Open and Closed Circle System

Open ring control system using the actuator (actuating device) directly to control the process without feedback. Example: Suppose the space temperature control systems in cold regions, set the desired room temperature by using a heater (heater). The heater can be made of an electrical circuit that cored the resistor R. If resistor R electrified, there will be a power dissipation I R2, which warms the room r.

Figure 2.30 Block Diagram of Temperature Control System Open Space Circle

Seen that the output does not affect the input. This system is called open ring control system. Closed-loop control system using the measurement output (actual response), which is used as feedback to be compared with the reference value (desired response), resulting in an error. With this error the controller can provide control signals so that the output process of reaching the desired condition.

With the same example in an open loop system added a switch S which will restrict the flow of electricity I. When the room temperature is less than or equal to the desired temperature, the switch must be closed, so that current flows and the room warmed up. When the room temperature is greater than the desired temperature, then the switch S must be opened to break the flow of electric current, so the room does not get hot.

It is necessary for an operator who is always observing the appointment thermometer T. This operator serves as an element of feedback and also as an error detector (together with the switch S).

Figure 2.31 Block Diagram of Room Temperature Control System Manual Ring Closed

These observed output function, then evaluate (comparing outputs and inputs) and generates the driving signal that will move the system so that the output as desired. Seen that affect the input output (via operator). This system is called closed-loop control system. Some terms are often used as follows.
a. System output is a variable that is set (controlled variable).
b. Input system consists of
 Put command (command input) = input fictitious informative = input, which by the input transducer is converted (if necessary) to the reference input (reference input)
 Input reference = physical input together with feedback signals balikakan generate driving signal (error signal).
c. An error signal is input from the controller (controller).
d. Put kendalian generated by the controller.
e.Elemen feedback mengumpanbalikkan to observe the output and input, with the feedback signal.

When only the switch S is installed, it still needed a yangsenantiasa operator must observe the designation of the thermometer. This system though sudahmerupakan closed-loop control system but still manual. With menambahkansebuah automatic switch (switch bimetal, Sb) which has been calibrated in accordance with the temperature yangdiinginkan then when the room temperature is less than or equal to the desired makasaklar Sb is closed and an electric current flows heat the room sedangkanbila room temperature is greater than the desired temperature then switch Sb will open danarus electricity disconnected. This closed-loop control system already works automatically.