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:
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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.
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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.
The green LED indicates that the logger is being initialized or that the sensor is starting up/rebooting. The green LED should only flicker once on startup. If it is flashing more often it is most likely crashing. Connecting your sensor to The PurpleAir Utility and viewing the sensor’s logs can help you troubleshoot this further.
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.
Do I need to connect my SD sensor to WiFi?
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.
What is the capacity of the microSD card?
A 16GB microSD card is included with PurpleAir sensors. This card should be able to store up to two years of data.
*Mid 2022 we switched from a 16GB microSD card to a 32GB microSD card. You will need to check your sensor to verify which one you have.
The maximum supported microSD card capacity is 32GB.
Can I replace the microSD Card?
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 32GB.
Can I erase or delete files from the microSD card?
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.
Can I Push Offline microSD card Data to the Cloud?
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.
Why does the SD data have an incorrect date?
Dates are recorded in UTC, and will not reflect your timezone. Check for the differences between UTC and your timezone to see if the timestamps are accurate.
Why does the SD data have a date off by decades?
SD capable sensors include a real-time clock to keep track of time even when powered off. If the dates recorded are January 1, 1970 or January 1, 2000, then your sensor’s real-time clock will need to be resynced.
This can be done by connecting your device to WiFi. After which the sensor will attempt to synchronize the time over the internet. You can check whether this is successful by looking at the WiFi Status Indicator for NTP.
If the dates are still off after accounting for UTC, try the following troubleshooting steps:
- First, move the SD data onto a computer, and reinsert the SD card to verify that incorrect dates are still being recorded. Dates previously written to the SD card are not updated when time is synchronized.
- Power cycle the sensor by unplugging it for 30 seconds and plugging it back in.
- If your sensor is a PurpleAir Classic SD, try unplugging the SD logger and plugging it back in. This video shows the SD logger 45 seconds in. Leave the logger attached to the side of the laser counters, and unplug the cable from the device board wrapped in tape. Once unplugged, try firmly plugging the logger back into the device board.
- If the above steps don’t work, please send an email to contact@purpleair.com. It’s possible that your sensor may need a new SD logger or that there is a board issue with the device.
What are the PA-II-SD headers?
We have an article describing the SD card headers in detail.