What Is a Particle Sensor?
A particle sensor is a device that counts the number of particles detected in the air over a certain period.
They are mainly used in clean rooms. Particles here refer to fine particles of foreign matter, and especially in semiconductor manufacturing, these particles must be controlled because they can cause defects and lower yields.
Particle counters are similar in function and application, but particle sensors are capable of continuous measurement, while some particle counters are not.
Particle counters tend to measure more accurately than particle sensors, tend to be larger devices, and many models can be used in liquid as well as air. High-performance models can measure particles 0.1㎛ and larger.
Applications of Particle Sensors
Particle sensors are mainly used in clean rooms to monitor the cleanliness of the room. Specifically, they are used to monitor the cleanliness of automobile painting processes and to control clean rooms in semiconductor manufacturing plants.
The range of applications is expanding. For example, there are particle sensors for in-vehicle use to measure PM2.5, which is believed to have an impact on the human body. Ultra-compact, fairly small models tend to be popular, and some models can be installed on DIN rails or mounted on walls to save space.
Principle of Particle Sensors
Particle sensors operate by two main principles: light scattering and light shielding. Both types of particle sensors have a built-in air suction pump and continuously measure particles at a constant speed, but the method of detecting particles differs.
1. Light Scattering Method
Particle sensors using the light-scattering method detect the scattering of light by a photodiode, which converts the scattered light into an electrical signal. With this method, the size and number of particles can be counted based on the number and strength of the electrical signal caused by the scattering light.
2. Light Shielding Method
Particle sensors using the light-shielding method constantly emit light onto the photodiode. These sensors count the size and number of particles by detecting the electrical signal of the weakening of the particles in the air between the light source and the photodiode as the light passes through.
The accuracy settings of particle sensors require careful attention. Regardless of the method of measurement, if the particle sensor’s measurement accuracy is too high for the cleanliness of the room, the measurement error tends to be large.
To use particle sensors within the desired measurement error for cleanliness control in clean rooms, it is necessary to select a model with an appropriate measurement range.
Other Information on Particle Sensors
1. Difference From Dust Meters
The most significant difference between a dust meter and a particle sensor or particle counter is the concentration of the particulate matter to be measured. Dust meters are usually designed to measure high concentrations of particulates of 0.01 mg/m3 or higher, and their concentration is evaluated based on the weight, not the quantity, of the particulates. On the other hand, particle sensors and particle counters differ in that they quantify their measurements by the number of particulates.
Particle counters, in particular, are mainly for single-shot measurement. They have specifications that are finely divided from Class 1 to Class 9 to withstand measurement in low-concentration, high-cleanliness environments, whereas dust counters are for continuous measurement and have a relatively wide concentration range that can be measured.
2. Portable Particle Sensor
Recently, cleanliness is required in a variety of environments and industries, and the measurement points are not limited to clean rooms.
Manufacturers are developing a variety of particle sensors to improve user convenience. Examples include:
- Lithium-ion battery-powered sensors that can be connected to a PC via USB for data analysis.
- Models that can be connected to a multipoint monitoring system.
- Models that are equipped with a built-in camera.