it would seem then, that to set:
log readings
energize fan
log readings
set a point no more than halfway between the low and high readings.
this is simple enough. I was starting down the path of running a standard deviation calculation and figured it might be better to ask.
Once the new parts arrive, I will put all the sensors on the bench
run for 100 data points or so
test for highest value
lowest value
and run a standard deviation calculation to see how they compare. (kicks and giggles)
as for inches of water vs in of Hg
atmospheric pressure starts with standard air density or standard atmospheric pressure
SAP = 70 deg F, at sea level at :
101,325 pascals
14.6959 pounds per square inch
29.92 in. HG
760 mmHG (Torr)
407.17227 inches of water.
so, YES MartT, I am using inHG
I spent many years with HVAC, air flow, and velocity pressure in the US. With Pitot tubes, we used inches of water
ditto for the pressure separations for clean rooms, dirty air filters and duct pressures.
I think It would be best is I used the raw data output from the BMP280 for the settings.
With a 'zero' of about 0.02 separation and a high of about 0.11 (inHG)
The difference for the fan on/off is just under 1 inch of water differential pressure.
by having one (inside of the greenhouse) to measure exhausted temperature and humidity and pressure
and one on the outside that see Outside temperature, humidity and pressure, I get to see a higher pressure difference.
When the fan is running, I really see the inside temp and humidity. Only when the fan is off, do I get actual outside temperature and humidity readings.