The State of the Art in Hall Effect Technology and Its Implications for Appliance Design and Development

Hall effect sensor technology has advanced signifi cantly, offering high performance, accuracy, consistency, reliability, and new feature sets at reasonable costs. Now leading the way in high-volume automotive applications, which are cost-sensitive, quality and reliability conscious, and subjected to harsh environments, Hall effect devices have distinguished themselves, and have become the preferred technology for many critical safety and performance uses involving the sensing of: motion, position, speed, direction, proximity, and electrical current. The highly successful application of Hall effect sensors in the automotive sector in many cases is directly transferable to appliances. Hall effect devices may not completely replace mechanical switches, but they do offer signifi cant advantages for appliances. Their major advantage versus other switch technologies is contact-less, bounce-free switching. This virtually eliminates failures induced by physical “wear and tear,” and they are not affected by dirt, dust, or other environmental factors normally associated with “harsh” conditions, but which are important for appliances as well. This paper briefl y reviews the basic principles of Hall effect technology and its evolution to today’s state of the art. This includes a look at historic areas of concern for the technology, and how these have been addressed. It also provides a comparison with mechanical switch technology. Lastly, an overview of how Hall effect technology has, and can be, used in various appliance applications is presented. THEORY OF OPERATION The basic element in a Hall effect device is a small sheet of semiconductor material represented by fi gure 1. When a constant voltage source is applied to the element, as shown in fi gure 2, it forces a constant bias current to fl ow in the element. The output takes the form of a voltage, which can be measured across the width of the sheet. On its own, this voltage has negligible strength, but if the biased Hall element is placed in a magnetic fi eld that has fl ux lines at right angles to the Hall current (fi gure 3), then the voltage output is amplifi ed, becoming directly proportional to the strength of the magnetic fi eld. This is the Hall Effect, discovered by E. F. Hall in 1879. This phenomenon is the basis of all Hall effect devices today. Using modern semiconductor manufacturing techniques and circuits, the basic Hall element can be augmented by: a) adding a voltage regulator to provide a stable power source over a wide range of input volt-ages, and b) adding an amplifi er to increase the usable signal.