# Tuning PID Controller

I have to determinate the power (Watts) for an oven to reach the Temperature Reference. And I have been given only the function to apply power to the oven and read the temperature.

I've reading the Ziegler-Nichols method. And the first step is to obtain the tangent in the inflection point, and then check the values of:

1. L : The point where the tangent intersect the x axis
2. T : The point where the tangent intersect the reference line

But I do not understand one thing, the range of the power I can apply power from 0 to 10,000(W).

Do I have to calc this tangent for a static random Power? But which value, because it will be the same in "production mode", when the power is vary because of the controller? If you apply an input power of 1, then the output plot you get gives you the value $K_p$ (you called it just K in your plot above). But if you input a power of $\Delta$u, then the output plot gives you the value $\Delta$u$K_p$. So to find the true value of $K_p$ you will divide by whatever power you input.