1 principle of automatic door

In the field of automatic door, the passive human pyroelectric infrared induction switch is widely used. Because of its stable performance and long-term stable and reliable operation, it is welcomed by the majority of users. This switch mainly consists of human pyroelectric infrared sensor, signal processing circuit, control and execution circuit, power circuit and other parts.

Pyroelectric infrared automatic gate is mainly composed of optical system, pyroelectric infrared sensor, signal filtering and amplification, signal processing and automatic gate circuit. Fresnel lens can focus the infrared radiation of human body on the pyroelectric infrared detector, at the same time, it can also produce alternating infrared radiation high sensitive area and blind area to adapt to the changing characteristics of pyroelectric detector signal; pyroelectric infrared sensor is the core device of alarm design, which can convert the infrared signal of human body into electrical signal for signal processing The signal processing is mainly to amplify, filter, delay and compare the weak electrical signals output by the sensor, which lays the foundation for the realization of the alarm function.

Analysis of the application principle of pyroelectric infrared sensor in automatic door


2. Principle of automatic door sensor

In the detection technology, the so-called “passive” means that the detector itself does not send out any form of energy, only by receiving natural energy or energy changes to complete the detection purpose. The feature of passive infrared automatic door is that it can respond to the change of infrared radiation caused by the movement of human body in the detection area, and can make the monitoring alarm generate alarm signal, so as to complete the alarm function.

When the infrared radiation of human body is focused on the detection element of pyroelectric infrared sensor through Fresnel lens, the sensor in the circuit will output voltage signal, and then make the signal pass through a band-pass filter composed of C1, C2, R1 and R2. The upper cut-off frequency of the filter is 16Hz, and the lower cut-off frequency is 0.16hz. Because the detection signal voltage output by the pyroelectric infrared sensor is very weak (usually only about 1mV), and it is a changing signal. At the same time, the function of Fresnel lens makes the output signal voltage in the form of pulse (the frequency of the pulse voltage is determined by the moving speed of the measured object, usually about 0.1-10hz), so the voltage signal output by the pyroelectric infrared sensor should be dealt with No. to enlarge. In this design, the integrated operational amplifier LM324 is used for two-stage amplification to obtain sufficient gain. When the sensor detects the infrared signal radiated by human body and sends it to the window comparator after amplification, if the signal amplitude exceeds the upper and lower limits of the window comparator, the system will output the high-level signal; if there is no abnormal situation, the system will output the low-level signal. In the comparator, R9, R10 and R11 are used as reference voltage, and two operational amplifiers are used for comparison. The main function of the two diodes is to make the output more stable. The upper and lower limit voltages of the window comparator are 3.8V and 1, respectively. 2V. The rising edge signal of the high and low level change signal is used as the trigger signal of the monostable circuit hef4538b, and a high level signal with a pulse width of about 10s is output. Then this pulse width signal is used as the input control signal of the alarm circuit KD9561 to generate an alarm signal for 10s. Finally, the triode VT1 and vt2 are used to amplify the electric signal again, so that there is enough current to drive the horn to make it emit an alarm sound for 10s continuously.

The first two LM324 are two-stage amplifiers. The sensor detects the infrared light of the human body and produces a weak sensing signal. Many bypass capacitors are set in the circuit to suppress interference and avoid misoperation. The last two LM324 are upper and lower voltage comparators. Only when the alternating signal induced by the sensor is amplified to a sufficient level can it be output to a high level to control whether the relay K1 at the back is powered on. K1 is powered on, at this time, it will enter the automatic door control part. When K1 is powered on, ka2 is powered on and closed. Ka2 is normally open and closed and self-locking. The motor starts to rotate forward and the door opens slowly. When the travel switch QS1 is contacted, the previously operated contact is reset, the motor stops, and the door is still in the open state. At the same time, the normally open contact of the travel switch is closed, and the power on delay of time relay KT is 5S. After 5S, KT is normally open and closed, Ka is powered on, KA3 is normally open and closed and self-locking, the motor starts to reverse until it touches the travel switch QS2, the door is closed, and the motor stops reversing. The above is all the process of circuit operation.

Responsible editor; ZL

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