Thermal Imaging

What is Thermal Imaging?

Thermal imaging is a sophisticated and non-invasive technique that utilizes infrared

technology to detect heat emissions from various objects. This process converts the infrared
energy, which is invisible to the human eye, into a visible light display. The infrared (IR)
energy, or thermal energy, is emitted by all objects above absolute zero temperature, and the
variations in these emissions form the basis of thermal imaging.

How Does Thermal Imaging Work?

Thermal imaging operates on a simple yet effective principle: all objects emit infrared energy
as a function of their temperature. This form of energy, invisible to the human eye, can be
detected and translated into a visual image by a thermal imaging system. Here's a step-by-step
look at the process:

1. The thermal camera, equipped with an infrared detector, captures the infrared radiation
emitted from all objects in its field of view.
2. The captured radiation data is then processed by the camera's built-in software. An
optical system focused infrared energy to a sensor array, or detector chip, with
thousands of pixels in a grid.
3. The software translates the data into an image, known as a thermal image or
thermogram, representing the temperature variations of the scene.
4. Each temperature value is assigned a different color. Typically, warmer areas are
represented in red, and cooler areas are shown in blue. A matrix of colors corresponding
to temperatures is sent to the camera display as a picture.
5. Leading thermal and infrared cameras from manufacturers like Fluke give you the
power to then edit, transfer, store, and analyze your thermal images.

Where did thermal imaging camera originate?

It is unclear the origins of thermal imaging. There have been numerous accounts of thermal
imaging by other names from the 1800’s but no confirmed inventor. The thermal imaging
cameras used today are based on technology that was originally developed for the military. In
1929, Hungarian physicist Kálmán Tihanyi invented the infrared-sensitive (night vision)
electronic television camera for anti-aircraft defense in Britain. The first American
thermographic cameras developed were infrared line scanners. Thermal imaging in its present
form was originally developed for military use during the Korean War

Where do we use thermal imaging?

Thermal imaging cameras have migrated into other fields and have found many uses.
Electrical maintenance uses for thermal imaging are extensive. For example, power line
technicians use thermal imaging to locate and pinpoint joints and parts that are at risk of
overheating as they’re already emitting more heat than the stronger sections. They can also
help spot loose connections or devices that are starting to fail.

Plumbers use thermal imagers to inspect sites of possible leaks, mainly through walls and pipes.
Since the devices can be used at a distance, they’re ideal for finding potential problems in
equipment that is either hard to reach or might otherwise pose safety issues to workers.

Mechanical and building construction technicians who work with thermal insulation use
imaging to quickly identify leaks, which is important to maintain efficient temperature
regulation in a building. At a glance, they can analyse a building’s structure and spot faults.
Heat loss from walls, HVAC equipment, doors and windows are common thermal performance
issues that are easily picked up by a thermal imager.
Animal and Pest management is a field which has a surprising number of uses for thermal
imagers. They can help spot pests or animals in dark roof areas without having to climb up into
them, and they can detect potential termite activity. Also, they’re commonly used to more
easily conduct wildlife surveys in a totally non-invasive, non-intrusive manner.

Transport navigation gets significant benefits from thermal imaging, particularly when
traveling at night. For example, maritime navigation uses it for clearly seeing other vessels,
people and obstructions during the night while out at sea. In recent years, cars have begun
incorporating infrared cameras to alert drivers of people or animals beyond streetlights or the
reach of their headlights.

Healthcare and medicine also have practical uses, such as to spot fevers and temperature
anomalies. This has proven to be especially important in airports where these thermal imaging
cameras can quickly and accurately scan all incoming or outgoing passengers for higher
temperatures, which was crucial during recent outbreaks of diseases like SARS and Ebola.
Additionally, thermal imagers have been proven to help diagnose a range of disorders
associated with the neck, back and limbs, as well as circulatory problems.

Fire-fighters use thermal imaging to help them see through smoke, particularly in rescue
missions when they’re searching for people in an otherwise obscured and dangerous
environment. They also use thermal cameras for rapid identification of spot fires, so they can
intervene before they spread.
Police and law enforcement agencies incorporate thermal imagers into their surveillance
equipment, used for locating suspects especially at night, as well as to investigate crime scenes
and also for search and rescue operations. They’re superior to night-vision devices, as they
don’t require any ambient light and are unaffected by bright lights, which is essential for tactical
missions

Science and research are undoubtedly sectors that draw significant benefits from using thermal
imagers, for accurate and precise visualisations of heat patterns such as dark side of the moon.

Other applications which use a thermal imaging camera include heating, ventilation and air
conditioning installations, mold detection, quality assurance in processes such as glass
manufacturing and many more.

Money saving is something you wouldn’t necessarily expect from a thermal imaging device,
but when you think about everything it can do, it definitely makes sense. After the upfront cost
of purchasing the device, they can undoubtedly save your business or home thousands of
dollars or more in potential maintenance and repair costs that might incur if faults, leaks or
weaknesses were not identified earlier.

