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Low-Cost Sensor POD Design Considerations
Citation:
Reece, S., A. Kaufman, G. Hagler, AND R. Williams. Low-Cost Sensor POD Design Considerations. EM: AIR AND WASTE MANAGEMENT ASSOCIATION'S MAGAZINE FOR ENVIRONMENTAL MANAGERS. Air & Waste Management Association, Pittsburgh, PA, , 24-30, (2017).
Impact/Purpose:
The design and level of sophistication of a sensor pod is influenced by the intended use in exploring environmental challenges. Regardless of application, all sensor pods are a compromise of a number of competing factors to maximize functionality. Materials for enclosures may range from metallic to plastic, custom-built or using a commercially-available enclosure. A benefit in metallic enclosures is the flexibility in customizing on-the-fly via drilling holes, cutting opening, etc. However, these cases are often heavier, can have inadvertent sharp edges, and require special equipment to make modifications. Plastic can be a less expensive alternative for enclosure designs and the rise of 3D printing supports rapid prototyping and iteration of a custom case. Additionally, a risk with plastic materials is potential interference; effort should be made to ensure the material is inert and is non-reactive with the target pollutant. A lightweight material is ideal for versatile and portable sensor pods. Such designs would also allow for mobile measurements, where the sensor pod is being worn or carried by the user. To ensure the sensor pod is durable, internal components should be packaged in a weather resistant, rugged enclosure to protect them from damage during transport and minimize interferences from environmental conditions. Depending on the performance specifications of the internal sensors, environmental conditions such as sunlight, precipitation, relative humidity (RH), and temperature can influence response.7-9 To ensure sensor pods are operated under proper conditions and measured values are representative of ambient concentrations, additional components such as fans/active sampling inlets, temperature sensors, RH sensors, and non-reactive samplings lines are factors we consider in the design of sensor pods. Appropriately positioned inlets and environmental sensors (e.g., temperature and RH) help to ensure more representative sampling of environmental conditions. Inadequate planning and testing of the design of a sensor pod can result in a device that produces results not reflective of true environmental conditions.
Description:
Public concern about air quality is growing in communities around the globe as citizens learn more about the potential health effects of the air they breathe. Air quality monitoring has often been restricted to organizations administering Federal Reference Method (FRM) or Federal Equivalent Method (FEM) equipment or other professional/academic institutions operating research-grade instrumentation. The rapid development of low-cost (<$2500) air quality sensors has generated opportunities for communities to engage in citizen science to address air quality concerns on a local level, but the performance specifications and data quality of many these low-cost sensors has not been fully evaluated. In an effort to gain perspective on sensor performance and support a wide range of interested stakeholders, the Environmental Protection Agency (EPA) has developed and deployed a variety of custom sensor pods in community settings to evaluate their performance under real-world conditions. These sensor pods were constructed by combining various low-cost original equipment manufacturer (OEM) component sensors and system integration technologies into a single unit in an effort to maximize ease of operation, while meeting a specific research requirement. Many of the sensor components selected for these pods were chosen based upon research findings from direct reference monitoring comparisons. This approach provides the ability to leverage knowledge gained regarding sensor operational requirements and general performance capabilities with application needs.