Transducers are sensors that convert physical and non-electrical quantities into electrical quantities. Examples are thermocouples and photodiodes, which convert temperature or brightness into voltage, or quartz crystals with which pressure can be converted into voltage.
There are transducers for all physical quantities: for strain and force, for weight and length, for angle of rotation and speed, for flow, electrical power and charge, resistance, frequency, field strength, volume, color and many other quantities. They, the transducers, turn a physical quantity into an electrical signal, a voltage or a current, which can then be measured with electrical measuring instruments and meters.
Since transmitters are generally passive and have a nonlinear relationship between the physical and electrical quantities, they must use nonlinear components and/or amplifiers with nonlinear characteristics to create a linear relationship between the two quantities. The output signal of transducers should be in a normalized voltage range corresponding to the measuring ranges of measuring instruments.
In contrast to measuring transducers, the same electrical quantity is converted into a smaller or larger value with measuring transducers.