Data Collection and Reliability

If you’re running a sensor for data collection purposes and want to ensure that you don’t experience any data loss, there are a few things you’ll want to consider. The following article offers considerations on power status, WiFi connection, and SD card data collection.

Power Status

Whether you’re collecting data via an SD card or over the internet, PurpleAir sensors need to be supplied with appropriate power to function. Any interruption in power to the sensor will cause data to be lost for that period of interruption. Power issues can be difficult to diagnose because even if the sensor works when first set up, the issue may present itself later. When collecting data over an extended period, you’ll want to closely consider the points below to minimize the chances of this happening:

  1. You will need to ensure that the power requirements for PurpleAir sensors are always fulfilled. Those power requirements are as follows: 5V USB Micro, 0.18A continuous, 600mA peak. Further information is available in this community article.

  2. Many people/organizations run sensors off the grid using battery or solar setups for power. Due to location, this can sometimes be necessary. However, errors can be common in these setups due to the number of components involved (e.g. a solar panel with a voltage controller and battery) and their complexity. When running a battery or solar setup, we recommend the following:

    • Run the setup in a controlled location to ensure it functions as intended. Leave the sensors operating for several days and check for any data interruptions.

    • Test the setup in the intended final location to ensure it functions as intended. Even if a setup works in one location, it might not in another. For solar panels, in particular, differences in shade between locations, or even a particularly cloudy day, can cause issues in one location but not another.

  3. In the event of extreme weather or power loss, you’ll want to make sure that your sensors are able to reconnect to power.

Getting Data Using a WiFi Connection

If you plan on collecting data via the PurpleAir Map or the API, your sensors will need to be connected to a WiFi network with an internet connection. This includes setups using a mobile hotspot. If the connected network loses internet connection or your sensors become disconnected from WiFi, they will stop reporting. If microSD cards are inserted and the sensors still have power, they will still record data to their microSD cards. However, this data will not be available on the map. More information is available on our FAQ page.

Mobile hotspots experience problems more frequently than traditional WiFi networks. If you’re planning on using a hotspot, take extra care to follow the steps below and ensure your setup is functioning properly.

  1. Check your sensors regularly to ensure they are still connected to PurpleAir servers. This is quite easy to do as long as you plan on having the devices connected consistently. All you have to do is check and ensure your devices are still online. If you plan on registering devices as private, they will still be viewable. Check out View Your Sensor on the Map for more information.

    • The interval at which you check the sensor’s connection status is up to you. However, please be aware that you must be okay with a loss of data equal to the chosen interval. If your chosen interval is two days, for example, then there could be up to two days of lost data before you discover the problem.

    • The Uptime data layer on the PurpleAir map can be a helpful tool when checking your sensors. This layer displays the time a sensor has been continuously connected to us. You can also use the averaging period setting and map graph to see if a sensor unexpectedly powered off at any time.

    • Ensure your map settings are configured appropriately to allow for easy viewing of your sensors. When accessing the map via a link, the majority of settings and your current view position will be saved to that link. We recommend creating a custom link to check your sensors by configuring your settings and copying the map’s URL. This can help you check your sensors quickly and ensure you’re always using the proper settings.

      • The “reporting or modified within” setting may hide your sensor if it hasn’t reported in some time. We recommend setting this to “All-time” to allow you to view all sensors that have ever reported. If your sensors were hidden this way, they will likely appear as gray on the map when the setting is changed.
  2. In the event of an internet outage, check your devices to ensure they successfully reconnected to the internet. Although uncommon, sensors can remain disconnected once the internet is restored.

Getting Data With a MicroSD Card

SD-capable sensors can record data to a microSD card. This can be used to obtain data in locations without WiFi or as an alternative source of data if your sensors lose internet connection. If you plan on collecting data via SD cards in your devices, there are a few issues you can run into. These can include SD hardware not being detected properly, data not recording to the microSD card, or SD data not appearing where it should be. To combat these issues, there are a few things you should consider.

  1. If recording data to microSD cards is a requirement of your use, make sure to purchase SD-capable PurpleAir sensors. Applicable models include the PurpleAir Flex, Zen, and Classic-SD. The Classic comes without a microSD reader by default, and the SD variant must be selected using the dropdown box on the product page.

    • The Classic-SD comes with a microSD card included, but the PurpleAir Flex and Zen do not. MicroSD cards are available for purchase in our store, but any microSD card matching these requirements will work.
  2. Examine our SD Card Logging and Troubleshooting article to ensure you’re aware of proper behavior and common issues you may run into.

  3. Test the sensors before deploying them to ensure SD data is being properly recorded.

  4. Set up a regular interval at which to check on the SD cards. This process would include pulling out the cards and plugging them into a reader to ensure that data is being written as intended. As with the suggestion above, you must be okay with a loss of data equal to the chosen interval. If your interval is two days, you could experience up to two days of data loss if an issue has occurred.

  5. When using SD cards, all data from a device should be written to .csv files on the cards. However, it is possible that data may be written to .log or .txt files in addition to, or instead of, the CSV files. To find any recoverable data, we always recommend using the PurpleAir Utility’s SD Data Tool tool on files recovered from microSD cards.

    • Practice using the SD Data Tool before your sensors are deployed so that the process is streamlined in the field if needed.

Learn More

API Landing Page
PurpleAir Map Guide
How Do I Download Sensor Data

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