Fluke 561 IR thermometer
Fluke 561 IR
for HVAC and Electrical Applications
Measuring chiller pump motor bearing and case temperature.
In contact thermometry, the measuring device transfers heat to
or from a contacted object until
it is at the same level of molecular activity, or temperature. It is
simple, sensible and intuitive.
All matter seeks temperature
equilibrium. Heat is transferred by
conduction, convection and radiation. Conduction is the transfer
of heat by molecular contact.
Convection is the transfer of heat
by the mixing of a fluid (gas or
liquid). Radiation is the transfer
of heat by transmission through
a medium or space, which is
independent of conduction or
convection. It is this invisible IR
radiation that an IR thermometer
is detecting and reporting as the
surface temperature of the source
of the radiation.
While all matter above absolute zero radiates/infrared energy
three major factors determine
how accurately we can measure
this radiated heat: emissivity,
reflectivity and transmissivity.
Infrared (IR) radiation
IR radiation is everywhere and
continuous. The greater the difference in material temperatures,
the more obvious IR radiation is.
The vacuum of space transmits
IR radiation emitted from the sun
93,000,000 miles to earth where
we absorb and are warmed by
that IR radiation as we stand in
view of the sun. We are cooled
Application Note
The Fluke 561 Infrared Thermometer
combines the best of contact and noncontact thermometry. It features higher
optical performance, measurement
accuracy, and professional quality for
a market that is overloaded with entry
level IR thermometers.
IR non-contact thermometry provides
speed, convenience, accessibility and,
sometimes, safety. Type-K thermocouple thermometry provides the accuracy
needed for critical measurements of
metallic objects, internal temperatures,
and ambient temperature with the
flexibility and precision provided by a
choice of many probe styles available
for the particular task at hand. It is
the best of both worlds, but they are
indeed different worlds and it is important to understand those differences.
by the IR radiation we emit to the
frozen foods as we walk down the
freezer isle at the grocery store.
These are two obvious examples
of the quality of IR radiation
effects. We feel the change so we
know it is occurring.
When we want to quantify the
effects by measuring the IR radiation temperature, we break out our
IR thermometer. Different materials exhibit different IR radiation
qualities. Before we interpret the
readings from an IR thermometer,
we need to understand the basic
principles of measuring IR radiation and the IR radiation characteristics of the particular material
being measured.
F ro m t h e F l u k e D i g i t a l L i b r a r y @ w w w. f l u k e . c o m / l i b r a r y
Emissivity is the quality of a
material that allows it to radiate
its heat from its surface.
Reflectivity is the quality of a
material that allows it to reflect
radiated heat from another
Transmissivity is the quality
of a material that allows radiation from another source to
pass through it.
Absorption is the quality of
a material to receive radiation
from another source.
IR radiation = absorption +
reflection + transmission
Copper blackened by very heavy
oxidation has even less reflectivWhatever IR radiation is emitted, ity with proportionately more
will be absorbed. So absorption
emissivity (0.88). Most painted
= emissivity. It is the IR radiation surfaces have very high emisemitted from a surface that the IR sivity (0.9-0.95) and negligible
thermometer reads. An IR therreflectivity.
mometer cannot read IR radiation
The only setting on most IR
transmitted in the air (gas), so
thermometers is for the emissivwe can ignore transmissivity by
ity rating of a material, and in
most field work. This leaves us
many cases, that will be preset
with a basic IR radiation meaat 0.95, which works quite well
surement formula.
for organic and painted surfaces.
An emissivity adjustment feaIR radiation = emissivity –
ture allows the thermometer to
compensate for less IR radiation
Reflectivity is inversely proportional to emissivity. The more an emitted by some material surfaces, particularly metals. Reflecobject reflects IR radiation, the
tivity is only an issue if there is a
less it emits. Reflectivity often
source of high temperature emiscan be relatively judged accordsion in the vicinity of a surface
ing to our visual determinations
being measured that can reflect
of reflectivity. New copper has
that nearby high temperature IR
a very high reflectivity and low
emissivity (0.07-0.2). Copper that radiation.
is oxidized has less reflectivity
and more emissivity (0.6-0.7).
