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The role of PM2.5 sensors in air purifiers

Update: 2019-10-08 16:13 Source: LUFTMY Reading: ↻ News
 

Air purifier, from its purchase to use, a wide range of "guides" on the Internet, the content is mostly uniform, nothing more than to teach users how to buy, how to use. But after watching it for so long, do you really know about the air purifier? Most of the purifiers are standardized, but 99% of users may ignore the component - PM2.5 dust particulate matter sensor.

Air purifier
Air purifier

1.Introduction to the working principle of sensors

In the current field of air purification, PM2.5 dust particle sensor has almost become a standard accessory of purification equipment. Its function is to monitor the concentration of PM2.5 and other particles in the air.The working principle is as follows: there are constant light sources (such as infrared light emitting diodes) inside the sensor. When the air passes through the light, the particles will scatter them, resulting in the attenuation of light intensity. The relative attenuation rate is proportional to the concentration of particulate matter.

On the other side diagonally to the light source, there is a light detector (such as phototransistor), which can detect the light reflected by particulate matter and output PWM signal (pulse width modulation signal) according to the intensity of the reflected light to judge the concentration of particulate matter. For different particle sizes (such as PM10 and PM2.5), it can output many different signals to distinguish them.

The seemingly simple work process actually contains light scattering, reflection, light intensity attenuation and complex algorithms. The sensor contributes a lot to the fact that we can see the air quality index directly on the sensor or in different colors or in digital form.

At present, the mainstream sensors in the market are divided into two kinds: infrared particle sensor and laser particle sensor. In terms of working principle, the difference between the two is not too big, but the structure is very different.

2. Contrast of two major mainstream sensors

Although it is the mainstream product, the structure of infrared sensor and laser sensor is quite different. The internal structure and circuit design of infrared sensor are relatively simple, while laser sensor is more complex. Different designs bring about different measurement accuracy. Infrared light-emitting diode is used as light source for infrared sensor, and more stable laser diode is used for laser PM2.5 sensor.

In the process of sensor operation, one of the necessary conditions is that the flowing air passes through the intersection area between the light source and the receiver. In order to drive air flow, infrared sensor uses resistance heating mode, using hot air to drive the surrounding air flow; laser sensor has a fixed fan inside.

In terms of signal output, the phototransistor inside the infrared sensor can only output the pulse width modulation signal (PWM signal), which can not directly show the concentration of particulate matter in the air. It needs further calculation to get the concentration range of particulate matter. The photoelectric effect of the photoelectric detector inside the laser sensor can produce current signal, which can be obtained by amplifying the circuit. The signal of particle concentration is usually output by serial port.

This explains why some purifiers can only indicate air quality through different color lights, while other purification products can display the specific air quality index in digital form.

In addition, infrared sensors use resistance heating to drive airflow, and the sampling number of particulate matter is small, which makes the measurement accuracy slightly inadequate; while laser PM2.5 sensors are driven by fan, the amount of data acquisition is large enough to ensure the accuracy of data to a certain extent.Of course, high precision also has some side effects - the lifetime of laser sensor is shorter than that of infrared sensor, but with the continuous improvement of technology, most of the sensors have good performance at present.

LD15 laser PM dust sensor
LD15 laser PM dust sensor

Dust sensor brand LUFTMY laser particle sensor LD15 is a high precision particle concentration sensor based on laser Michaelis MIE scattering theory. It can continuously collect and calculate particle concentration distribution, and output in the form of universal digital interface. LD15 has the characteristics of small size, high precision, strong anti-interference ability, low power consumption, long life and short response time of zero error alarm rate. LUFTMY dust detection sensor LD15 can be embedded in various instruments or environmental improvement equipment related to the concentration of suspended particulate matter in the air to provide timely and accurate concentration data.

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