... | ... | @@ -4,6 +4,7 @@ The OpenSense measurement platform is based on the prototype platform developed |
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![](img/misc/box_closed.jpg)
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![](img/misc/box_side.jpg)
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![](img/misc/box_open.jpg)
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*The OpenSense measurement box*
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Every station is equipped with an O3, CO, NO2, and a ultrafine particle (UFP) sensor. The ozone sensor-a metal oxide semiconductor gas sensor-performs measurements by heating up the surface of a small microchip with a thin layer of a semiconducting metal oxide to several 100°C. When ozone gas is present, the electric conductivity of the semiconductor is altered. The CO and NO2 sensors are electrochemical gas sensors that measure the concentration of a target gas by oxidizing and reducing the target gas at the electrode. The mounting points of all gas sensors are covered with a thin Teflon layer to minimize interference of the target gases with the dust cover of the measurement station.
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... | ... | @@ -32,7 +33,7 @@ The second station is statically positioned next to the [NABEL](http://www.empa. |
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For calibrating the sensors, we implemented three calibration schemes for mobile sensor nodes. We investigate single-hop and multi-hop calibration given a reference station which can be reached by the mobile stations from time to time. The first scheme implements a standard way of calibrating gas sensors while the other two approaches show different trade-offs between measurement accuracy and calibration delay. We showed though experiments that when using these calibration schemes for ozone sensors we are able to measure ozone concentrations with an average error of 2ppb compared to the measurements done by the [NABEL](http://www.empa.ch/plugin/template/empa/699/*/---/l=2) station. This is remarkable as the accuracy given in the datasheet of the sensor is 20ppb. Furthermore, we found a linear dependency of the calibration accuracy on the number of calibration hops. The accuracy loss is tolerable as long as the number of calibration hops is rather limited which is the case in public transport networks.
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![](img/misc/hardware_arch_htc.png)
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![](img/misc/wair.png)
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![](img/misc/wair.jpeg)
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*Participatory and personal sensing. Left: Hardware architecture of a ozone sensor connected to a HTC smartphone. Right: Wearable device featuring two metaloxide gas sensors (VOC and O3)*
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