Nowadays, thermal imaging is an important diagnostic process that is widely used in industry, particularly as thermal surveys have become part of many fixed wiring inspections.
What Are Thermal Cameras?
Thermal cameras consist of a lens which allows infrared radiation to be focused onto an infrared sensor. The camera has specialist dedicated software which then translates the collected radiation into a visible image which can be viewed and analysed by the thermal imaging camera user.
The thermal image will naturally draw the un-trained eye to the hottest parts of the image and the user may therefore assume that this is where there is a problem. This is not always the case because there are many different factors that must be taken into account when a thermal image is analysed. Next we will examine two of the things that can cause errors by discussing the two most common mistakes that are made by those using thermal cameras, without training, for electrical inspections.
Reflections Can Be Misinterpreted by the User
Reflections can be seen all the time with natural visible light. Glass, mirrors and polished shiny surfaces such as vehicles will all reflect their natural surroundings. Radiated heat reflections are similarly affected.
If you point a thermal camera at a polished surface, like metals such as steel, copper or aluminium, then only a small percentage of what the camera is recording is actually radiated from the metal. Most of it will be reflections coming from other objects reflecting in turn from the metal.
The above image shows a thermal image of copper being heated on a hotplate. In this example a piece of black plastic electrical tape is covering a part of the metal to ensure that we do indeed see an accurate temperature reading.
We have placed two spot tools onto the thermal image. Spot 1 is on the black tape, showing a temperature reading of 76.7°C. Spot 2, located on the copper, is showing a temperature of only 26.2°C! The surface of the copper plate is reflecting the heat radiated from the objects that are in front of the copper! This means that the copper actually appears cooler than it is which, of course, is not correct!
What this means is that, due to the likely presence of different types of metal in an electrical environment, there is a large potential for error when diagnosing faults. If the user of the thermal camera does not understand this then potentially dangerous problems could be missed or even signed off as safe in a report! For this reason we would highly recommend specialist thermography training for users of this type of equipment.
Emissivity and Reflected Apparent Temperature Controls
Thermal cameras have a number of specialist settings that can be adjusted by the user. The correct settings need to be applied to get reliable results.
Temperature readings are important; firstly you must understand that the image will often look the same regardless of any of the settings. Secondly, the use of temperature readings in electrical applications is paramount, as this information will allows you to classify the fault in terms of its severity and to make the best informed recommendations to resolve any issue.
The two settings that will have the most importance are emissivity and the reflected apparent temperature.
Emissivity is basically the capacity of an object to emit, or radiate, heat. Objects that have a low emissivity are not really suited to infrared thermography. Low emissivity objects reflect more and it is therefore difficult to gain an accurate temperature reading from them.
Reflected Apparent Temperature
The reflected apparent temperature is the culmination of all of the radiation from the objects impacting on the target. This setting will need to be varied depending on the local environment.
Consider Taking a Thermography Training Course or Seminar
It should be apparent from the above that it is far too easy for users of thermal cameras to obtain inaccurate results. Inaccurate results could drive poor decision making, potentially creating unexpected risks to people and property.
For these reasons, it is important to ensure that thermal camera users are fully trained both in the use of the equipment and in the evaluation of their results as well.
The most sensible course of action is to find a reliable provider of thermography training. In this way you will be able to fully utilise a thermal camera in order to get accurate and useful results from any use of them. Look for companies, such as Instrotech for instance, who will offer a full range of training, from free seminars through to formal thermography training courses including the use of thermography in electrical and building applications.