However, it’s important to recognise that while thermal imaging has all these applications, it’s
often best to use additional instruments or tools when appropriate to confirm what you’re
seeing. Additionally, it’s worth noting that thermal imaging cameras are unable to
see through walls and objects, but rather, they only pick up what’s reflected off them.
Hall Effect Sensors

Hall Effect Sensors are devices which are activated by an external magnetic field. We know
that a magnetic field has two important characteristics flux density, (B) and polarity (North and
South Poles).
The output signal from a Hall effect sensor is the function of magnetic field density around the
device. When the magnetic flux density around the sensor exceeds a certain pre-set threshold,
the sensor detects it and generates an output voltage called the Hall Voltage, VH. Consider the
diagram below.

Hall Effect Sensor Principles

Hall Effect Sensors consist basically of a thin piece of rectangular p-type semiconductor
material such as gallium arsenide (GaAs), indium antimonide (InSb) or indium arsenide (InAs)
passing a continuous current through itself.
When the device is placed within a magnetic field, the magnetic flux lines exert a force on the
semiconductor material which deflects the charge carriers, electrons and holes, to either side
of the semiconductor slab. This movement of charge carriers is a result of the magnetic force
they experience passing through the semiconductor material.
As these electrons and holes move side wards a potential difference is produced between the
two sides of the semiconductor material by the build-up of these charge carriers. Then the
movement of electrons through the semiconductor material is affected by the presence of an
external magnetic field which is at right angles to it and this effect is greater in a flat rectangular
shaped material.
The effect of generating a measurable voltage by using a magnetic field is called the Hall
Effect after Edwin Hall who discovered it back in the 1870’s with the basic physical principle
underlying the Hall effect being Lorentz force. To generate a potential difference across the
device the magnetic flux lines must be perpendicular, (90o) to the flow of current and be of the
correct polarity, generally a south pole.
The Hall effect provides information regarding the type of magnetic pole and magnitude of the
magnetic field. For example, a south pole would cause the device to produce a voltage output
while a north pole would have no effect. Generally, Hall Effect sensors and switches are
designed to be in the “OFF”, (open circuit condition) when there is no magnetic field present.
They only turn “ON”, (closed circuit condition) when subjected to a magnetic field of sufficient
strength and polarity.

Hall Effect Applications

Hall effect sensors are activated by a magnetic field and in many applications the device can
be operated by a single permanent magnet attached to a moving shaft or device. There are many
different types of magnet movements, such as “Head-on”, “Sideways”, “Push-pull” or “Push-
push” etc sensing movements.
Which every type of configuration is used, to ensure maximum sensitivity the magnetic lines
of flux must always be perpendicular to the sensing area of the device and must be of the correct
polarity.
Also to ensure linearity, high field strength magnets are required that produce a large change
in field strength for the required movement. There are several possible paths of motion for
detecting a magnetic field, and below are two of the more common sensing configurations
using a single magnet: Head-on Detection and Sideways Detection.

Head-on Detection

As its name implies, “head-on detection” requires that the magnetic field is perpendicular to
the hall effect sensing device and that for detection, it approaches the sensor straight on towards
the active face. A sort of “head-on” approach.
This head-on approach generates an output signal, VH which in the linear devices represents
the strength of the magnetic field, the magnetic flux density, as a function of distance away
from the hall effect sensor. The nearer and therefore the stronger the magnetic field, the greater
the output voltage and vice versa.
Linear devices can also differentiate between positive and negative magnetic fields. Non-linear
devices can be made to trigger the output “ON” at a pre-set air gap distance away from the
magnet for indicating positional detection.

Sideways Detection

The second sensing configuration is “sideways detection”. This requires moving the magnet
across the face of the Hall effect element in a sideways motion.
Sideways or slide-by detection is useful for detecting the presence of a magnetic field as it
moves across the face of the Hall element within a fixed air gap distance for example, counting
rotational magnets or the speed of rotation of motors.
Depending upon the position of the magnetic field as it passes by the zero field centre line of
the sensor, a linear output voltage representing both a positive and a negative output can be
produced. This allows for directional movement detection which can be vertical as well as
horizontal.
There are many different applications for Hall Effect Sensors especially as proximity sensors.
They can be used instead of optical and light sensors were the environmental conditions consist
of water, vibration, dirt or oil such as in automotive applications. Hall effect devices can also
be used for current sensing.
We know that when a current passes through a conductor, a circular electromagnetic field is
produced around it. By placing the Hall sensor next to the conductor, electrical currents from
a few milliamps into thousands of amperes can be measured from the generated magnetic field
without the need of large or expensive transformers and coils.
As well as detecting the presence or absence of magnets and magnetic fields, Hall effect sensors
can also be used to detect ferromagnetic materials such as iron and steel by placing a small
permanent “biasing” magnet behind the active area of the device. The sensor now sits in a
permanent and static magnetic field, and any change or disturbance to this magnetic field by
the introduction of a ferrous material will be detected with sensitivities as low as mV/G
possible.
Positional Detector

This head-on positional detector will be “OFF” when there is no magnetic field present, (0
gauss). When the permanent magnets south pole (positive gauss) is moved perpendicular
towards the active area of the Hall effect sensor the device turns “ON” and lights the LED.
Once switched “ON” the Hall effect sensor stays “ON”.
To turn the device and therefore the LED “OFF” the magnetic field must be reduced to below
the release point for unipolar sensors or exposed to a magnetic north pole (negative gauss) for
bipolar sensors. The LED can be replaced with a larger power transistor if the output of the Hall
Effect Sensor is required to switch larger current loads.