If you’re using a microSD card to collect data with your PurpleAir sensor and notice that some data is missing, this guide will help you identify the cause and direct you to the right solution.
Quick Links: If you’re not missing any data but have another SD issue, navigate to:
- SD Card Overview — For a general overview of SD card usage with PurpleAir sensors
- SD Card Troubleshooting — For troubleshooting issues with SD data collection, such as your microSD card not being detected
- Understanding SD Card Data Columns — For understanding the different columns of data on your microSD card
Start Here
There are four things that we recommend doing first to see why you may be missing data. Please follow these checks before continuing with the rest of this article.
Check 1: Check Your Sensor’s SD Status
Follow the steps for Identifying Your Sensor’s SD Status
Check 2: Does Your Sensor Have Consistent Power?
Look at the last timestamp in your data and consider:
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Was there a power outage on or after that date?
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Could someone have unplugged the sensor?
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Is the sensor still plugged in and receiving power now?
If power was lost (outage, unplugged, faulty supply):
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The sensor cannot record data without power
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Solution: Ensure a consistent power supply
Check 3: Is Your Data Recoverable with our SD Data Tool?
It may be that your SD card is detected and your sensor has power, but you’re still missing data. If this is the case, try using our SD Data Tool to see if this resolves the issue.
Check 4: Investigate Sensor Issues:
It’s possible that your sensor is crashing repeatedly, causing it to be unable to write to its SD card.
To troubleshoot what may be causing this, we recommend going to this article to download our PurpleAir Utility tool, as this can provide information on your sensor’s behavior. This article details how to copy the logs from your sensor with the tool, which you can then send to us at contact@purpleair.com so that we can assist in the troubleshooting process.
Next: What Are You Seeing Now?
Select the situation that best describes what you’re experiencing:
No Data on SD Card
If you insert your SD card into a computer and find no data files, you’ve confirmed your sensor is powered, and the SD card is detected, and you’ve run our SD Data Tool, reach out to us at contact@purpleair.com.
Data Stops at a Certain Date
If your SD card has data up to a certain date, but then no new data appears after that:
Is the SD Card Full?
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Insert the SD card into your computer
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Check the card’s available space
If the card shows 0 bytes available or very little space remaining:
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The card is full. Sensors will not overwrite old data
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Solution: Back up your data and delete old files to free up space, or use a larger card (up to 32GB maximum)
Gaps or Missing Time Periods
If you have data before and after a gap, but nothing during a specific time period:
How Long is the Gap?
Gap of a few seconds to a few minutes:
Gap of hours to days:
- If you’re seeing gaps or missing time periods for hours or days, you’ve confirmed your sensor is powered, and the SD card is detected, and you’ve run our SD Data Tool, reach out to us at contact@purpleair.com
Wrong Dates or Times
If the timestamps in your data don’t match when you collected it:
Check 1: Time Zone Difference
SD data is recorded in UTC, not your local time zone.
Calculate the difference:
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If your data appears to be off by a consistent number of hours (e.g., 7 or 8 hours), this is likely a time zone difference
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Go To: Time Zone Differences
Check 2: Dates such as 1970 or 2000
If you see dates such as January 1, 1970, or January 1, 2000:
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The sensor’s real-time clock (RTC) was not synced
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Go To: Real-Time Clock Not Synced
Check 3: Dates Gradually Drift
If timestamps were correct initially but became increasingly inaccurate over time:
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The RTC is drifting without regular NTP syncing
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Go To: Clock Drift Over Time
Check 4: Clock Resets After Power Loss
If the clock resets to 1970/2000 every time the sensor loses power:
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The RTC battery may be depleted (very rare)
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Go To: Depleted RTC Battery
Inconsistent Data Intervals
If you notice that most data points are exactly 2 minutes apart, but occasionally you see different intervals (often approximately 1 minute 51 seconds):
Go To: Understanding the 20-Minute Soft Reboot Pattern
If Your Issue is not Addressed Here:
Contact support at contact@purpleair.com with:
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Your sensor’s Device ID
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Description of what data you’re seeing or not seeing
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When you noticed the issue
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Any troubleshooting steps you’ve already tried