No problem with noncontacting sensors

Sept. 21, 2000
Invensys Sensor Systems, El Paso, Tex., (Clarostat Div.) has developed a rotary Hall-effect position sensor, the HRS100, that cuts cost by integrating all compensation circuitry into a single factory-programmed sensor ASIC.
As the shaft/magnet holder assembly rotates, the magnets move relative to the sensor, such that the magnetic field strength of the sensor changes with rotation. The integrated sensor IC provides gain and offset adjustment and temperature compensation that can be adjusted and stored in the device after assembly.

Resistive potentiometers or "pots" have long been used for rotary position sensing in automotive and industrial applications because they are simple and inexpensive. But, because they operate by sliding a wiper contact over a resistive surface, pots eventually wear out and need to be replaced. Furthermore, the wear gets worse in continuously vibrating applications.

The Hall effect is a reaction in a current-carrying conductor to the presence of an external magnetic field. It has been adapted as a noncontacting technology for proximity and speed sensing, but its use for precise position sensing has been limited by the need for more complex and expensive gain and offset adjustment and temperature compensation.

For the first time, according to Invensys, a temperature-stable rotary Hall sensor with high linearity is available at prices that rival the resistive potentiometers they replace.

In the HRS100, the shaft/magnet holder assembly rotates, moving the magnets relative to the sensor. The device uses a newly developed sensor IC containing a Hall sensor element along with additional electronics which provide gain and offset adjustment as well as temperature compensation.

Standard features include 5-Vdc operation and various output voltage ranges available over mechanical rotations up to 180°, with 1% or better linearity. Rotational life is more than 50 million full cycles and 100 million dither cycles.

The HRS100 is housed in a compact, shielded stainless-steel package and is available with "designer curves," which means virtually any output curve can be tailored to provide the response needed for a particular application. For instance, an electric vehicle motor controller is often used with a resistive pot in which the ends of the element are wired together as one signal, and the wiper contact as the other. This creates a parabolic resistance curve that, along with directional switches, the controller translates into smooth forward and reverse movement. Designer curves can produce the same response in the HRS100. By also adding integrated hard-contact switches, a single compact noncontacting control can replace both the resistive pot and two separate switches.

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