Luc, Sorry, but I have to bark in again. *Temperature and humidity are independent values.* *There is no direct relation between the two*. It's a normal, natural occurrence to see them move with different sign day by day. You can measure humidity by itself - hygrometers are stand-alone instruments you can buy in stores, either analog or digital. I repeat, *there is no direct relation*. (There exist indirect relations, though, like the sun drying up humidity in the air, etc.) You cannot use one to calculate/tune the other by definition.
Please see the PDF specification sheet of the actual humidity sensor used in the ISS. I've linked it before, if you don't find it, I will link it again. That is something that will help you with the calculations. Also, please feel free to ask a weather technician or meteorologist if you don't believe me - there's a common friend of ours. Just email him (it's private info so I won't mention his name but you'll know). Of course there are learning/study material on the net in great numbers. You see a positive relation between humidity and temperature because of the nature of the humidity calculation. The calculation relies on the capacitance of the sensor. Temperature increases -> humidity in the air is getting lower -> resonant frequency of the cap is getting lower -> its reciprocal, the period is getting higher. I think what we have as raw humidity value is the period pertaining to the frequency, expressed in some digital unit: it's x times the actual periods in millisecs, for instance. If we can find x, we can make a formula. There's also some constant shift, since the cap only works from 10% to 90% (per specs). On Wednesday, April 3, 2019 at 2:16:39 PM UTC+2, [email protected] wrote: > > Paul, > > For the parsing of your analog humidity sensor we need probably a look up > table, as we have used similar for the soul moisture and leaf-wetness > sensor data. > > There is a positive relation between the raw humidity value and the > temperature as you can see in the attached table. > Each set with the same raw humidity codes has different humidity > percentages as result of different outTemps. > > For the look up table I will need the raw data over a as big humidity > range as possible. 0-100 % would be ideal, but let's see how far we come. > > Paul, what are the lowest and highest humidity values you have recorded > the last months? With this range we got to work. > And which driver you use on your other computer? Is this the weewx-vantage > driver? > > I suggest we do the following: > 1. I modify both weewx-vantage and weewx-rtldriver so, that they will > output a debug line showing the raw values (rtldavis) and decoded values > (vantage). > 2. You run both programs during a week. The RPI saves 8 days of syslog. > 3. Assuming both computers running these drivers have about the same > system times, we can combine these two sets of debug data in one table and > come with a table similar as attached below, but with a greater range. > 4. With this set we can try to find a correlation formula. > 5. When a correlation formula could not be found, I will compose a lookup > table with segments where the values within can be interpolated lineair. > > What do you think? > > Luc >
