How to Calibrate an IR Thermometer Webinar Presented by Fluke Calibration

Frank Liebmann IR112 © 2019 Fluke Calibration 1
IR Thermometer Calibration
Radiation Thermometry Series

Outline
• Introduction
• Sources of Uncertainty
• Calibration Equipment
• Traceability Schemes
• Laboratory Setup
• Calibration Procedure
• Uncertainty Analysis
• Reporting your Results
• Question Time

Introduction
• IR thermometry calibration can be accurate
• Proper procedure must be followed
• ASTM E2847, “Standard Practice for Calibration and Accuracy
Verification of Wideband Infrared Thermometers”

Outline
• Introduction
• Question Time

Sources of Uncertainty
• Major
– Emissivity estimation of the calibration source
– Field-of-view of the infrared thermometer
– Temperature gradients on the radiation source
– Improper alignment of the infrared thermometer
– Calibration temperature of the radiation source
– Ambient temperature
– Reflected temperature
• Minor
– Source heat exchange
– Atmospheric absorption
– Noise
– Display Resolution

Outline
• Introduction
• Question Time

Calibration Equipment
• Mandatory
– Thermal radiation source
– Transfer Standard
– Ambient Temperature Thermometer
– Mounting Device
– Distance Measuring Device
• Non-mandatory
– Purge Cavity

Thermal Radiation Source
• Calibrated source
– Flat Plate
– Cavity
• Provides thermal radiation

Thermal Radiation Source
Size of the thermal radiation source
• For Fluke IR thermometer models
– 5” (~ 125 mm) diameter is enough
• Other IR thermometer manufacturers
– Consult manufacturer
– Testing

Transfer Standard
• Contact Thermometry (Scheme I)
– PRT, thermistor, or thermocouple
• Non-contact Thermometry (Scheme II)
– Radiation thermometer
• More discussion under ‘Traceability Schemes’
• Implementation
– Internal
– Third-party laboratory

Ambient Temperature Thermometer
• Monitor laboratory conditions
• Use to control uncertainties
– Reflected ambient radiation
– Ambient temperature

Mounting Device
• Holds IR thermometer
• Maintains alignment and measuring distance
• May be any of the following
– A tripod
– A fixture
– A hand

Distance Measuring Device
• Used to verify measuring distance
• Measuring distance: “Distance or distance range between the
radiation thermometer and the target (measured object) for which
the radiation thermometer is designed.” IEC 62492-1
• Use:
– Tape measure
– Measuring rod

Non-mandatory Equipment
Items that may be used on special calibrations
• Aperture
• Frost / dew prevention

Outline
• Introduction
• Question Time

Traceability Schemes
• Scheme I
– Contact traceability
• Scheme II
– Radiometric traceability

4180 and 4181 scheme
Traceability Schemes
SCHEME I
SCHEME II SCHEME II

Outline
• Introduction
• Question Time

Laboratory Setup
• Laboratory temperature limits
– Ambient temperature uncertainty
– Reflected temperature uncertainty

Laboratory Setup - Incorrect
• A heat source facing a
flat-plate
• A flat-plate facing an
exterior wall
– Especially a window
• A flat-plate in the vicinity
of air drafts
– HVAC vent
– Commonly used traffic
way

flat-plate
exterior wall
of air drafts
– HVAC vent
way

Laboratory Setup - Correct
• Well controlled reflected temperature
• Sufficient spacing from other instruments
• Isolated from air drafts in room

Controlling Reflected Temperature
• Especially a concern for lower temperature calibrations

Outline
• Introduction
• Question Time

Calibration Procedure
• Preparation
• Calibration Points
• Procedure

Preparation
• Allow infrared thermometer time to reach room temperature (at least
15 minutes)
• Lens cleaning
– Only clean if requested by customer
– Clean per manufacture's instructions
• Set up any special equipment
• Set radiation source to desired temperature
• Allow radiation source time to stabilize

Calibration Points
What calibrations point to use?
• Determined by the customer
• Laboratory may offer advice
– Over wide range, minimum 3 points
– Narrow range, 1 or 2 points may be fine
• Best practice to perform calibration from lowest cal point to highest

Calibration Procedure
Procedure for each calibration point
• Set IR thermometer reflected temperature (if available)
• εIRT = εS
– εS is adjustable on a 4180 and 4181
• Align IR thermometer
– Set distance (Z-direction)
– Align side-to-side and up-and-down (X- and Y-directions)
– IR thermometer should be no more than 5° from normal to
target surface
• Make measurement
– Make measurement 10 times IR thermometer response time
– For instance: IR thermometer response time 0.5 s, make measurement
for 5 s
• Procedure < 15 s

Procedure – Measuring Distance

Procedure - Alignment
• Laser Alignment
• Maximizing Alignment

Procedure – Adjustment
• Most IR thermometers are not adjustable

Outline
• Introduction
• Question Time

Uncertainty Analysis
IR Thermometer Model X12, 100 °C
Uncertainty Desig.
Value
(K)
Source
Calibration temperature u 1 0.117
Reflected ambient radiation u 2 0.053
Source uniformity u 3 0.092
IR Thermometer
Size-of-Source effect u 4 0.029
Spectral response u 5 0.064
Atmospheric absorption u 6 0.010
Display Resolution u 7 0.029
Reproducibility
General reproducibility u 8 0.090
Ambient reproducibility u 9 0.049
Combined Standard Uncertainty (k = 1) 0.203
Combined Expanded Uncertainty (k = 2) 0.41

Outline
• Introduction
• Question Time

Reporting Your Results
Every Report of Calibration Should Contain:
• Title *
• Name and address of the laboratory *
• Unique identification of the calibrated infrared thermometer *
• Method used *
• Date of calibration *
• Statements *
– that results only pertain to infrared thermometer calibrated
– traceability
– of conformity (if needed)
• Results *
– Source temperature versus infrared thermometer readout temperature
– Measurement uncertainties
– Before and after the adjustment
• Measuring distance
• Emissivity setting of the infrared thermometer
• Diameter of the source
• Ambient temperature and humidity *
• Description of the aperture including aperture distance (if used)
• Person authorizing the report *
* 17025:2017 requirement

Conclusion
• Follow proper procedure
• Better calibration
• Happy customers

Question Time
• Frank Liebmann – Frank.Liebmann@Flukecal.com

Questions or Comments?
Email Nicole VanWert-Quinzi nicole.vanwert@Transcat.com
Transcat: 800-828-1470
www.Transcat.com
For related product information, go to:
https://www.transcat.com/brand/fluke-calibration

How to Calibrate an IR Thermometer Webinar Presented by Fluke Calibration

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How to Calibrate an IR Thermometer Webinar Presented by Fluke Calibration