Thermal imaging is becoming an important diagnostic process in many of today’s industries. Insurance companies are making it compulsory in some cases with regard to fire prevention, whilst the majority of electrical contractors are being asked to carry out thermal surveys as part of the fixed wiring inspections.
In this article we are going to consider how the cameras are used in an electrical application.
So, is it as easy as purchasing a camera, pointing and shooting then relying on the software to do the work? Can the cameras lie and if so, just how serious can misinterpretation of a thermal image be?
In order to answer this question, we first need to understand a bit about thermography. Thermal cameras are made up of a lens, that allows infrared radiation to transmit through to an infrared detector. The camera software then translates the radiation into a visible image that can be viewed on screen and analysed by the user.
To the untrained eye, it is very easy to be drawn to the hotter parts on a thermal image and immediately assume there is a problem, but this is not always the case. There are many factors that need to be taken into consideration when analysing a thermal image and many things that can cause errors. We are now going to consider the two most common mistakes made in the use of thermal cameras for electrical inspections.
Misinterpretation of Reflections
With visible light we see reflections all the time, mirrors, glass, polished surfaces will all reflect their surroundings. Similarly, reflections of heat are also present in the infrared spectrum.
When a thermal camera is pointed at polished surfaces, such as copper, steel and aluminium, only a very small percentage of what the camera is seeing is radiated from the actual metal itself, the vast majority of it is coming from other objects impacting on the target.
To illustrate this, the following example shows a piece of copper heated up on a hotplate. In the example a piece of black electrical tape has been placed over the copper to give a true temperature reading and use as a reference point:
Two spot tools have been placed onto the thermal image, spot 1 is on the black tape, reading 76.7°C giving us a true reading, whereas spot 2, which is on the copper plate, reads only 26.2°C. The surface of the copper plate is reflecting, so what the camera is actually reading here is the reflected radiation from the objects in front of the copper. To the camera, the copper appears cooler than it actually is.
Considering how many times you would come across metal contacts in an electrical environment, there is huge room for error when diagnosing faults. Failure to understand this will result in potentially dangerous problems being missed and even worse, being signed off as safe in a report.
Reflected Apparent Temperature & Emissivity
Following on from the above example, thermal cameras have a number of settings that can be adjusted. In order to get as accurate a temperature measurement as possible, the correct settings need to be applied.
You may ask why temperature readings are important, after all surely you can spot the problems simply by looking for the hotter parts on the image? Firstly, it is important to understand that the image will often look the same regardless of the settings used – this is illustrated below. Secondly, when it comes to electrical applications, use of temperature readings is paramount, as this information will enable you to classify the severity of a fault and make recommendations for timely maintenance.
Some settings in the camera will have only a small impact on the temperature values, however the two that will have the greatest impact are emissivity and reflected apparent temperature.
Emissivity is the capacity of an object to emit, or give off, heat. Objects with low emissivity are not suited to infrared thermography, as is shown in our previous example. Low emissivity objects will reflect more and getting a true temperature reading can be at best difficult and often impossible.
Reflected apparent temperature is a culmination of radiation from all objects impacting on the target, when outdoors this will also include the sky. This setting will vary from place to place and it does impact on any temperature readings the camera shows.
Below we have two examples to illustrate the impact of these two settings.
Fig 1 Values
- Reflected Temperature = 20.0°C
- Spot Temperature = 55.7°C
Fig 2 Values
- Reflected Temperature = 76.0°C
- Spot Temperature = 52.9°C
Fig 1 Values
- Emissivity = 0.95
- Spot Temperature = 55.7°C
Fig 2 Values
- Emissivity = 0.50
- Spot Temperature = 29.3°C
Note with each example above, the colouration of the image is exactly the same, only the settings have changed. Whilst we have used some fairly drastic examples, it illustrates just how easy it is for a thermal camera to lie when it is not used correctly!
Considering the example above, an incorrect emissivity setting could lead to the user reporting the temperature as being a lot lower than it actually is. The potential impact of this is that a dangerous fault can then be missed, or signed off as within acceptable limits. In this scenario, if the fault is not rectified, it will get worse over time and potentially result in a fire.
