Fluke 4180 Quick start guide

4180, 4181
Precision Infrared Calibrator
Technical Guide
March 2013, Rev. 1, 11/20
© 2013-2020 Fluke Corporation. All rights reserved. Specifications are subject to change without notice.
All product names are trademarks of their respective companies.

LIMITED WARRANTY AND LIMITATION OF LIABILITY
Each Fluke product is warranted to be free from defects in material and workmanship under normal use and
service. The warranty period is one year and begins on the date of shipment. Parts, product repairs, and services
are warranted for 90 days. This warranty extends only to the original buyer or end-user customer of a Fluke
authorized reseller, and does not apply to fuses, disposable batteries, or to any product which, in Fluke's opinion,
has been misused, altered, neglected, contaminated, or damaged by accident or abnormal conditions of operation
or handling. Fluke warrants that software will operate substantially in accordance with its functional specifications
for 90 days and that it has been properly recorded on non-defective media. Fluke does not warrant that software
will be error free or operate without interruption.
Fluke authorized resellers shall extend this warranty on new and unused products to end-user customers only but
have no authority to extend a greater or different warranty on behalf of Fluke. Warranty support is available only if
product is purchased through a Fluke authorized sales outlet or Buyer has paid the applicable international price.
Fluke reserves the right to invoice Buyer for importation costs of repair/replacement parts when product purchased
in one country is submitted for repair in another country.
Fluke's warranty obligation is limited, at Fluke's option, to refund of the purchase price, free of charge repair, or
replacement of a defective product which is returned to a Fluke authorized service center within the warranty
period.
To obtain warranty service, contact your nearest Fluke authorized service center to obtain return authorization
information, then send the product to that service center, with a description of the difficulty, postage and insurance
prepaid (FOB Destination). Fluke assumes no risk for damage in transit. Following warranty repair, the product will
be returned to Buyer, transportation prepaid (FOB Destination). If Fluke determines that failure was caused by
neglect, misuse, contamination, alteration, accident, or abnormal condition of operation or handling, including
overvoltage failures caused by use outside the product's specified rating, or normal wear and tear of mechanical
components, Fluke will provide an estimate of repair costs and obtain authorization before commencing the work.
Following repair, the product will be returned to the Buyer transportation prepaid and the Buyer will be billed for the
repair and return transportation charges (FOB Shipping Point).
THIS WARRANTY IS BUYER'S SOLE AND EXCLUSIVE REMEDY AND IS IN LIEU OF ALL OTHER
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SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES OR LOSSES, INCLUDING LOSS OF
DATA, ARISING FROM ANY CAUSE OR THEORY.
Since some countries or states do not allow limitation of the term of an implied warranty, or exclusion or limitation
of incidental or consequential damages, the limitations and exclusions of this warranty may not apply to every
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11/99
Fluke Corporation
P.O. Box 9090
Everett, WA 98206-9090
U.S.A.
Fluke Europe B.V
P.O. Box 1186
5602 BD Eindhoven
The Netherlands

i
Table of Contents
Title Page
Introduction................................................................................................ 1
Contact Fluke Calibration .......................................................................... 1
Safety Information ..................................................................................... 2
Service Information.................................................................................... 3
Specifications and Environmental Conditions ........................................... 3
Product Operation ..................................................................................... 3
Main Screen.......................................................................................... 3
Main Menu ............................................................................................ 4
TEMP SETUP .................................................................................. 4
SETUP ........................................................................................ 4
IRT .............................................................................................. 5
IRT ε........................................................................................... 5
CUTOUT .................................................................................... 5
PROG MENU................................................................................... 6
SELECT PROG .......................................................................... 6
PROG OPTION .......................................................................... 7
RUN PROG ................................................................................ 7
SYSTEM MENU............................................................................... 7
SYSTEM SETUP ........................................................................ 7
PASSWORD .............................................................................. 8
CALIBRATE ............................................................................... 8
SYSTEM INFO (View Only) ....................................................... 10
VIEW TEMP..................................................................................... 10
BLOCK TEMP (View Only) ......................................................... 10
Basic Infrared Thermometry Theory - Relating to the use of the Product . 10
Apparent Temperature.......................................................................... 10
Spectral Response (Wavelength) ......................................................... 11
Emissivity.............................................................................................. 13
Uncertainty Caused by Emissivity....................................................13
Effect of Background Temperature .................................................. 14
Effect of Angle on Emissivity............................................................ 15
Center of Spot.................................................................................. 15
Size of Spot, Size of Source and Scatter......................................... 16
Distance to Target............................................................................ 16
Knowing the Correct Geometry........................................................ 16

