Technical Types of Magnetic Sensors

There are many technical types of magnetic sensors

A magnetic sensor is an electronic component that converts magnetic signals into electrical signals. Magnetic sensor applications are often in automatic machinery and equipment to provide information feedback for the control system and achieve the function of detecting the linear position of the cylinder piston. Choose the right magnetic sensor technology to maximize device performance, space, and reliability, depending on the application environment. The main realization technologies of the magnetic sensors include Hall technology, dry reed mechanical, anisotropic magnetic resistance technology (AMR), giant magnetic resistance technology (GMR), etc. In the future, magnetic sensors will develop towards miniaturization, integration, intelligence, low power consumption, anti-interference, and high sensitivity.

Reed Tube Switch

A magnetic spring switch is a kind of mechanical switch with a dry reed tube as the core part. The fully sealed structure of the reed tube enables it to work in a variety of environments. When the external magnetic field approaches, the reeds on the dry reed tube are magnetized by the magnetic field and are attracted to each other. At this time, the circuit turns on and provides information feedback for the control system.

Pneumatic reed switch is cost-effective and can connect ALTERNATING and direct current; The contacts in the dry spring tube are sealed in the glass tube with inert gas, which is less affected by the external environment. The contacts have excellent corrosion resistance and wear resistance, thus increasing the life of reed switching times. Due to the physical characteristics of dry reed tubes, reed switches have certain limitations. First of all, the conduction of the reed switch depends on the contact of the reed, which is a mechanical process. Therefore, the switching cycle of reed contacts is limited and needs to be maintained during the use of the machine. The reed switch is not suitable for exposure to equipment with high vibration or strong impact. Violent vibration will cause the contact of the reed to deviate, resulting in an unstable or ineffective reed connection. The switching characteristics of reed switches can also lead to accidental double switching. Double switching means that the sensor output switches "ON" and "OFF" twice, while the cylindrical magnet switches ON and OFF once by means of a reed. The sensor output error double switch is due to the uneven strength of the magnetic field. The strength of the magnetic field is strongest at each pole of the magnet and weakest in the center between each pole. If the piston magnet is not strong enough, it may cause the switch output to double switch as it passes through the sensor. Finally, reed switches activate relatively slowly compared to solid state sensors, making them unsuitable for applications requiring fast response times.

In practical applications, reed switches are widely used on cylinders. This benefits from a relatively low price and does not require additional switching load to work under DC or AC conditions

Hall Effect Sensor

A Hall sensor is a magnetic proximity switch. The Hall sensor has a conductive plate, charge carrier flows from A to B and through the conductive plate. At this time, an external magnetic field is introduced, and under the action of Lorentz force, the linear movement of charge carriers interferes with, and electrons will guide one side of the plate to offset, thus generating potential difference at both ends of the conductive plate. This voltage is called hall voltage. Hall voltage changes with the magnetic field intensity, the stronger the magnetic field, the higher the voltage; The weaker the field, the lower the voltage. Hall voltages are usually only a few microvolts per gauss, and the equipment requires a high-efficiency amplifier built in to amplify the voltage enough to produce a strong signal. Hall sensors come in two classes, providing analog signal output and digital signal output. The former is composed of a hall element of the voltage regulator and amplifier, suitable for measuring distance; The latter provides only two output states of "on" or "off". This type of Hall sensor requires additional Summit triggers to provide delay or two different threshold voltages. So the output potential can only be high or low. Hall sensors are different from reed switches in that they do not include moving components and have a smaller installation space. The solid-state design extends the life of the sensor and also resists shock and vibration. Compared with the mechanical contact of the reed switch, it overcomes the inertia caused by reed contact, so it is more suitable for applications requiring rapid signal switching. In addition, hall sensor sensitivity is low. Depending on the diameter and thickness of the cylinder block, the switch output may not make the correct instructions in time. Hall effect switches are commonly used as limit switches in 3D printers and CNC machine tools and detection and positioning in industrial automation systems. In addition, Hall sensors are also used as wheel speed sensors and crankshaft or camshaft position sensors.

Advantage:

(1) The magnetic range with the best performance of anisotropic reluctance technology is centered on the Earth's magnetic field, which has a wide operating space for sensor applications with the Earth's magnetic field as the basic operating space.

(2) Anisotropic reluctance technology is the only semiconductor technology that has been verified and can achieve a degree of orientation accuracy in the earth's magnetic field. Other technologies that can achieve the same precision are processes that cannot be integrated with semiconductors. Thus, AMR can be integrated with CMOS or MEMS on the same silicon chip and provide sufficient precision.

AMR technology only requires a layer of magnetic film and convenient production.

(3)AMR technology has high frequency, low noise, and other characteristics, suitable for a variety of applications.

(4)Similar to hall effect sensors, AMR sensors act quickly, are wear-free, and are resilient to shock and vibration.

(5)Because it can detect weaker magnetic fields, it can improve piston detection at longer distances. Because of the higher sensitivity, the possibility of double switching points is eliminated.

Giant Magnetoresistance Sensor (GMR)

A giant magnetoresistance sensor (GMR) is a solid magnetic proximity sensor. The magnetoresistance effect is a phenomenon in which the resistance value of a conductor or semiconductor changes under the action of a magnetic field. The ferromagnetic layers in magnetic multilayers such as Fe/Cr and Co/Cu are separated by non-magnetic materials of nanometer thickness. Under certain conditions, the reduction of resistivity is quite large, which is about 10 times higher than that of magnetic metals and alloys. This phenomenon is called the "giant magnetoresistance effect".