OPEN-LOOP CONTROL SYSTEMThere are different ways to control a system, open loop is the basic one, because it is mainly manual. In this type of control tuning method the system responds quickly to changes in the set point; to perform it in the laboratory it was necessary to take out the pH sensor from it original place and put it directly into the reaction tank, this allowed the project team to build the characterization curve. The diagram shown in figure 23 (took from the User's Manual Number 10), shows how the system must be set to perform this type of tuning.
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To obtain the necessary values to set the controller, a characterization curve must be built. In order to make it, the process must be in steady state, after that, a step change in the controller's output must be initiated, which will provoke a change in the response, the last can be recorded to obtain the values needed.
The following video shows all the work performed to obtain the change response graph using the open loop configuration.
Video 3. Open Loop Control System for the Amatrol's T-5554. Obtained from https://www.youtube.com/watch?v=eO43FByY8I8
Open Loop Response Graph
Fig 24. Open Loop Response Graph