Polludron V2
Last updated
Last updated
Polludrone second version designed in March 2015. The idea behind the design the to make a robust, independent air quality monitor. Device is IP-65 design with inbuilt battery storage.
The Design contains a vacuum form casing with sensor unit on the bottom. Top face is a solar panel inclined on an angle of 22.5 degree to gain maximum efficiency. The sensor casing is a laser cut casing for better strength and the net pattern for smooth air flow.
At this early stage, it was difficult to invest in tooling as company was bootstrapped. Polludrone is designed in such a way that costing for tooling and manufacturing is minimum. The Product is also designed in such a way that it looks as product, but not a machine. The solar panel is part of enclosure to give it a product look and feel.
Device runs 100% on solar. Device has 12V 15W Poly-crystalline solar panel on top. Device also has inbuilt charge controller and Led-Acid battery for backup.
Led-Acid Battery: 12V 7A AGM battery (Exide) Charge controller: Northgreen - Local quality controller with basic functionality. It also offers 5V USB direct output. (Price Rs. 950) Sukam: Low cost basic PWM controller with no basic features (No recommended) (Rs. 750) Luminus: One of the best charge controller. All the features required for maximum output from solar and better battery life.
Product Casing is made out of vacuum formed 5 mm strong ABS-PC alloy sheet. ABS-PC alloy gives product protection against all types of weather condition. Sensor casing is made out of fabricated sheet plate with laser cut net for easy air flow in the chamber.
Device enclosure is made out of vacuum formed sheet. The basic reason behind choosing this process is to get all features of plastic alloy without investing much amount like injection moulding. The die for the vacuum form is made out of wood. but it is advisable to get the die made out of aluminium as it increases the life of the mold and also provides good finish. It is possible to achieve all types of surface finish on the material. There are wide material range available as option (some of them with texture on surface). 6mm ABS-PC alloy is used for polludrone casing.
There are few limitation of the process which needs to be kept in mind while designing the packaging. Uniform thickness in difficult to achieve in this process.
The sensor casing is made out of sheet metal fabrication. Steel sheet is laser cut first to achieve uniform hole grid for smooth air circulation in the sensor casing. The sheet later processed into casing with bending and welding. As many of the operations are manual, high precision machines and skilled labor is required. The casing has powder coat finish. The casing is also designed in such a way that it has a hole for nut-insert to fit. Nut-insert provides threads to the casing to fit on the top enclosure.
Note: Choosing material for Sensor casing is very crucial. Most of the parameters are reactive gases and can react aggressively with casing material. Glass, PP and SS316 with surface treatment is advisable.
Base for battery and controller is also made out of sheet metal. Advantage of sheet metal fabrication is one can achieve good quality and accurate part with very low cost.
The entire assembly is done in Four parts. three sub assembly and one master assembly.
Step one: Mount charge controller and battery to the base plate and make connections to the solar panel. (Make sure that you keep connection wire long for solar panel)
Step two: Create hole for solar panel mount and sensor casing mount. It is advisable to use stencils created for the same. Perform rubber gasket on the peripheral surface where solar panel is to be fitted. Also fit nut-insert to the solar panel. (Nut-insert: 9 mm) (Device: bought in-house)
Step three: Mount PCB on sensor casing with M3 foam tape. Also perform gasket to isolate controller from the atmosphere.
Step four: Sandwitch the enclosure face with base plate on the top and sensor casing in the bottom enclosure cavity. Make sure you connect controller from PCB to the charge controller and check the data. Fix the switch and make the connection. Fix the sensor casing to the enclosure with six bolts from the top. Check the data and fit the solar panel on the top with five bolts.
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All the sensors are mounted on the PCB on the same direction. Sensors are facing down side which is most advisable position for sensor mounting.
In initial version, both PM and gas sensors were in same space. In second version, Dust has its own path for inlet and outlet where gas sensors are exposed in controlled environment with regulated air flow.
Sensor details for working principles and performance analysis is documented here.
Polludrone device was kept side by side with BAM sampling device for 24 hours. BAM devices gave a single reading every hours and polludrone device gave 5min average. Two experiment were conducted, one in Atira campus near IIM campus and another near Shyamal cross road. Device installation height: 6 feet (Exp-1), 15 feet (Exp-2) Both the devices were following the same air quality phenomena and 30-40 % variation in data was observed.
Polludrone device was installed near GPCB continuous air quality monitoring station for the month of September. Polludrone device gave data every 5 mins where GPCB device gave 30 mins average. Air quality phenomena was quite similar for both the devices where daily average of both the devices shown difference in few PPBs. Device Installation height: 30 feet
Similar experiment was carried out with GPCB monitoring station in R.K Puram, Delhi for three weeks. The readings shown quite similar for both the device and both the device followed similar phenomena. Device Installation height: 6 feet from the ground
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In a long run, it is important to set up an in-house calibration lab to ensure performance of the devices. So initial calibration was designed to calibrate 5 set of pcbs together.
We couldn't detect reactive gases like NO2, SO2, H2S, O3. Initial reason we thought that the gas coming out of the cylinder might get diluted in the chamber air. Later we figured out that it was because of the surface reaction caused by the reactive gases.
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Second calibration set up was a pipe with input and output for gases to pass. one face of the pipe is open and is mounted on PCB so that the sensor directly get exposed to the gases. The casing is a ABS 3D printed body. The advantage of this design over previous design is that the volume where sensors will get exposed is quite small which allows sensors to directly get in touch with the gases with uniform flow rate.
We got quite accurate response for all the gas parameters. In the third iteration, the casing is developed from SS316 which does not react to the gases.
Determining the increase in AQI could only be detected by installing pollution stations at key junction areas of Ahmedabad. Oizom along with Ahmedabad Municipal Corporation installed Polludrones at 10 selected traffic junctions in Ahmedabad where there is constant traffic flow and public movement. The activity detected there is a sudden increase in the PM2.5 and PM10 levels during early morning and during peak hours of the day. The activity suggested that there are a lot of suspended particles floating in the air which settle down during the morning hours and the reason for the increase in PM levels is the vehicular emission. Ahmedabad Municipal Corporation has decided to create a visual system which can be installed at government offices and public billboards to create awareness about the pollution levels in Ahmedabad.
Polludrone is compatible to measure wide range of parameters with different range. Below is the link for the product specification.