2 Fluke Corporation
Fluke 561 Infrared Thermometer for HVAC and Electrical Applications
The Fluke 561 Infrared Thermometer has three emissivity
settings: High (0.95), medium
(0.7), and low (0.4). There are
three methods of determining
the emissivity. One, use a chart
that lists the emissivity of various
materials, or two, apply a piece
of black electrical tape to the surface being measured. Apply the
tape to the surface, compare the
measured IR temperature of the
taped to the bare surface, adjust
emissivity until the temperatures
match or closely match. The third
method is to plug a K-type contact probe into the Fluke 561 IR
Thermometer to measure surface
temperature while reading IR
temperature, then adjust emissivity until the IR temperature
display most closely matches the
KTC temperature display.
Polished Brass: 0.03
Oxidized Brass: 0.61
Roughly Polished Copper: 0.07
Black Oxidized Copper: 0.78
Black Lacquer Paint: 0.96
Commercial Sheet Aluminum: 0.09
Oxidized Lead: 0.43
Rusted Iron: 0.78
Organic/painted materials 0.95
IR or contact thermometry: the choices
Use the IR temperature function when speed, convenience,
accessibility, safety, trending,
surface temperature or temperature comparisons are the key
Use the contact thermocouple
function when internal temperature, ambient temperature or the
accuracy of critical temperatures
of metallic objects are prime.
Use both together when a temperature differential between a
surface (IR) and the air (KTC) is
key, or when adjusting the IR
emissivity setting.
The IR advantage
Speed, convenience and accessibility top the list for IR vs.
contact thermometry. The Fluke
561 IR Thermometer takes less
than 500 milliseconds to display an IR temperature. With
contact thermometry, the probe
must be in good thermal contact with a cleaned surface, and
time allowed for the probe to
sink heat and reach equilibrium
with the surface. This can take
minutes, and the surface must be
accessible and safe to measure.
Many IR temperature readings
can be made in less time than it
takes to prepare a surface, attach
a probe, and wait for temperature equilibrium.
Many of the temperatures
sought in several trades are more
qualitative than quantitative
(“qualitative” meaning relative/
comparative temperatures and
“quantitative” meaning specific,
accurate temperatures). And, on
most surfaces, the IR temperature is highly accurate and will
be your primary choice except
on critical temperatures such as
superheat and subcooling, or for
air temperatures which a IR thermometer cannot read directly.
While scanning without the
thermocouple connected, the
Fluke 561 IR Thermometer can
record maximum, minimum, and
differential temperatures. One
at a time, these temperatures
can be read in the secondary
display. During or after the scan,
the rocker button can be used
to scroll between these values.
Releasing and pulling the trigger
will begin recording new values
to store.
Measuring temperature of fuses and electrical connections.
3 Fluke Corporation
Fluke 561 Infrared Thermometer for HVAC and Electrical Applications
• IR thermometers are invalu-
able for walk-through assessments of building surfaces
from indoors or outdoors.
Providing accessibility through
heights and distances, an IR
thermometer can scan building
envelope surfaces for temperatures that could indicate points
of infiltration or insulation
deficiencies. Scan along baseboards and around windows
and doors for building envelope integrity.
• Discharge temperatures of
grills, diffusers and registers
can be quickly determined
from a comfortable stance in
a convenient location. The IR
thermometer does not directly
measure the temperature of
the air but of a nearby surface
that has equilibrated to the
air stream. Effects of register
throw and evidence of stagnant zones can be determined
by scanning ceiling and wall
• Scanning ductwork for air leaks
or quality of insulation is quick
work. Duct insulation surface
temperature should never be
less than 5 °F (-15 °C) above
the highest ambient dew point
temperature to prevent sweating. Relative humidity at the
duct insulation surface should
remain below 60 % RH to
prevent mold growth. These
same rules apply for scanning basement or crawlspace
surfaces. The Fluke 971 Humidity meter is a perfect companion for the Fluke 561 when
checking for conditions that
can support mold growth. The
Fluke 971 displays air temperature, wet bulb temperature,
dew point temperature, and
relative humidity.
To troubleshoot compressor discharge line temperature use an IR thermometer
to survey temperatures at the compressor head, compressor oil sump,
evaporator coil and suction line, discharge line, condensor coil and liquid line,
and fan motor.
• IR thermometers are perfect
for routine trending of equipment operating temperatures.
Scan compressor discharge
and suction line temperatures,
compressor head and sump
temperatures, capacity control
• Compare motor or blower bearings for equivalent operating
temperatures. Scan sheaves
from the hub to the circumference for even temperature.
Elevated sheave temperature
at the circumference points to
slipping belts. (Don’t try this
with a contact thermometer
• Scan evaporator or condenser
hairpins and U-bends, distributor tubes, or driers for restrictions.
• Scan reversing valve pilot
tubes for proper discharge or
suction gas flow.
