how to calibrate an ir thermometer, frank liebmann, 2013 05-07

© 2013 Fluke Corporation.

Fluke Calibration Web Seminar Series

Real-world expertise and practical tips about electrical, flow, pressure, RF and temperature calibration

How to Calibrate an

Infrared Thermometer

Today’s Web Seminar

How to Calibrate an IR Thermometer

May 7, 2013

How do you know that your infrared calibrations are accurate? Register for this free

webinar from Fluke Calibration to learn how to improve the accuracy of your infrared

thermometer calibrations. Topics discussed will include sources of uncertainty,

calibration equipment required, overview of the calibration procedure, review of a

sample uncertainty budget, and recommendations for reporting results.

2

Your Presenter

Frank Liebmann

• B.S. Electrical Engineering University of Utah

• 9 years with Fluke/Hart Scientific

– Sr. Design Engineer

– Radiation Thermometry Engineer

• Chairman ASTM Subcommittee E20.02 on Radiation Thermometry

• 20 years U.S. Army

• frank.liebmann@fluke.com

• Phone: 801.763.1700

3

What we will be talking about…

• Sources of uncertainty

• Calibration equipment

• Traceability schemes

• Laboratory setup

• Calibration procedure

• Uncertainty analysis

• Reporting your results

• Questions

4

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”

5

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

6

Calibration Equipment

• Mandatory

– Thermal radiation source

– Transfer Standard

– Ambient Temperature Thermometer

– Mounting Device

– Distance Measuring Device

• Non-mandatory

7

Thermal Radiation Source

• Calibrated source

– Flat Plate

– Cavity

• Provides thermal radiation

8

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

9

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

10

Ambient Temperature Thermometer

• Monitor laboratory conditions

• Use to control uncertainties

– Reflected ambient radiation

– Ambient temperature

11

Mounting Device

• Holds IR thermometer

• Maintains alignment and measuring distance

• May be any of the following

– A tripod

– A fixture

– A hand

12

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

13

Non-mandatory Equipment

Items that may be used on special calibrations

• Aperture

• Frost / dew prevention

14

Traceability Schemes

• Scheme I

– Contact traceability

• Scheme II

– Radiometric traceability

15

Traceability Schemes

4180 and 4181 scheme

16

SCHEME I

SCHEME II

SCHEME II

Laboratory Setup

• Laboratory temperature limits

– Ambient temperature uncertainty

– Reflected temperature uncertainty

17

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

18

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

19

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

20

Laboratory Setup - Correct

• Well controlled reflected temperature

• Sufficient spacing from other instruments

• Isolated from air drafts in room

21

Controlling Reflected Temperature

• Especially a concern for lower temperature calibrations

22

Calibration Procedure

• Preparation

• Calibration Points

• Procedure

23

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

24

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

25

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 respose time 0.5 s, make measurement for 5 s

• Procedure < 15 s

26

Procedure – Measuring Distance

27

Procedure - Alignment

• Laser Alignment

• Maximizing Alignment

28

Uncertainty Analysis

29

Uncertainty Desig. Type U(100 °C)

(°C)

So

urc

e

Calibration temperature U1 B 0.268

Source emissivity U2 B 0.128

Reflected ambient radiation U3 A 0.031

Source heat exchange U4 B 0.012

Ambient Conditions U5 B 0.001

Source uniformity U6 A 0.163

Infr

are

d

Th

erm

om

ete

r

Size-of-source effect U7 B 0.019

Ambient temperature U8 A 0.050

Atmospheric absorption U9 B 0.020

Noise U10 A 0.100

Display Resolution U11 A 0.058

Combined Expanded Uncertainty (k=2) 0.364

Reporting Your Results

Every report of calibration should contain:

• Title

• Unique identification of the calibrated infrared thermometer

• Record of the person who performed the calibration

• Date of calibration

• Source temperature versus infrared thermometer readout

temperature

• Measuring distance

• Emissivity setting of the infrared thermometer

• Diameter of the source

• Ambient temperature

• Description of the aperture including aperture distance (if used)

• Measurement uncertainties

30

Supplemental Information

• Description of the calibration procedure

• List of reference instruments

• Traceability statement

• Description of the uncertainty budget

31

Summary

• Follow proper procedure

• Better calibration

• Happy customers

32

© 2013 Fluke Corporation

Thank you.

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