Now consider the consequences for someone who has incorrectly signed off equipment as being safe, or within acceptable limits. If that equipment were to subsequently fail and cause a fire as a result of a fault that had been missed, there could be serious implications for the person who carried out the survey, especially if their report was called into question and the camera settings were found to be incorrect. Remember that insurance companies will always look for a reason not to pay out!
If the cameras can lie, what is the point in using them?
The answer is that you have to understand how to use the camera correctly and look for the areas or materials that will give you the best temperature measurement and provide accurate information to your clients.
In addition, it is important to understand how to analyse thermal patterns in order to determine types of faults and the impact that a fault may have on other equipment.
There are many ways that you can work around the problems we have illustrated, and account for the impact of reflections and emissivity when carrying out your survey. This information is here to show you that it is not simply a case of buying a camera, taking it out on site and pointing and shooting an image. There is a lot more involved in carrying out a proper thermographic survey, regardless of the application.
Get the best out of your investment with a training course
At Instrotech we are keen to ensure that users understand how to get the best out of their camera. Whether you are buying or hiring a basic model, or investing money in a top of the range camera, understanding how to use it for your application will ensure that you issue meaningful reports and avoid making potentially dangerous mistakes. If you are purchasing a thermal camera, always ask the sales person about any relevant training that is available.
We offer a range of training courses, which are ITC (Infrared Training Center) approved, designed to teach you how to use the camera, avoid making common mistakes, how to set up for a survey and what goes in to producing a report. Details of the courses available are listed below.
Electrical Thermography* – Course Cost: £276.00 + VAT per person
Duration: 1 day
If you’re an electrical contractor or maintenance engineer currently carrying out thermal inspections, or considering starting, then this course is for you.
*Delegates attending this course should have attended either the Introduction to Thermography or a Level 1 training course.
Course Content
- Basics of Thermography
- Basics of Emissivity
- Reflected Apparent Temperature
- Camera Handling & Setup
- Basics of Heat Transfer
- Radiative Transfer
- Electrical Systems
- Important Properties of Materials
- Most Common Problems
- Case Studies
- Common Mistakes
- The Right Approach
- Practical Labs & Report Generation
Along with the above there is also a practical session and every delegate will also be issued with a certificate of attendance and full course notes.
Basic Building Thermography* – Course Cost: £276.00 + VAT per person
Duration: 1 day
The building thermography course gives you a general overview on its specific uses for inspections of buildings and how to use your camera to locate heat loss, missing insulation, damp, air leaks and more.
During the day you will learn about different types of heat transfer and look at specfic real world examples and how to understand what the thermal pattern is indicating.
*Delegates attending this course should have attended either the Introduction to Thermography or a Level 1 training course.
Course Content
- Basics of Thermography
- Basics of Emissivity
- Reflected Apparent Temperature
- Camera Handling & Setup
- Basics of Heat Transfer
- Radiative Transfer
- Definition of a Building Envelope
- Important Physical Characteristics to Know
- Three Major Categories for Faults
- Case Studies
- Moisture Detection
- Mold & Poorly Insulated Areas
- Thermal Bridges
- Water Infiltration in Flat Roofs
- Leaks in Hot Water Pipes
- Data analysis & reports
Every delegate will also be issued with a diploma of attendance and full course notes.
Level 1 Certification Course – Course Cost £1,600.00 + VAT
Duration: 5 days
ITC offers certification training to recognised standards and is an accredited Authorised Training Organisation (ATO) for the British Institute of Non Destructive Testing (BINDT) as per the requirements of ISO 18436. BINDT is an accredited certification body offering personnel certification against criteria set out in International and European standards.
This course prepares you for qualification as a category 1 certified thermographer. You will learn about the basics of infrared, how to operate the camera under different conditions and for various purposes, how to do an appropriate judgement of the measurement situation in the field and identify potential error sources. You will be able to do IR inspections following written guidelines and to report the result of this inspection.
At the end of the course there is a certification test (50 multiple choice questions), all delegates who pass are issued with a certificate and ITC licence.
Course dates and venues are set throughout the year at various places in the UK.
Please call us on 01923 442244 for more information.
