UK Thermography
Predictive & Preventative Maintenance Service

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This section is for students or those with an interest in thermal imaging in general. Content is always being added and updated so please add this page to your favourites for future reference. If you have any questions regarding thermography please feel free to contact us, we are happy to help.


Infrared Discovery
 
 Who discovered infrared radiation and how?

Frederick William Herschel, (15 November 1738 - 25 August 1822) was a German-born British astronomer, he was also a composer, known for creating 24 symphonies throughout his life. Not only being an astronomer and composer he was also a technical expert. William Herschel was born in Hanover, Germany in 1738. He followed his father into the Military Band of Hanover, before emigrating to Britain at age 19 where he pursued his passion for astronomy. He became famous for his discovery of the planet Uranus and two of its major moons (Titania and Oberon). He also discovered two moons of Saturn. In addition to this, he was the first person to discover the existence of the infrared part of the electromagnetic spectrum.

On 11 February 1800, Herschel was testing different telescope filters so he could observe sun spots. When using a red filter he found there was a lot of heat produced. To understand why, he carried out an experiment where he passed sunlight  through a prism thus creating a breakdown of the visible parts and colours of the electromagnetic spectrum. He placed a thermometer just beyond the red end of the visible part of the spectrum to create a control reading of ambient air temperature for his experiment. He was shocked when it showed a higher temperature than the visible spectrum and more so than the ambient temperature. Further experimentation led to Herschel's conclusion that there must be a form of light beyond the visible spectrum not seen by the naked eye. This part of the spectrum is what we now know as infrared.

The electromagnetic spectrum can be seen in the table below.



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What is thermography? 

Although thermography has been around for over 50 years, many people have not heard of it, or know the full potential of what it can offer. The word 'thermography', put simply, means 'the study of a thermal image'. Everything above absolute zero (-273.15 Deg C or 0 Deg Kelvin) gives off infrared radiation, or heat as its more commonly known. Thermographers use a special piece of equipment called a thermographic camera, (sometimes known as a thermal imager or infrared camera). This receives infrared radiation (heat) to create a thermal image known as a thermogram. This is a process similar to that of a photographic digital camera. The photographic digital camera receives light tones through a glass or plastic lens which are then focussed to hit an array of microscopic light sensitive cells. These light variations are then converted into a photograph. The more light sensitive cells a camera has, the more detail a photograph can display, In photography this measured in megapixel. A thermographic camera on the other hand receives temperature variations that hit an array of microscopic heat sensitive cells known as micro-bolometers placed on an FPA (Focal Plain Array). Lenses in these cameras are usually made of germanium which is one of the few substances that allows infrared radiation to pass through it and enables this to be focussed onto the sensor.  The variants in temperature hitting this sensor is then converted into a visual image on the thermal cameras screen. Most cameras have several pallets to chose from, some give a wide range of colours (The Rainbow Pallet) and are more suited for lower temperatures or situations where the temperature span is small, Others such as the Iron Pallet are similar to that of glowing metal where white is hot through to amber, red and eventually black which is the cooler end of the scale. Most people will be familiar with the emergency services using thermal cameras mounted on a helicopter to find criminals or for search and rescue purposes. These are a modified version of the hand held thermal camera's we use for thermographic surveys. The thermographer uses this equipment to convert infrared radiation into a visual thermogram that can be used to give a clear surface heat signature of an object. Where in a photographic camera each light sensitive cell (pixel) produces lighter or darker values in a photograph, pixels in the Thermogram give temperature information about the object being viewed. An example where this is used would be in a thermographic building survey. In this instance the thermal camera is used to see where heat is being lost or gained that could cause energy loss, additional insulation can be installed in the areas highlighted reducing this inefficiency. Another common use is to inspect an electrical control system for overheating cables and components. Electrical thermographic surveys are now recognised as a valuable part of site maintenance programs and can help reduce unexpected down time by finding faults before they become problematic or a fire risk. Thermography is a non-invasive zero contact tool that has many uses. If used correctly, with the appropriate training, infrared thermography can be used in a wide veriety of applications.













The First Thermographic Camera 

The first true thermographic cameras began with the development of the first infrared line scanner.  This was created by the US military and in 1947 and took one hour to produce a single image.  While several approaches were investigated to improve the speed and accuracy of the technology, one of the most crucial factors that needed to be considered dealt with scanning an image, which the AGA company was able to commercialise using a cooled photoconductor. This work was further developed at the Royal Signals and Radar Establishment in the UK when they discovered mercury cadmium telluride could be used as a conductor that required much less cooling.  Honeywell, in the United States also developed arrays of detectors which could cool at a lower temperature, but they scanned mechanically.  This method had several disadvantages which could be overcome using an electrical scanning system.  In 1969 Michael Francis Tompsett at the English Electric Valve Company in the UK patented a camera which scanned pyro-electronically and which reached a high level of performance after several other breakthroughs throughout the 1970s. Tompsett also proposed an idea for solid-state thermal-imaging arrays, which eventually led to modern hydridised single-crystal-slice imaging devices.






