Several Important Indicators for Selecting PIR Motion Sensor for Anti-theft Alarm

May 26,2023


PIR motion sensors can be used in passive infrared detection—that is, in common anti-theft alarms, which is the application of PIR motion sensors in the security field.

However, in the actual environment, there are many targets that may trigger alarms or generate false alarms, such as suddenly appearing small animals, passing pedestrians, passing cars, high and low voltage electrical pipelines, or radio wave emitting equipment and lighting fixtures.

In the face of complex application environments, common alarms on the market may have defects such as being susceptible to interference from various heat sources or sunlight sources, radio frequency radiation interference, and detection failure when the ambient temperature and human body temperature are close.

How can a high-performance PIR motion sensor be selected to improve the accuracy of passive infrared detectors?

Several important indicators of passive infrared detectors

1. Anti-white light interference

In reality, not only the human body emits infrared energy, but many objects emit infrared energy under certain conditions, and this energy is particularly prominent in visible light, so the anti-white light interference of passive infrared detectors has become an important indicator.

To improve the anti-white light interference of passive infrared detectors, it is necessary to select sensor filter materials with shorter wavelengths. Make it have good wavelength selective characteristics. While allowing the infrared light emitted by the human body to pass through, as far as possible, light, sunlight and other wavelengths of infrared radiation are kept out to eliminate white light interference.

2. Anti-radio frequency interference

Radio frequency is a kind of high-frequency alternating current, which is commonly referred to as electromagnetic wave, and radio frequency interference is the interference caused by electromagnetic wave. During the use of conventional PIR motion sensors, when there is a mobile phone nearby for communication, false touches may occur at the moment of connection, which is a manifestation of weak anti-radio frequency interference ability.

The use of resistance-capacitance filter circuit and resistance-capacitance frequency selection circuit can enhance the electromagnetic compatibility of the PIR motion sensor, make the sensor have high immunity to radio frequency interference (RFI), and effectively resist radio frequency interference.

3. Anti-environmental interference

The strength of the passive infrared detector detection signal is closely related to the change of human body and ambient temperature. Under normal circumstances, there is a significant difference between the human body temperature and the ambient temperature. When the intruder moves, the infrared signal received by the sensor also changes greatly, and an alarm will be triggered at this time. But when the ambient temperature is very close to the human body temperature, this range of change is not easy to be captured, and at this time it is possible that the alarm cannot be triggered because the signal is small.

There are several types of PIR motion sensors, such as unit, binary and quaternary, and those used for human detection generally adopt binary or quaternary structures. The sensor with dual-element infrared sensing unit structure uses the principle that two interference signals with opposite polarities and equal magnitudes can cancel each other out internally to play a compensating role and eliminate the interference caused by ambient temperature and its own changes.

Passive infrared detectors are one of the most common devices used in intrusion alarm systems. As an important part of it, PIR motion sensor products put forward higher requirements for technology when they are applied to the security field. The problems addressed by each technology are also different. Some have enhanced filtering of white light, some have enhanced anti-high-frequency interference, and some specifically solve animal interference false alarms.

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