Hi,
I have been meddling with the OSPID and various sous vide setups ranging from twin heater elements, to slow cooker, to the best i found so far, a deep fryer surprisingly. Characteristics are that it holds its temp really really well because of good insulation, it heats up extremely fast, and it has very little moisture loss when closed. However, it continues to heat up even when power is off due to the fact that its heating element is so massive, and autotune just refuses to work, it brings the water all the way up to a boil. Can anyone give me some advice what would be nice params or help me to get to some nice params?
If we see this image
The autotune brings heats up the water very linearly until boil... this was the second round already so seeing it was about to boil its head off i killed autotune and manually turned off output to 0. Why doesnt autotune want to work?
If we take a look here
The residual heat continues heating up the water. What settings would let the PID know that the water will continue being heated for X amount time before it stabilizes?
We can see the insulation is quite good.. the temp remains quite stable without additional heating, so from a logic point of view the PID should heat up the elements just a bit.. and let residual heat from the element heat up the water to set value
I tried a guesswork value of P=1, I=0.5, D=0.5 and got an average overshoot of 1.3C and under value of 0.2C. This is when the water was already around the preset temp.
I read through this but dont get a few points...
https://groups.google.com/forum/?fromgroups#!topic/diy-pid-control/0bswXHDhJAsWhat did he mean by "Choose a Kp such that your output will greatly exceed your maximum
output limit until you get close to the set point". Whats the "maximum output limit" that he is talking about?
Btw im using an SSR. So i have a output update time of 1s. Do help.. anyone! thanks so much!