How are electrical faults discovered using thermography. 

Without going into electrical theory basically when electrical equipment operates it generates heat. When you look with a thermal camera at an electrical control panel for example, there are tens sometimes hundreds of components all operating at different temperatures. So how do we know what is good and bad heat? Any thermographer carrying out an electrical thermographic survey, must have a good knowledge of circuit operations and component function and identification. Without this knowledge many heat sources will be listed as a fault which may not actually be a problem at all. Most components will have manufacturers recommended operational temperature limits printed on them. If a component is exceeding these limits, degradation will start to occur. This is when a component would be identified as faulty in a thermographic survey report. There are many ways to identify the type of fault by understanding the heat pattern you see with the thermal imaging camera. Insecure connections cause high resistance which generates heat, distinctive heat patterns can be seen which identify which terminal, cable, or joint is at fault and the thermographers electrical knowledge will enable them to make the correct recommendation to resolve the issue. If you want to know more about how to identify faults in electrical systems please have a look at the courses UK Thermography have on offer. There is something for everyone especially those starting up in thermal imaging. The idea of electrical thermography is to help predict faults and failures which in turn save on potential production loss, downtime and component replacement. The last thing a client wants is to be given a list of remedial actions for images taken that are not actually a fault! See out training page for more information.

Alternate Uses 

Infrared Thermography is making continuous advancements, especially the medical and vetrinary fields. Medical thermology can be used to see injuries that can't be seen using alternate scanning methods such as X-Ray, MRI and ultrasound. Equine thermographic surveys are also becoming more commonplace as it is a fast, effective way of locating injuries such as sprains and tissue damage, thus enabling prompt treatment to specific areas. Injuries can be monitored to ensure healing is continuing and blood flow to areas restored. One of the key advantages of thermal imaging is that it is non invasive. Where MRI, X-Ray, Ultrasound and CT Scans emit energy at varying wavelengths to penetrate the body which in turn can cause additional problems, thermal imaging equipment simply receives infrared radiation that is naturally given off by the body. The only affect this can have on a person is a little inconvenience of having to stabilise the body's temperature in a controlled environment to guarantee accurate readings. Some tests may require reducing parts of the body to a lower than normal temperature to see how blood flow is affected which can highlight circulatory problems.
Modern day warfare has been revolutionised with heat seeking missiles and night vision aids. Thermography is being used for airport and boarder security to allow covert monitoring of controlled areas. Due to infrared cameras not requiring light to operate, images can clearly be seen even through fog and smoke. The Fire and Rescue service regularly use thermal cameras to find trapped people in smoke filled buildings and also ensure flames in contained buildings have not spread to other inaccessible areas. One use that was highly publicised was following the SARS outbreak in 2008. Infrared cameras started to be seen at airport customs, these were checking for raised body temperatures indicating potential infection. Jaguar were one of the first car companies to incorporate infrared cameras into their high end cars as a visual aid in fog, the list goes on... Infrared thermal imaging surveys can see what the eye cant and help predict failures in electrical systems thus preventing and reducing downtime. Please contact us if you have any questions regarding thermal imaging and its uses,













Encountered Problems and Limitations 

Advancements in technology and microelectronics have enabled a new breed of infrared camera to enter the market, The 'tool box' infrared camera is now an affordable piece of equipment for many engineers. Given this it has also opened up the market to low end thermographic surveys! just as you would not expect a professional photographer to photograph a wedding using a mobile telephone camera, you can not fault find on a site comprehensively using a budget camera. Professional thermographic surveys should be carried out using professional equipment. I personally surveyed a site several years ago where a budget camera was being used regularly, I still managed to highlight in excess of 25 faults 7 of which severe faults one being a mains supply cable operating at over 200 deg C and clearly had been there for some time. Most of these had been overlooked simply due to two factors, budget cameras and limited thermodynamic knowledge. Thermography can be deceiving, this is why training and the appropriate equipment for the job in hand are paramount to any person using a thermal camera and analysing thermograms. Without getting heavily into the laws of thermodynamics, a key problem encountered when analysing data is that every surface gives off a different amount of infrared radiation, this is referred to as it's emissivity. Calculations are used to monitor surface temperature and give accurate data. If the emissivity of a surface is too low, the camera will read a significantly different temperature that that actually present. This type of surface can have lots of reflective thermal interference from other heat sources in its surroundings including that given off by the thermal camera operator. Calculations are based on the theoretical perfect infrared emitter, this is what's called a 'black body', and has an emissivity of 1.0.  Anything lower than this requires specific offset calculations to generate accurate temperature data. Below is a table of common emissivity values for various surfaces. Modern thermographic cameras have built in calculations to cater for this variation and all the thermographer needs to do is enter a correct emissivity value into the camera and the calculation is done in real time for you. For more comprehensive training on thermography and analysing thermograms please see our training section and contact us to discuss your requirements.

