Hi!
I have a question about the morbidostat and dosing. Below is an experiment that has run for 6 days with target growth rate = 0.1.
When growth rate increases (purple) it is followed by an increase in alt. media fraction (orange) but why does the fraction decrease with growth rate when it is still far from my threshold of 0.1 (dashed line)?
Hi @xsunni
Did you modify the PID parameters at all for this experiment? This PID parameters, located in config’s [dosing_automation.pid_morbidostat], control how much alt-media to add. The defaults are probably not the best for your system.
why does the fraction decrease with growth rate when it is still far from my threshold of 0.1
For the alt-media fraction, F%, to increase (or stay the same), the added dose needs to have higher concentration than F% (or the same, respectively). But as the growth rate decreases, the concentration in the dose decreases (since growth rate is closer to target 0.1 - see PID), and so the overall F% decreases. This is assuming Kp>0, Ki=0, Kd=0.
Hi @CamDavidsonPilon !
I have changed my PID settings Kp= 2.5 (Ki and Kd unchanged at 0).
I have similar oscillations with default settings, although more frequent.
As I am aiming at adaptation to the alternative media, what can I change if I want a stronger selection pressure?
Try a lower Kp (atleast half) first. PID tuning is difficult, especially with slower feedback loops. If still a problem, maybe a very small Ki is needed.
Ok great, I will try these settinhs and get back to you 
Thanks!
