Sensors & Actuators

14 EE March 1988 SENSORS & ACTUATORS Radiant, mechanical, thermal, magnetic, and chemical effects in our environment are nowadays normally detected and measured by electronic means. The conversion of these (analogue) effects into (digital) electrical signals is invariably effected by sensors. These transducers have become so important that without them life on earth would almost literally come to a standstill. Sensors come in a wide variety: it is estimated that there are close to 20,000 different types produced by thousands of manufacturers all over the world. The most important types are used in the detection or measurement of tempera- ture, pressure, gases, radiation, hu- midity, magnetism, acceleration, direc- tion, angle, flow, level, presence, pos- ition, displacement, and many more. The operation of most sensors depends on optics (lasers, optical fibre, infra-red emitters and detectors), semiconduc- tivity (photo transistors, photo diodes), thermoelectricity (thermocouples)...