Specifications of non-contact thermometer
Non-contact thermometer (non-contact thermometer) An interesting and useful feature of non-contact pressure gauges is that their calibration does not depend on the distance of the sensor from the target surface. This is anti-mood for anyone who has ever stood near a source of intense radiant heat: for example, standing near a fire, for example, at a much warmer temperature than the skin, to stay away from it. Why do none of the non-contact sensors detect a colder contact without contact with the target temperature, given that infrared radiation is emitted from the body as the separation distance increases? The fact that an infrared compass does not suffer from this limitation is useful for measuring our temperature, but does not seem logical at first.
One of the most important understandings of this paradox is to quantify the experience of fire, where the perceived temperature decreases with increasing distance. In physics, this is known as the inverse law of squares: the intensity of a ray falling from a point source decreases by the square of the distance separating the radiation source from the object. Returning to a distance twice the distance from the fire reduces the received infrared radiation fourfold. The way back to three times the distance leads to a 9-fold reduction in received radiation. Placing a sensor at three integer intervals (x, 2x and 3x) from a point on the radiation source results in a relative power of 100%, 25% (a quarter) and 11.1% (a ninth) on the sensor. In that place:
This is a basic physical principle for all types of radiography based on simple geometry. If we examine the flux of a beam from a point source, we find that it must move in straight lines, and this propagation occurs at the speed specified by the square of the distance. An analogy to this phenomenon is to imagine a spherical latex balloon in which air is blown. The area of the balloon is proportional to the square of its radius. Similarly, the flux of a ray emanating from a point source propagates in straight lines, reaching in all directions the total area proportional to the square of the distance from the point (center). The total flux measured as a sphere will be the same regardless of the distance from the source point, but the area divided by it increases by the square of the distance, and so any object in the fixed region that moves away from a point – the radiation source with The smaller the fraction, the smaller the flux. If non-contact thermometers are really looking for an infrared source, their signals will be reduced by a distance. The advantage of saving here is that the non-contact edges of the devices are light-focused and have a clear field of view, and this field of view must always be completely filled by the intended target (assuming it is at a uniform temperature).
By changing the distance between the perimeter and the target, the conical field of view covers an area in that object that is proportional to the square of the distance. Returning three times the distance increases the viewing area by nine times:
Thus, although the inverse square law correctly states that the rays from the hot wall (which may be considered as a set of point sources) decrease in intensity with the square of the distance, this observed increase is perfectly balanced. Becomes. Surrounding area. The separation distance skepticism leads to flux from any given point in the wall, which expands by a factor of four, but now sees four times as many similar points in the wall as in the past. As long as all points in the field of view are uniform in temperature, the result is a complete cancellation with a barometer that provides exactly the same measurement of temperature at any distance from the target.
If the view of the non-contact thermometer (sensor) is wide enough to be able to record objects other than the temperature we are measuring, measurement errors will result. The sensor now averages the weight of all objects in its field of view, so it is important to ensure that this range is limited to covering only the object to be measured. Non-contact sensor fields are typically specified as either angles, distance ratios, or both. For example, the image below shows a temperature sensor without contact with the 5: 1 field of view (approximately 11o ) :