What is a pyroelectric infrared sensor?
Release time:
2020-07-30
As we all know, infrared light is a type of light that is invisible to the naked eye. A prominent characteristic of infrared light is its thermal effect—meaning that any substance above absolute zero can emit infrared radiation. Infrared technology can be used to control a wide variety of products, especially in the field of automatic control—for example, in automatic energy-saving lamps. These lamps utilize the infrared radiation emitted by the human body: when a person enters the sensor's detection range, the infrared sensor detects changes in the human body’s infrared spectrum and automatically activates the output circuit, turning on the corresponding load. Once the person leaves, the output circuit automatically shuts off, thereby achieving energy-saving effects. A pyroelectric infrared sensor is a type of sensor that can detect infrared radiation emitted by humans or animals and convert it into an electrical signal. It can be used as an input device in control circuits.
As we all know, infrared light is a type of light that is invisible to the naked eye. A prominent characteristic of infrared light is its thermal effect—meaning that any substance above absolute zero can emit infrared radiation. Infrared technology can be used to control a wide variety of products, especially in the field of automatic control—for example, in automatic energy-saving lamps. These lamps utilize the infrared radiation emitted by the human body: when a person enters the sensor’s detection range, the infrared sensor detects changes in the human body’s infrared spectrum, automatically activating the output circuit and turning on the corresponding load. Once the person leaves, the output circuit automatically shuts off, thereby achieving energy savings. A pyroelectric infrared sensor is a type of sensor that detects infrared radiation emitted by humans or animals and converts it into an electrical signal. It can be used as an input device in control circuits.
1. Fresnel lens
This type of lens, also known as a threaded lens, is made from either polymer or glass. Its function is to collect infrared radiation emitted by the human body, with the aim of enhancing the sensitivity of the input signal.
2. Pyroelectric sensor
The detection of pyroelectric sensor infrared signals is significantly enhanced by the magnifying effect of a Fresnel lens. Passive sensors typically have three pins: the power supply terminal—corresponding to the drain (D) of the internal switching transistor; the signal output terminal—corresponding to the source (S) of the internal switching transistor; and the ground terminal. Commonly used sensors include RE200B, PIS209, and LHI878, among others.
3. Amplifier
Although the output signal from the pyroelectric sensor, after being amplified by the lens, has reached a certain level, the amplification factor is still insufficient. Therefore, we’ve added an additional amplification circuit here to further boost the signal and enhance system stability.
4. Comparator
Without exception, almost all signal circuits are inevitably affected by various types of interference signals. Some of these are noise disturbances. Pyroelectric infrared sensors are sensitive to infrared radiation. To enhance the operational reliability of the system and minimize the probability of false activations, comparators typically feature a threshold voltage. This threshold voltage can be adjusted according to the actual environmental noise levels. When the external signal reaches the threshold value, the system determines that it’s time to start operating.
5. Control circuit
The control circuit typically includes a light-controlled circuit and a delay circuit. The light-controlled input signal, together with the signal from the comparator, serves to regulate the system’s operation. As for the delay circuit, it ensures that after the signal is interrupted, the system’s output remains active for a certain period before finally turning off—thus avoiding the awkward situation where the output would immediately shut down as soon as the person leaves. Some control circuits also incorporate a sound-controlled circuit component, which allows for precise control of sound decibels and enables multi-condition control over the entire system.
6. Output circuit
The output circuit is relatively simple, primarily responsible for outputting signals to the actuator circuit.
Nowadays, many sensor circuits are integrated and modularized, eliminating the need for unnecessary designs in peripheral circuits.
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