• Scan steam pipes and traps for
proper operation, or indicators
that will lead to the source of
4 Fluke Corporation
• Scan for temperature differen-
tial between hydronic supply
and return loops and temperature rise across boiler supply
and return lines.
• Scan to locate radiant heat
• Scan energy recovery wheels
for effectiveness.
• Scan for discharge temperatures of unit heaters mounted
high above a warehouse floor.
• Scan a room thermostat case
to compare to temperature
displayed by the thermostat.
IR thermometers allow you to
safely check temperatures in
locations such as live electrical
circuits that would be difficult
or dangerous to access with a
contact thermometer. Loose or
poor quality electrical connections are sure to fail, sometimes
catastrophically. Poor electrical
connections have increased resistance, which results in increased
temperature. Elevated temperatures will direct the mechanic to
Fluke 561 Infrared Thermometer for HVAC and Electrical Applications
a closer mechanical inspection of
the device. Relays and contactors have full load operating
temperature rise specifications
that can assist in the determination whether or
not they are operating within
• Scan contactors or starters for
elevated temperatures between
fixed and movable contacts,
and at the lug connections.
Look for temperature differentials between poles. Each
pole should have equivalent
temperatures under equivalent
load. If one pole has elevated
temperatures compared to the
other poles, that indicates a
• Scan relay connections and
relay case for elevated temperatures.
• Scan disconnects, buss connections and fuses for elevated
temperatures. Look for equivalent temperatures between
poles. Remember that the
emissivity for the paper covering of a fuse is higher than
the emissivity of a clean bare
• Scan wire nut or bug connections for elevated temperature.
• Scan along the length of
conductor insulation for consistent temperature.
Remember to always follow
electrical safety procedures. The
higher the voltage, the quicker
it can find an alternate path to
ground. Don’t let that path be you.
Taking a contact temperature measurement at the compressor outlet on the liquid line.
Contact thermometry
There are times when there is no
substitute for contact thermometry. Critical temperatures such as
superheat and subcooling require
good contact thermometry to
obtain the required accuracy and
precision. Suction line superheat
of systems using a fixed restrictor metering device is a critical
Forty years ago, expected
liquid line subcooling may have
been 20 °F (-6 °C) or even more
for some equipment. Today,
especially with the new 13 SEER
minimum efficiency requirement
of all single phase comfort cooling air conditioners and heat
pumps 5 tons or less, liquid line
subcooling of thermal expansion valve equipment is a critical temperature. 10 °F (-12 °C)
of subcooling for modern TXV
equipped systems is no longer
necessarily a valid target. High
efficient equipment frequently
requires subcooling values less
than 10 °F. Subcooling values
are sometimes listed with tenths
of a degree target value. Some
smaller capacity equipment is
even listed with subcooling values as low as 3 °F (-16 °C). So
now, even subcooling is a critical
An IR thermometer cannot measure air temperature
directly, so contact thermometry
is required for this purpose. Air
temperature rise across a furnace still requires a probe to
be inserted into the ductwork.
Accurate conditioned space or
outdoor air temperatures need
to be taken by the thermocouple
probe. Low mass boilers should
have the temperature rise taken
by contact thermocouples for
When IR temperatures are not
what is expected, use a thermocouple probe to verify accuracy.
Technicians rarely rely on a single test, or reading, to condemn
a process. They use all of the
techniques in their bag of tricks
to validate their diagnosis. With
two temperature technologies
in one tool, with simultaneous
display, the technological bag of
tricks just expanded.
The Fluke 561 IR Thermometer
comes equipped with a type-K
thermocouple, complete with a
Velcro strap for fastening to pipe
surfaces. Any of the other type-K
thermocouples with a standard
mini-connector you may already
have can also be used. While
bead thermocouples are versatile
and very portable, they are not
necessarily the best choice for all
The Fluke 80PK-8 pipe clamp
thermocouple is a perfect and
fast solution for any temperature
measurement from tubing and
pipes; Subcooling, superheat,
hydronics, service water supply.
The 80PK-26 general purpose
probe with its 8 inch insertion
length and low mass casing
tip is well suited for speedy air
temperatures and surface contact measurements. For both air,
surface and liquid immersion, the
8 inch probe length with pointed
tip of the 80PK-25 is likely to
become one of your essentials.
kPa psi
cmHg in Hg
Use a multimeter and a pressure module to quickly and
accurately determine suction pressure.