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Traceability ........................................................................................... 16
Treatment of IR Thermometers ............................................................ 17
Use of the Product in the Context of IR Theory.................................... 18
Example of the Product Spectral Emissivity and Calibration
Spectral Response ............................................................................... 19
Example of an Uncertainty Budget for an IR Thermometer
Calibration ............................................................................................ 20
Example IR Thermometer Uncertainty Budget ................................ 21
Explanations .................................................................................... 22
Further Reading.................................................................................... 23
Digital Communication Interface ............................................................... 24
Wiring ................................................................................................... 24
Setup................................................................................................ 25
Serial Operation ............................................................................... 25
Command Syntax ................................................................................. 25
Commands by Function or Group......................................................... 26
Serial Commands - Alphabetic Listing.................................................. 28
Terminology.......................................................................................... 41
Fundamentals....................................................................................... 41
Environmental Conditions..................................................................... 41
Calibration Equipment .......................................................................... 41
Procedure ............................................................................................. 43
Visual Inspection.............................................................................. 43
Manual IR Target Calibration ........................................................... 43
General ...................................................................................... 43
Radiometer ................................................................................. 43
Frost Control .............................................................................. 44
Preparation for IR Target Calibration ......................................... 46
Settings ...................................................................................... 47
Manual IR Target Calibration Process ....................................... 48

1
Introduction
Note
This manual is intended to be used with the Operators Manual and Safety Information
documents.
The Fluke Calibration 4180, 4181 Precision Infrared Calibrator (The Product) is a portable instrument
or bench-top temperature calibrator used to calibrate IR thermometers. The Product is small enough to
use in the field, and accurate enough to use in the lab.
The Product features:
• Rapid heating and cooling
• RS-232 interface capability
Built in programmable features include:
• Temperature scan rate control
• Eight set-point memory
• Adjustable readout in °C or °F
• Adjustable Emissivity
The temperature is accurately controlled by the digital controller. The controller uses a precision
platinum RTD as a sensor and controls the surface temperature with a solid state relay (triac) driven
heater (4181) and FET driven Peltier modules (4180).
With proper use, the Product will provide continued accurate calibration of IR temperature
measurement devices. Familiarize yourself with the safety guidelines and operating procedures of the
Product. See Safety Information.
Contact Fluke Calibration
Fluke Corporation operates worldwide. For local contact information, go to our website:
www.flukecal.com
To register your product, view, print, or download the latest manual or manual supplement, go to our
website.
Fluke Corporation
P.O. Box 9090
Everett, WA 98206-9090
[phone]
[email protected]

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Safety Information
General Safety Information is located in the printed Safety Information document that ships with the
Product. It can also be found online at www.Flukecal.com. More specific safety information is listed
where applicable in this manual.
A Warning identifies conditions and procedures that are dangerous to the user. A Caution identifies
conditions and procedures that can cause damage to the Product or the equipment under test.
Follow these guidelines closely to make sure that the safety mechanisms in this Product operate
properly. This Product must be plugged into an AC-only outlet according to the Specifications and
Environmental Conditions. The power cord of the Product has a three-pronged grounding plug for your
protection against electrical shock. Plug the power cord directly into a properly grounded three-prong
receptacle. The receptacle must be installed in accordance with local codes and ordinances. Consult a
qualified electrician.
WCaution
To prevent damage to the Product:
• Always replace the fuse with one of the same rating, voltage, and type.
• Always replace the power cord with an approved cord of the correct rating and type.
• Protect the target against dirt and damage - scrapes and scratches. A well-kept target
surface, free from dirt and damage, produces better measurements. Use the target
cover whenever the Product is not in use to protect the target. Always use the target
cover when transporting the Product, but remember to never transport the Product
when the target temperature is >50 °C.
• Do not touch the target. Oils and salts from the skin will permanently damage the
target surface at high temperatures.
• Do not use fluids to clean the target surface.
• Do not use shop air to clean the target surface. Oil and contaminants in the shop air
could contaminate the surface.
• Do not use canned, compressed air (used to clean a computer) to clean the target
surface. Chemicals in the air could contaminate the target surface.
• When ice forms on the target, change the instrument set-point >50 °C to melt the
excess ice. DO NOT wipe the front plate (target). Change the set-point to 100 °C or
higher to evaporate the excess water.
• Do not force cool the surface. The surface should not be cooled by any method other
than natural convection. Forced air can often have oil or water in it. Even water can
leave mineral deposits on the surface. Trying to cool the surface too quickly can also
cause thermal shock to the emissive surface.
• Do not use liquid nitrogen (LN2) to quick cool the target.
• Do not plug the Product into 230 V if the fuse holder reads 115 V. This action will
cause the fuses to blow and may damage the Product.
• Component lifetime can be shortened by continuous high temperature operation.

