This thread actually provides the reason why thermal imaging systems have become so popular as their price has reduced. The IR thermometer was a common, and affordable, way to measure a target surfaces temperature without contact. There were some rules for obtaining decent accuracy though. The target surface Emissivity should be known, or estimated using Emissivity tables, and the target surface should fill the IR thermometers field of view.
If the Emissivity is incorrectly set on the IR thermometer, an error will be introduced into the measurement. If the target surface does not fill the IR viewers FOV, the average of the target and surrounding surface or background will be measured and this can result in significant measurement errors. Measuring a surface of uneven Emissivity will also introduce an error. The quality and specification of the IR thermometer dictates its accuracy and can influence the measuring spot size at various distances. The spot size to distance ratio is normally detailed in the specification and a smaller spot size for a given distance is needed where a target is small. Cheap IR thermometers tend to use a single fresnel lens or no lens at all and they can have very poor spot size to distance ratios. High quality IR thermometers designed to provide very small spot sizes at significant distances are often built with high quality, expensive, optics so cost more to purchase.
Thermal imaging cameras provide the user with an array of spot temperature measurements from which to select those associated with the region of interest using the spot measurement function. As such the thermal scene provides more information on the target area and its surroundings. Even low resolution 16 x 16 pixel thermal arrays can provide decent target measurement where the user can see that they are selecting only the pixels that are illuminated by the target area. Greater thermal sensor resolution can provide more pixel coverage of the target area, depending upon the optical systems specifications. IFOV comes into play here.
In thermal imaging, the context of the thermal scene image when compared to the users visible light view of the scene can significantly aid a better understanding of the thermal energy distribution and any anomalies present. A classic example used in advertising is a utility mains breaker board where a thermal imaging camera can clearly show a breaker or contactor that is suffering an overload or failure condition. To achieve the same with an IR thermometer, a model with the correct spot size to distance ratio should be selected to differentiate between breakers or contactors and the IR thermometer is carefully scanned across the target panel looking for anomalies. The human brain tracks the temperatures measured and maps then against the area of the panel highlighted by the laser spot indicator. If an anomaly is detected, the user can move closer to the target panel to better localise the issue. That does take the user closer to potential danger however (In the case of High energy systems)
How much simpler it is to use the thermal camera, with a decent specification, to view the panel from a safe working distance and actually see the variance in temperature across the thermal scene, this enables the user to see the thermal average of a scene and areas that are either hotter or cooler than the surrounding ‘reference’ areas. Hard to achieve with a single pixel IR Thermometer.
Out of this thermal imaging advantage some more affordable thermal imaging tools were born. IRISYS (UK) were manufacturing RedEye thermopile arrays at low cost for people counting devices that they produced. These Thermopile arrays started out as 16 x 16 pixel devices but 32 x 32 and 47 x 47 pixel models followed. With such low Native resolution arrays, interpolation was used to create acceptable thermal images. The RedEye thermopile device was then married up with a VGA visible light camera in a handheld design and the images combined using thermal-visible light scene fusion. The visible light image provided scene context and the low resolution thermal scene overlay provided the scenes thermal profile, albeit at low resolution so quite large IFOV on target. The Visual Thermometer was born ! The two models made by IRISYS were the VT02 (16x16 pixels) and VT04 (32 x 32 pixels). I own a couple of the original VT02 prototypes in the original IRISYS red cases. The visual thermometer was an interesting idea and FLUKE bought IRISYS. The VT serieswere sold as an affordable thermal imaging device for the trade etc. Sadly the timing was not great as the FLIR Lepton and Seek Thermal cores were soon released and basically placed the low resolution VT series ‘in the shade’. The far greater resolution of the seek and a FLIR offerings made affordable thermal imaging cameras a reality for the masses.
FLIR has not ignored the appeal of the simple Visual Thermometer though. They have a range of devices that use the 80 x 60 pixel Lepton core as a Visual Thermometer or thermal viewer that competes directly with FLUKE’s VT series. FLIR want their toe in every market, including any, and all, that FLUKE are present in. There have been some interesting work done by FLIR on low end visual thermometers for users who neither need the capabilities of a ‘full’ industrial thermal camera or have the appetite for its relatively high price tag. A hybrid Single pixel Thermopile IR thermometer with Lepton 80 x 60 pixel thermal camera was born ! It is a weird beast that measures temperature using conventional IR thermometer technology, yet provides a thermal scene for context on its display using the lepton core. The Lepton is not the most accurate measurement device so maybe FLIR decided the IR thermometer provided a more accurate measurement system ? it brings with it the issue of spot size to distance ratio though
I attach pictures of the ‘hybrid’ TG165 visual IR thermometer.
Fraser