Pyroelectric sensors can be used for passive infrared detection-that is, in common burglar alarms. This is the application of infrared pyroelectric sensors in the security field.
However, in the actual environment, there are many targets that may trigger alarms or produce false alarms. For example, sudden appearance of small animals, passing pedestrians, passing cars, high and low voltage electrical pipelines or radio wave transmitting equipment and lighting fixtures.
In the face of complex application environments, common alarms on the market may have defects such as susceptibility to interference from various heat sources or sunlight sources, susceptibility to interference from radio frequency radiation, and detection failure when the ambient temperature and human body temperature are close.
How can we choose a high-performance pyroelectric sensor to improve the accuracy 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. This energy is especially prominent in visible light, so the white light interference resistance of a passive infrared detector has become an important indicator.
To improve the resistance of passive infrared detectors to white light interference, it is necessary to select a sensor filter material with a shorter wavelength to make it have good wavelength selection characteristics. While allowing the infrared light emitted by the human body to pass through, the infrared radiation of light, sunlight and other wavelengths should be excluded as far as possible to eliminate the interference of white light.
2. Anti-radio frequency interference
Radio-frequency is a kind of high-frequency alternating current, also known as electromagnetic waves. Radio-frequency interference is the interference caused by electromagnetic waves. When a conventional pyroelectric sensor is in use, it may cause a false touch when there is a nearby mobile phone communication. This is the performance of relatively weak anti-radio frequency interference.
The use of resistance-capacitance filter circuit and resistance-capacitance frequency selection circuit can enhance the electromagnetic compatibility of the pyroelectric sensor, so that the sensor has high immunity to radio frequency interference (RFI) and effectively resists radio frequency interference.
3. Anti-environmental interference
The strength of the passive infrared detector's detection signal is closely related to the change of the human body and environmental temperature. Under normal circumstances, there is a significant gap between human body temperature and ambient temperature. When the intruder moves, the infrared signal received by the sensor varies greatly, and an alarm is triggered at this time. However, when the ambient temperature is very close to the human body temperature, this change range is not easy to be captured. At this time, it is possible that the alarm cannot be triggered because of the small signal.
There are several types of infrared pyroelectrics, such as unit, dual element and quaternary element. Generally, dual element or quaternary element structure is adopted for human body detection. 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 internally to compensate and eliminate the interference caused by environmental temperature and self-change.