Chapter 9 - Application-Specific Sensors

Abstract

This chapter discusses few of the application-specific Hall-effect sensors that are commercially available. Hall-effect sensors, in combination with an actuator magnet, are used to make high-reliability user-interface controls. Since there are no contacts to corrode or wear and no moving parts other than the actuator magnet assembly, it is possible to build logic-level controls with high expected mean-time-to-failure. Only a small amount of electronics is needed to perform the power switching, so the electronics necessary to control the power-cycling and retain the output state of the Hall-effect sensor are more costly. The portable battery-operated applications are very useful leading to the emergence of low-power Hall-effect sensors. The Hall-effect devices operate by power-cycling the Hall-effect transducer and its associated bias and amplifier circuitry. Transmitting data signals in the form of a current as opposed to a voltage results in a higher immunity to the external electrical noise sources. Thus signaling methods such as the “4–20 mA current loop” are useful in noisy environments. Another advantage of current-loop signaling is that if the sensor is powered by a voltage applied across the transmission leads, then only two wires (V+, V–) are required.