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Magnetostrictive Principle and Advantage

Author:iTarget Sensors Date:2011-9-12 19:26:10

Magnetostrictive displacement/position sensor

1. Overview
Magnetostrictive displacement (liquid level) sensor is a sensor which measures product’s displacement through accurately measuring the absolute position of the moveable position magnet  ring with inner non-contact observation and control technology. Because of its high-accuracy and reliability, this sensor has been used in thousands of cases.
As the moveable position magnet  ring (used for measuring position) has no direct contact with sensitive elements, the sensor can work in severe environment and is free of bad influence of oil stain, solution, dust or other pollution. Otherwise, high-tech material and advanced electron processing technology has been used in the sensor, so it can be used in environment with high temperature, high pressure and strong vibration.  The output signal of the sensor is absolute displacement, so the data won’t be lost despite of power failure and power reset. Return to zero is unnecessary. For the sensitive element is non-contact, repeating measure contributes no wear to the sensor, thus the reliability and working life of the sensor is immensely elongated.

2. Operation Principle
Magnetostrictive displacement sensor(liquid level sensor), which based on magnetostriction theory, accurately measures position via strain pulse signal from two different magnetic fields. The measurement is a waveguide, the sensitive element in which is made of magnetostrictive material. When measuring, the electron room in the sensor gives out current pulse, which can be transferred in the waveguide and generate circle magnetic fields outside the waveguide. When this magnetic field meets the one from the moveable position magnet ring which representing position change, magnetostrictive effect happens. There’ll be a mechanical strain pulse inside the waveguide, which is transferred at constant speed and will soon be detected by the electron room.
The time of the mechanical strain pulse transferred in the waveguide is in proportion to the distance between the moveable position magnet ring and the electron room, so we can accurately measure the distance though measuring time. In addition, the output signal is a absolute value, not ratable or amplification signal, so signal drifting or value change do not exist and regularly rescaling is not necessary.
Magnetostrictive displacement sensor(liquid level sensor) is a high-accuracy and long distance absolute displacement measuring sensor that based on magnetostriction. For it has no contact with the moveable position magnet ring, it is free of wear, friction and it has long working life, good adaptation for environment, reliable safety and is suitable for automation. Even under the severe environment (oil, dust or other environment with pollution), it can normally work. Besides, it can stand high temperature, high pressure and strong vibration and has been widely used for measuring displacement and mechanical control. Its stroke length can be as long as 3 meters or longer and its nominal accuracy is 0.05% F/s. Accuracy of those whose stroke length longer than 1 meter can reach 0.02% F/S and repeatability can be 0.002% F/S(
iTarget Sensor can be 0.002%). So it is widely used in petrochemical industry, aviation, electric power and water conservancy, etc.











Magnetostriction and Magnetostrictive Material
We all know that substances expand with heat and contract with cold. Besides heat, magnetic field and electric field can also make objects longer or shorter. Ferromagnetic substance can become longer or shorter under the exterior magnetic field, when the magnetic field is removed, it restores. This is Magnetostriction. The theory of this is as follows: ferromagnetic or ferrimagnetic material can spontaneously magnetize under Curie point, thus forming magnetic domain. Within each magnetic domain, lattice deformation happens in the direction of magnetization intensity.
Under the influence of magnetic field, the free magnetic domain within material will rotate to make the magnetization direction of each magnetic domain consistent. Macroscopically, the subject becomes longer or shorter in the direction of the magnetic field.
There are mainly three categories of magnetostrictive material: magnetostrictive metal or alloy and ferrite magnetostrictive material. The above two are traditional magnetostrictive material which hasn’t been widely used. Later on, people discovered electrostriction material, whose electrostriction coefficient is larger than that of metal or alloy by 200~400ppm, so it doesn’t take long before it is widely used. The third category is IMC (intermetallic compound) magnetostrictive material which has been developed lately.

3. Magnetostrictive sensor’s advantage and Its Application Fields
Feature and advantage: 
interior non-contact measuring
high cost performance
multi output mode available
avoiding electrical surge and radio-frequency interference (RFI)
no regular demarcate and maintenance needed
easy installation
high stability
high reliability
long working life
defensive function of input power reversed polarity available
delicate structure 
good environmental adaptation and isolative explosion proof(optional).

Application Fields (replacement): 
piston position feedback or preset of Servo hydraulic oil cylinder and grind machine
position and control of wood processing 
opening detection and controlling of water turbine guide vane 
molding of paper and plastic film 
squeeze injection mould 
blow molding 
mechanic machinery 
metal molding/cut pressing and other machine position and replacement measuring 
dam brake 
piston position feedback or preset of Servo cylinders 
replacement control of cast and forging machine tool 
position decision and detection of moldboard of injection molding machine 
opening detection and controlling of gas resistance valve of steam turbine 
pressing of glass 
transform of plastic machinery 
pneumatic linear actuator 
Steel rolling 
food processing 
harbor machinery 
servo system of shipping steering engine

Application Fields (liquid level measurement): Widely used in petroleum, chemical industry, water conservancy, pharmacy, food and beverage industry for controlling and measuring liquid level of kinds of cans, also used in aerospace refueling system, car refueling system and diesel refueling system for hydrology monitoring and water disposing, etc.

Advantage of magnetostrictive liquid level sensor:
1. High Reliability: Magnetostrictive liquidometer is on the basis of waveguide theory and without mechanical parts, so it is free of friction and wear. The whole convertor was secluded in the stainless steel tube, non-contact with measuring medium. So it is reliable and enduring.
2. High Accuracy: Magnetostrictive liquidometer is on the basis of waveguide pulse, it measures the replacement by the time of initial pulse and terminal pulse, so its accuracy is very high. Resolution ratio is better than 0.01%FS, which is beyond other sesors.
3. Safety: Anti-explosion function of magnetostrictive liquidometer is satisfactory. With intrinsically safe explosion-proof, it is very safe. So it is particularly qualified for measuring of chemical material and flammable liquid. When measuring, you needn’t open the tanks, thus avoiding danger.
4. Easy installation and maintenance: Generally, magnetostrictive liquidometer can be installed through existing orifice on the tanks, particularly convenient for the sunken tank and commissioning tanks. Besides, during installation, work is not impacted.
5. Convenient for the system’s automation: The output signal of magnetostrictive liquidometer’s secondary meter is standard, so it is very convenient for the microcomputer to processing information and easy to get into networking, thus improving the automation of the measuring system.