Timing of Data records and readings

Hello, I have some questions about how the Flex stores data on a MicroSD card.

The sensors record a line of data roughly every two minutes. Do these values reflect a two-minute average, or are they real-time readings taken at the moment of the time stamp?

As for the timing of the entries, there are often ten entries spaced exactly two minutes apart, followed by another block of ten entries two minutes apart separated by roughly a 100-second gap. This causes the dataset to not reflect uniform entries every two minutes. For example, if the sensor was to record an entry every two minutes, there would be 720 entries per day, but the sensors typically record 732 entries per day. Is it possible to have the sensor store entries only every two minutes?


The data recorded to a sensor’s MicroSD card reflects data averaged across two minutes. If a sensor is connected to WiFi, this is also the same data that’s sent to the PurpleAir Map and shown as real-time averages.

The occasional gap you noticed is fully explained in our Why is there a gap in the SD card data article. This is due to a soft reboot of the device which can’t be disabled.

Feel free to let us know if you have further questions.

Probably the more entries, the more of a real-time snapshot of general ambient air pollution. It just means there are more than the normal 720 readings per day taken. So you have a better chance of catching the day’s high and low readings. I see nothing wrong with more frequent readings.

Hi Daniel,

Escambia County is operating 12 PA Flex sensors, which we have collocated with PM 2.5 Monitor operated by FDEP. I intend to analyze the data to observe the differences between the sensors and monitor and within the group of sensors. EPA provides standardization and guidance on this kind of activity through its Macro Analysis Tool. Unfortunately a limitation of this tool is that it requires even intervals to occur been entries, so if the PA Flex was able to only collect 720 evenly spaced data points per day, the analysis could be completed by simply averaging every other one of the 1440 data points collected daily by FDEP’s Monitor on each minute of the day. Simply deleting ten or so of the data points from the PA Flex’s daily dataset introduces subjectivity and bias into the analysis.