Precision Infrared Calibrator
Service Information
3
• Do not change the values of the calibration constants from the factory set values.
Calibration constants shall only be changed by qualified and authorized personnel.
The correct setting of these parameters is important to the safety and proper
operation of the Product.
• Use a ground fault interrupt device.
• Always operate this Product at room temperatures as stated in Specifications and
Environmental Conditions.
• The Product is a precision instrument. Handle the Product with care. It is important to
keep the calibration well and the IR target surface clean and clear of any foreign
matter.
• If a main supply power fluctuation occurs, immediately turn off the Product. Wait until
the power has stabilized before re-energizing the Product.
• Always carry the Product in an upright position. The convenient pull-up handle al-
lows one hand carrying.
• Do not operate the instrument in excessively wet, oily, dusty, or dirty environments.
• DO NOT operate near flammable materials.
• If a main supply power fluctuation occurs, immediately turn off the Product. Wait until
the power has stabilized before re-energizing the Product.
• Use the target cover at temperatures below ambient (25 °C). If ice or liquid water
forms on the target, IR thermometers will not indicate the correct temperature.
Service Information
Contact an authorized Fluke Calibration Service Center if the Product needs calibration or repair during
the warranty period. See Contact Fluke Calibration. Please have Product information such as the
purchase date and serial number ready when you schedule a repair.
Specifications and Environmental Conditions
The Product specifications can be found in the 4180 Operators Manual located at www.Fluke.com.
Product Operation
This section discusses how to operate the control panel. Using the front panel you can monitor the
target temperature, set the temperature set-point in °C or °F, monitor the heater output power, monitor
the stability, set the cutout set-point, set the operating parameters, and configure the communication
interface. When active, menu keys are selected using the soft keys (F1-F4).
Main Screen
The display shows the control temperature (actual target temperature), heating or cooling power,
stability state, current set-point information, and current program information. The temperature is either
in °C or °F. Push C/F to change temperature units.
APPARENT TEMPERATURE
This is the radiometric temperature of the target surface as calculated from the control sensor
temperature. The calculation depends on the emissivity setting. The controller heats or cools the target
to force the control temperature equal to the set-point.

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SET-POINT (SETPT)
This is the current set-point.
IRT ε
IRT εis the Product apparent emissivity. The emissivity setting should match that of the device under
test (DUT).
CAL λ
CAL λis the bandwidth of the Product calibration. It can be set to either 8-14 μm or User.
CONTROL - HEAT/COOL
Is the relative heating or cooling power (duty cycle) in percent.
HEATING, COOLING, CUTOUT
Is the status of heating or cooling or the cutout when activated. The bar graph indicates the relative
heating or cooling power.
STABLE INDICATION (Graphic)
Is the stability of the target. When the stability is within the STABLE LIMIT setting, this line is flat.
Main Menu
Note
For more information on the menu structure, see Menu Structures in the Operators Manual.
Push MENU to access the Main Menu and the main submenus. Use the submenus to set up the
Product as desired and to change system parameters as needed.
TEMP SETUP
The TEMP SETUP (TEMPERATURE SETUP) contains functions related to temperature setup. See
the Operators Manual.
SETUP
The SETUP menu contains the parameters that set the stability limit and scan rate for the Product.
SCAN RATE
The SCAN RATE parameter can be set such that when the set-point is changed, the Product heats or
cools at a specified rate, degrees per minute (°C/min or °F/min), until it reaches the new set-point.
The Scan Rate can be set from 0.1 °C/min to 500 °C/min (0.2 °F/min to 900 °F/min). However, the
maximum scan rate is limited by the natural heating or cooling rate of the Product, which is often much
less than 500 °C/min (900 °F/min), especially when cooling.
Use the arrow buttons to adjust the scan rate. Once the scan rate has been set, push ENTER to accept
the new scan rate.

