(2) Magnetoelectric speed sensor-analog AC signal generator, which generates AC signal, usually consists of a magnetic core with two ends and a coil. The gears on the magnetic assembly wheel will produce a series of pulses corresponding to each other, and their shapes are the same. The amplitude of the output signal is directly proportional to the rotating speed (vehicle speed) of the magnetic assembly wheel, and the frequency of the signal is reflected in the rotating speed of the magnetic assembly wheel. It is through this synchronous pulse signal that the engine control computer or ignition module determines the time to trigger electric ignition or fuel injection.
Magnetoelectric speed sensor mainly uses magnetoresistive elements to measure speed. One characteristic of magnetoresistive element is that its impedance value will change with the strength of magnetic field. Usually, magnetoelectric sensors are equipped with magnets, so that the sensors have a certain magnetic field in advance. When the metal detection gear is close to the sensing element, the magnetic field changes caused by the tooth top and tooth valley of the gear make the magnetic impedance of the sensing element change accordingly. However, the impedance value of magnetoresistive elements varies greatly with temperature. When measuring the rotating speed with magnetoresistive elements, the influence of temperature drift is very serious, which greatly limits the application of magnetoresistive elements. But the sensors of our Xiao Ye detector are different. It adopts two magnetoresistive elements, which not only compensates the influence of temperature, but also greatly enhances the sensitivity of the sensor.
The above picture is the schematic diagram of the magnetoelectric speed sensor. The bridge circuit consists of two magnetoresistive elements and two resistors, and its differential output signal, namely the detection signal, is taken out and sent directly to the DC amplifier for amplification. The following is a brief description of the block diagram. In order to adjust the impedance difference between the two magnetoresistive elements, an adjustable potentiometer is added in the bridge loop as the balance adjustment of impedance. The output of the balance bridge is connected with a DC amplifier. If involute gear is used for detection, the output waveform is almost the same as sine wave. After the signal is amplified, it is sent to the shaping loop for shaping, so that it becomes a rectangular wave with fast jumping up and down edges. The output loop adopts collector output, and the output impedance is about 330 Ω. With the Hi and Lo conversion of the output waveform, the indicator LED will go out. The whole circuit is driven by 5V voltage, and there is an actuator with 5V voltage output in the circuit. The input voltage of the power supply is the same as other sensors, which is DC 12V 2V. The magnetoresistive element is encapsulated on the top of the sensor, so the sensor is marked with a position alignment mark in consideration of directionality during installation.
(3) Hall-type speed sensor-mainly used for crank angle and camshaft position, used for switching ignition and fuel injection circuit triggering, and also used in other computer circuits that need to control the position and speed of rotating parts. It consists of an almost completely closed magnetic circuit, including a permanent magnet and a magnetic pole part. The rotor of the soft magnet blade passes through the air gap between the magnet and the magnetic pole. The window on the blade rotor allows the magnetic field to pass through and reach the Hall effect sensor unaffected, while the part without the window will interrupt the magnetic field.
(4) Wheel speed sensor-detects the wheel speed and outputs the detection result to ECU, which is mainly used for automobile braking and driving control;
(5) Engine speed sensor-detects the engine speed, and usually uses a crankshaft position sensor to detect the engine speed and output it. Used for fuel injection quantity, ignition advance angle, power transmission control, etc.
(6) Deceleration sensor-its main function is to detect the deceleration speed when the car is decelerating, and at the same time, it also feeds this signal back to ECU for the control of braking and driving control of the car.
(7) Speed sensor-usually obtained by directly or indirectly detecting the speed of automobile tires, mainly because we can know our driving speed when the automobile is driving.
(8) Structure and characteristics of speed sensor
The speed sensor is divided into contact type and non-contact type according to the installation form.
