A controller with properly tuned PID values reacts quickly to changes in the set point, but does not overshoot much. It settles quickly from any oscillations and hovers really close to the set point. What do I mean by close? The average error for my kiln on a 13 hour schedule is .75 degrees F... and I have a noisy thermocouple, so it is possible to do even better.
Contributor [ADQ](https://github.com/adq) worked hard on creating a [Ziegler Nicols auto-tuner](ziegler_tuning.md) which is python script that heats your kiln, saves data to a csv, and then gives you PID parameters for config.py.
Even if you used the tuner above, it's likely you'll need to do some manual tuning. Let's start with some reasonable values for PID settings in config.py...
Run a test schedule. I used a schedule that switches between 200 and 250 F every 30 minutes. The kiln will likely shoot past 200. This is normal. We'll eventually get rid of most of the overshoot, but probably not all.
Let's balance pid_ki first (the integral). The lower the pid_ki, the greater the impact it will have on the system. If a system is consistently low or high, the integral is used to help bring the system closer to the set point. The integral accumulates over time and has [potentially] a bigger and bigger impact.
Let's set pid_kp next (proportional). Think of pid_kp as a dimmable light switch that turns on the heat when below the set point and turns it off when above. The brightness of the dimmable light is defined by pid_kp. Be careful reducing pid_kp too much. It can result in strange behavior.
Expect some overshoot as the kiln reaches the set temperature the first time, but no oscillation. Any holds or ramps after that should have a smooth transition and should remain really close to the set point [1 or 2 degrees F].