Precision Infrared Calibrator
Product Operation
5
STABLE LIMIT
Note
The Product should not be expected to operate better than the listed stability specification. The
minimum setting of the stability limit should not be less than the stability specification.
The STABLE LIMIT parameter notifies the user when it has achieved the stability limit set in this
parameter. There are two notifications: visual and audible. The visual notification is always active. As
the Product operates within the stability limit, the stability graph on the main screen remains flat once
the Product is within the given specification for 1 minute. Otherwise the graph indicates that the
Product is not yet stable. The audible, if enabled, alerts the user once per set-point when the Product
achieves the set stability limit. Use the arrow buttons to set the desired stability limit and push ENTER
to accept the new stability limit.
Example
A special calibration process requires the Product to operate within ±0.5 °C. Enter 0.5 into the stability
limit parameter. When the Product stability is within ±0.5 °C for one minute, the graph is flat and the
audible alarm (if enabled) notifies the user that the Product is operating within ±0.5 °C. Use the arrow
keys to set the desired stability limit and push ENTER to accept the new stability limit.
STABLE ALARM
To turn on or off the audible alarm described in STABLE LIMIT, use the STABLE ALARM parameter.
Push the left or right arrow button to select either Enable or Disable and push ENTER to accept the
selection.
IRT
The IRT menu contains the user-settable emissivity parameter to set the display emissivity.
IRT ε
The IRT εparameter allows the user to change the display emissivity setting to match the IR
thermometer emissivity setting.
CUTOUT
The CUTOUT menu contains the SOFT CUTOUT and HARD CUTOUT functions of the Product. As a
protection against software or hardware fault or user error, the Product has an adjustable cutout device
that shuts off power to the heat source if the target temperature exceeds a set value. The factory
default is 10 degrees above the high limit of the Product. If the cutout is activated because of excessive
target temperature, power to the heat source shuts off and the Product cools. The Product remains in
cutout mode and active heating and cooling are disabled until the user manually resets the cutout. If
the over-temperature cutout is triggered, the Product displays CUTOUT above the duty cycle bar
graph, which indicates a cutout condition. The Product remains in cutout mode until the temperature is
reduced and the cutout is reset. The target temperature must drop a few degrees below the cutout set-
point before the cutout can be reset. For safety reasons, the cutout only has one mode - manual reset.
Manual reset mode means the cutout must be reset by the operator after the temperature falls below
the set-point.
Note
CUTOUT RESET: If the Product exceeds the temperature set in the soft cutout menu or if it
exceeds the maximum operating temperature of the Product, a cutout condition occurs. If this
happens, the Product enters cutout mode and will not actively heat or cool until the user resets
the Product.

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To reset the cutout, the Product temperature must cool to lower than the cutout set-point. Once the
Product has cooled, push SET PT., then ENTER, and then ENTER again to reset and engage the
Product.
SOFT CUTOUT
The SOFT CUTOUT is user settable. The SOFT CUTOUT parameter can be set to any temperature
under the range of the Product. The cutout should be set within 5 ° to 10 ° of the safety limit of the
equipment being calibrated or used with the Product.
HARD CUTOUT
The HARD CUTOUT is not user settable. The HARD CUTOUT parameter is a view-only function and
indicates the factory setting for the hard cutout.
PROG MENU
Use the PROG MENU (PROGRAM MENU) to access automated and manual program selections.
SELECT PROG
Use the SELECT PROG menu to select a program, 1 - 8.
PROGRAM
Select the PROGRAM from the listing.
EDIT PROG
Use the EDIT PROG (EDIT PROGRAM) menu edit program parameters.
PROGRAM (view Only)
The PROGRAM parameter indicates the number of the selected program.
NAME (view Only)
Program NAME indicates the program name. To set the program name, see the PROG:[n]NAME serial
command. Example: a thermometer model number.
IRT ε
IRT εis the emissivity setting of the IR thermometer to be calibrated.
DISTANCE
DISTANCE is the distance in centimeters (cm) from the IR target to the DUT.
APERTURE
Select YES or NO. Yes indicates that an external aperture is required during calibration.
NO. SETPOINTS
The NO. SETPOINTS is the number of set-points defined for a given program. The number of set-
points for each program can be set from 1 to 8 and vary depending on the needs of the user. Set the
maximum number of set-points needed for the program selected. Once the number of set-points is
selected, push ENTER to accept the new setting.
SETPOINT n:
Use SETPOINT n to set the temperature for each given set-point. n is a number from 1 to No. Set-
points.

