electric CONNECTIONS and The open loop diagram
The open loop control is also known as a manual system or a non-feedback system. This kind of system is characterized by the use of only a few automatic control features for the control of the desired output value.
When the controller is in Manual mode, the operator adjust the output signal to the final control element manually, as figure 1 shows. Manual contol is very helpful when designing or troubleshooting a process. Manually placing demands on the system allows the operator to determine how to properly program the controller to respond to similar demands during normal operations [3]. A process system that uses an electronic loop controller in manual model generally behaves as an open loop system. However, the operator can make output adjustments to control the process if necessary. Figure 2 shows an example of a manual open loop temperature control process that uses an electronic controller. In our system, the process fluid is being heated to a specific temperature by controlling the flow rate of the heating fluid flowing through the heat exchanger. Because the system is open loop, there is no Automatic feedback [3]. However the operator monitors the temperature using the temperature of the gauge of the process fluid outlet of the heat exchanger. In this system, the operator does not have to program any particular parameter. The operator simply places the controller into the manual mode and adjust the output based upon the change in temperature. If the temperature rises too hot, the operator adjust the controller output to restrict the valve and reduce the flow of strain. If the temperature drops too low, the operator adjust the controller output to open the valve and increase the steam flow rate. Essentially the controller acts like a hand valve that is able to make very small adjustments [3]. Another characteristic of the system is that the output does not have an effect over the controller, for this reason is recommended the use of the open loop in only process that do not have to be exactly controlled. For the Amatrol T5553, an open loop control system must have a set-point that will be the value given by the user, the controller and the actuators. This can be seen see at the (Figure 3). We control the valve with electrical energy, but we do it manually or with the help of the controller which values are changing manually (We are making orders to the controller, not letting the PID to command the process by itself). (Figure 4). |
Figure 1. Manual closed loop control system with an electronic controller.
Figure 2. Open Loop level control process with controller in manual mode.
Figure 3. Open loop system
Figure 4. Thermal System Open Loop Control Diagram.
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