Humidity control in the climate chamber?

[carpenter]

I need to control the temperature and humidity in a climatic chamber.
I have no problem with temperature control, PID and PWM.
I'm groping a little like moisture.
Technically, for example, I need to have 70C and 80% humidity in the chamber for x hours.
Practically, I can only increase the humidity using a peristltic pump with a capacity of 0-15ml / min.
The water we pour into the chamber on the heating element turns into steam after a while and increases the humidity in the chamber.
The question is how to control it?

1 The first variant
I know the volume of air in the empty chamber, I know the temperature and humidity, I can calculate the amount of missing water and supply it.
I don't know, but the actual volume of air in the chamber,
I do not know losses by natural ventilation

2. The second option
also use a PID with some long time constant and a maximum dose of water per pass through the loop
It is universal, but it can take a long time to reach the required humidity.

Does anyone have experience with this?

 

[KlausST]

Hi,

No real experience with humidity control, but was involved....

some recommendations:
* use demineralized water
* maybe use a peltier to reduce humidity
* you may do humidity setpoint calculations using relative_humidity
* but do your regulation loop with absolute_humidity (to get a constant loop gain)

I´d go for PID. With the correct setup you get fast humidity regulation.

Why don´t you know the volume of the chamber? Is it variable?

Klaus

 

[BradtheRad]

After a dose of water there's the time delay until your humidity detector notices an increase.
It reaches a plateau, then after a while starts to drop.
A cycle lasts several minutes, probably.

I think you need to observe the entire timeframe (after the first dose), so you can have an idea how much and how often to add doses. You need to wait and see humidity drop at least once. You're applying the concept of hysteresis similar to a thermostat.

There's the question which method is easier to control: a) volume of a dose, b) time a dose lasts, c) time between doses. It's up to you what to decide what to use.