There are a few things you’ll want to watch for when placing your PA-II-SD in an area without WiFi, to ensure your microSD card is logging data properly. After powering on the sensor or replacing the microSD card, the blue LED will flicker and should then go quiet. From then on, it should flicker roughly every two minutes. This indicates data is being logged correctly. The following LED behaviors signify potential problems:
The blue LED flickers continuously - this occurs when the sensor is outputting supplemental status information such as WiFi connection and disconnection, uploading of data, or other information that is not necessary to record. The logging of this additional information may cause the microSD card to reach capacity well before the estimated two-year mark. However, it is likely that useful CSV data can be recovered in this situation.
The blue LED repeatedly flashes three times in quick succession - this occurs when the microSD card has not been loaded properly, and absolutely no data is being recorded.
If possible, it’s very beneficial to connect your SD sensor to WiFi every so often to synchronize the real-time clock. Connecting your sensor to WiFi also enables you to make sure the microSD card has been properly detected. Below are examples of two different sensors’ map marker pop-up windows from the PurpleAir map: on the left is a window for a sensor whose SD card is detected and logging data properly, while the window on the right is for a sensor whose SD card is not detected and data is not being written to it.
Additionally, if there is a firmware update available, connecting to WiFi will automatically update the sensor. Also keep in mind, it is recommended to perform a power cycle after inserting a microSD card.
It is helpful to connect your SD sensor to WiFi every so often to synchronize the real-time clock. Connecting your sensor to WiFi also enables you to make sure the microSD card has been properly detected. If there is a firmware update available, connecting to WiFi will update the sensor.
A 16GB microSD card is included with PurpleAir sensors. This card should be able to store up to two years of data.
The maximum supported microSD card capacity is 64GB.
It is possible to swap out the microSD card that comes with a PA-II-SD sensor. The replacement SD card must be formatted using FAT32. Online tutorials can be found for help with completing this task for both Mac and Windows .
We recommend using a card with a minimum writing speed of 10 megabytes per second, or a Speed Class of C10/U1/V1. You can read this article from the SD Association explaining more about Speed Classes. The maximum supported microSD card capacity is 64GB.
Yes - you can erase or delete files when the microSD card is connected to your computer. If you are using an adapter to read the card, you will need to ensure that adapter is not locked. Usually there is a switch on the adaptor to lock it and prevent files from being deleted. This switch will need to be in the unlocked position in order to delete files. Diskpart has a good article with more information on deleting files.
At this time, when the sensor is out of network range and recording to the microSD card, the data is solely stored on the card. When you come back into network range, the data that was logged when offline is not synced up to the cloud. The microSD card would have to be pulled to extract that data.
We have an article describing the SD card headers in detail.