Sharp Corp developed a sensor module that can detect 2.5μm and smaller particulates, or PM2.5, and started to ship samples of the module Dec 25, 2013.
It features a small size (53 x 51 x 40mm, excluding protrusions) and a short detection time (up to 10 seconds). It is expected to be used for home appliaces such as air cleaners and air conditioners.
"With the small size, it can be incorporated in a variety of devices," Sharp said.
The price of the sample is ¥10,000 (approx US$95.6). The company is planning to start volume production in February 2014 with a monthly production rate of 80,000 units.
The new sensor module consists mainly of two components: (1) a "particulate separator," which separates 2.5μm and smaller particulates from particles such as dust particles in the air, and (2) an optical sensor that detects particulates. Though there are some methods for separating particulates such as "cyclone method," "impactor method" and "virtual impactor method," Sharp employed the virtual impactor method this time because it is suited for small devices.
With Sharp's virtual impactor method, an air current is generated with a fan located in the sensor module to separate 2.5μm and smaller particulates from coarse particles. In the sensor module, particulates float because of their low inertia and go through a different route than coarse particles. The optical sensor is located in the route and detects the particulates.
The light source and photo detector of the optical sensor use LEDs and photo diodes (PDs), respectively. Only when particulates pass through the sensor, LED light reflected from the particulates enters the PDs. And PM2.5 is detected by measuring the output from the PDs.
The optical sensor has the same mechanism as Sharp's "dust sensor," which is used for air cleaners, etc, but the company improved its sensitivity by 100% or more this time. The measuring range of the sensor module is 25μ-500μg/m3 for PM2.5.
If the fan is operated intermittently to let particles larger than PM2.5 pass through the optical sensor, the module can be used as a dust sensor.
The output voltage of the sensor module is 3.4V or higher. The power supply voltages of the sensor part and fan are 5±0.5V. Their power consumptions are 40mW and 1,100mW, respectively. The operating temperature range of the module is -10 to +60°C.
Sharp will provide the product as (1) a sensor module, (2) module combined with a control board and (3) module combined with a control board and LCD display unit.