Precision Infrared Calibrator
Product Operation
7
PROG OPTION
Use the PROG OPTION (PROG OPTION) to set program parameters.
SETTLE TEST
SETTLE TEST is the criteria to determine when the temperature of the surface is stable. The options
are: AUTO and LIMIT. AUTO uses a predetermined value for the stability. LIMIT uses the value set by
the STABLE LIMIT parameter in the TEMP SETUP|SETUP|STABLE LIMIT window.
SOAK MINUTES
The SOAK MINUTES parameter is the number of minutes that each of the program set-points is
maintained. The time starts when the temperature settles to within the specified stability. The stability
limit is set in the TEMP SETUP|SETUP|STABLE LIMIT window.
ADVANCE
Use ADVANCE to set the choice to advance to the next step in the program automatically (AUTO) or to
be prompted from the screen (PROMPT).
CYCLES
CYCLES is the number of times that the Product repeats the program.
RUN PROG
Use the RUN PROG (RUN PROGRAM) menu to access the program status feature.
PROGRAM (view Only)
The PROGRAM parameter indicates the number of the program that is selected.
NAME (view Only)
Program NAME indicates the program name. To set the program name, see the PROG:[n]NAME serial
command. Example: a thermometer model number.
STATUS
The STATUS option controls the state of the program. The user selects RUN to run the program or
OFF to turn the program off.
SYSTEM MENU
Use the SYSTEM MENU to set up the display settings, communications protocol, password settings,
calibrations settings, and to view system information.
SYSTEM SETUP
The SYSTEM SETUP menu contains the menus for the display and communications parameters.
DISPLY SETUP
The DISPLY SETUP (DISPLAY SETUP) menu contains the language selection, decimal separator,
and keypad sound parameters.
LANGUAGE
See Languages in the Operators Manual.

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DECIMAL
Use the DECIMAL parameter to determine the decimal separator: a comma or a period. Push the right
or left arrow to select the desired decimal separator and then push ENTER to accept the selection.
KEY AUDIO
The KEY AUDIO parameter (F1 and F3 pushed simultaneously) enables or disables the button push
beep.
COMM SETUP
The COMM SETUP (COMMUNICATIONS SETUP) menu contains the serial interface parameters. The
parameters in the menu are: BAUD RATE and LINEFEED.
BAUD RATE
The BAUD RATE parameter determines the serial communication transmission rate or baud. BAUD
RATE may be programmed to 1200, 2400, 4800, 9600, 19200, or 38400 baud.
LINEFEED
The LINEFEED enables (ON) or disables (OFF) transmission of a line feed character (LF, ASCII 10)
after transmission of any carriage return. The LINEFEED default setting is on. The line-feed parameter
can be turned on or off as needed.
PASSWORD
Use the PASSWORD (PASSWORD SETUP) menu to set the system password or set the level of
protection that conditionally engages or disengages protection of certain groups of parameters.
USER PASSWORD
Use the USER PASSWORD parameter to enter and change the system and conditional password
used to access protected menus. The PASSWORD is a number between one and four digits. Each
digit of the password can be a number from 0 to 9. The default System Password is 1234. Use the up,
down arrow buttons to enter the new password, and then push ENTER.
PROTECTION
Use the PROTECTION parameter to enable (HIGH) or disable (LOW) password protection for the
conditional parameters. The password is the same as the system password. You can conditionally
password-protect the SOFT CUTOUT and all of the PROGRAM MENU parameters except SELECT
PROG and RUN PROG. Select HIGH or LOW with the left and right arrow buttons and push ENTER to
accept the selection.
CALIBRATE
WCaution
Calibration parameters must be correct for the Product to function properly.
Use the CALIB (CALIBRATION) menu to access to the calibration parameters for the Product. Access
to the IR target calibration parameters is password protected. Calibration parameters are programmed
at the factory when the Product is calibrated. Qualified personnel can adjust these parameters when
needed to improve the accuracy of the Product.

