Photoelectric sensor is a device that converts optical signal into electrical signal. Its working principle is based on photoelectric effect. Photoelectric effect refers to the phenomenon that when the light irradiates on some materials, the electrons of the matter absorb the energy of photons, and the corresponding electrical effect occurs.
Photoelectric sensor is a device that converts optical signal into electrical signal. Its working principle is based on photoelectric effect. Photoelectric effect refers to the phenomenon that when the light irradiates on some materials, the electrons of the matter absorb the energy of photons, and the corresponding electrical effect occurs. According to the different phenomena of photoelectric effect, photoelectric effect can be divided into three categories: external photoelectric effect, internal photoelectric effect and photogenerated voltage effect. Photoelectric devices include photocell, photomultiplier tube, photosensitive resistor, photosensitive diode, photosensitive triode, photocell, etc. The performance and characteristic curve of optoelectronic devices are analyzed.
Overview of sensors
光电传感器一般由处理通路和处理元件 2 部分组成。其基本原理是以光电效应为基础，把被测量的变化转换成光信号的变化，然后借助光电元件进一步将非电信号转换成电信号。光电效应是指用光照射某一物体，可以看作是一连串带有一定能量为的光子轰击在这个物体上，此时光子能量就传递给电子，并且是一个光子的全部能量一次性地被一个电子所吸收，电子得到光子传递的能量后其状态就会发生变化，从而使受光照射的物体产生相应的电效应。通常把光电效应分为 3 类：（1 ）在光线作用下能使电子溢出物体表面的现象称为外光电效应，如光电管、光电倍增管等；（2 ）在光线作用下能使物体的电阻率改变的现象称为内光电效应，如光敏电阻、光敏晶体管等；（3 ）在光线作用下，物体产生一定方向电动势的现象称为光生伏特效应，如光电池等。
Photoelectric sensor is generally composed of two parts: processing channel and processing element. Its basic principle is based on photoelectric effect, the measured change is converted into the change of optical signal, and then the non electrical signal is further converted into electrical signal with the help of photoelectric element. Photoelectric effect refers to the use of light to irradiate an object, which can be regarded as a series of photons with a certain energy to bombard the object. At this time, the photon energy is transferred to the electron, and all the energy of a photon is absorbed by an electron at one time. After the electron gets the energy transmitted by the photons, its state will change, so that the object irradiated by light will produce corresponding The electrical effect of. Generally, photoelectric effects are divided into three categories: (1) the phenomenon that electrons can overflow the surface of objects under the action of light is called external photoelectric effects, such as phototubes, photomultiplier tubes, etc.; 2) the phenomena that can change the resistivity of objects under the action of light are called internal photoelectric effects, such as photoresistors, photosensitive transistors, etc.; 3 ）Under the action of light, the phenomenon that an object produces a certain direction of electromotive force is called photovoltaic effect, such as photocell.
Photoelectric detection method has the advantages of high precision, fast response, non-contact, and many parameters can be measured. The structure of sensor is simple and the form is flexible. Therefore, photoelectric sensor is widely used in detection and control.
Photoelectric sensor is the key component to realize photoelectric conversion in various photoelectric detection systems. It is a device that transforms optical signal (visible and ultraviolet laser light) into electrical signal.
光电式传感器是以光电器件作为转换元件的传感器。它可用于检测直接引起光量变化的非电物理量，如光强、光照度、辐射测温、气体成分分析等；也可用来检测能转换成光量变化的其他非电量，如零件直径、表面粗糙度、应变、位移、振动、速度、加速度，以及物体的形状、工作状态的识别等。光电式传感器具有非接触、响应快、性能可靠等特点，因此在工业自动化装置和机器人中获得广泛应用。新的光电器件不断涌现，特别是 CCD 图像传感器的诞生，为光电传感器的进一步应用开创了新的一页。
Photoelectric sensor is a kind of sensor with photoelectric device as conversion element. It can be used to detect the non electrical physical quantities that directly cause the change of light quantity, such as light intensity, illumination, radiation temperature measurement, gas composition analysis, etc.; it can also be used to detect other non electrical quantities that can be converted into light quantity changes, such as the diameter of parts, surface roughness, strain, displacement, vibration, speed, acceleration, as well as the identification of the shape and working state of objects. Photoelectric sensors are widely used in industrial automation devices and robots because of their non-contact, fast response and reliable performance. The emergence of new photoelectric devices, especially the birth of CCD image sensor, creates a new page for the further application of photoelectric sensors.
