Magnetic Pick-Ups

Miniature magnetic 'pick-up' transducers suitable for use in a wide range of sensing applications. Each device responds to movement of ferrous parts past the pole on the end of the unit. Used extensively in areas such as speed regulation of motors, when sensing for example, the teeth on a gear wheel. However, magnetic pick-ups may be used to implement feedback and control functions in many fields. Automotive applications include crank angle sensing, ignition timing, anti-skid systems and diagnostics. Applications in the computer peripherals area encompass disc drives, line printers, card punches/readers and printer terminals. The diagrams indicate the two basic modes of using these components. Note especially their small size in relation to their high signal output, enabling their deployment where many conventional sensors cannot be fitted. Fully encapsulated construction for reliable operation, but not intended for immersion in liquids.

Honeywell VRS Sensors

Honeywell offers VRS sensors for high output, general purpose, power output, high resolution, high temperature, and hazardous location applications. High Output VRS sensors are designed for use in applications where higher output voltages are needed. For best performance use in applications of low to medium speeds with medium to high impedance loads. General Purpose VRS sensors are designed for use in applications with medium to high speeds or in electrically noisy environments with relatively small air gaps. Passive Front-End Sealed versions are available for use where the sensor is exposed to fluids, lubricants or adverse environmental conditions. VRS (Variable Reluctance Speed) Magnetic Speed sensors are simple, rugged devices that do not require an external voltage source for operation.

The fixed magnetic field is established by use of a permanent magnet. As a ferrous metal object approaches and passes near the sensing area the flux lines of the magnetic field change in strength. This change in magnetic field strength induces a current into a coil winding, which is attached to the output terminals. The output signal of a VRS sensor is an ac voltage that varies in amplitude and wave frequency as the speed of the monitored device changes, and is usually expressed in peak to peak voltage. One complete waveform occurs as each target passes the sensor’s pole piece. If a standard gear were used as a target, this output signal would resemble a sine wave if viewed on an oscilloscope.

Self-powered operation
Direct conversion of actuator speed to output frequency
Simple installation
No moving parts
Designed for use over a wide range of speeds
Adaptable to a wide variety of configurations
Customized VRS products for unique speed sensing applications

Potential Applications:
Engine RPM measurement
Motor RPM measurement
Process speed measurement
Speed measurement of pumps, blowers, mixers, exhaust and ventilating fans
Flow measurement on turbine meters
Wheel-slip measurement on autos and locomotives
Gear speed measurement