I do some tests with my Sunlu dryer. It work for some hours. It has no filament and it was empty.
PLA mode: Minimum %RH - 24-25%, temp - 55С - in dryer.
Nylon mode: Minimum %RH - 14-15%, temp - 70С - in dryer.
Then I put the hygrometer in the dryer with an empty spool. Empty spool I use then the hygrometer does not touch the hot tapes of dryer.
The humidity has risen slightly.
PLA mode:
Minimum %RH - 24-26%, temp - 55С - in dryer.
Minimum %RH - 20%, temp - 49.9С - in hygrometer.
Nylon mode:
Minimum %RH - 12-14%, temp - 70С - in dryer.
Minimum %RH - 20%, temp - 54.5С - in hygrometer #1.
Minimum %RH - 20%, temp - 58.3С - in hygrometer #2.
My hygrometers has a temperature limit of min-max -50C - 50C, humidity limit of min-max 10% - 99%. Temperature errors up to 1-2C, humidity up to 5%.
It seems minimum %RH of my hygrometers is 20% instead as factory says 10%.
At the end of the test (after 4-5 hours of dryer work) I decided to check the %RH and temp again on empty dryer:
PLA mode: Minimum %RH - 18-20%, temp - 55С - in dryer.
Nylon mode: Minimum %RH - 12-14%, temp - 70С - in dryer.
It seems that to get the best results I need to preheat the dryer before drying the filament.
I have 29,5C in room now and 70%RH.
As far as I understand, my dryer work not bad but with my dryer it is impossible to get a lower %RH value then 12-20% in my environment, and especially with the filament. 
Maybe when %RH of environment will be down I will get better results. I want to achieve at least 10% humidity in dryer, but it seems not now…
Do I right understand or I forget something?
p.s. I ordered weigher, they should arrive tomorrow. In the meantime, I’m guided by the %RH.
I continue to solve the problem…