Infrared thermal image detection: strict control of vehicle reliability

With the continuous development of automotive intelligence, the importance of automotive electronics has become more prominent. The huge increase in hardware and software has made the heating of automotive electronics a concentration point. If the heat and heat dissipation of electronic systems cannot be properly handled, The consequences of system operation efficiency, crashes and even fires.

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The traditional temperature detection method of automotive electronics is thermocouple, which is contact temperature measurement, but there are still many shortcomings in reaction speed, small target detection, work efficiency, etc., and the infrared thermal imager can be from the temperature distribution of the surface of the electronic system. Quickly identify problems in contact with the analysis and analyze with the help of professional software to efficiently complete the heat and heat detection tasks of automotive electronics.

Development of infrared thermal imaging and current status of use in China

1. Development history of infrared camera

Since the discovery of infrared radiation by Herschel's most primitive thermal detectors made with mercury thermometers in 1800, various methods have been used to detect infrared radiation.

The infrared camera is a kind of device that can detect the infrared radiation of the target and convert the temperature distribution image of the target object into a video image through photoelectric conversion and electrical signal processing. It is a cutting-edge technology such as light collection, machine and electricity. In one of the high-tech products. Because of its non-contact temperature measurement, fast reaction speed and temperature data analysis, it has been widely used in research and development, quality management, equipment maintenance, building inspection and other fields.

2. Infrared thermal imaging technology in domestic application

With the advancement of technology, infrared thermal imaging technology has also been greatly developed in the construction and industrial fields. The infrared camera uses an uncooled focal plane gaze-type infrared thermal imager with a long-wavelength of 8 to 14 μm. Its volume, weight and operability are greatly improved compared with the first-generation refrigeration infrared camera.

At present, infrared thermal imaging cameras are mainly used in the following industries in China:

- R&D and quality management: It mainly detects the heat state of the product and improves the quality of the product.

- Predictive maintenance of the device: It mainly checks the working status of the device and discovers problems in the device in advance.

- Building inspection: testing the energy, leakage and empty drums of the house.

- Fire protection: search and rescue and daily fire safety testing.

- Others: such as research, education, medical care, etc.

Application status of infrared thermal imaging technology in domestic automotive electronics enterprises

1. Application status of thermal imager in automotive electronics

At present, infrared thermal imaging cameras have been used in many domestic automotive electronics companies. The main applications are:

R & D temperature analysis:

Device heating analysis

Thermal efficiency analysis

Temperature analysis of the outer casing or surrounding parts

Trend analysis of temperature over time

Product quality testing:

Quality inspection of outsourcing parts

Production line quality control

Aging test

2, the difference between thermal imager and contact thermometer / temperature data collector

The data collector uses a contact thermometer as a sensing unit. The system integrates several to dozens of sensors. The sensors are usually attached or fixed to the target to be measured. The system analyzes the temperature distribution state of the measured object according to the temperature data of each sensor. Some data collectors can expand the number of channels to hundreds or even thousands, but they are limited by the size of the target. These channels are often theoretical and rarely used in actual testing.

The advantages of A thermal imaging camera

Because the data collector uses a contact thermometer as the sensing unit, it has the following disadvantages:

· Less detection points, the target temperature distribution is not clear

The number of contact temperature sensing units of the data collector is small, especially for electronic devices with the same small area, the sensing unit that can be fixed on the device can only be counted in number, so the data collector is used for detection. The part is relatively fuzzy.

The infrared camera has tens of thousands of detection points, so it can clearly show the temperature distribution of the target, which is good for observing small temperature anomalies.

· Slow response

The response temperature of the contact temperature sensing unit of the data collector is usually in the range of ten seconds to several minutes. If the target has a relatively fast temperature change, the data collector cannot change the temperature of the target, causing the temperature display to lag. Affect the judgment of the user.

The response time of the thermal imaging camera is usually within 1 second, and the temperature change of the target can be displayed in real time.

· will destroy the original temperature field of the target

The sensor of the data collector must be in contact with the surface of the target to be measured, which will affect the heat dissipation of the surface (especially for objects with small area or less heat), and the temperature of the target to be measured changes.

The infrared camera uses non-contact temperature measurement, which can be detected away from the target, so it will not damage the original temperature field of the target and ensure accurate temperature measurement.

B Temperature Data Collector Advantages

· Due to the flexible wiring of the thermocouple, it can be detected in areas where the camera cannot be photographed, such as the lower layer of the multilayer circuit board and the components inside the product casing.

· Thermocouples can record long-term temperature data and perform switching or 4-20mA signal control.

C Collaboration of thermal imaging cameras and temperature data collectors

The infrared camera mainly detects the temperature distribution state of the target surface. For the internal detection and the part that needs temperature control, the temperature data collector cooperates and supplements.

