Real CIJ printers use nozzle sizes like 0.06mm and 0.075mm.

Because of that, I replaced the 0.2mm nozzle with a 0.1mm nozzle which is closer to that. 

0.1mm is also ( as far as I know ) the smallest size of 3D printer nozzles that you can buy and I really want to prevent the use of specialized CIJ printer nozzles to keep the design cheap and only made out of easily accessible parts.

With the new nozzle, the timer chamber takes way longer to run out of ink so it has to be filled less often and the viscosity is also measured less often - changed from around one minute to a few minutes.

I doubt that the viscosity will increase much in that time so a reading like every 5 minutes should also be ok

For testing, I set the ink pressure to 40 psi and the pump pressure to 60 psi so that the ink exiting the nozzle at 40 psi and the timer is filled with 60 psi - which causes a short increase of ink pressure while filling from 40 psi to 60 psi and with that also a short increase of ink stream velocity from 23.5 m/s to 28.8 m/s. At the moment I don't know if that's a problem but I assume that I will later have to build a circuit that measures the frequency of the charged ink drops entering the return block and with that a feature that can adjust the point in time when it has to charge a particular ink drop to the increasing and later decreasing ink stream velocity. This will be a challenge in the future, but for now, I have to spend my time writing the Arduino and Python code for the ink cycle.