Hey everybody,
I have already leaked some pictures on my new autoclave setup in the group and want to record the transformation here now.
There is a link to the video that inspired me: Myers Mushrooms PID pressure cooker
So, this is the old version of my autoclave - I can’t find any other pictures right now. You can see it has this knob to adjust the voltage but that didn’t work well since I never quite hit the right temperature and had no way to know the temperature but through the pressure. Furthermore, I wasn’t sure the pressure gauge was working properly.
So I got a cheap PID controller which I wanted to integrate into the system. After some trial and error, I decided to mount it instead of the knob inside the little box on the side of the actual sterilization chamber. A temperature sensor (I think it’s type K), is fixed into a little depression in the lid that is meant for a thermometer by the manufacturer with silicone.
I kept the one lamp that’s still working to know if the system is currently heating or not (connected in parallel to the heating element which is just a resistance coiled once around the bottom of the metal vessel). The other I kept for style reasons although it’s not working anymore (I even had to cut it up to fit everything into the box).
I believe I haven’t done this according to electrical assembly standards of Germany but it’s working well now and I’m planning to improve the savety of my design soon.
This is what it looks like right now, fully functional and very reliably working so far (did a few runs so far and I’m really happy with the result).
A few questions remain:
- How precise is the measured temperature at the lid?
- How can I actually use the PID control? (I used the autotuning function of the controller and now I have an on-off controller with a deadband. It has a different settings menu which I can’t exit anymore!)
- How robust is my system? (I believe it’s quite robust since the heating element is just a metal resistance which can be turned on and off many times)
Problems that I encountered:
- Me not knowing anything about electrical circuits
- Causing a short (actually three) and thus frying my solid state relais (took me about a week to find out what the actual problem was!)
- Having trouble operating the cheap Chinese PID controller I bought
- Underestimating the strong influence of the volume of air in the autoclave has on pressure! (the pressure with air inside was about 1.5 times higher than without!!)
Learnings:
- Releasing air from the vessel before sterilization is really important
- Electrical circuits are a lot of fun!
- I can learn new stuff and will come out more confident on the other side
I hope you enjoyed the read and I hope I inspire some people here to do their own projects involving electronics!
Great Work! 