Application case of infrared thermal image in automotive electronic detection

1, circuit board and component testing

A board test

Currently, the main form of failure of electronic equipment is thermal failure. The system that converts a car into a kinetic energy from thermal energy has higher requirements for electronic equipment. According to statistics, 55% of electronic equipment failures are caused by temperature exceeding the specified value. As the temperature increases, the failure rate of electronic equipment increases exponentially. In general, the operational reliability of electronic components is extremely sensitive to temperature. For every 1 °C increase in device temperature at 70-80 ° C, the reliability is reduced by 5%.

The thermal imager can fully detect the temperature of each component on the circuit board, which is not possible with other temperature measurement tools; the temperature of each component on the control panel of the air conditioner can be greatly controlled within the limits. Operating stability and product life.

Figure 1: The PCB board is transferred to the back due to heat from the power device, and the local temperature is high.

Figure 2: The power diode is in a hot state. The maximum temperature for a long time must not exceed 100 °C.

B Heating test of automotive electronic systems

In the automotive electronics circuit development process, load analysis is a must; the thermal imager provides a means of load analysis through temperature detection, through the thermal image can be very intuitive to identify high-power parts, improve the circuit for engineers, It provides a strong basis for improving conversion efficiency, reducing power consumption, and reducing the internal temperature rise of the circuit.

Figure 3: Power module heat test Figure 4: Power board transformer, infrared heat map easily find the heating of the left and right transformers are inconsistent, which is caused by the inconsistent load of different transformers.

Figure 5: Heat sink heat dissipation test (left is infrared heat map, right is visible light)

C Thermal testing of automotive electronic systems

The heat sink plays a role in cooling the chip or component. Without the heat sink, poor heat sink design or improper material selection of the heat sink, the heat dissipation effect will be seriously affected, resulting in shortened device life.

The research and development department project team designed the heat sink solution for the chip, which needs to take into account the heat dissipation effect and size. For this purpose, six kinds of heat sinks are designed for research; see the figure, lower left, lower middle, lower right, upper left, upper middle, upper right, heat sink in turn. The area is increased, the same chip, the same input voltage and current, and the same time are used to observe the heat generation of different heat sinks, which provides a temperature basis for the design of the heat sink.

In the figure, the temperature of the “middle and upper” is 48.1 °C, which is inconsistent with the temperature trend of the heat sink size. The normal calculation should be between 43-44 °C, indicating that there is a problem in the heat sink design or material selection. The figure can also be used for quantitative analysis of heat dissipation per unit area for area size and temperature.

Figure 6: Square heat sink, distribution of diagonal diagonal temperature 2, car light detection

A. LED lamp temperature detection

From the perspective of personal safety and LED quality, the maximum temperature of the surface of LED lamps is generally required to be below 65 °C; if the temperature is too high, it is easy to cause the lamp to die, the light decay is serious, and even the brightness index is not reached.

LED lighting fixtures consist of dozens to hundreds of LED lamp beads. The quality of each lamp bead may be different, or the lamp bead heat is not good due to design reasons. The direct result is uneven illumination or even The problem of a small number of lamp beads affects the overall life of the entire LED lamp; however, because the light radiation angle of each lamp bead is superimposed, it is difficult to detect which lamp bead is directly from visible light, and the thermal imager is detected by infrared radiation. The difference in temperature distribution in the luminaire confirms the location of the problem lamp bead or corrects the heat dissipation problem in the design.

Figure 7: (Left) Domestic LED white illumination array, the center-right part is significantly higher than the left side temperature by 2 °C, indicating that the lamp bead consistency is not good, visible light (right) can be vaguely seen on the left side There is a defect in the brightness of the illumination (at the black circle), but the visible light map does not indicate which light beads have a quality deviation.

B Car lamp cover temperature detection

As the power of the lamp is continuously increased, the surface temperature of the lamp cover of the lamp is gradually increased, and the material of the lamp cover is usually PC, PMMA, etc., so the surface of the lamp cover cannot withstand too high temperature, otherwise the structural strength of the lamp cover will be affected; The temperature distribution on the surface of the lampshade also reflects the heat generation inside the lamp, and the degree of design of the heat dissipation system can be evaluated.

Figure 8: Easily view the surface temperature distribution of the lampshade by infrared heat map to analyze the internal heat state of the lamp.

C Trend Analysis Software Application

The development and quality management of automotive electronics usually requires continuous monitoring. Fluke's custom analysis software can digitally store high and low temperature automatic capture points and center point temperatures in continuous video signals. The saved content is temperature value and time, and establishes trends. Analyze the graph: the graph with the abscissa is time and the ordinate is temperature, see the figure below.

Trend analysis software combines various types of accessories to continuously capture and analyze the target, and realizes small target detection, real-time temperature recording and graphs through various accessories and software, which facilitates on-site shooting, recording and analysis. And provide a key basis for development work.

In summary, the infrared camera is widely used in various research and new technologies because it adopts the non-contact temperature measurement method in which the detector receives infrared radiation, so it is free from on-site light interference, fast response, and image analysis. In the development of new products, we provide important temperature data for R&D personnel to improve the reliability of automotive electronics.

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