Magnetic sensors have a wide range of applications, has been in the national economy, national defense construction, science and technology, health care and other fields are playing an important role, and become a major branch of the modern sensor industry. In the traditional industrial applications and transformation, resource exploration and comprehensive utilization, environmental protection, bio-engineering, intelligent control of transportation and other aspects, they play an increasingly important role. Here are some important aspects of the application of a discussion. Magnetic sensors have been industrialized in many fields, and the total number of magnetic sensors required each year is in the billions.
1.1 Motor Industry
Brushless motors have a series of advantages such as small size, light weight, high efficiency, easy speed regulation, low maintenance, long life, no electromagnetic interference, etc., and the annual demand is in the billions.
In brushless motors, magnetic sensors are used for rotor pole position sensing and stator armature current commutator. Many magnetic sensors, Hall devices, Wiegand devices, magnetoresistive devices, etc. can be used, but a large number of use, mainly Hall devices.
Rotary encoders are used for speed detection and control of motors, and optical encoders were mostly used in the past. The use of magnetic encoder shows more and more advantages, is gradually replacing the optical device. The use of magnetic sensors can also motor overload protection (mainly with Hall current sensors) and torque detection.
1.2 Power Electronics Technology
Power electronic meter technology is a combination of power technology and electronics technology, can realize the mutual conversion of AC and DC current, and can realize the free regulation of current, voltage and frequency in the required range. The use of these technologies and products, can be made into a variety of special power supply (such as UPS, high-frequency power supply, switching power supply, arc welding machine inverter power supply, etc.) and AC frequency converter and other products (AC frequency converter used for motor speed control, energy-saving effect is excellent). The core of these current converters is a high-power semiconductor device. Various current sensors based on magnetic sensors are used to monitor, control and protect these high-power devices. Hall current sensor response speed, and rely on the magnetic field and the controlled circuit coupling, not access to the main circuit, and thus low power consumption, strong overload resistance, good linearity, high reliability, can be used as a high-power device overcurrent protection driver, but also as a feedback device, become a control link in the self-control loop. The use of variable current technology can be a large amount of energy saving, 95% of the power used abroad is transformed to the domestic variable current technology has been highly valued, but only 5% of the power through this transformation, which can be seen to have a huge application prospects. Among them, may absorb a large number of current sensors, is another huge industrial application of magnetic sensors.
1.3 Energy Management
The automatic detection system of the power grid needs to collect a large amount of data, and after processing by the computer, it monitors the operation of the power grid, and carries out the distribution of load regulation and safety protection. Each control link of the automatic monitoring system can be realized by current sensors and transformers based on magnetic sensors. Hall current sensor has been gradually applied in the power grid system. With Hall devices made of electricity meter has gradually turned from the development of practical, they can automatically billing and can display the power factor, in order to adjust at any time, to ensure efficient use of electricity.
1.4 computer technology and information reading and writing magnetic head
Magnetic information recording devices in addition to magnetic tape, disk, etc., there are also magnetic cards, magnetic ink recording books, magnetic recording of banknotes, etc., there is a huge demand for magnetic information storage and read out sensors. Induction magnetic heads, thin-film magnetoresistive magnetic heads, amorphous magnetic heads, etc. have gained a lot of use. As recording densities increase, for example, as high as 100 Gbytes, magnetic heads with higher sensitivity and spatial resolution are required. Giant magnetoresistive heads based on multilayer metal films, amorphous alloy heads made from amorphous alloy wires, and giant magneto-impedance heads are in fierce competition.
1.5 Automotive Industry
In the automobile, the use of a large number of motors (advanced cars require about 40 to 60 motors each, and 15 in general cars, these motors show a trend of brushless), which uses the number of magnetic sensors, self-evident; another large number of magnetic sensors is the automobile's ABS system (antilock braking system), an average of every Automobile to use 4 to 6 speed sensors, the use of the main inductive speed sensor. Is gradually promoting the new Hall gear sensors, as well as Weiss devices, amorphous devices, magnetoresistive devices will soon enter this field.
Another is the automobile engine system ignition timing speed sensor and igniter. Inductive sensors are also mainly used in these areas. Hall gear sensors and Hall chip switches are already in use in some models. Honeywell reported that as of June 1996, they had supplied 80 million Hall wing blade switches and 3 million Hall gear speed sensors to the automotive industry. It is predicted that in the future, more than 30 magnetic sensors like Hall sensors will be used in a single automobile.
