IR thermography is now a mature technology and many of the applications are very familiar. This has encouraged IR camera manufacturers to produce a wide and potentially confusing range of products, but how should the user decide which one is right for the application and, most importantly, the available budget.
The decision should be made by considering the most basic parameters of wavelength, temperature range, thermal sensitivity, spatial resolution, detector size, application and budget. essay writing service Let’s look at these individually:
Wavelength is seldom considered when selecting an IR camera as the vast majority of building and industrial cameras use uncooled FPA (Focal Plane Array) detectors operating in the LW (Long Wave) band of the IR portion of the electromagnetic spectrum from 8 – 14 µm (micron). There are however some specialised applications such as gas detection and furnace tube inspection that require a camera operating in the MW (Mid Wave) from 2 – 5µm. These MW IR cameras typically require cooled detectors with specialist spectral filters and are significantly more expensive. For general use an uncooled LW IR camera will be totally suitable.
Temperature range is fundamental and the most important consideration. It is determined by the intended application and an error can leave you with a virtually useless piece of equipment. In recent years, manufacturers have offered cameras that are optimised for building applications with narrow temperature ranges eg. -20⁰C to + 60⁰C. If you intend to use such a camera for other applications such as electrical inspection, this maximum of this temperature range is far too limited. Standard IR cameras may offer a temperature range up to 600⁰C which will cover many electrical and mechanical applications but will again be insufficient for some process applications involving kilns and furnaces found in steel, glass and petrochemical industries. In these cases enhanced temperature ranges as far as 2000⁰C may be required which will require the IR camera to be specially calibrated by the manufacturer using specialised filters. Consider your application and check the temperature range carefully in the IR camera specification.
Thermal sensitivity (NETD Noise Equivalent Temperature Difference) defines the smallest temperature difference an IR camera can resolve. It can be found in the IR camera specification and is usually described in terms of ⁰C at a certain temperature eg. ≤ 0.10 °C at 30 °C target temperature. Be aware that this is not the measurement accuracy of the instrument and do not expect to measure such a small difference. It is an expression of temperature difference resolved by the detector in a laboratory environment. Put simply, the lower the figure the smaller the thermal differences you will be able to see in the display. This is most critical in building applications where only differences in tenths of 1⁰C need to be observed to highlight heat transfer through building envelopes. The ability to accurately measure temperature depends on many other variables such as object emissivity, background temperature, distance, ambient conditions. I would strongly recommend first time users to take part in a certified Level 1 IR thermography course to fully understand the principles of remote temperature measurement.
Spatial resolution could also be described as picture quality and is always expressed as an angle eg. IFOV (Instantaneous Field of View) 3.39 mRad (milliradians). It defines the smallest object an IR camera can resolve (see) at a specified distance. Put simply, if you need to resolve objects at a distance, the smaller the IFOV angle the better your ability to see objects at a distance. Spatial resolution is determined by the IR camera detector and lens and these are major influences on camera price. Bear in mind that seeing an object is not the same as being able to measure the object accurately so the bigger the object in your image, the better the chance of an accurate measurement.
Detector size has a huge impact on spatial resolution and camera price. As with a regular digital camera, the greater the number of pixels, the better the picture quality. Typical IR detector sizes are 160 x 120 (19,200 pixels), 320 x 240 (76,800 pixels), 640 x 480 (307,200 pixels). When choosing an IR camera, in general select one with the highest number of pixels you can afford but this should also be related to your application as a lower resolution detector is perfectly adequate for occasional use and many applications. Do not however expect to find small defects on a power transmission line at a distance with a 160 x 120 pixel detector.
The intended application is a vital consideration as we have seen in all the previous topics. Let’s take a look at some of the common applications and suggest some considerations:
Building inspection: Choose a camera optimised for that application and these are clearly distinguished as a separate product family by the major manufacturers. They will have a low and narrow temperature range but will use the full dynamic range of the detector to maximise sensitivity within that range enabling you to discern very small surface anomalies. Beware however if you intend to use the camera for other applications as even for electrical inspection the range will be too limited and you may need to move consider a rather more expensive camera with several selectable ranges and a higher resolution detector to effectively cover both applications.
Electrical inspection (indoor): This is the most widely used application for IR cameras and perhaps the most forgiving. An inexpensive IR camera can be kept in a toolbox for occasional use to look for thermal anomalies much more effectively than a spot temperature measurement device. These basic IR cameras have reached very low prices and can be a first step into thermography but beware their limitations in picture quality and diagnostic capability. Choose an IR camera with a higher resolution detector to find individual high resistance connections and one that offers the ability to attach a wide angle lens for use in switchrooms where access is limited.
Electrical inspection (outdoor): In this application which usually requires the inspection of transmission lines and substations, spatial resolution is critical to be able to resolve and measure small objects at a distance. As a minimum a 320 x 240 pixel detector will be required and a telescope lens may be invaluable. Consider purchasing additional batteries to ensure the inspection can be completed before recharging is required.
Mechanical applications: IR thermography is usually the first inspection technique for motors, bearings and all types of mechanical installations and a basic IR camera will provide a quick and effective method to detect thermal anomalies such as overheated bearings before other technologies such as vibration analysis or oil analysis are employed for further diagnostics. Consider a higher resolution detector if there is restricted access that prevents getting close to the target objects.
Process applications: In these applications much higher temperatures can be expected in kilns, furnaces and other process plant where refractory lining should be regularly inspected with IR thermography. These plants will often include steam systems where correct operation of steam traps, leaks or poor insulation can be easily identified. Be sure to choose an IR camera with a high enough temperature range for this application and one that is robust enough for these harsh environments.
Now we have considered the technical requirements to look for in the camera specification are there any other considerations before fitting these to the available budget.
Don’t overlook how the IR camera will either store thermal images on board or download them by wi-fi, Bluetooth or other methods. Regular use of an IR camera will produce thousands of thermal images so think about how these will be stored, filed and later retrieved in the tidiest way possible. If you store images onto an SD card within the IR camera, ensure that the card has enough storage space but however large the card, download the images and back them up daily. If you are comfortable with wi-fi or Bluetooth technology to securely download images in the field then you can speed and simplify the process and this capability should be on your shopping list.
Consider how you will present the results of your IR thermography inspection. This is normally in the form of an electronic or printed report. Most IR camera manufacturers offer excellent software packages for analysis and report writing and often at no charge for download from their websites. There are however additional packages from them and third parties with enhanced features that could save a considerable amount of time or link to other software packages such as asset management or building analysis. Consider carefully if these will benefit you and build the cost into you IR camera budget.
Tailor your budget to your requirements and don’t assume that all IR cameras are the same. If you are going to use the camera regularly then spend the money on one that is robust, has at least a 320 x 240 pixel detector, accepts accessory lenses and does not compromise on your end product which is a clear and accurate thermal image suitable to base predictive maintenance and other decisions on that may have significant onward cost implications. The entire cost of the IR camera can easily be recovered if one breakdown leading to production or other loss can be prevented.
Last but not least, build the cost of a certified Level 1 training course into your IR camera budget. Although IR camera manufacturers have made their cameras very easy to use with many automated functions, you will only get the best out of the cheapest to the most expensive IR camera if you understand the principles of heat transfer and remote temperature measurement and can apply them to your application. Avoid costly mistakes and prove your competence as a thermographer by taking a training course, it could be the most rewarding part of your IR camera investment.
Level 2 Certified Infrared Thermographer
Infrared Thermography Instructor
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