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Invensys introduces rotary Hall-effect sensor

Resistive potentiometers or "pots" are a mainstay of rotary position sensing. They are simple and inexpensive, but because they operate by sliding a wiper contact over a resistive surface, they eventually wear out and require replacement. The wear is worse in applications where the pot is exposed to continuous vibration.

Invensys' Hall-effect Clarostat HRS100 temperature-stable, rotary position sensor offers enhanced linearity over resistive potentiometers.

The Hall effect has long been used as a noncontact sensing technology for proximity and speed sensing. Its application in precision position sensing, however, has been stalled by the need for elaborate gain and offset adjustment as well as temperature compensation. These requirements have kept their complexity and price significantly higher than resistive potentiometers.

Invensys Sensor Systems' Speed and Position Business Unit has developed a rotary Hall-effect position sensor under its Clarostat brand name. The HRS100 integrates all compensation circuitry into a single factory-programmed sensor application-specific integrated circuit (ASIC). According to Invensys, it is a temperature-stable rotary position sensor that offers improved linearity at a price that rivals those of the resistive potentiometers they replace. It allows programmable customization of temperature coefficient, offset, and gain control at the time of manufacture. The HRS100 is already being used in forklift controls and marine throttle applications. Other applications include pedal position sensing, tilt control, steering, and active suspensions.

Schematic of the HRS100.

Similar to resistive potentiometers, Hall-effect sensors provide a voltage output ratio as a function of the mechanical angle of a shaft as it rotates. The basic HRS100 features 5-V dc operation and a variety of output voltage ranges including 0-5 V, 0.5-4.5 V, 0.25-2.25 V, and 0.25-4.75 V. These voltages are available over mechanical rotations up to 180°, with 1% or better linearity. Rotational life is in excess of 50 million full cycles and 100 million dither cycles. The HRS100 is housed in a compact 25 x 15 mm (1 x 0.6 in) shielded stainless-steel package. A 3/8-in threaded bushing and 1/4-in stainless-steel shaft are standard.

Features available on the HRS100 include 12-V dc operation, ratiometric outputs, and a variety of cable and connector options. Hard-contact switches (e.g., for throttle directional signals) can be integrated into the control, eliminating the need for external microswitches and cams and the associated installation labor, adjustment, and maintenance.

The HRS100 is also available with Invensys' Designer Curves, in which virtually any output curve can be tailored precisely to give the necessary response for a particular application. An electric vehicle motor controller is often used with a resistive pot that has the ends of the element wired together as one signal and the wiper contact as the other. This creates a somewhat parabolic resistance curve that, along with directional switches, the controller translates into smooth forward and reverse movement. With Designer Curves, this same response can be created in the HRS100. By also adding integrated hard-contact switches, a single compact noncontact control can replace both the resistive pot and two separate switches.

Magnetic mold change system from Stäubli

According to Stäubli Corp., its new magnetic quick mold change (QMC) system for injection-molding applications will maximize productivity and reduce machine downtime. The QMC120 system uses magnetics to provide a higher clamping accuracy with lower maintenance than conventional physical systems. The innovative QMC120 features an all-steel surface that provides better wear resistance and thermal stability than hard resins. Stäubli uses magnetic materials that work at higher temperatures and result in longer product life.

The Stäubli system features an innovative built-in magnetic measuring device that improves safety. Immediately following magnetization, the magnetic flux is analyzed, and an indicator from the control system provides the appropriate signal. A failure would occur if the mold was not flat enough against the magnet or if the base-plate material was not permeable. Stäubli claims that no other magnetic system offers this capability. Other systems typically check to see if enough electrical current was used during the magnetizing process without addressing air-gap and material conditions.

Another unique magnetic detection feature provided by the QMC120 ensures that good contact with the mold is maintained. The slightest movement of the mold causes a change of magnetic flux that is measured electronically. The system is immediately shut down if a change is detected, giving an added measure of security that is not provided by proximity probes.

Stäubli also uses unique circuitry in the magnet to minimize power consumption, resulting in improved reliability and faster cycling times (generally less than 1 s/50 poles for both magnetizing and demagnetizing). The magnetizing phase operates twice automatically, which is important since the mold may not be placed perfectly against the magnet and a small air gap may be present. The first magnetization pulls the mold to the magnet and the second ensures proper contact with the mold and then maximizes the clamp force.

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