Also in the field of industrial automation, robotics, office automation, home appliances and a variety of security systems, in addition to the large number of brushless DC motors, AC inverters, etc., in the refrigerator, air conditioner, rice cooker, and other devices, the use of a large number of magnetic temperature controllers, in the mid-80s of the last century, has been more than hundreds of millions of them. Reportedly, in 1995 only the global market for industrial process control sensors has reached 26 billion U.S. dollars; in 2001 the market for SV-GMR heads for computer HDD exceeded 400 billion yen (about 3.4 billion U.S. dollars). If the new miniature magnetic sensors, not only make the operation easier, but also improve the reliability, growth of the device life, reduce costs.
The use of new magnetic sensors can significantly improve the measurement and control accuracy, such as the use of GMI (Giant Magnetic Impedance) magnetic field sensors, detection resolution and commonly used fluxgate magnetometers, while the response speed is twice as fast, consuming only 1% of the latter's power; if you use the Hall device, the resolution is only 4A / m, and the required external field than the former more than 300 times higher; in the stress detection, the SI The sensitivity of the sensor is 2000 times higher than the commonly used resistance wire, and 20 to 40 times higher than the semiconductor strain gauge. Industrial machine tools, hydraulic or pneumatic cylinder piston position detection, widely used in the piston rod on the permanent magnet ring and AMR components composed of magnetic sensors, detection accuracy of 0.1mm, detection speed can be in 0 ~ 500mm / s within the high and low speed change; change to GMI or SV-GMR sensor, the measurement accuracy can be improved by at least 1 order of magnitude. In the era of CNC machine tools, digital magnetic scales help designers realize closed-loop control. The use of absolute signal output of the magnetic scale, is not subject to noise, power supply voltage fluctuations and other interference, and do not have to home reset. Conversion between manual and CNC control can also be accomplished with the use of an operating state magnetic switch.
Rotary magnetic encoder in the rotating amount of detection and control plays a key role, it is in the CNC machine tools, robots, factory automation equipment, position detection, transmission speed control, disks, printers and other automation equipment, communication equipment, such as rotating amount of communication equipment detection is indispensable to the important components. Its detection object is optical-magnetic graphics, not subject to the influence of oil mist and dust, so than the current state-of-the-art optical encoder of high reliability and long life, especially suitable for automated welding, painting robots and steel-related position detection and a variety of metals, wood, plastics and other processing industries. While still using a large number of optical encoders, due to the susceptibility of such devices to dust, oil and smoke, used in automatic welding, paint robots, textiles and processing of steel, wood, plastics, etc., the reliability is extremely poor. The application of AMR, GMR, GMI sensitive components constitute the rotary magnetic encoder, there is no such shortcomings, therefore, their market demand annual growth rate of more than 30%. In household appliances and energy-saving products also has its wide application potential, in energy saving and environmental protection products are also useful. If the use of miniature magnetic encoder and control microcomputer integration, more conducive to simplify the structure of the control system, reduce the number of components and the occupied volume, which is very significant in the precision manufacturing and processing industry. For centuries, people have been using magnetic compass in navigation. Some data show that as early as two thousand years ago the Chinese began to use natural magnets - a kind of magnetite to indicate the horizontal direction. Electronic compass (digital compass, electronic compass, digital compass) is a more economical electronic instrument for measuring azimuth (heading angle). Today electronic compasses are widely used in automotive and handheld electronic compasses, watches, cell phones, walkie-talkies, radar detectors, telescopes, starfinders, Muslim Mecca detectors (Muslim clocks), handheld GPS systems, wayfinders, weapons/missile navigation ( heading derivation), position/azimuth systems, security/location devices, high performance navigation devices for automotive, marine and aviation, video game console devices and other devices that require a Orientation or attitude displays.
The Earth itself is a large magnet, and the magnetic field at the Earth's surface is about 0.5 Oe, with the geomagnetic field parallel to the Earth's surface and always pointing north. Sensors for detecting the geomagnetic field can be made using GMR films. Figure 5 shows how this sensor works. We can make an integrated GMR sensor that can detect the X and Y components of the magnetic field. This sensor can be used as a compass and as a navigational device in various vehicles. The American company NVE has already used GMR sensors in traffic control systems for vehicles. For example, GMR sensors placed at the side of a highway can count and differentiate vehicles that pass the sensor. If the two GMR sensors are placed separately at the same time, the speed and length of the vehicle can also be detected. Of course, GMR can also be used in the toll booths of the highway, thus realizing the automatic control of tolls. In addition, high sensitivity and low magnetic field sensors can be used in aviation, aerospace and satellite communication technology. As you know, in the military industry, with the development of wave-absorbing technology, military objects can be hidden by covering a layer of wave-absorbing materials, but they will generate magnetic fields anyway, so through the GMR magnetic field sensors can find out the hidden objects. Of course, GMR magnetic field sensors can be used on satellites to detect objects on the Earth's surface and the distribution of mineral deposits underneath.
These are just some of the applications, and I won't go into more detail for the sake of space.