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Making sense out of sensors

09 October 2017

The market for sensors in industry, domestic appliances, automotive and industrial plant, building automation and smart homes is growing very rapidly. ZF Sensors are available in many forms and in two main technology types.

Angular position sensor

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The following overview is intended to assist designers in making the correct choice of sensor to meet the needs of their particular requirements.

What’s the difference between hall-effect and reed sensors?

Although both types of sensor detect the proximity of a magnet, Hall and Reed sensors differ greatly in the way they function. Hall sensors are solid-state devices whose output changes when exposed to a magnetic field. Reed sensors, on the other hand, are electrically switched with two tiny contacts in a vacuum tube that open or close in the presence or absence of a magnetic field.

What are the advantages of reed sensors?

The main advantage of reed sensors is that they consume zero power in standby mode, making them extremely energy efficient. In addition, they are immune to ESD and serve as a low-cost alternative to Hall technology, which requires ESD protection. Another use for Reed technology is in applications with supply voltages outside the 5 to 24 VDC range typical of Hall-Effect sensors. Reed sensors can effectively switch 110 V DC at low current.

What are the advantages of hall-effect sensors?

Hall-effect sensors have no mechanical interface and therefore no parts to wear out or jam and offer a virtually unlimited life. They are ideally suited for sensing a rotating magnet that passes the sensor millions of times. Reed sensors have a very long life compared to other electromechanical switch solutions but they can´t match the extremely long life of a solid-state Hall sensor. Hall sensors are ideal for sensing gear teeth or speed, whereas reed sensors are limited to bipolar position sensing.

What options are available in reed sensors?

Reed sensors are available with normally closed, normally open or changeover contacts that change state when a magnetic field is applied. These sensors act as non-latching electrical switches.

How do reed sensors function?

The structure is simple: a hermetically sealed reed consisting of iron-nickel alloy, forming a normally opened or normally closed contact. A magnet approaching this ferromagnetic reed leads to switching.

Reed switch magnetic proximity sensors 

Omnipolar Reed-based sensors are hermetically sealed for long life, have zero power consumption in standby and are suitable for DC and AC circuits.

Typical applications include door position and interlock, limit switch, flow/speed measurement, building security and pedal switch.

What options are available in hall-effect sensors?

The flexibility in sensing and packaging of hall-effect sensors has enabled manufacturers to develop sensors for specific applications as follows;

Gear tooth speed sensors 

Sensors designed for use in applications where ferrous edge detection/near zero speed sensing is needed. 

Applications include;

• Speedometers

• Anti-lock braking systems

• Exercise equipment

• CNC machine tools

Speed and direction sensors

Speed and direction sensors have two Hall cells, one that detects speed while the other detects the direction of movement. Modular design versions are available to allow customers to specify a sensor in various standard configurations, including immersion depth and output interface.

Digital vane sensor

Applications include;

• Electric drives (stationary and mobile)

Automation systems

• Conveyor belts

• Wind turbines

Angular position sensors

Angular position sensors provide a linear change in voltage output corresponding to the angular rotation of the axis. Non-, semi- or fully- redundant outputs are available. Custom programming of angle range, slope and PWM output is generally available. Angular position sensors are widely used to replace potentiometers. Applications include:

• Implement (fork lift, agricultural trailer hitch, etc.) position sensing

• Gear selection

• Outboard trim sensing

• Farming machinery

• Printing equipment

• Fork Lift Position Sensing

• Foot Pedal

• Throttle /Brake /Steer by Wire

Linear position sensors

Non-contact linear position sensors are equipped with one or two independent outputs. They provide a linear change in voltage output (ratiometric to the input voltage) corresponding to a linear displacement of the actuator magnet. The actuator magnet included in the set will be specifically adapted and calibrated to the sensor. Dual independent (semi-redundant) outputs are available to assure high reliability.

Typical applications include;

• Hydraulic valves

• Hydraulic controls

• Electric drives

• Pneumatic controls

• Zero-contact encoder alternative

• Gear selection/shifting position

Digital vane sensors

A digital vane sensor has a hall-effect in one fork and a permanent magnet in the other fork, typically separated by a 3.4mm (0.135") airgap. The output switches when a ferrous target passes between the forks. They are mechanically interchangeable with optical switches and provide robust sensing even in dusty environments. Have no mechanical wear, are reliable and repeatable and immune to moisture and dust.

Typical applications include;

• rotary vanes

• saw teeth moving in a linear direction

• openings in a metal band

• door/gate position control

• exercise equipment and printers

For further information on the ZF sensor product range, contact its product specialists. 

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