular gradient profile
The first comes from the dry block’s uncertainty from its
curves, which is a good check of the gradient measurement.
calibration. The second comes from the long term stability of
See Fig. 2b.
thedry-block.Driftoftemperaturesensorsisdiscussedmorein
8.6.2 Design Consideration for Axial Gradient Probes—
8.12.
The gradient thermometer shall be one with a very short sensor
8.5 Display Resolution Uncertainty:
length in order to detect changes in gradiant over a small
distance. A maximum sensor length of 5 mm is recommended
to establish a value for small sensor lengths and thermometer
ASTM E644 Test Methods for Testing Industrial Resistance Thermometers. designs. The stem conduction of the probe shall be minimal.A
E3186 − 19
a b
FIG. 2 Axial Gradient Data
maximum diameter of 6.35 mm is recommended with smaller However, sensors with widely different sensor lengths or large
diameters helping to reduce stem conduction. The sensor for
axial gradient errors or both may benefit from insertions that
the design may be a platinum resistance thermometer (PRT), align the centers of the sensitive portions. This is only of
thermistor, or thermocouple with an adequate temperature
benefit if the location and length of the sensors are known with
range to cover the calibration range. Thermocouples are some degree of accuracy. In the case that the calibrator itself
subject to inhomogeneity errors. If a thermocouple is used, it is
has been calibrated and is serving as the reference, the center
recommended to use a new thermocouple. For greater sensi- of the reference thermometer is not that of the control sensor
tivity it is recommended that where practical PRTs, rather than
but the center location of the sensor with which the dry block
thermocouples, be used.The stability of the thermometer is not
was calibrated.
critical as long as it is sufficiently stable over the duration of
8.7 Radial Temperature Uniformity:
the test to make an accurate temperature difference measure-
8.7.1 These errors result from temperature gradients be-
ment.
tween multiple borings as a result of hot or cold variations in
8.6.3 Normally the maximum uncertainty from the axial
the block or sleeve. This error is strongly influenced by the
temperature uniformity measurement will be used for estab-
difference between the block and ambient temperatures. The
lishing total uncertainty. However, in some cases, the uncer-
larger the temperature difference, the larger the potential
tainty may be reduced.
gradient. Immersion depth of the sensor into the heated zone of
8.6.4 The best calibration results will be achieved when the
the device should be at a minimum of 10 cm (4 inches) to
thermal characteristics including physical size of the reference
mitigate this influence. Measuring the radial gradient requires
thermometer and UUT are identical. It is assumed that the
stable thermometers and readout instruments. Secondary level
sensing element in a thermometer integrates the effect of the
standard thermometers or standard platinum resistance ther-
gradient profile over its effective length.As such, the tempera-
mometers (SPRTs) work best. The test shall be performed with
ture measured by two different probes immersed into the
boring diameters that match the thermometers to be used. In its
boring may be different. The temperature error as a result of
simplest form, the measurement may be made by moving a
gradient profiles over specific length sensors can be estimated
single thermometer from boring to boring.With this method of
by integrating the gradient profile over each sensor length
study, the level of control stability of the heated bore over time
desired. In this example, a known profile was integrated over
is critical to reduce influence of temperature cycling. The
the two sensor lengths of interest. Error deviations at their
calibrator shall be allowed to re-stabilize each time
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...