Dust and Airborne Particulate Matter Sensors

Laser Sensor for Detecting Airborne Particulate Matter

The article discusses Honeywell's first laser particle sensor of the HPM series.

A comparison is given between laser and LED technologies for detecting airborne particles.

Fig. 1. HPM series airborne particulate matter detection sensor

Particle Sensor

Honeywell has developed a new sensor for detecting airborne particulate matter (Fig. 1).

The HPM series sensor is a device built around a laser, which uses the light-scattering method to ensure reliable and accurate detection of contaminant particles in the ambient air. As a rule, contaminant particles are formed as a result of burning various types of organic fuel and a number of technological processes associated with the operation of industrial enterprises. Such particles can remain in the ambient air for a long time, reaching concentrations of up to 1000 µg/m3. The sensor analyzes the ambient air and presents the result as an estimate of particle concentration in the air in real time.

HPM sensors can detect contaminant particles suspended in an air sample with sizes from PM2.5 to PM10. Examples of airborne contaminants are shown in Figs. 2 and 3. These are dust, dirt, soot, smoke, liquid droplets, etc.

Fig. 2. Types of suspended particles polluting the air

Fig. 3. Categories of airborne particulate matter by size, PM10 on top, PM2.5 below

Operating Principle of HPM Sensors

The operating principle of the HPM sensor is shown in Fig. 4. Air from the ambient environment is drawn in by a fan and enters the sensor through the air sample inlet (1). The air sample passes through the laser beam, which is projected by a lens onto a photodiode (2). The photodiode transmits information to the photoelectric converter (3), where the sizes and repetition rate of the particles suspended in the air sample are determined. This data is sent to the microcontroller unit (4), where it is processed according to a programmed algorithm and output as a digital value in µg/m3.

Laser or LED

Some sensors that use LED technology are significantly inferior in accuracy to sensors built on lasers. The reason is that most LED emitters have a wide radiation pattern, and the light captures a wider zone inside the device's chamber. Excessive light scattering negatively affects the sensor's ability to detect particles suspended in the air flow. A laser, in contrast, generates a thin, high-intensity beam of light, which allows HPM series sensors to more accurately determine particles and transmit data to the control device in real time. Comparative characteristics of the HPM sensor and competing solutions based on LED technology are given in the table.

Conclusion

The transition from LED particle sensors to laser sensors provides the following advantages:

• the ability to more accurately and economically monitor and control environmental pollution;
• a long service life — 20 thousand hours of continuous operation, which corresponds to seven years with an eight-hour working day;
• proven and confirmed resistance to external electromagnetic interference due to compliance with the IEC 61000 electromagnetic compatibility standard, which guarantees stable operation and low measurement error;
• increased reliability, allowing these sensors to be used in the harshest environmental conditions.
  

  Fig. 4. Diagram of the particle sensor's operation

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04/27/2018 | Sensors and Detectors