**5. Conclusions**

256 Introduction to PID Controllers – Theory, Tuning and Application to Frontier Areas

The best parameters found after this fine tuning were: Kc=35%/°C, i = 28s and d = 7s (PID2). Figure 4.4 shows the behavior of the tank temperature under well-tuned

Fine tuning was then conducted to adjust these parameters by trial-and-error procedure. In these closed loop experiments, the following indices of performance were considered:

Fig. 4.4. Behavior of the controlled and manipulated variables under PID1 control

Table 4.2 presents quantitative and qualitative analyses of the performance of the

**Overshoot (ºC)** 5.0 3.9 3.1 **Rise time (s)** 281 200 171 **Response time (s)** - 710 400 **Pump saturation time (s)** - 141 130 **ITAE (x103)** 950.5 187 80.3 **Specific enzymatic activity (U/g)** 0.32 0.96 1.03 **Eletric energy comsuption (kWh)** 42.00 5.75 9.11

From these results, it is clear that PID controllers performed satisfactorily in controlling the temperature of the precipitation process. However, the PID2 controller kept the variation closer to the set-point, which is important for enzyme activity recovery, since the enzyme is highly sensitive to temperature changes. The early stage of ethanol addition is critical. In

Open-loop PID1 PID2

(Kc=8%/°C, i = 28s e d = 1,5s) and PID2 (Kc=35%/°C, i = 28s e d = 7s).

**Performance parameters** Controller

Table 4.2. Performance parameters of the PID controllers.

ITAE, response time and saturation of the final element of control.

conventional PID.

implemented controllers.

PID control tuning are popular and offer many benefits such ease of use, new development help to implement other PID controller variants, and control for common industry applications.

In this chapter, two techniques from PID tuning were applied for the temperature control of the practical applications: 1-polymerization system and 2-bromelain precipitation. The main feature of these process is its complex nonlinear behavior, wich poses a challenging control system design for the batch reactor.

In the first case a PID controller experiment was designed to be implemented later in the pilot plant. The controller was developed from the relay method proposed by Astrom and Haglund.

In the second case the controller was designed based on reaction curve method of Ziegler and Nichols, by disturbances in a real experimental system bromelain precipitation. The authors carried out fine-tuning of this controller, which was subsequently implemented efficiently in maintaining the process temperature.

The methods performed well for estimation of the PID controller, easy to apply and prove to be an effective option in practical cases will help achieve the proposed objectives*.* There is a large number of tuning methods, but related methods cover most practical cases and common industry applications.
