PMS
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fu-hsi
Null values at constant intervals
Looks familiar?
id dt pm1 pm25 pm10
------ ------------------- ------ ------ --------
134853 2018-11-24 13:22:59 (NULL) (NULL) (NULL)
134852 2018-11-24 13:20:13 16 30 36
134851 2018-11-24 13:17:27 14 30 36
134850 2018-11-24 13:14:42 12 26 32
134849 2018-11-24 13:11:58 10 24 24
134848 2018-11-24 13:09:12 8 20 20
134847 2018-11-24 13:06:28 8 20 20
134846 2018-11-24 13:03:42 2 16 16
134845 2018-11-24 13:00:58 (NULL) (NULL) (NULL)
134844 2018-11-24 12:58:12 14 24 34
134843 2018-11-24 12:55:27 12 22 34
134842 2018-11-24 12:52:43 10 22 24
134841 2018-11-24 12:49:58 10 18 18
134840 2018-11-24 12:47:12 6 16 16
134839 2018-11-24 12:44:28 4 16 16
134838 2018-11-24 12:41:42 0 6 6
134837 2018-11-24 12:38:58 (NULL) (NULL) (NULL)
In passive mode I receive NULL values from PMS 7003 sensor with constant intervals. I have not received any complaints from others, these are my observations only.
Simple solution without modify library: Increase default timeout value for readUntil().
E.g.
pms.readUntil(data, 2000);
In next release I will use flush() after all commands to the sensor to be sure that the whole message has arrived.
@fu-hsi yes I have the same issue. I am also getting NULL in passive mode. I will try increasing the timeout as you suggest and let you know.
As noted by adafruit (https://cdn-learn.adafruit.com/downloads/pdf/pm25-air-quality-sensor.pdf , pg.13) there is a delay in the refresh rate abound 2.3 seconds max when there is no change in the particle counting, but it can speed up to 200-800ms refresh rate.
As noted by adafruit (https://cdn-learn.adafruit.com/downloads/pdf/pm25-air-quality-sensor.pdf , pg.13) there is a delay in the refresh rate abound 2.3 seconds max when there is no change in the particle counting, but it can speed up to 200-800ms refresh rate.
It's referred to the Active mode (default). From official documentation:
There are two options for digital output: passive and active. Default mode is active after power up. In this mode sensor would send serial data to the host automatically .The active mode is divided into two sub-modes: stable mode and fast mode. If the concentration change is small the sensor would run at stable mode with the real interval of 2.3s.And if the change is big the sensor would be changed to fast mode automatically with the interval of 200~800ms, the higher of the concentration, the shorter of the interval.
But in our example (Passive mode) response time is less than 1s, but I recommend setting to 2s.