The flaw:
When humidity measurements are made by an Si7021 sensor, the following can occur:
After some usage time, the sensor soaks up moist, and measured humidity values increase with an offset,
measuring values to over 100.
Due to limitations in the electronic design, at 120 %, the Analog-to-Digital converter runs over,
and measurements are from there on presented as -6 % and upwards.
The fix:
To overcome this, an algorithm is applied to the measured values:
When they suddenly drop, from then on 120 is added.
The reverse is also done at sudden rises.
Apart from the effect, that the measurement range still has its offset, this works reasonably well, if the offset is not too large.
The source code used for this can be seen here
The pages linked to below show the effect of the application of the algorithm,
for 2 regular Meetjestad stations, and for 12 stations in Sudan.
station 410 measurements
station 499 measurements
station 238 measurements
station 392 measurements
station 520 measurements
station 529 measurements
station 546 measurements
station 849 measurements
station 850 measurements
station 853 measurements
station 854 measurements
station 855 measurements
station 856 measurements
station 858 measurements