Precision Infrared Calibrator
Product Operation
9
WCaution
Do not change the calibration values or control parameters from the factory-set values
unless recalibrating the Product. The correct setting of these parameters is important
to the safe and proper operation of the Product.
The parameters in the CALIB menu are set at the factory and must not be altered unless recalibrating
the Product. Recalibration of the Product should be performed by qualified personnel. The correct
values are important to the accuracy and safe operation of the Product. Access to these parameters is
password protected. In the event that the calibration parameters need to be reentered into the Product,
the constants and their settings are listed in the Report of Calibration shipped with the Product.
CONT SETUP
Use the CONT SETUP (CONTROL SETUP) to access the controller parameters.
TEMP PBAND
The TEMP PBAND parameter is the proportional band in °C that the Product's proportional-integral-
derivative (PID) controller uses for control.
TEMP INT
The TEMP INT parameter is the integration time in seconds that the Product's PID controller uses for
control.
TEMP DER
The TEMP DER parameter is the derivative time in seconds that the Product's PID controller uses for
control.
IR CAL
The IR CAL (IR CALIBRATION) menu contains the IR target calibration constants: IR CAL 1, IR CAL 2,
and IR CAL 3. Use the arrow buttons to enter the set-point for each calibration point and push ENTER
to accept the entry. The calibration points should be selected applicable to model with a low, mid-
range, and high set-point.
IR CAL 1
The IR CAL 1 parameter is the offset in °C for the IR target accuracy at the 1st calibration point.
IR CAL 2
The IR CAL 2 parameter is the offset in °C for the IR target accuracy at the 2nd calibration point.
IR CAL 3
The IR CAL 3 parameter is the offset in °C for the IR target accuracy at the 3rd calibration point.
WAVELENGTH
The WAVELENGTH parameter can be set to the default 8 µm to 14 µm or USER selectable. This is to
remind the user that the nominal emissivity and calibration of the Product pertains to the 8 μm to 14 μm
band.
CALDATE
The CALDATE parameter is the calibration date for the IR target. Use the arrow buttons to enter the
calibration date in the format yyyy,mm,dd.

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SYSTEM INFO (View Only)
The SYSTEM INFO (SYSTEM INFORMATION) menu displays manufacturer information regarding the
Product.
MODEL
The MODEL parameter displays the model number of the Product.
SERIAL
The SERIAL (SERIAL NUMBER) parameter displays the serial number of the Product.
FW VERSION
The FW VERSION (FIRMWARE VERSION) parameter displays the firmware version used in the
Product.
CAL DATE
The CAL DATE (CALIBRATION DATE) parameter displays the calibration date of the IR target.
VIEW TEMP
Use the VIEW TEMP (VIEW TEMPERATURE) to view the BLOCK TEMPERATURE parameter.
BLOCK TEMP (View Only)
Use the BLOCK TEMP (BLOCK TEMPERATURE) parameter to view the uncompensated control
sensor temperature.
Basic Infrared Thermometry Theory - Relating to the use of the Product
Typically, infrared (IR) thermometers have not been used for measurements requiring low
uncertainties. Their application has been for use at extremely high temperatures and in applications
where accuracy is less important than repeatability.
As infrared thermometers and our understanding of their advantages improve, both absolute accuracy
and calibration become more important. This section gives a brief explanation of some important
issues surrounding the use and calibration of IR thermometers and how this information relates to the
use of the Product.
Apparent Temperature
The Product is calibrated using a radiometric calibration. The main display temperature is based on this
radiometric calibration. This temperature shows the user what an IR thermometer with a given
emissivity setting should read. This is called apparent temperature. The apparent temperature is
defined as the temperature an IR thermometer set to emissivity (ε) should read when measuring the IR
calibrator’s surface.
In other words, the display temperature shows what temperature the target appears to be to the IR
thermometer.

Precision Infrared Calibrator
Basic Infrared Thermometry Theory - Relating to the use of the Product
11
Spectral Response (Wavelength)
Every object with a temperature above absolute zero (0 Kelvin) radiates energy over a wide spectral
band. For example, if a significant part of this energy is within the band of 400–700 nm, we can see that
energy. This is the visible light band. This is the case with an electric stove burner at a temperature of
800 °C. The burner appears red or orange to the eye (red hot). That burner is also emitting energy at
other wavelengths, which we can not see. This includes wavelengths in the infrared portion of the
electromagnetic spectrum.
An example of an object emitting energy at wavelengths we can see is the sun. The sun’s surface
temperature is about 5750 K. According to Wien’s Displacement Law, see Equation 1, the peak
wavelength for this temperature is about 500 nm which happens to be in the visible light band. Thus the
eye detects wavelengths corresponding to the temperature of the Sun.
By the same respect, if we are measuring an object at room temperature, (23 °C or about 296 K), the
peak wavelength is 9.8 μm which is inside the 8 μm to 14 μm band. In fact the temperature
corresponding to a peak wavelength at 8 μm is 89 °C and the temperature corresponding to a peak
wavelength at 14 μm is -66 °C. This is one of the reasons the 8 μm to 14 μm is widely used in handheld
IR thermometers.
IR thermometers take advantage of this peak wavelength phenomenon. They measure the amount of
energy radiating from an object and calculate temperature based on this measured energy. In most
handheld IR thermometers, the sensor and optical system measure IR energy in the 8 μm to 14 μm
band.
The mathematical equation describing the spectral power radiated by a perfect blackbody for a given
wavelength is Planck's Law. If Planck's Law, see Equation 2, is integrated over the entire electro-
magnetic spectrum, this gives us the Stefan-Boltzmann Law. This is the T to the 4th law (T4). The
problem with the Stefan-Boltzmann Law, see Equation 3, is that it is not limited to a specific band. To
get the energy within a certain band, we would need to integrate Planck's Law for the limits of this
bandwidth. This integral cannot be solved analytically.
The mathematical equation describing the peak wavelength for a given temperature is Wien’s
Displacement Law.
λmaxT=c3
Equation 1: Wien’s Displacement Law
Equation 2: Planck’s Law
LλT,() c1L
λc2
λT
-------


