SDS011 warm up time

irukard · June 10, 2021, 9:00am

As for now, we got 15 seconds of warm up time for SDS011.

opendata-stuttgart/sensors-software/blob/master/airrohr-firmware/defines.h#L49


      
          #define DEBUG_WARNING 2
          #define DEBUG_MIN_INFO 3
          #define DEBUG_MED_INFO 4
          #define DEBUG_MAX_INFO 5
          
          /******************************************************************
           * Constants                                                      *
           ******************************************************************/
          constexpr const unsigned long SAMPLETIME_MS = 30000;									// time between two measurements of the PPD42NS
          constexpr const unsigned long SAMPLETIME_SDS_MS = 1000;								// time between two measurements of the SDS011, PMSx003, Honeywell PM sensor
          constexpr const unsigned long WARMUPTIME_SDS_MS = 15000;								// time needed to "warm up" the sensor before we can take the first measurement
          constexpr const unsigned long READINGTIME_SDS_MS = 5000;								// how long we read data from the PM sensors
          constexpr const unsigned long SAMPLETIME_NPM_MS = 1000;
          constexpr const unsigned long WARMUPTIME_NPM_MS = 15000;
          constexpr const unsigned long READINGTIME_NPM_MS = 15000;                // how long we read data from the PM sensors
          constexpr const unsigned long SAMPLETIME_GPS_MS = 50;
          constexpr const unsigned long DISPLAY_UPDATE_INTERVAL_MS = 5000;						// time between switching display to next "screen"
          constexpr const unsigned long ONE_DAY_IN_MS = 24 * 60 * 60 * 1000;
          constexpr const unsigned long PAUSE_BETWEEN_UPDATE_ATTEMPTS_MS = ONE_DAY_IN_MS;		// check for firmware updates once a day
          constexpr const unsigned long DURATION_BEFORE_FORCED_RESTART_MS = ONE_DAY_IN_MS * 28;	// force a reboot every ~4 weeks

According to Laser Dust Sensor Control Protocol V1.3 from NovaFitness, page 8:

Notes: The data is stable when the sensor works after 30 seconds;

So my question is: Why 15 seconds instead of manufacturer recommended 30?

pjg · June 10, 2021, 9:37am

I can’t remember how it really works but I think you can also add some other ms before it really starts to measure. Actually it should make a few measurements and calculate an average. Let’s analyse the firmware.

ricki-z · June 10, 2021, 3:55pm

The 30 seconds are for the worst case scenario of a 1 meter pipe. But we normally use a pipe of 20 cm. So outside air will reach the sensor much faster.
We needed to minimize the runtime of the sensor to get a longer lifetime.

irukard · June 14, 2021, 9:33am

Do you have any information from NovaFitness to back up this statement? Or is it just your observation?

ricki-z · June 14, 2021, 11:20am

This is our observation. The first months our firmware couldn’t shut down the SDS011. So we had measurements to compare with.
The ‘communication’ with Nova Fitness isn’t really easy. We tried to get the protocol documentation for the sensor. After weeks and many emails we got this info …