GT6520 Photoresist Characteristic Measuring Instrument A photosensitive sensor is a sensor that converts an optical signal into an electrical signal, also called a photoelectric sensor, which can be used to detect non-electricity directly causing a change in light intensity, such as light intensity, illuminance, radiation temperature measurement, gas composition analysis, etc.; To detect other non-electric quantities that can be converted into changes in light quantity, such as part diameter, surface roughness, displacement, velocity, acceleration and shape of the object, and identification of working conditions. Photosensitive sensors are widely used in industrial automation and intelligent robots because of their non-contact, fast response and reliable performance. The physical basis of a photosensitive sensor is the photoelectric effect, that is, many of the electrical properties of the photosensitive material are changed by exposure to light. Photoelectric effect is usually divided into two categories: external photoelectric effect and internal photoelectric effect. The external photoelectric effect refers to the phenomenon that electrons escape from the surface of the object under the illumination of light, which is also called the photoelectric emission effect. The photoelectric device based on this effect has a phototube, a photomultiplier tube and the like. The internal photoelectric effect refers to the physical phenomenon that the incident light intensity changes the conductivity of the substance, which is called the photoconductive effect. Almost all sensors for optoelectronic control applications are of this type, usually with photoresistors, photodiodes, phototransistors, silicon photocells, etc. Of course, in recent years, new photosensitive devices have emerged, such as APD avalanche photodiodes with high-speed response and amplification, semiconductor photosensors, photo-thyristors, light-guide tubes, CCD image sensors, etc., creating a new application for photoelectric sensors. A new page. The basic characteristics of photosensitive devices include: volt-ampere characteristics, illumination characteristics, spectral characteristics, frequency characteristics, and temperature characteristics. This experiment mainly studies the volt-ampere characteristics and illumination characteristics of the photoresistor, and grasps the measurement method of the basic characteristics of the photoresistor. The photoresistor is a photovoltaic element fabricated from a semiconductor material that operates using an internal photoelectric effect. Its resistance is often reduced under the action of light. This phenomenon is called light guiding effect. Therefore, the photoresistor is also called light pipe. The materials used to make the photoresistor are mainly semiconductors such as sulfides, selenides and tellurides. Generally, a thin photoresistor and a comb-shaped ohmic electrode are formed on the insulating substrate by coating, spraying, sintering, etc., and then the lead is taken out and packaged in a sealed case having a light-transmitting mirror to protect the sensitivity from moisture. In the dark environment, its resistance value is very high. When the light is received, as long as the photon energy is greater than the forbidden band width of the semiconductor material, the electrons in the valence band absorb the energy of a photon and then transition to the conduction band, and in the valence band. A positively charged cavity is generated. This electron-hole pair generated by illumination increases the number of carriers in the semiconductor material, making the resistivity smaller, resulting in a decrease in the resistance of the photoresistor. The stronger the light, the lower the resistance. After the incident light disappears, the electron-hole pairs generated by photon excitation will gradually recombine, and the resistance of the photoresistor will gradually return to the original value. A voltage is applied between the metal electrodes at both ends of the photoresistor, and a current is passed therethrough. When irradiated with light of a suitable wavelength, the current becomes larger as the light intensity increases, thereby realizing photoelectric conversion. The photoresistor has no polarity and is purely a resistive device. It can be used with either a DC voltage or an AC voltage. First, the purpose of the experiment 1. Understand the basic characteristics of the photoresistor. 2. Measure its volt-ampere characteristic curve and illumination characteristic curve. Second, the basic characteristics of photosensitive resistors and experimental principles 1, volt-ampere characteristics Photosensitive sensor At a certain incident illumination, the relationship between the current I of the photosensitive element and the applied voltage U is called the volt-ampere characteristic of the photosensitive device. Change the illuminance to get one The group volt-ampere characteristic curve, which is an important basis for selecting parameters when designing the sensor application. The volt-ampere characteristic curve of a certain photoresistor is shown in Fig. 1. It can be seen from the volt-ampere characteristics of the above figure that the photoresistor is similar to a pure resistor, and its volt-ampere characteristic is linear. Under certain illumination, the larger the voltage, the larger the photocurrent, but it must be tested. Considering the maximum dissipated power of the photoresistor, exceeding the rated voltage and maximum current may cause permanent damage to the photoresistor. 2, lighting characteristics The relationship between the spectral sensitivity of the photosensitive sensor and the incident light intensity is called the illumination characteristic. Sometimes the relationship between the output voltage or current of the photosensitive sensor and the incident light intensity is also called Lighting characteristics, it is also an important basis for the selection of parameters for the application of photosensitive sensor applications. The illumination characteristics of a photoresistor are shown in Figure 2. It can be seen from the illumination characteristics of the above-mentioned photoresistor that the illumination characteristics of the photoresistor are nonlinear, and it is generally unsuitable for cooperation with linear detection elements. Figure 1 volt-ampere characteristic curve of the photoresistor Figure 2 Photoelectric characteristics of the photoresistor Third, the experimental instrument The GT6520 photoresistor characteristic measuring instrument consists of the following parts: photoresistor, test stand, GT-VC3 DC constant voltage source, nine-hole plate, multimeter, resistor component box and adapter box. During the experiment, the light source power socket and the sensor jack in the test rack are connected to the nine-hole board through the transfer box, and other connections are realized in the nine-hole board. Figure 3 GT-VC3 DC constant voltage source panel Figure 7 nine-hole plate Figure 4 resistance box Figure 5 transfer box Figure 6 test stand Fourth, the experimental content The corresponding illumination intensity in the experiment is relative light intensity, and the relative light intensity can be adjusted by changing the point source voltage or changing the distance between the point source and the photoresistor. The adjustment range of the light source voltage is 0 to 12V, and the effective range of the distance between the light source and the sensor is 0 to 200 mm, and the actual distance is 50 to 250 mm. 1. Photoresist volt-ampere characteristic test experiment (1) Connect the experimental circuit according to the schematic diagram 8. Place the light source with the standard tungsten wire lamp and the measuring photoresistor in the test frame. The resistor box and the transfer box are inserted in a six-hole board, and the power supply is provided by a GT-VC3 DC constant voltage source. (2) Change the light source voltage or adjust the distance between the light source and the photoresistor to provide a certain intensity, each time at a certain Under the illumination condition, the voltage U applied to the photoresistor is measured as +2V, +4V, +6V, +8V, +10V. Figure 8 Photoresist volt-ampere characteristic test circuit 5 photocurrent data, ie At the same time, calculate the resistance of the photoresistor at this time. Gradually increase the relative light in the future The above experiment was strongly repeated, and data measurement of different light intensity experiments was performed 5 to 6 times. (3) Experimental data plots a set of volt-ampere characteristics of the photoresistor. 2, photosensitive resistance test test (1) Connect the experimental circuit according to the schematic diagram 8. The light source is placed in the test frame with the standard tungsten wire lamp and the detecting photoresistor. The resistance box and the adapter box are inserted in the six-hole board. The source is GT-VC3 DC. Constant pressure source is provided. (2) From U=0 to U=12V, the photoresistor is measured at a certain applied voltage each time. Light intensity from "weak light" to progressively enhanced photocurrent data, ie: At the same time, calculate the resistance of the photoresistor at this time, namely: (3) Draw a set of illumination characteristics of the photoresistor based on the experimental data. Five, thinking questions 1. Verify that the illumination intensity is inversely proportional to the square of the distance (approximating the experimental setup to a point source). 2. When the light intensity of the photoresistor changes, the photocurrent will reach the steady state value after a period of time. 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