There are many kinds of optical measurement and control systems, which are made of different action principles of luminous flux on photoelectric elements. According to the output properties of photoelectric elements (optical measurement and control system), they can be divided into two types: analog photoelectric sensors and pulse (switch) photoelectric sensors. Analog photoelectric sensor is to be measured and converted
Photodiodes are the most common light sensors. The shape of photodiode is the same as that of ordinary diode. When there is no light, it is the same as ordinary diode, and the reverse current is very small, which is called the dark current of photodiode. When there is light, the carrier is excited and produces electron hole, which is called photoelectricity
光敏三极管除了具有光敏二极管能将光信号转换成电信号的功能外，还有对电信号放大的功能。光敏三级管的外型与一般三极管相差不大，一般光敏三极管只引出两个极——发射极和集电极，基极不引出，管壳同样开窗口，以便光线射入。为增大光照，基区面积做得很大，发射区较小，入射光主要被基区吸收。工作时集电结反偏，发射结正偏。在无光照时管子流过的电流为暗电流 Iceo=（1+β）Icbo（很小），比一般三极管的穿透电流还小；当有光照时，激发大量的电子-空穴对，使得基极产生的电流 Ib 增大，此刻流过管子的电流称为光电流，发射极电流 Ie=（1+β）Ib，可见光电三极管要比光电二极管具有更高的灵敏度。
Photosensitive triode not only has the function that photodiode can convert light signal into electric signal, but also has the function of amplifying electric signal. In order to lead out the general triode, the same as that of the triode. In order to increase the illumination, the base area is large and the emission area is small. The incident light is mainly absorbed by the base region. When working, the collector junction is in reverse bias, and the transmitting junction is positive biased. When there is no light, the current flowing through the tube is dark current ICEO = (1 + β) Icbo (very small), which is smaller than the penetration current of ordinary triode. When there is light, a large number of electron hole pairs are excited, which makes the current IB generated by the base increase. At this moment, the current flowing through the tube is called photoelectric current and emitter current Ie = (1 + β) IB, visible phototriode has higher sensitivity than photodiode.
The photoelectric sensor is controlled by converting the change of light intensity into the change of electric signal.
Photoelectric sensor in general, there are three parts, they are divided into: transmitter, receiver and detection circuit.
The transmitter aims at the target and emits light beam, which is generally from semiconductor light source, light-emitting diode (LED), laser diode and infrared emitting diode. The beam is emitted continuously, or the pulse width is changed. The receiver consists of photodiode, photoelectric triode and photocell. In front of the receiver, there are optical elements such as lens and aperture. Behind it is the detection circuit, which can filter out the effective signal and apply the signal.
In addition, the structural elements of the photoelectric switch include a transmitting plate and an optical fiber.
Classification and working methods
(1) slot type photoelectric sensor
A light emitter and a receiver are installed face-to-face on both sides of a slot to form a trough photoelectricity. The light emitting device can emit infrared light or visible light, and the light receiver can receive light without resistance. However, when the detected object passes through the slot and the light is blocked, the photoelectric switch will act and output a switch control signal to cut off or connect the load current, thus completing a control action. The detection distance of slot switch is only a few centimeters because of the limitation of the whole structure.
(2) for the opposite type photoelectric sensor, if the luminous device and the light collector are separated, the detection distance can be increased. A light emitting device and a light collector form a separate type photoelectric switch, which is referred to as the opposite type photoelectric switch. The detection distance of the photoelectric switch can reach several meters or even tens of meters. When using the opposite photoelectric switch, the luminous device and the light collector are respectively installed on both sides of the path through which the detected object passes. When the detected object passes through the light path, the light receiving device acts and outputs a switch control signal.
