The photoelectric pressure transducer uses a phototube and a light source (either a stable source of light or ac modulated light) separated by a window, whose aperture is controlled by the force summing device of the pressure transducer as illustrated in the figure below:
The displacement of the force summing device modulates the quantity of incident light falling on the phototube; applied pressure or force changes the position of the force summing device which in turn changes the position of the window hence causing a change in incident light. A change in light intensity varies the photoemissive property of the photoelectric transducer/phototube at a rate approximately linear with displacement. A current (which is typically very small) is produced as a result of incident light on a phototube. This current is then amplified to provide a usable output.
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