This post’s subject is the description of other methods to tune a PID controller. CHR (Chien, Hrone e Reswick) and CC (Cohen e Coon).

In case you don’t know what is PID, access the link below before continuing.

**The CHR method**

All tuning methods for PID controller consist in calculate values of proportional (K_{p}), derivative (K_{p}) and integral (K_{i}) gains. The CHR method was developed in 1952, as an alternative to solve problems with step response. Despite gains being smaller than the ones obtained by Ziegler-Nichols, the system has more stability when adopts the CHR method.

Defines tuning laws for setpoint change and regulation resistant to disturbances.

**Performance criteria**

The following tables show gain calculations to obtain the fastest response as possible with 0 or 20% of overshoot for both problems.

**Gain calculation table for problems with regulation with robustness**

T_{N} and T_{V} are integral and derivative times. Reminding that integral Ki and derivative Kd gains are calculated with the equations below.
Ki=\frac{Kp}{T_{N}}

Kd=Kp\cdot T_{V}

**Gain calculation table for servo problem (setpoint change)**

**Cohen-Coon (CC) method**

Developed in 1953, this method is also used for step response and for a system with longer dead time, considering 0,6<\frac{\theta }{\tau }<4,5. However, robustness with be bad if \frac{\theta }{\tau }\leq 2.

The method Ziegler-Nichols and Cohen-Coon were created to obtain a quarter amplitude damping. In case you want to avoid oscillation, the gain K_{c} must be smaller than the calculated.

In addition to the ones presented today, exist other PID tuning method which will be for future posts.