How Sick sensors work

SICK sensors are sensors that use a photoelectric element as a detection element. It first converts the measured change into a change in the optical signal, and then further converts the optical signal into an electrical signal with the help of an optoelectronic component. Photoelectric sensors are generally composed of three parts: light source, optical path and optoelectronic components.

　　According to the nature of the output of the optoelectronic element (optical measurement and control system), it can be divided into two categories, namely analog photoelectric sensor and pulse (switch) photoelectric sensor.

An analog photoelectric sensor converts the measured photoelectric sensor into a continuously varying photocurrent, which has a single-value relationship with the measured photoelectric sensor. Analog photoelectric sensors can be divided into three categories: transmission (absorption), diffuse reflection and shading (beam blocking) according to the method to be measured (detecting the target object). The so-called transmission type means that the measured object is placed in the optical path, and the light energy emitted by the constant light source passes through the measured object, and after part of it is absorbed, the transmitted light is projected onto the optoelectronic element; The so-called diffuse reflection type refers to the projection of the light emitted by the constant light source onto the measured object, and then reflected from the surface of the measured object and projected onto the optoelectronic element; The so-called shading type means that when the luminous flux emitted by the light source is shaded by one part of the measured object, the luminous flux on the projected photoelectric element is changed, and the degree of change is related to the position of the measured object in the optical path. Photodiodes are the most common light sensors. The appearance of the photodiode is the same as that of the general diode, but it has a window embedded with glass on the tube shell to facilitate the light to enter, in order to increase the light-receiving area, the area of the PN junction is larger, the photodiode works in the working state of reverse bias, and is connected in series with the load resistance, when there is no light, it is the same as the ordinary diode, the reverse current is very small (<μA), which is called the dark current of the photodiode; When there is illumination, the carriers are excited, producing electron-holes, called photoelectric sensor carriers. Under the action of an external electric field, the photoelectric carriers participate in the conduction, forming a reverse current that is much larger than the dark current, which is called the photocurrent. The magnitude of the photocurrent is proportional to the light intensity, so the electrical signal that varies with the light intensity can be obtained from the load resistance. In addition to the function of the photodiode to convert the optical signal into an electrical signal, the phototransistor also has the function of amplifying the electrical signal. The appearance of the photosensitive tertiary tube is not much different from the general triode, the general photosensitive triode only leads out two poles - emitter and collector, the base does not lead out, and the tube shell also opens a window so that the light can enter. In order to increase the illumination, the base area is made large, the emission area is small, and the incident light is mainly absorbed by the base area. When working, the collector junction is reversed, and the transmitting junction is positively 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 the general transistor; When there is illumination, a large number of electron-hole pairs are excited, so that the current Ib generated by the base increases, and the current flowing through the tube at this moment is called photocurrent, and the collector current Ic=(1+β)Ib, it can be seen that the phototriode has higher sensitivity than the photodiode.

How Sick sensors work

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