Infrared Detector, What Does Infrared Detector Mean

Infrared detection is a special technology to inspect and measure the surface of equipment or materials and other objects by using the principle of infrared radiation. It is also a means to collect the surface temperature information of objects.

Principle of infrared detection

The change of surface temperature distribution detected by infrared is shown in Figure 1.

Fig. 1 Schematic diagram of surface temperature change of infrared detection object

It can be seen from the figure that the heat flow injection is uniform. For an object without defects, the temperature field distribution on the front and back is basically uniform. If there are defects in the object, the temperature distribution at the defects will change. For thermal insulation defects, the front detection method shows that the defects are "hot spots" due to heat accumulation, and the back detection shows that the defects are low-temperature points; For thermal conductivity defects, during front detection, the temperature at the defect is a low temperature point, and the temperature at the defect detected on the back is a "hot spot". It can be seen that the surface and shallow defects and range of materials can be visually detected by using infrared detection technology.

When an object itself has a temperature different from the surrounding environment, whether the temperature of the object is higher or lower than the ambient temperature; Whether the high temperature of an object is caused by the injection of external heat or by the heat generated inside it, heat flow will be generated inside the object. In the path of heat flow diffusion and transmission inside the object, due to different thermophysical properties of materials or projections, or blocked accumulation, or unobstructed transmission, the corresponding "hot zone" and "cold zone" will eventually be formed on the surface of the object. This temperature difference phenomenon from the inside and the surface is the basic principle of infrared detection.

Classification of infrared detectors

Infrared detector is an important part of infrared spectrophotometer, and there are many kinds of infrared detectors.

Infrared detectors are divided into thermoelectric detectors and optical detectors. The thermoelectric detector converts the infrared radiant heat energy into electric energy, so as to detect the electrical signal to measure the strength of infrared. The optical detector uses the infrared heat energy to change the temperature of the detector, so as to change the conductivity. At this time, the strength of the infrared signal is measured by measuring the resistance.

Thermoelectric detectors include: DTGs (deuterated sulfur tripeptide), litapo3 (lithium tantalate), etc.

Optical detectors include: MCT (mercury chromium tellurium), inte (indium antimonide), etc.

Basic methods of infrared detection

The basic methods of infrared detection are divided into two types: passive and active. Passive infrared detection is widely used in infrared detection and diagnosis technology of equipment; Active infrared detection can be divided into single-sided method and double-sided method

In infrared detection, the heating methods of the measured target are also divided into steady-state heating and unsteady state heating.

The installation and transportation modes of infrared detection instruments include fixed, portable, vehicle mounted and airborne (helicopter mounted) and so on.

(1) Passive infrared detection

The so-called passive type refers to the method of infrared detection in the process of heat exchange between the measured target and the environment without heating the measured target and only using the condition that the temperature of the measured target is different from the ambient temperature. Passive infrared detection is used in running equipment, components and scientific experiments. Because it does not need additional heat source, this method is basically adopted in the production site.

(2) Active infrared detection

Active infrared detection is to actively heat the measured target before infrared detection. The heating source can come from the outside or inside of the measured target. The heating methods include steady-state and unsteady state. Infrared detection can be carried out during the heating process or after stopping heating for a certain time according to different conditions.

1) Single side method: the heating and infrared detection of the measured target are carried out on the same side of the measured target.

2) Double sided method: compared with the above single-sided method, the double-sided method is to separate the heating and infrared detection of the measured target

On the positive and negative sides of the target.

(3) Heating mode

1) Steady state heating: when the measured target is heated until its internal temperature reaches a uniform and stable state, it is placed in an environment lower (or higher) than the constant temperature for infrared detection.

This method is mostly used for material quality detection. If there are cracks, holes, debonding and other defects in the tested object, the heat flow in the heat exchange between the tested object and the environment will be hindered by the defects, and the corresponding outer surface will have a temperature change, and there will be a temperature difference compared with the surface without defects.

2) Unsteady heating: when heating the measured target, it is not necessary to make its internal temperature reach a uniform and stable state, but infrared detection is carried out when its internal temperature is not uniform and has heat conduction.

3) If heat is evenly injected into the measured target, the speed of heat flow into the interior shall be determined by its internal conditions. If there are defects in the interior, it will become the thermal resistance of blocking heat flow. After a certain period of time, heat accumulation will occur, and thermal abnormalities will occur on its corresponding surface. The change of heat flow caused by defects depends on the location, direction, geometric size and thermophysical properties of materials.

Installation and operation mode of infrared detection instrument

(1) Fixed type: it is used to monitor the failure of rotating equipment, key equipment and the process and quality of on-line products.

(2) Portable: portable infrared detection instruments are widely used. Portable instruments should be used (mainly or in combination) in daily patrol inspection, regular general measurement, equipment maintenance and tracking monitoring.

(3) On board type: during the regular general test of equipment, due to the large number of tested equipment and long test route, on-board type test must be adopted. The vehicle mounted thermal imager is loaded on the vehicle (or other vehicles), and two groups of lenses with different ranging can be used to capture infrared images of far and near equipment; For the target that cannot be reached by the car, walk in place for detection; There is an image monitor display in the vehicle. If the operator finds any abnormality (including the need for immediate maintenance and further investigation and monitoring), he shall immediately record and print it on the vehicle, and submit the infrared detection report to the supervisor in time; In case of an emergency that needs to be handled in time, radio and telephone can be used to get in touch.

(4) Airborne: for targets that need to be detected in the sky, especially equipment detection at high mountains with extremely long distance and inconvenient access for personnel and vehicles, helicopter mounted thermal imager shall be used.

Advantages of infrared detection

As one of many non-destructive detection methods, infrared detection has its own characteristics in comparison, but infrared detection has its unique advantages, which can complete the detection that cannot be performed by X-ray, ultrasound, acoustic emission and laser holographic detection.

(1) Non contact: the implementation of infrared detection does not need to contact the tested object. The tested object can be static and movable. It can be a hot body with up to thousands of degrees Celsius or a cold body with very low temperature. Therefore, the application range of infrared detection is very wide, and it is convenient to inspect and measure equipment, materials and products at the production site.

(2) Extremely safe: because infrared detection itself is to detect infrared radiation everywhere in nature, its detection process will not pose any harm to personnel, equipment and materials; Its detection method does not touch the detected object, so even if the detected object is harmful to human health, it will avoid the danger due to the remote detection of infrared technology.

(3) Detection accuracy: the temperature resolution and spatial resolution of infrared detection can reach a very high level, and the accuracy of detection results is very high. For example, it can detect the temperature difference of 0.1 ℃ or even 0.01 ℃; It can also detect the distribution of temperature field on the target with the size of several millimeters; Infrared microscopic detection can even detect the object surface as small as 0.025mm, which is very useful in the diagnosis of circuit board. In a sense, as long as the fault and defect of equipment or material can affect the heat flow transmission in it, the infrared detection method can be detected without the limitation of the structure of the object.

(4) Convenient operation: the infrared detection equipment is relatively simple compared with others, but its detection speed is very high. For example, the response time of the infrared detection system is based on μ S or MS meter, scanning an object can be completed in seconds or minutes, especially in the application of infrared equipment diagnosis technology, infrared detection is often completed in the operation of the equipment, which brings little trouble to other aspects, and the control, processing and storage of detection results are quite simple.

Infrared Detector, What Does Infrared Detector Mean 1

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