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POSTED BY: millekragh
DATE: 03.12.2012
SUBJECT: Motion Sensor Light Swtch
LOCATION: geifei, China

For nulling or centering applications, the spatial resolution of a continuous device is inferior to that of a comparable Light Sensor Switch. This stems from the lower signal-to-noise ratio of continuous devices. So continuous position sensors work best for measuring a light spot's movement over a wide range.


Continuous position sensors are available in one and two dimensional configurations, and come in four types-duo-lateral, tetra-lateral, pin-cushion and transparent duo-lateral.


The duo-lateral type has electrodes on both its front and rear surfaces. From the equivalent circuit it can be seen that each position signal is divided into just two parts…but by two separate resistive layers. This approach produces Motion Sensor Light Swtch sensing error and very high resolution.


Tetra-lateral types have four electrodes on the front surface of the photodiode. As such, the total induced photocurrent is divided into four parts by the same resistive layer. Compared with the duo-lateral type, tetra-lateral devices are more non-linear for positions further from their mechanical centers. However, the tetra-lateral devices produce less dark current and have a faster response time. And they are somewhat easier to operate since minimal, or even zero, bias voltage is required.


Pin-cushion devices are basically an improved tetra-lateral, with reduced signal non-linearity at the edges.This is achieved by increasing the photodiode's surface sensitivity and modifying its electrodes. The pin-cushion device offers all the advantages of the tetra-lateral type, namely, low dark current, fast response, and minimal bias-voltage requirements.


Transparent duo-lateral detectors are essentially the same in principle as Light Sensor. However, they are constructed by depositing amorphous silicon on a transparent substrate. Thus, an incident beam can pass right through the detector after experiencing a small amount of attenuation and diffusion.









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