May I ask what the input and output of an automatic control system are? How to understand it?
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The output variable of the system is the controlled variable; for example, if it is the liquid level, it passes through a measuring element transmitter and is compared with a set value. Can this point be considered an input terminal? Is the output the liquid level detected by the sensing element?
The last edit to this post was made by wasting time on 2017-3-27 at 00:15. Input and output refer to the same system; it’s not possible to compare systems that are different from each other. What is the output of one system might be the input of another system. I don’t have an accurate verbal description of the system here; I can only say that it’s similar to analyzing forces on an object in physics. If the signal from the sensor is an input intended for the controller, then after it is compared with the set value, the controller generates an output; as for the comparison that takes place within the controller, that is a matter of the program.
In my opinion, the input variables are those measured by instruments, such as liquid level and pressure. These values are compared with our desired values, and the resulting output is used to control the operation of the actuators on site, so that the measured values match our desired values
The input/output of a control system refers to the entire system as a whole. For example, in a single-loop feedback control system, the system output is the controlled variable (temperature, pressure, level, flow rate, composition, etc.), while the system inputs are disturbances and setpoints. The feedback path of the system when measuring the transmitted signal is a signal channel within the system. For example, in a level feedback control system, the output of the system (i.e., the controlled variable) is the liquid level; the output of the measuring transmitter is the liquid level measurement signal, which is not the output of the system. The input to the system is either interference (that is, the factor that affects the liquid level), or it is a setpoint for the system; for example, changing the liquid level setpoint from 50% to 60%.
First, it is necessary to determine how to understand a “control system” – whether it refers to the entire system that includes all sensor signals, the control system itself, and the output actuation devices, or merely the “control system” alone. For a \"control system\", its input is the source signal or data that it needs to process, such as electrical signals transmitted by transmitters or manually entered set values; its output, on the other hand, is the electrical signal resulting from processing operations, which is used for external adjustment or control. This signal then drives the actuator/devices to carry out the corresponding actions. Regarding the “input side” and “input terminals,” these can be understood as the I/O cards in a control system, or the connection terminals on those cards; or, in the case of cards installed inside a cabinet that are connected to the terminal board of the cabinet after passing through several devices, those terminals can also be considered as input/output terminals in a broader sense.