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Automation Technologies 4/2016

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Automation Technologies 4/2016

Temperature guns versus

Temperature guns versus thermal imaging technology About Flir Flir systems, based in Oregon, United States of America, is one of the largest companies in the world specializing in the design and manufacturing of thermal imaging cameras, components and imaging sensors. The company has more than 3,215 (2011) employees worldwide and an annual revenue of $ 1.5 billion US-$ (2015). The Flir T1K thermal camera brings true HD infrared to a handheld camera MACHINE VISION Joachim Sarfels Thermal imaging cameras and spot pyrometers are used for non-contact temperature measurements in companies all over the world. Both cameras work according to the same principle; they detect infrared radiation and translate it into a temperature reading. Thermal cameras however, have a lot of advantages compared to spot pyrometers. The spot pyrometer is also known as temperature gun or infrared thermometer. Because it works according to the same physical principle as a thermal camera, a spot pyrometer can be seen as a thermal camera with only one pixel. Such a tool can be very useful for many tasks, but because it only measures the temperature of one single spot the operator can easily miss crucial information. The high temperature of certain critical components that are near failue and need repair might go unnoticed. Use thousands of spot pyrometers at the same time A thermal imaging camera also provides non contact temperature readings, just like a spot pyrometer does. Unlike a spot pyrometer thermal imaging cameras produce not one, but thousands of temperature readings at the same time, one for each pixel in the thermal image. Using one thermal imaging camera therefore corresponds to thousands of spot pyrometer measurements. The Flir E40sc thermal imaging camera has an image resolution of 160 × 120 pixels, resulting in 19,200 temperature readings at a glance. The Flir T1030sc, one of the top models for industrial R&D/ Science applications, has an image resolution of 1024 × 768 pixels, giving you 786,432 temperature readings at once. See the heat A thermal imaging camera not only gives thousands of temperature readings, it also translates these readings into a thermal image. This Author: Joachim Sarfels, Flir Systems GmbH, R&D-Science Division, Area Sales Manager Central Europe AUTOMATION TECHNOLOGIES 4/2016

conversion into an image results in a complete overview over the inspected equipment and allows the operator to immediately see small hot spots that would be easily missed with a spot pyrometer. Using a thermal imaging camera also saves time. Scanning large areas with many components using a spot pyrometer is a very time consuming task, because you have to scan every component separately. A thermal imaging camera can be used to check heat dissipation on printed circuit boards, to do quality checks or inspect thermal impact in the automotive sector, or to do failure analysis in the lab. Another advantage of thermal imaging cameras compared to temperature guns is that they can accurately measure temperatures from larger distances. The distance at which a certain spot pyrometer is able to measure a target of a given size is often described with the “Distance to spot size ratio” (D:S) or ‘Spot Size Ratio’ (SSR). But where does that value come from and what does it stand for? The ‘spot size’ of a spot pyrometer is the smallest area that still can be measured accurately with the device. That means that the object of which you want to measure the temperature, also referred to as the target, needs to cover the entire spot size. The infrared radiation that is emitted by the target passes through the spot pyrometer’s optics and is projected onto the detector. If the object is smaller than the spot size, the detector will also be hit by parts of the radiation coming from the object’s surroundings. Hence, the device will not read the object’s temperature only but a mixture of the temperatures of the object and its surroundings. The farther away you hold the spot pyrometer from the object that you want to measure, the larger the spot size will become, due to the nature of optics. Consequently, the smaller the target, the closer you need to hold the spot pyrometer in order to accurately measure its temperature. It is therefore very important to keep an eye on the 01a A temperature gun measures the temperature of one spot 01b The thermal imaging camera FLIR E40sc measures the temperature of 19,200 spots How to calculates the spot size In the situation where a thermal imaging camera is used to measure the temperature of a certain target we assume that the distance to the target equals the radius of the circle and we also consider the target to be rather flat. Since the viewing angle of a single detector element is small, we can assume that the tangent of this angle is approximately equal to its value in radian. Innovative thermal cameras bring true HD infrared to a handheld camera spot size and make sure that you stand close enough to cover the entire spot size with the target, preferably even a bit closer to create a safety margin. The Spot Size Ratio defines a spot pyrometer’s spot size for any given distance to the target. If the SSR of a spot pyrometer is 1:30, for instance, this means that the temperature of a spot with a size of 1 cm in diameter can be accurately measured at a distance of 30 cm. The temperature of a spot having a size of 4 cm can be measured from a distance of 120 cm (1.2 meters). Most spot pyrometers have an SSR between 1:5 and 1:50. This means that most spot pyrometers can measure the temperature of a target of 1 centimeter in diameter from a distance of 5 - 50 cm. Spot size ratio of a thermal imaging camera Thermal imaging cameras are very similar to spot pyrometers in that infrared radiation is projected onto a detector matrix, with each single pixel in the image corresponding to a temperature measurement. Thermal imaging camera producers usually do not specify SSR values to describe the spatial resolution of their products; but use instead the Instantaneous Field of View (IFOV). The IFOV is defined as the field of view of a single detector element of the camera’s detector array. Theoretically the IFOV directly determines the spot size ratio of a thermal imaging camera. As the infrared radiation that is emitted by the target passes through the optics and is projected on the detector, the projected infrared radiation should completely cover at least one detector element, which corresponds to one pixel in the thermal image. So in theory covering one pixel in the thermal image should be sufficient to ensure correct temperature measurements. All the latest CMOS Global Shutter on one cameraplatform •Small&robust Housing29mm x29mm •Fast &easy to connect via GigEVision&USB3Vision •Sensorswith up to 12 MP •Full interfacespeed utilizationwithall sensors •Customization and developmentfor allmodels Check out the features!


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