1–exp
--------------------------------------=

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Equation 3: Stefan-Boltzmann Law
The relationship between Planck’s Law and Wien’s Displacement Law is shown in Figure 1. Notice that
the energy peak for the Sun is about 0.5 μm (500 nm), while at room temperature, 23 °C, it is just
below 10 μm.
Figure 1. Relation between Planck’s Law and Wien’s Displacement Law
MσT4πLλT,()λd
0
∞

==
Spectral Radiance and Temperature
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Wavelength ( m)
Spectral Radiance (W m-2 m-1 sr-1)
Sun
1000°C
500°C
100°C
23°C
-50°C
Peak

Precision Infrared Calibrator
Basic Infrared Thermometry Theory - Relating to the use of the Product
13
Emissivity
Emissivity is defined as the ratio of the energy emitted at a temperature to the energy emitted by a
perfect blackbody at that same temperature. A perfect blackbody would have an emissivity of 1.0.
However, in the real world there is no such thing as a perfect blackbody.
For example, if a perfect blackbody emits 10000 W/m2 at a given temperature and a material emits
5000 W/m2at that same temperature, then the emissivity of that material is 0.5 or 50 %. If another
material emits 9500 W/m2at that same temperature, it has an emissivity of 0.95.
It is important to note that for any opaque material, the ratio of energy rejected plus the ratio of energy
transmitted is equal to 1.0 (this is known as Kirchhoff’s Law). So if a material’s emissivity is 0.95, the
material rejects 5 % of the energy radiated by objects facing it. By contrast, if an object has an
emissivity of 0.50, the material rejects 50 % of the energy radiated by objects facing it. This means this
rejected energy can contribute to measurement accuracy. This is especially true when measuring
materials with lower emissivity, and objects at lower temperatures.
Uncertainty Caused by Emissivity
A lack of knowledge of emissivity itself can contribute greatly to inaccuracy in IR temperature
measurement. Figure 2shows a graph of this phenomenon in the 8 μm to 14 μm band.
For an example, say we are measuring an object at 500 °C. We assume it has an emissivity of 0.95.
However, its emissivity is really 0.93. This would cause our 8 μm to 14 μm IR thermometer to read the
temperature 6.7 degrees low, a -6.7 °C error in temperature measurement.
Figure 2. Effect of a 1 % Increase of Emissivity on Measured Temperature
Effect of a 1% Increase of Emissivity on Measured Temp
TBG=23°C, =0.95, =8 to14 m
-1.500
-1.000
-0.500
0.000
0.500
1.000
1.500
2.000
2.500
3.000
3.500
4.000
-50 0 50 100 150 200 250 300 350 400 450 500
Target Temperature (°C)
Measured Temperature Change (°C)

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Technical Guide
14
The emissivity of an object is not an easy thing to determine. One method is to take a calibrated
variable-emissivity IR thermometer, aim it properly at the object in question, and adjust its emissivity
until its reading matches the known temperature of the object. This gives an average emissivity of the
object over the IR thermometer’s bandwidth. This method assumes the measured object is gray.
We term an object as having constant emissivity over all wavelengths as being gray or a gray body. It
should be noted that most objects tend not to have a constant emissivity over all bandwidths, thus
these objects are not perfect gray bodies. Uncertainties in emissivity values need to be considered in
the total uncertainty of measurements with IR thermometers.
One widely used and accepted method in determining the spectral dependence on emissivity (or how
emissivity varies with wavelength) is Fourier Transform Infrared (FTIR) testing. A graph from such a
test is shown in Figure 6.
Effect of Background Temperature
Another effect related to emissivity is that of background temperature. Background temperature is the
temperature of objects facing the measured surface. Remember that when an object has an emissivity
of 0.95, it is rejecting 0.05 of background object’s radiation energy. Of course the amount of
background radiation is a function of the background objects’ temperature. An example of this effect is
shown in Figure 3.
Figure 3. Effect of a 1 % Increase in Background Temperature in the 8 μm to14 μm Band
Effect of a 1°C Increase in Background Temp on Measured Temp
TBG=23°C, =0.95, =8 to14 m
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
-50 0 50 100 150 200 250 300 350 400 450 500
Target Temperature (°C)
Measured Temperature Change (°C)

