ASTM E220 Calibration of Thermocouples By Comparison Techniques

ASTM E220 is used to describe the principle, apparatus, and procedure to calibrate thermocouples by comparing them with a reference thermometer.

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ASTM E220 Calibration of Thermocouples By Comparison Techniques

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Overview
Scope, Applications, and Benefits
Test Process
Specifications
Instrumentation
Results and Deliverables

Overview

ASTM E220 specifies a standardized procedure for calibrating unused thermocouples in relation to a reference thermometer. It specifies the procedures for measuring the differences in the electrical potential generated by the thermocouple and the reference standard at a given temperature.

This procedure is applicable to unused thermocouples. It cannot be applied to thermocouples that have already been used because inhomogeneity of the materials may be present and cannot be detected using calibration procedures. When calibrating thermoelements with large diameters and sheathed thermocouples, special attention must be taken to reduce thermal conduction losses.

Scope, Applications, and Benefits

Scope

The test specimen is installed between two reverberation rooms, and a diffuse sound field is generated in the source room. Sound energy strikes the specimen, causing it to vibrate and transmit sound into the receiving room. Sound pressure levels are measured in both rooms, and the sound absorption in the receiving room is determined. For improved accuracy, the test may be repeated with the source and receiving rooms reversed, and the results are averaged to obtain the final transmission loss values.

Applications

Thermocouple manufacturing quality control
Calibration laboratories
Industrial temperature measurement systems
Furnace and heat-treatment process validation
Power generation industries
Research and development laboratories
Metrology and standards verification

Benefits

Ensures thermocouple accuracy before use
Provides traceable calibration data
Detects deviations from standard EMF tables
Improves measurement reliability
Supports compliance with quality standards
Applicable over a wide temperature range
Offers multiple calibration approaches

Test Process

Measurement Setup

Thermocouples are connected via automated scanning or manual sequence, with reference readings taken for accuracy.

EMF Measurement

EMF is measured for each thermocouple, or directly as a differential EMF in the differential method.

Temperature Stabilization

Measurements are repeated at the same stabilized temperature to ensure consistency and minimize variation.

Data Calculation

ΔE is calculated as Er – E, where Er is the reference EMF and E is the measured EMF.

Technical Specifications

Parameter	Details
Calibration Range	-195°C to 1700°C
Applicable Specimens	Unused thermocouples only
Measurement Output	Electromotive Force (EMF) deviation
Calculation Formula	ΔE = Er – E
Reference Requirement	Standard EMF reference tables
Limitation	Not applicable to used thermocouples

Instrumentation Used for Testing

Reference thermometer (meeting required uncertainty)
Voltmeter (high-precision EMF measurement)
Scanning unit (for automated method)
Data acquisition and storage system
Calibration furnace or temperature source
Calibrated EMF reference source
Switching system (manual method)

Results and Deliverables

EMF deviation values at calibration points
Calibration tables across temperature range
Measurement uncertainty evaluation
Compliance verification with reference tables
Traceable calibration report

Frequently Asked Questions

The ASTM E220 standard calibrates a thermocouple by matching its EMF response with that of a reference sensor at the same temperatures. Such a method of comparison allows for the calibration of a thermocouple at various temperatures within a reasonable testing period.

The comparison medium ensures that both sensors are exposed to the same temperature. Liquid baths reduce temperature gradients at lower to moderate temperatures, while furnaces with equalization blocks are used at higher temperatures.

ASTM E220 is applicable to base metal and noble metal thermocouples over a wide range of temperatures. The type of the reference sensor depends on the temperature range, which ensures accuracy in comparison and reduces the uncertainty of measurement for various thermocouple configurations.

The results of the calibration process include the nominal temperature, reference temperature, and the deviation of the thermocouple. These results are used to determine the correction factors or coefficients that can be used in the instrumentation to improve the accuracy of temperature measurement.

ASTM E220 can be applied across a wide temperature range depending on thermocouple type and comparison medium, allowing accurate calibration from cryogenic temperatures up to high-temperature furnace conditions using appropriate reference sensors.