(9) The contact speed sensor is simple in structure and convenient to use. It is necessary to apply a certain positive pressure on the surface of the contact roller or use materials with high friction coefficient to minimize slippage. According to the sensor market report of consulting firm INTECHNOCONSULTING, the global sensor market capacity was 50.6 billion dollars in 2008, and it is predicted that the global sensor market will reach more than 60 billion dollars in 20 10. The survey shows that Eastern Europe, Asia-Pacific and Canada have become the fastest growing regions of the sensor market, while the United States, Germany and Japan are still the regions with the largest distribution of the sensor market. As far as the world is concerned, the fastest growing sensor market is still the automobile market, followed by the process control market, which is optimistic about the prospects of the communication market.
Some sensor markets, such as pressure sensors, temperature sensors, flow sensors and liquid level sensors, have shown the characteristics of mature markets. The market scale of flow sensor, pressure sensor and temperature sensor is the largest, accounting for 2 1%, 19% and 14% of the whole sensor market respectively. The main growth of sensor market comes from emerging sensors, such as wireless sensors, MEMS sensors and biosensors. Among them, the compound annual growth rate of wireless sensors in 2007-20 10 is expected to exceed 25%.
In the 2 1 century, the global sensor market shows a rapid growth trend in constant change and innovation. Experts pointed out that the main technologies in the sensor field will be extended and improved on the existing basis, and countries will compete to speed up the research and development and industrialization of a new generation of sensors, and the competition will become increasingly fierce. The development of new technologies will redefine the sensor market in the future, such as the emergence of new sensors such as wireless sensors, optical fiber sensors, smart sensors and metal oxide sensors and the expansion of market share. The speed sensor will be used in the automobile inspection market.
Modern cars are generally equipped with engine control, automatic driving, ABS, TRC, automatic door lock, active suspension, guidance system, electronic instruments and other devices, which all need speed signals. Therefore, the accuracy and stability of measuring the output signal of the speed sensor of the vehicle will have a great influence on these control units. Most automobile speed sensors adopt Hall structure. Hall speed sensor is a magnetoelectric sensor based on Hall effect, which has the characteristics of high sensitivity to magnetic field, stable output signal, high frequency response, strong anti-electromagnetic interference ability, simple structure and convenient use. It is mainly composed of permanent magnets (usually 4 or 8 pairs) with specific magnetic pole pairs, Hall elements, rotating mechanisms and input/output plug-ins. Its working principle is that when the rotating mechanism of the sensor rotates under the action of external drive, it will drive the permanent magnet to rotate, and the magnetic field passing through the Hall element will change periodically, causing the output voltage of the Hall element to change, and a stable pulse voltage signal will be formed as the output signal of the vehicle speed sensor after subsequent circuit processing. The main electrical technical parameters of Hall structure speed sensor include: output signal high voltage, low voltage, duty ratio, period, rise time, fall time, number of periodic pulses, etc. In order to ensure the reliability of products, these parameters must be quantitatively tested before leaving the factory. Integrated and intelligent test system, with efficient automatic measurement, software calculation and graphic or digital table display of test results, is increasingly favored by automobile speed sensor manufacturers. A comprehensive detection device is developed by measuring the performance of commonly used Hall velocity sensors. Considering the cost, the high-speed counter port of the microprocessor is used as the data acquisition of the vehicle speed sensor, and the calculation and graphic display processing of the collected data are realized through software control. The completed detection device has the advantages of high test accuracy, reliable data communication, graphical user interface, strong anti-interference ability, simple and intuitive detection process, low system development cost and so on, and has a good promotion market, so the speed sensor will have great application prospects in vehicle speed detection. The speed sensor of belt conveyor adopts Hall sensor, which mainly uses Hall effect to realize magnetoelectric conversion. Hall effect has a history of more than 100 years since it was discovered in 1879. However, due to the rapid development of microelectronics technology, its application was paid attention to and popularized in the 1950s, and various Hall elements were continuously developed. Since 1970s, China has increased the research on Hall elements. After decades of research and development, Hall elements with various performances have been produced, such as common type, high sensitivity type, low temperature coefficient type, temperature measuring and magnetic measuring type and switch type. Hall sensor has the characteristics of high sensitivity, good linearity, high stability, small size and high temperature resistance, and is widely used in various industrial fields such as automatic control of non-electric quantity measurement, computer equipment and modern military technology.