工程师 - What Is A Closed Loop Control System?

闭环控制系统的原理与应用

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hi everyone in this video we're going to be talking about closed-loop control systems.

we'll talk about what they are and we'll use an example to ensure you understand.

unlike in an open-loop control system, in a closed-loop control system the input to the system does depend on the output.

but what does this mean exactly?

let's write a feedback control loop to better understand how a closed loop control system actually works.

so as we can see here it all begins with the setpoint.

remember that the setpoint is our desired value.

so let's say we are trying to cool our tank that I mentioned in our orders of control system video.

in this case the setpoint is the 40 degrees catalyst temperature as this is our ideal storage temperature.

moving on we can see we have a little circle here with a plus and a minus.

what does this mean?

this little circle is called the summing point and it simply means to algebraically sum or add together all the positive inputs and subtract any negative inputs.

so basically the sensor which in our case will be a thermocouple indicator will determine the temperature that the tank is actually at.

so if our sense it returns the temperature lower than 40 degrees our error term which is the output of the summation point will be positive.

since in this case we know that we can lower our coolant flow rate to allow the tank temperature to closer approach 40 degrees.

our computer will process the error term input until the actuator to slow or increase the coolant flow rate to closer achieve the setpoint value.

lastly the process block is the actual process that is occurring plus any disturbances.

remember our disturbances are things that affect our process but we have no control on them.

the output of the process block is what is sent to the sensor for the feedback loop and is the actual output that we would read on a thermocouple.

hopefully now the description I gave earlier of what a closed loop control system should make a bit more sense

we can now see how the output of the process leads to the input being affected.

remember the error term changing will affect the actuator to increase or decrease coolant flow rate

just in case you don't know what an actuator is, it is just a piece of equipment that is able to move or control something through an electric control signal

so think of opening or closing a valve as a simple example

you may also see a simple closed loop control system that looks like this and the only thing that is different is the actuator and sensor are equivalent to one