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In PM2.5 sensor, the difference between laser and infrared principle

by:Rika Sensors     2021-11-28
In PM2.5 sensor, the difference between laser and infrared principle
PM is the abbreviation of 'particulate matterCompared with coarser particles, fine particles are richer in toxic and harmful substances, and can stay in the atmosphere for a longer time, transport distance is also longer, and have a greater impact on the atmospheric environment and human health, causing black The main killer of lungs and haze.

In the particulate matter PM2.5 monitoring equipment, there are mainly two types of sensors: infrared principle PM2.5 sensor and laser principle PM2.5 sensor.

The infrared principle PM2.5 sensor is mainly used for industrial and mining dust due to insufficient accuracy. The detection object is large particle size and high concentration dust. The detection level is mg/m3. It cannot accurately measure the concentration of PM2.5, but can only detect dust. The degree of pollution, of course, the early air purifiers also used this principle sensor. The measurement results are for reference only, and the accuracy is low. It is generally used to determine the level of dust pollution.

Later, the laser type PM2.5 sensor was born, which can accurately measure the concentration of PM2.5. It is mainly used in the field of PM2.5 detection. It can be embedded in home (vehicle, handheld) air detectors and air purifiers. Laser PM2.5 sensor is based on quantitative measurement, can detect 0.3μm particles, can accurately measure the value of PM1.0, PM2.5, PM10, with high accuracy.

So what is the difference between the two?

1. Structural principle

The structure and circuit of the infrared principle PM2.5 sensor are relatively simple. The light source is an infrared LED light source. The air inlet and outlet mainly rely on resistance to heat to obtain the hot air flow. When particles pass through, reflection occurs after touching the LED light source. The photosensitive detector receives the reflected light of different intensities, and then passes through the amplification process. And the test result is obtained after calculation.

The structure and circuit of the PM2.5 sensor based on the laser principle are relatively complicated. The light source is a laser diode. The sampled air is pushed by a fan or blower and passed through a complicatedly designed air duct for detection. When fine particles in the air enter the area where the laser beam is located, the laser will be scattered; scattered light is radiated at 360° in space, and a photodetector is placed in an appropriate position to receive the scattered light, and then it is produced by the photoelectric effect of the photodetector After the current signal is amplified and processed by the operational amplifier circuit, the concentration of fine particles can be obtained. The output signal can be in a variety of ways such as serial port, I²C, and PWM.

2. Measurement accuracy and lifespan

The infrared principle PM2.5 sensor can only detect particles above 1um, and the measurement accuracy is insufficient. Because the particle signal of infrared LED light scattering is weak, it only responds to large particles larger than 1um, and only the heating resistor is used to push the sampling airflow, the number of samples is small, and the data calculation is completely handed over to the host computer.

The laser principle PM2.5 sensor can detect particles above 0.3um. Because it comes with a high-performance MCU, uses a fan or blower to collect a large amount of data, and is analyzed by a professional particle counting algorithm, it has more advantages than an infrared PM2.5 sensor in terms of sampling method, data accuracy, and algorithm processing.

3. Price and cost

Due to the simple structure of the infrared principle PM2.5 sensor, the cost is generally between 20 and 50 yuan.

The laser principle PM2.5 sensor has a relatively complex structure, and the market price is between 90-180 yuan. Because of the addition of laser generators and fans and the need for complex circuit structures, the technical threshold is higher, so the price is more expensive.

4. Development trend

Before the laser principle PM2.5 sensor entered the civilian field, many instruments for monitoring PM2.5 used the infrared principle PM2.5 sensor. However, with the development of the sensor industry, coupled with the realization of mass production of laser-based PM2.5 sensors by some major manufacturers, the cost of laser-based PM2.5 sensors is gradually decreasing.

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