Complex control systems all make use of signals that may be easily measured and altered remotely. Automatically operated machines or actuators have to be powered either by piezoelectric crystal, pneumatic or hydraulic cylinders.
The most frequent signals sent out from a transducer are electric voltage or current and pneumatic pressure. These signals can easily be interpreted by controls. Visual measuring apparatus such as liquid lubricant thermometers aren’t able to be utilized in automatic control methods since there are not any electric or pneumatic signals.
But when some additional part is added to it to allow it to provide a corresponding signal, then the measuring device becomes a transducer.
A transducer is a device to convert a signal (representing a physical volume) of one form into a corresponding signal of some other form, keeping the amplitude variations of energy being transformed.
Just for instance, a microphone is a solid transducer (acoustic to electric) and a loudspeaker is an electric transducer (electric to acoustic). A transducer could be an essential portion of the measuring device, for example pressure to displacement at a Bourdon pressure gauge. It might also be a distinct unit converter especially suitable to alter the signal to some much better form for remote transmission, e.g. displacement to electric in a differential transformer.
How can these transducers do the job?
To convert physical motion to electric signals, some devices take advantage of variable resistors. Any motion will make a slider to modify place against a resistance cable resulting in a change in electric voltage or current. Other devices may use the motion to change the place of an induction coil relative to the magnetic center, resulting in a change in the induced current from the circuit. Others might use the motion to change the air gap between two capacitance plates, resulting in a change in the current from the circuit.