Temperature Scales & History


Over the centuries various temperature scales have been created, there are 3 primary ones used today which are Kelvin, Celsius & Fahrenheit. Two other scales used are Rankine and Raumur, Rankine is mainly used scientific applications and Raumur is now somewhat obsolete. Sometimes Temperature is confused for Heat, these are very different. Heat is measured in W (watt) and temperature in Degrees. One is a power and the other a scale which are not the same.
 
Kelvin

The Kelvin Scale is what's called an absolute temperature scale. This is based on 'Absolute Zero', a theoretically temperature where scientists have determined molecular motion would stop. This temperature has never been reached although scientists have come close to the -273.15 Deg C mark. It has the same scaling as Celsius, however, Celsius is based on the freezing point of water (0 Deg C) and not molecules as Kelvin is. To convert to Kelvin from Celsius, simply add 273.15  to the Celsius temperature (0 Deg C = 273.15 Kelvin), note that Kelvin is not measured in Degrees, its simply Kelvin (K). The scale was created by William Thompson, also known as Lord Kelvin, a British scientist who made important discoveries about heat in the 1800's.

For an in-depth description of Lord Kelvin and his discoveries, click on his image to the right.

 
Celsius

The Celsius Scale (otherwise known as Centigrade) is what's called a 'relative' temperature scale. The measurement was known as centigrade until 1948 from the Latin word Centrum meaning 100, and Gradus, meaning Steps and is now named after the Swedish astronomer, Andres Celsius (1701 - 1744). It is based on the freezing and boiling point of water (0 Deg C  to 100 Deg C). From 1743 - until 1954 these temperatures were defined using a standard given the folowing constants, 1 standard atmosphere and the expansion of mercury being used to gain the measurement. This is what is commonly taught in schools today however, by international agreement the unit 'degree Celsius' and the Celsius scale are presently defined by 2 different temperatures; absolute Zero and the triple point of VSMOW (specially purified water). This definition precisely relates the Celsius scale to the Kelvin scale as described above. Celsius, along with Fahrenheit are one of the most commonly used scales today. Depending where you are from in the world you will find either of these temperatures referred to when temperatures are quoted.

For more information on Andres Celsius click on the image to the right.


 
Fahrenheit

In 1724 Daniel Gabriel Fahrenheit proposed the Fahrenheit Scale. This scale is still used as the primary measurement in some countries and is commonly seen alongside the Celsius scale on thermometers. Fahrenheit is a 'relative' temperature scale and it was originally based on the freezing point of brine. Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees—on Fahrenheit's original scale the freezing point of brine was zero degrees. This puts the boiling and freezing points of water exactly 180 degrees apart. Therefore, a degree on the Fahrenheit scale is 1180 of the interval between the freezing point and the boiling point.

For more information on Daniel Gabriel Fahrenheit, click on the image to the right.




 
Rankine

The Rankine Scale was proposed in 1859 by the engineer and physicist William John Macquorn Rankine. Like the Kelvin scale this is also an 'absolute' temperature scale. Rankine scale measurements however are based on the Fahrenheit scale and is measured in degrees. The symbol for degrees Rankine is °R (or °Ra if necessary to distinguish it from the Romer and Reaumur scales). Zero on both the Kelvin and Rankine scales is 'absolute zero', but the Rankine degree is defined as equal to one degree Faherenheit, rather than the one degree Celsius which is used by the Kelvin scale. A temperature of −459.67 °F is exactly equal to 0 °R. Some engineering fields in the U.S. measure thermodynamic temperature using the Rankine scale, however In the scientific world, thermodynamic temperature is usually measured using the Kelvin scale. The US NIST (National Institute of Standards and Technology) recommends not using degrees Rankine in NIST publications.

For more information on William John Macquorn Rankine, click on the image to the right.

 








 

Thermal Imaging Software & Tools*
 
Software and Demo's Available to download from the following suppliers.


Please click the logo above each software description to be taken to the relevant page.


FLIR Tools / FLIR Tools+ 3.1 (3.1.13080.1002)

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ThermaCAM Reporter 2000 Viewer (Dec 2002 Edition)

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ThermaCAM Reporter 7.0 SR4


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FLIR ResearchIR 3.4 SP1,
30-Day Evaluation (3.4.13126.2002)

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FLIR IR Camera Player 2.3.0

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IR Lens Calculator v.5



*All software in this section is to be used as per the suppliers license rules. Whilst every effort is taken to ensure links are correct and safe, UK Thermography accept no responsibility for the content or use of downloaded software or damage it may cause to operating systems. We have no affiliation with the companies contained in these links and are only sharing these links for informative purposes.

 


Professional Bodies

United Kingdom
Thermography Association



The British Institute of
Non Destructive Testing


Building Services Research
and Information Association



 

Thermal Camera Manufacturers


FLIR Systems



Thermoteknix



LAND IR



NEC
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