This essay explains all the common transducers and their uses and benefits. For example, a yardstick measure length, a graduated beaker measures volume, a spring scale measures force, a beam balance measures mass, a potentiometer measures voltage, a Wheatstone bridge measures resistance, and a clock measures time. In many transducers the unknown is first converted to an intermediate quantity such as a displacement and that intermediate quantity is then converted to the output quantity, such as electric voltage. The output quantity is often then digitized. Transducers are used instead of isometer instruments when they are smaller and more rugged, the measurement must be transmitted through a distance, the measurement is part of a feedback control system, the required range, speed, accuracy, or frequency response of an isometer instrument is inadequate, a human readable display is wanted.
Color is analyzed by prisms and photoelectric cells.
The resulting displacement, in turn, moves a needle over a scale, changes an electrical impedance, changes a pneumatic resistance. Temperature also directly generates voltage in thermocouples and thermistors. Their resistances change and the change is measured electrically. Many transducers first convert their sensed quantity into strain, by bending a diaphragm for example, and then measuring that strain. They also precess gyroscopes.