1 automatic door principle

In the field of automatic doors, passive human pyroelectric infrared sensor switches are widely used, and are popular among users because of their stable performance and long-term stability and reliable operation. These switches are mainly composed of human pyroelectric infrared sensors and signal processing. Circuit, control and execution circuit, power supply circuit and other components.

Pyroelectric infrared automatic door is mainly composed of optical system, pyroelectric infrared sensor, signal filtering and amplification, signal processing and automatic gate circuit. The Fresnel lens can focus the infrared radiation radiated by the human body onto the pyroelectric infrared detector element, and also generate alternating high-sensitivity areas and blind spots of infrared radiation to adapt to the changing characteristics of the pyroelectric detection element; The electric infrared sensor is the core device in the design of the alarm. It can convert the infrared signal of the human body into an electrical signal for the signal processing part. The signal processing mainly amplifies, filters, delays and compares the weak electrical signal output by the sensor. Lay the foundation for the realization of the alarm function.

2. Automatic door sensor principle

In this detection technique, the so-called “passive” means that the detector itself does not emit any form of energy, but only by receiving natural energy or energy changes to complete the detection purpose. The passive infrared automatic door is characterized by being able to respond to changes in infrared radiation caused by the movement of the human body in the detection area, and enables the monitoring alarm to generate an alarm signal, thereby completing the alarm function.

When the infrared radiation radiated by the human body is focused on the detector element of the pyroelectric infrared sensor through the Fresnel lens, the sensor in the circuit will output a voltage signal, and then the signal is first passed through a C1, C2, R1, R2 Bandpass filter with an upper cutoff frequency of 16 Hz and a lower cutoff frequency of 0.16 Hz. Because the pyroelectric infrared sensor output detection signal voltage is very weak (usually only about 1mV), and is a changing signal, while the Fresnel lens makes the output signal voltage pulsed (the frequency of the pulse voltage is The moving speed of the measuring object is usually determined to be about 0.1 to 10 Hz. Therefore, the voltage signal output from the pyroelectric infrared sensor should be amplified. This design uses an integrated operational amplifier, the LM324, for two-stage amplification to achieve sufficient gain. When the sensor detects the infrared signal radiated by the 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 a high level signal; when there is no abnormality, the low level signal will be output. In this comparator, R9, R10, and R11 are used as reference voltages, and two op amps are used for comparison. The main function of the two diodes is to make the output more stable. The upper and lower voltages of the window comparator, that is, the reference voltages are 3.8V and 1.2V, respectively. The rising edge signal of this high and low level signal is used as the trigger signal of the one-shot circuit HEF4538B, and is allowed to output a high level signal with a pulse width of about 10 s. This pulse width signal is used as the input control signal of the alarm circuit KD9561 to make the circuit generate an alarm signal of 10s. Finally, the electric signals are amplified again by the transistors VT1 and VT2, so that there is enough current to drive the horn. A 10 s alarm sounds continuously.

The first two LM324s are two-stage amplifiers. The sensor generates a weak signal after detecting the infrared light of the human body. Many bypass capacitors are installed in the circuit to suppress interference and avoid malfunction. The last two LM324 are the upper and lower voltage comparators. Only the alternating signal induced by the sensor is amplified to a sufficient level to make its output high to control whether the relay K1 is powered. K1 is energized and will enter the automatic door control section. When K1 is energized, KA2 is energized, KA2 is normally open and closed, and the motor starts to rotate forward, and the door slowly opens. When the contact switch QS1 is touched, the contact of the previous action is reset, the motor stops, the door does not move, and it is always on. At the same time, the normally open contact of the travel switch is closed, and the time relay KT is delayed by 5S. After 5S, KT is normally open and closed, KA is energized, KA3 is normally open and closed, and the motor starts to reverse. Until the stroke switch QS2 is touched, the door is closed and the motor stops reverse. The above is all the process of circuit operation.

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