Arijit Sen Faculty Department of Mechanical Engineering IUBAT Mec 337 Chapter - 6 Arijit Sen Faculty Department of Mechanical Engineering IUBAT

Sensor Iout = f(Iin) Transfer efficiency = Iout /Iin η = dIout /dIin

Loading of the Signal Source Energy will always be taken from the signal source by the measuring system, which means that the information source will always be changed by the act of measurement. This is a measurement axiom. This effect is referred to as loading the smaller the load placed on the signal source by the measuring system, the better.

Classification of First Stage device Class I: first stage elements used as detectors only Class II: first stage elements used as detector and single transducer Class III: first stage elements used as detector with two transducer.

Advantage of electrical transducer Amplification or attenuation can be easily obtained Mass inertia effects are minimized An output power of almost any magnitude can be provided Remote indication or recording can be feasible. The transducer can often be miniaturized.

Variable resistance transducer element R= ρL/A

Piezoelectric Sensor Certain materials can generate an electrical charge when subject to mechanical strain or, conversely, can change their shape when subject to voltage. This is known as piezoelectric effect. Vo(t) = Q(t)/Ct Vo = Ghσ Where G is a material constant, h thickness and σ is stress.

Light Detecting Transducer Photoemissive detector Photoconductive cell Photovoltaic Cell Photodiode