5 Fluke Corporation
Fluke 561 Infrared Thermometer for HVAC and Electrical Applications
There is one contradictory
requirement of the two temperature measurement requirements
of the Fluke 561 IR Thermometer. Oxidized copper will result
in more accurate IR temperature
readings, but contact thermometry requires that the copper
be clean since oxidation acts as
an insulator and will retard the
transfer of heat by conduction.
• Superheat is a critical measurement that must be taken on
equipment utilizing a fixed
restrictor metering device.
Without specific instructions
from the equipment manufacturer, measure superheat
6 inches from the compressor
suction stub. Superheat equals
suction line temperature minus
evaporator temperature. While
a TXV continuously adjusts
refrigerant flow to maintain
a predetermined amount of
superheat at the evaporator outlet, a fixed restrictor
system’s superheat is dependent on several variables that
can be broken down into two:
heat applied to the evaporator
and condensing temperature.
Most superheat tables specify
400 cfm of air per ton of capacity as a baseline for continuing. Given the proper airflow
across a clean evaporator and
condenser, the superheat is
determined by the wet bulb
temperature of the return
air and the outdoor ambient
temperature at the condensing unit (air temperature in
the shade to avoid the effects
of radiant heat from the sun).
6 Fluke Corporation
A quick infrared survey can check for leaks and uneven temperatures in both the heater and pipes.
Since this superheat is a
critical temperature, no “rules
of thumb” should be used in
its place. If the equipment
manufacturer’s superheat chart
or slide rule is not available,
use one supplied by another
manufacturer. Remember that a
good technician will not bless
or condemn a process based on
a single test.
Checking superheat is the last
step. First check cleanliness of
coils, filters, blowers, air flow,
electrical, etc. and know that the
system is ready for the final fine
tuning that superheat assures.
Superheat is the amount of sensible heat added to the refrigerant after all of the refrigerant
Fluke 561 Infrared Thermometer for HVAC and Electrical Applications
in the evaporator is “boiled” to
a vapor. Adding refrigerant will
reduce the amount of superheat. Recovering refrigerant will
increase the amount of superheat. Low suction pressures do
not necessarily mean low charge.
Check for evaporator and filter
cleanliness, proper air flow, and
suction line temperature before
adding refrigerant.
• Subcooling should be measured
with a contact thermometer
probe. The new NAECA 13
SEER minimum requirement
that became effective in
January 2006 for single phase
equipment 5 tons or less may
introduce you to subcooling
values lower than you are
subcooling. Too little refrigerant results in an undercharge
and insufficient subcooling.
Subcooling equals condensing
temperature minus liquid line
temperature. Some manufacturers may substitute “approach”
temperature values for subcooling temperature values. While
subcooling compares liquid
line temperature to condensing temperature, the approach
temperature compares liquid
line temperature to outdoor
ambient air temperature. The
manufacturer has calculated
what the approach temperature should be to achieve
the desired subcooling. This
allows a technician to check
the charge without attaching gauges. If the approach
temperature is OK and all
of the other checks confirm
proper operation, then there is
no need to attach gauges.
A quick scan can pick up substantial differences in temperature values
that could indicate an insulation leak. Don’t rely on the exact temperature
readings, however, without first adjusting for the emissivity and
reflectivity of the insulation material.
accustomed to seeing. Expect
to see more match-ups that
require thermal expansion
valve metering, high efficiency
condenser and evaporator
motors, and even larger heat
transfer coils.
Since thermal expansion valves
control superheat, liquid line
subcooling is the method
for fine-tuning the refrigerant charge. Proper air flows,
cleanliness of coils and filters,
mechanical integrity and
electrical should be confirmed
correct before adjusting charge
to subcooling values.
7 Fluke Corporation
Subcooling measures how
much the refrigerant has been
cooled below its condensing temperature. In order to
cool the refrigerant below its
condensing temperature, the
refrigerant must be exposed to
the condensing medium long
enough for its temperature
to be reduced sufficiently. In
an air-cooled condenser, the
refrigerant backs up into the
condenser for the air to cool
it below its condensing
temperature. Too much
refrigerant backed up into the
condenser results in an overcharge indicated by too much
Fluke 561 Infrared Thermometer for HVAC and Electrical Applications
Higher optical performance, measurement accuracy, and professional quality are reason enough
to choose the Fluke 561 IR Thermometer. Add to this single hand
operation, laser sighting, MIN/
MAX/DIF temperature, high-medium-low emissivity adjustment,
bead thermocouple with Velcro
fastener included and you have
a highly accurate and versatile
tool. Equipped with the standard
miniconnector jack for type-K
thermocouples, there are many
general purpose and specialty
probes that can be used in place
of the provided Velcro pipe probe
thermocouple. Additionally, the
companion user guide that comes
with the thermometer has extensive step-by-step procedures for
most of the applications outlined
in this article.
