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Laser thermometer

Sight technologies enable the precise application of infrared temperature measurement devices. Simple, cost-effective handheld laser thermometers utilize a single-point laser pointer in order to indicate the center of the measuring spot with a certain amount of parallax error. Here it is left to the user to estimate the size of the measuring spot by means of the measuring spot diagram and the distance. If the measurement object only captures a part of the measuring spot, the measured temperature will be represented as the mean value between the hot and cold surface areas of the measuring spot. With small measurement objects in particular, this can lead to the distortion of the measurement result, meaning potentially critical situations are not recognized. In order to properly display the measuring spot in its full size, laser thermometers with optical sights were developed which use crosshairs to mark the size, thus allowing for precise targeting.

Crosshair principle optris Pyrometer
Crosshair principle optris Pyrometer

Laser thermometer with dual laser

In a dual laser system, two laser beams being emitted from the lens approximately depict the narrowing or widening of the measuring beam from larger distances. The diameter of the measuring spot is indicated by means of the distance between the two laser points on its circumference. The simultaneous usage of the video module and a crosshair marking allows video pyrometers to precisely mark the measurement field.

Laser thermometer with crosshair sight

Thanks to the use of new laser illumination technologies, it is possible to represent the measuring spots of infrared thermometers as an accurately sized crosshair whose dimensions precisely match those of the measuring spot. Here, four laser diodes which are symmetrically arranged around the infrared optical measuring channel are equipped with line generators which generate a line of a particular length at the focusing distance determined by the lens. Opposing pairs of projected laser lines fully overlap at the focus point in such a way that they form a measuring cross or crosshairs which precisely depict the measuring spot. For shorter or longer measurement distances, the overlapping is only partial, meaning that the length of the line and, as a result, the size of the measuring cross will change for the user. Thanks to this technology the precise dimensions of the measuring spot can be clearly measured using a laser thermometer. This means a considerable improvement in the practical applicability of devices with good optical performance.

Laser thermometer with focus point switching

In the areas of electronic maintenance and industrial quality control in particular, small measurement objects often need to be measured at short distances (0.75 – 2.5 m). Here, the development of new measurement devices allows the measuring spot to be focused within certain limits. In the process the respective laser thermometers employ a technology in which a twin-lens optical system can be switched to measure very small measuring spots by mechanically adjusting the inner lens position – similar to macro mode in digital cameras. However this is restricted to a fixed distance. If you move closer to or further away from the measurement object, the measuring spot rapidly increases in size. With the aid of two overlapping laser beams which display a laser point diameter of exactly 1 millimeter at the position of the smallest measuring spot, it is possible to set both the optimum distance and the optimum measuring spot size. However, setting measuring spot sizes of less than one millimeter remains a technical challenge even for laser thermometers with focus point switching. The following illustration shows the optical system of a modern infrared thermometer in which the lens position is adjustable and various laser illumination systems can simultaneously be used for an actual-size display of the measuring spot.

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