Precision Infrared Calibrator
Basic Infrared Thermometry Theory - Relating to the use of the Product
15
As can be seen in the graph, the effect of background temperature is more troublesome when you
measure lower temperatures than when you measure higher temperatures. The point of this discussion
is that in order to do good IR thermometry, background temperature must be controlled.
Effect of Angle on Emissivity
Another topic to be aware of relating to emissivity is that emissivity varies with angle. Typically,
emissivity is maximum when taking a measurement normal to an object and is zero when taking a
measurement parallel to an object. An example of this effect when using the Product is shown in
Figure 4. As can be seen in the graph, any measurements made within 15° of normal will cause an
error less than 0.001 in emissivity. This number can be evaluated against the graph in Figure 4to
obtain uncertainty due to angular deviation from normal.
Figure 4. Effect of Angular Emissivity Calibration Geometry
Along with emissivity, calibration geometry is one of the most misunderstood topics related to the
calibration and use of IR thermometers. Among the topics that are misunderstood are center of spot,
size of spot, scatter, size of source and distance to target.
Center of Spot
Many IR thermometers include lasers as a guide to show the user where to point them. These act as
approximating guides only. In reality, IR thermometers see areas much bigger than that small laser dot.
Also, an IR thermometer’s center of spot may not be exactly at the point where the laser is pointed. To
understand the impact of these two factors on a calibration, testing should be done to determine the
center of the spot. This information may be provided by the manufacturer as well.
Directional Emissivity
0.890
0.900
0.910
0.920
0.930
0.940
0.950
0.960
0 5 10 15 20 25 30 35 40 45 50 55 60
Angle (°)
Emissivit
y

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Technical Guide
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Size of Spot, Size of Source and Scatter
IR thermometer manufacturers frequently indicate a distance-to-spot-size ratio. It is computed at
specific distances. The spot size is the diameter that contains a given amount of energy detected by
the IR thermometer. This is typically 90 % to 95 % of the energy. This information is also just an
approximating guide. The energy outside this detection area is referred to as scatter. This means that a
surface area much larger than the given spot size is needed when calibrating IR thermometers. Spot
size is often referred to as size of source effect.
Two solutions to size of source effect problems are available through the calibration of the IR
thermometer, both related to calibration geometry including distance and target size. One method is to
calibrate the instrument under the same conditions under which it is used. That is, you point it at the
same size of target at a known surface temperature as what it is used to measure, from the same
distance, and under similar ambient conditions.
The other method is to duplicate the calibration geometry used by the manufacturer of that device. This
information should be available from the manufacturer. Under either method, you calibrate in a certain
intended amount of scatter into your measurement.
The target size needed to calibrate a given IR thermometer is dependent on the IR thermometer’s
optical system. Many IR thermometers come with a spot size diagram. These diagrams can be
misleading. As mentioned above, all of the energy the IR thermometer detects is within the given spot
diagram. Generally you will need at least 2 to 3 times the spot size diameter to use for calibration.
The Product provides a 150 mm (6 inch) diameter flat plate. This gives the user a large temperature
controlled surface to calibrate IR thermometers. 150 mm (6 inches) is a large enough diameter to
accommodate most handheld IR thermometers.
Distance to Target
The third topic of concern with calibration geometry is distance between the calibration target and the
IR thermometer being calibrated. It is important not to have the IR thermometer too close to the target.
This will cause the IR thermometer’s optics to heat excessively which will cause false readings. It is
also important to be not too far away. This will cause the target to not fill the IR thermometer’s spot size
and will cause a false reading.
Knowing the Correct Geometry
Information on these 3 factors, center of spot, size of source, and distance to target, should be
provided by the IR thermometer manufacturer. If this information cannot be obtained, ASTM provides a
guideline (ASTM Standard E1256-95) to determine some of these parameters.
Traceability
Fluke Calibration’s traceability for the Product calibration comes through a radiometric transfer
standard. The Product is calibrated with an 8 μm to 14 μm highly-accurate IR thermometer
(radiometer). This IR thermometer is calibrated with blackbody cavity baths. The temperature of these
baths is measured by PRTs which have a calibration traceable to NIST. A diagram of this traceability is
shown in Figure 5.