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1) dark resistance photoconductive resistance at room temperature, total dark conditions stable resistance called dark resistance, at the current flow resistance is called dark current.
2) light resistance photoconductive resistance at room temperature and certain lighting conditions stable resistance measured, right now is called light resistance of current flow resistance is called light current.
4, volt-ampere characteristics of both ends photoconductive resistance added voltage and current flows through photoconductive resistance of the relationship between called volt-ampere characteristics shown, as shown in figure 5. From the graph, the approximate linear volt-ampere characteristics that use should be limited, but when the voltage ends photoconductive resistance, lest than shown dotted lines of power consumption area
5, photoelectric characteristics photoconductive resistance between the poles, light when voltage fixed the relationship between with bright current photoelectric characteristics. Called Photoconductive resistance photoelectric characteristics is nonlinear, this is one of the major drawback of photoconductive resistance.
6, spectral characteristics is not the same incident wavelength, the sensitivity of photoconductive resistance is different also. Incidence wavelength and photodetector the relationship between relative sensitivity called spectral characteristics. When used according to the wavelength range by metering, choose different material photoconductive resistance.
7, response time by photoconductive resistance after photo-current need light, over a period of time (time) rise to reach its steady value. Similarly, in stop light photo-current also need, over a period of time (down time) to restore the its dark current, this is photoconductive resistance delay characteristics. Photoconductive resistance rise response time and falling response time about 10-1 ~ 10-3s, namely the frequency response is 10Hz ~ 1000Hz, visible photoconductive resistance cannot be used in demand quick response occasion, this is one of the main photoconductive resistance shortcomings.
8 and temperature characteristic photoconductive resistance by temperature affects greatly, temperature rise, dark current increase, reduced sensitivity, which is another photoconductive resistance shortcomings.
9, frequency characteristic frequency characteristics refers to an external voltage and incident light, strong must be photo-current I and incident light modulation frequency, the relationship between the f, photoelectric diode is the frequency characteristic of the photoelectric triode frequency characteristics, this is because of the photoelectric triode shot "yankees there capacitance and carrier base-combed need time's sake. By using the principle of the photoelectric efficiency of optoelectronics manufacturing frequency characteristics of the worst, this is due to capture charge carriers and release charge need a certain time's sake.
Three, photoelectric sensors
Photoelectric sensor is through the light intensity changes into electrical signal changes to achieve control, its basic structure, it first figure 6 by measuring the change of change of converting the light signal, and then using photoelectric element further will light signals into electrical signal by photoelectric sensor general. Illuminant, optical path and optoelectronics. Three components of photoelectric detection method has high precision, fast response, non-contact wait for an advantage, but measurable parameters of simple structure, sensors, form flexible, therefore, photoelectric sensor in the test and control is widely used.
By photoelectric sensor generally is composed of three parts, they are pided into: transmitter and receiver and detection circuit shown, as shown in figure 7, transmitter aimed at the target launch beam, the launch of the beam from semiconductor illuminant, general light emitting diode (LED), laser diode and infrared emission diode. Beam uninterrupted launch, or change the pulse width. Receivers have photoelectric diode, photoelectric triode, composed si-based ones. In front of the receiver, equipped with optical components such as lens and aperture, etc. In its back is detection circuit, it can filter out effective signal and the application of the signal. In addition, the structural components in photoelectric switch and launch plate and optical fiber, triangle reflex plate is solid structure launch device. It consists of small triangle cone of reflective materials, can make a beam accurately reflected back from plate, with practical significance. It can be in with the scope of optical axis 0 to 25, make beams change launch Angle from a root almost after launch line, passes reflection or from the rotating polygon.some basic returns.