Lets make a mind experiment:
We have plain SDS011 sensor → Type A
We have SDS011 with preheater which is constant ON → Type B
We have SDS011 with preheater which is ON when rel. Humidity >70% → Type C
Normal (clean air) condition wit rel. humidity less then 70%. What values could every type show?
A: values as expected
B: same result graphic, but all values will be less by some percentage (that is my guess, but it is in accordance to the experiment we made in Moscow - see graphic below)
C: same result as A
Clean air and rel. humidity above 70 %
A: results are alarmingly high (sensor became “blind”)
B: higher then normal, but not alarming
C: higher then normal, but not alarming
Dusty air (for example fire brokeout nearby) and rel. humidity above 70 %
A: same high alarming results as in (2)
B: high alarming values
C: high alarming values
Conclusion: sensor with heater above 70 percent will give a possibility to distinguish dusty air from clean one.
Type B will lover results when humidity is less 70 percent.
Here is an experimental setup
Sensor with constant ON pre heater before SDS011
https://api-rrd.madavi.de/grafana/d/GUaL5aZMz/pm-sensors?orgId=1&var-chipID=esp8266-4013924
Sensor without pre heater on the same location
https://api-rrd.madavi.de/grafana/d/GUaL5aZMz/pm-sensors?orgId=1&var-chipID=esp8266-3840225