(3) type photoelectric switch
The light-emitting device and the light receiving device are installed in the same device, and a reflector is installed in the front. The photoelectric control function is completed by using the reflection principle, which is called the reflector reflection type (or mirror reflection type) photoelectric switch. Under normal conditions, the light source emitted by the luminous device is reflected back by the reflector and then received by the light collector; once the light path is blocked by the detected object and the light cannot be received by the light collector, the photoelectric switch will act and output a switch control signal.
(4) diffuse reflection photoelectric switch
There is also a luminous device and a light collector in the detection head of the diffuse reflection photoelectric switch, but there is no reflector in front of the diffuse reflection photoelectric switch. Normally, the light emitted by the light emitting device cannot be found. In the detection, when the detected object blocks the light and reflects the light part back, the optical receiver receives the optical signal and outputs a switch signal.
Reason for no signal output
The first thing to consider is wiring or configuration. For the opposite type photoelectric sensor, it must be combined by the light projection part and the light receiving part, and both ends need to be powered; while the regression reflection type must be used by the combination of the sensor probe and the regression reflection plate; at the same time, the user must provide the sensor with stable power supply. If it is DC power supply, the positive and negative poles must be confirmed. If the positive and negative poles are connected incorrectly, the output signal will not be available.
The above reason analysis is the consideration of the photoelectric sensor itself. We also need to consider the position of the detected object. If the detected object is not in the detection area, such detection is futile. The detection object must be in the area that the sensor can detect, that is, the photoelectric sensing range. Secondly, to consider whether the optical axis of the sensor is aligned, the optical axis of the projection part and the light receiving part of the opposite type must be aligned, and the corresponding probe part of the regression reflection type must be aligned with the optical axis of the reflector. It is also necessary to consider whether the detection object meets the standard detection object or the minimum detection object standard. The detection object can not be smaller than the minimum detection object standard, so as to avoid the reflection type and the reflection type being unable to detect the transparent object well. For example, the reflection type has requirements on the color of the detected object. The deeper the color is, the closer the detection distance is.
If all of the above can be clearly eliminated, what we need to do is to detect environmental interference factors. If there is a large interference between the sensors and the environment, we must take measures to prevent the interference of the sensors from interfering with each other. If the above-mentioned one by one investigation, these factors can be clearly ruled out, or there is no signal output, it is recommended to return to the manufacturer for detection and judgment.
Photoelectric sensor is usually composed of three parts: transmitter, receiver and detection circuit.
The transmitter is equipped with a calibration lens to focus the light on the receiver. The cable from the receiver connects the device to a vacuum tube amplifier. In the metal cylinder, there is a small incandescent lamp as the light source. These small and strong incandescent lamp sensors are the prototype of photoelectric sensors.
The receiver consists of photodiode, photoelectric triode and photocell. Photodiodes are now the most common sensor. The shape of the photodiode of photoelectric sensor is the same as that of the general diode, except that there is a glass window on the shell of the photodiode to facilitate the light to enter. In order to increase the light receiving area, PN When there is no light, it is the same as the ordinary diode, the reverse current is very small, which is called the dark current of the photodiode. When there is light, the carrier is excited to produce electron hole, which is called photoelectric carrier.
此外，光电传感器的结构元件中还有发射板和光导纤维。角反射板是结构牢固的发射装置，它由很小的三角锥体反射材料组成，能够使光束准确地从反射板中返回。它可以在与光轴 0 到 25 的范围改变发射角，使光束几乎是从一根发射线，经过反射后，仍从这根反射线返回。
In addition, the structural elements of the photoelectric sensor include a transmitting plate and an optical fiber. The corner reflecting plate is a kind of transmitting device with strong structure. It is composed of a very small triangular cone reflecting material, which can make the beam return from the reflector accurately. It can change the emission angle in the range of 0 to 25 with the optical axis, so that the beam almost comes from a emitting ray, and after reflection, it still returns from the reflected ray.
(1) slot type photoelectric sensor
A light emitter and a receiver are mounted face to face on both sides of a slot. The light emitting device can emit infrared light or visible light, and the light receiver can receive light without resistance. But when the detected object passes through the slot, the light is blocked and the photoelectric switch acts. Output a switch control signal to cut off or connect the load current to complete a control action. The detection distance of slot switch is only a few centimeters because of the limitation of the whole structure.
(2) opposed photoelectric sensor