How Do I Know if my Sensor is Working Properly?

FAQ
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This article covers simple checks and steps you can take to make sure your PurpleAir sensor is working as it should. These include using the PurpleAir map, checking your sensor’s data, and performing a few easy tests.

Using the PurpleAir Map

The PurpleAir map is a great tool to check if your sensor is running correctly.

  1. Start by finding your sensor on the map and clicking its dot. A popup window will appear. Toward the bottom of this popup, you’ll see a line with a few icons followed by a checkmark :check_mark: and a number with a percentage. This number is your sensor’s confidence score. If your sensor is working normally, this score should be around 100%. If it drops or stays low for a while, it could mean something is wrong.

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  1. Outdoor PurpleAir sensors also have two built-in laser counters (called channels A and B) that take separate readings. These channels are located very close to each other, so they should give nearly the same results. If you see big differences between them, that may mean the sensor needs attention.

  2. You can also compare your sensor’s readings to those of other nearby sensors on the map. Although their values might be slightly different due to location, the general trend in air quality should be similar. If your sensor shows a very different trend, it might be worth checking.

Looking at Data

If you can’t access the map—for example, if your sensor is offline or you’ve downloaded the data—you can still check how well it’s working by comparing channel data. The data will look a little bit different depending on where you’ve gotten it from.

If You’re Using an SD Card

Data saved to an SD card includes channels A and B in the file. For example, looking at outdoor data you’ll see:

  1. pm2_5_atm → Channel A

  2. pm2_5_atm_b → Channel B

The field without a letter at the end is Channel A, and the one ending in B is Channel B.

If You’re Using the API

API data works a bit differently:

  1. pm2.5_atm → the average of both channels

  2. pm2.5_atm_a → Channel A

  3. pm2.5_atm_b → Channel B

The field without a letter at the end is the average of A and B. Readings from channels A and B end in A and B.

Additionally, as mentioned in step 3 above, if you’re collecting data from multiple sensors in the same area, you can compare their readings to see if they follow the same general trends.

Testing Your Sensor

You can also do some quick tests, especially for indoor sensors without two channels.

If your indoor sensor doesn’t seem to be detecting anything or the numbers seem too high, try placing it outside for a while. It should begin to show similar patterns as nearby outdoor sensors.

To test if your indoor sensor responds to particles:

  • Spray something like hairspray or an aerosol near the sensor and see if the readings spike.

  • Move the sensor to your kitchen while cooking, especially near the stove. Cooking often produces particulates that sensors can detect.

If you notice the levels change after doing one of these things, your sensor is likely working properly.

Learn More

PurpleAir Map Guide
How do I download sensor data?
Indoor Sources of Particulate Matter (PM)

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