Design Mechanism Of Magneto-resistive Sensors

By Author: Control Products
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Magneto-resistive linear position sensors provide a non-contact, non-wear-out solution ensuring a long life span. The device consists of an array of sensors, a magnet and signal conditioning electronics. This design offers a low power solution and high accuracy readings. Magneto-resistive linear position sensors can be quite beneficial in certain applications.

Linear position sensors play an important role in automation control that requires precise positioning. Manufacturers are constantly looking for new technological advancements and approaches to be able to meet the high reliability and accuracy requirements set by clients.

Magneto-resistive sensors provide a non-contact, solid state, long lasting design with no moving parts to wear out. This is often a major downfall of traditional contact-based position sensors. When you need sensors for rugged environments such as high temperature settings, magneto-resistive sensors are a great solution.

The mechanism measures the angle direction of the field from the magnet. This design allows the sensor to be tolerant of the air gap between the sensor and magnet. ...
... These sensors are also less sensitive to shock and high vibration then traditional models, and insensitive to the temperature coefficient of the magnet.

The system is made up of a multitude of magneto-resistive sensors and a moving magnet inside. The sensors measure the angle direction of a field from a magnet against the strength of a magnetic field, which is created by a permanent magnet. The field has the ability to keep the sensors in saturation mode, minimizing the effects of the field and providing a linear operating range.

As the measured object uses a magnetic field as a media, it has no contact with the sensor and therefore, no parts to wear out. This technology provides for an absolute reading with no reference point required. The technician can find pinpoint accuracy readings at any time.

The system has three major elements – the magnet, an array of sensors, and the signal conditioning electronics. When a sensor is connected to the supply voltage, it converts the applied magnetic field to a voltage output. When operating in saturation mode, the device is designed to be sensitive to the direction of the magnetic field. Saturation mode is created when external magnetic fields cross a certain field strength level. The output of the device in this case reflects the direction of the field and not the strength.

Space between the sensors depends on the magnet strength and desired system accuracy. Once the magnet length and gap is finalized the linear output range of each sensor is determined. Sensor output is a sine function, which means the linear range of each sensor output is dependent on the system accuracy. For obtaining better accuracy, the sensors should be brought closer together. Traveling length is the major factor that determines the number of sensors in the array.

Any change in the gap distance between the sensor array and the magnet increases the linear range and slightly decreases sensitivity. This allows the sensors to perform in a high vibration environment and is easy to install. The advantage roots in the direction measurement of field strength versus the magnetic field.

The magnet is a crucial part of these linear position sensor devices. Ideally the sensor should be mounted with the North and South poles perpendicular to the sensor array. It must create a field robust enough to maintain three sensors at the minimum for proper saturation. The field could be in different directions, but the total field strength should be higher than a certain level.

The author of the article is associated with Control Products Inc. that deals in thermal switches, switch freezes, waterproof switches, sensors and other such components.