Infrared alarm principle, function and installation method

4,028 Published by xia, Crystal Oct 30,2018

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The infrared alarm can detect the infrared rays emitted by the human body, and is composed of an infrared sensor, a signal amplifying circuit, a voltage comparator, a delay circuit and an alarm indicating circuit. When a person enters the monitoring area of the alarm, an alarm signal can be issued, which is suitable for burglar alarms in important places such as homes, offices, warehouses, and laboratories. For the infrared alarm, we need to know a lot of knowledge, the following is to introduce you to the principle, function and installation method of the infrared alarm.



Infrared alarm principle

1. Infrared alarms are divided into active and passive. The active infrared alarm device is an alarm that actively emits infrared rays. When the infrared rays hit an obstacle, they will bounce back and be received by the probe of the alarm. If the probe is detected, the infrared light is still, that is, the red line is continuously emitted and rebounds continuously, then the alarm will not alarm. When a moving object violates this invisible red line, the probe will detect an abnormality and will alarm.

2. The main materials of the pyroelectric infrared sensor are lithium tantalate (LiTao3), triglycine sulfate (LATGS) and lead zirconate titanate (PZT), which have internal structure and appearance. It is on a piezoelectric crystal such as barium titanate, with electrodes on the upper and lower surfaces and a black film on the surface. When infrared rays are intermittently irradiated, the surface temperature thereof rises, causing a change in the arrangement of atoms inside the crystal, that is, causing spontaneous polarization charges. This phenomenon is called pyroelectric effect and is a kind of thermoelectric effect. The surface charge generated by the pyroelectric effect is temporary, and as soon as it occurs, it is quickly neutralized by ions in the air. For this reason, when the infrared sensor is fabricated by the pyroelectric effect, a mechanical periodic light-shielding device is often placed in front of its component so that the spontaneous polarization charge periodically appears, and is not used when detecting a moving object. Since the output impedance of the pyroelectric sensor is large and the output voltage signal is extremely weak, a field effect transistor and a thin film resistor Rg are added inside the sensor to change the impedance. Rs is the load resistance, and some pyroelectric sensors have no Rs and need to be connected externally. For different detection purposes, a filter is placed on the window that enters the infrared to filter out unwanted spectra.

3. As a pyroelectric infrared sensor for human body detection, it is mostly composed of two components. The first feature of the two components is that when the energy of the human shot is sequentially incident on the two components, since the two components are connected in series, the output is twice as high as that of the one component; the other is because the two components are connected in reverse, for the same At the same time, the input energy will cancel each other, such as infrared interference in sunlight and errors caused by changes in ambient temperature. A pyroelectric infrared sensor application circuit that prevents outsiders from invading, such as when a person enters the field of view to be protected, the sensor generates an AC induced voltage whose frequency is related to the speed of movement of the human body, usually around 5 to 6 Hz. It can control 10~12m mobile human body with a field of view of about 70 degrees.

4. Infrared alarm is to use infrared sensors to detect the presence of foreign matter. When an object is found to be moving, the infrared alarm will immediately sound an alarm. Infrared alarms are relatively high-tech products. Many infrared alarms are installed in places where valuables are stored. With this kind of infrared alarm, everyone will be more at ease.

Infrared alarm function

1. The infrared alarm has 100 independent wireless zones, which can be spread separately. Convenient and practical;

2. The detector of the infrared alarm and the host can wirelessly code. Learning coding makes the expansion of the system easier and faster;

3. The alarm sound and volume of the infrared alarm can be freely selected to enhance the security of the security system;

4. The host of the infrared alarm has the function of setting the time of the switch and the status prompt of the power on and off;

5. The infrared alarm can display the alarm information, which is convenient for reminding the security personnel of the specific location and time of the alarm;

6. Infrared alarm can query the alarm record, with storage function;

7. The infrared alarm has a built-in backup power supply to prevent the security function from continuing after the power failure;

8. When the infrared alarm is activated, the call can be automatically made to realize the emergency call and alarm call function.

Infrared alarm installation method

The infrared alarm is an alarm system consisting of an alarm host and an infrared detector. Among them, the infrared detector is a weak signal detection device, so attention should be paid to some details such as sensitivity and height during installation. So how do you install a passive infrared detector? Then you must follow these steps:

1. Must have a special understanding of the performance of the infrared detector, this is the basic work of the installation of the alarm;

2. Determine the installation location of the infrared detector, which is a high problem;

3. The infrared detector must be carefully debugged, his sensitivity is well debugged, this is the key to the installation.

4. Height adjustment:

How to debug the sensitivity of this debugging? The height of the installation will affect the sensitivity of the detector. The height of the detector will be different, and the frequency of the cutting area and the dark area will be different.

5. Environmental adjustment:

In addition to the high degree of sensitivity, the environment surrounding the infrared detector also affects its sensitivity. For example, if the passive infrared detector is facing the glass door and window, it will cause two problems: one is the environmental disturbance outside the door and window, the flow of the crowd and the vehicle will affect the judgment of the detector on the signal; the other is the white light interference. The PIR of the infrared detector has a strong suppression function for white light, but this is not completely suppressed, so avoiding the source of white light can avoid the interference of strong light.

6. Temperature adjustment:

The infrared infrared detector’s passive infrared detector’s induction is closely related to the temperature change. The hot and cold temperature is likely to cause false alarms from the infrared detector. If it is a low-performance detector, the air convection of the door and window will also cause false alarms. Therefore, it is necessary to select detectors with different sensitivities according to the temperature change of the environment, which is a point to be considered for the installation of the infrared horn.


The above is about the principle, function and installation method of the infrared alarm, I hope to help friends who want to understand the infrared alarm. Yaoertai Technology has been focusing on infrared alarms, security alarms and other fields for more than ten years. Welcome to consult!

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