IR thermometer specifications
IR thermometer models are designed
with variable characteristics depending
on the application design. Variables
in model design include distance to
spot ratio, field of view, focus and focal
distance, wavelength of emitted IR
radiation, and environmental operating
D:S = 12:1 at focal point
132 mm @ 1500 mm
(5.3 in @ 60 in)
38 mm @ 300mm
(1.5 in @ 12 in)
5 mm @ 900 mm
(3 in @ 36 in)
When measuring smaller objects, use
the Fluke 561 within 6 ft (1.75 m) of
the intended target. The measured area
increases with distance (the distance
divided by 12, approximately).
Distance to Spot Ratio
(D:S) is a handy way to approximate the size of the measurement spot on the target relative
to the distance the thermometer
is from the target. A D:S of 12:1
would result in a three inch spot
at a target distance of 36 inches
or a slightly larger than one foot
spot at a target distance of 12
feet. At a given distance, the
larger the D:S ratio, the smaller
the spot. An IR thermometer with
a 90:1 ratio would have about
a 1-1/16 inch measuring spot
at an eight ft distance to target,
to 150 °F. An adjustment period
is required for sudden changes
of 10 °F or more degrees for
the thermometer to be accurate
under the new conditions.
Particulates in the air (e.g.,
steam, dust, smoke) between the
thermometer and the target will
Field of View refers to the
distort the readings.
spot size in relationship to the
Some of the other basic
surface being measured. The
report ranges,
spot size should be contained
within the perimeter of the target
The Fluke 561 IR thermometer
surface, centered on the area
temperature measuring range is
of interest. Ideally, the surface
from -40 °F to 1022 °F at an IR
being measured should be at
wavelength of 8 to 14 microns
least twice the diameter of the
with a response time of less than
spot size for greatest accuracy.
500 milli-seconds. The K-type
Focus is preset in most IR therthermocouple included with the
mometers at infinity.
Fluke 561 has a range is from
Minimum Focal Distance is the -32 °F to 212 °F. Also within are
other specifications and features
distance from target that results
that make this an especially
in the smallest spot size. With
attractive thermometer such as
the Fluke 561 IR Thermometer,
the minimum focal distance is 36 the ability to record in real time
inches. As thermometer distance maximum, minimum and relative IR temperatures. Or a single
to the target is either increased
or decreased, the measuring spot handed operation for point and
shoot measurements with the
size will increase.
index finger, guided by a laser
Environmental Conditions
beam site, while simultaneously
are factors that affect the opera- scrolling through temperature
tion of the IR thermometer.
variables with the thumb on a
The ambient operating range
rocker button.
(temperature of the Fluke 561)
should be between 32 °F to
120 °F within a relative humidity between 0 % to 90 % RH as
long as moisture from the air
does not condense onto or into
the thermometer. Accuracy is
compromised outside of these
conditions. A thermometer stored
Fluke.Keeping your world
overnight in a 30 °F van and
up and running.®
then brought into a
70 °F, 25 % RH (32 °F DPT)
Fluke Corporation
environment will cause moisture
PO Box 9090, Everett, WA USA 98206
from the air to condense on the
Fluke Europe B.V.
PO Box 1186, 5602 BD
cold surfaces of the thermomEindhoven, The Netherlands
eter. The thermometer storage
For more information call:
temperature range is from -4 °F
In the U.S.A. (800) 443-5853 or
while a thermometer with a 12:1
ratio would have about an 8 inch
measuring spot at an 8 ft distance to target. The laser spot is
for targeting purposes only and
is unrelated to the IR measuring
spot size.
Fax (425) 446-5116
In Europe/M-East/Africa (31 40) 2 675 200 or
Fax (31 40) 2 675 222
In Canada (800) 36-FLUKE or
Fax (905) 890-6866
From other countries +1 (425) 446-5500 or
Fax +1 (425) 446-5116
Web access: http://www.fluke.com
©2006-2007 Fluke Corporation. Specifications
subject to change without notice. Printed in U.S.A.
9/2007 2634903 A-EN-N Rev B
8 Fluke Corporation
Fluke 561 Infrared Thermometer for HVAC and Electrical Applications
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