An input sensor or transducer is a device which permits the conversion of energy from one form to another. It is the first element in an instrumentation or measurement system. For example, it might convert temperature to voltage. A broader definition might substitute ‘information’ for ‘energy’. Its linearity, range, noise and dynamic response largely determine the resolution, sensitivity and bandwidth of the overall system. A transducer is a device that, in some way, obeys reciprocity (e.g. the physical input quantity is converted to an output voltage and if a voltage is applied to the output terminals, the input quantity is generated at the input interface of the transducer). Examples of transducers include piezoelectric crystals used to sense force or pressure, and electrodynamic devices such as loudspeakers and D’Arsonval meter movements. Obviously, not all sensors are transducers.