Basic definitions of the subject

Comparison of manual control method and automatic control method

(elements of the control systems)

Brain	Thermostat (Reference input or desired output)
Nervous system	Differencing junction
Hand	Amplifier, Motor and Wheel drivers
Eyes and Skin sensor	Temperature sensor
Mixer Valve	Mixer Valve

Definition	Description
Control	changing the state of the object depending on the goals
Controlled object (plant or process)	The object meets the requirements: 1) we can affect the object; 2) these effects can change the state of the object in the desired direction; 3)changes of the object’s state can be observed
Object of automatic control	The object meets the requirements: 1) we can affect the object by control signal; 2) control signal let us change the state of the object within a finite time; 3) output signal can be measured by sensors.
Controlled variables	Parameters of the controlled object, which varies or remains unchanged while control process
Disturbance, f(t)	Negative effect that interfere with the normal operation of the object. One of the thing that makes control science interesting is that all real life systems are acted on by noise and external disturbances. These factors can have a significant impact on the performance of the system. As a simple example, aircraft are subject to disturbances in the form of wind-gusts, and cruise controllers in cars have to cope with different road gradients and different car loadings.

The general scheme of automatic control system shows how its main parts interact with each other.

Figure 1.5. General scheme of automatic control system - example of table rotation

Description of interaction

sensor	It measures the output signal value and send it to the control unit (or control device)
control unit (or control device)	It is the “brain” of the control system. This unit examines the accepted value of output signal, compares with the fact that we need and make decision about the way of changing input signal. Then it sends the command to the actuator (or executive unit). Control unit may contain different converter because the input and output may have different dimensions or different structure (or the input signal may be digital, and the output - analog, and vice versa).
executive unit (or actuator)	It takes the signal from the control unit, and executes it. It sends a new control signal to controlled object. The value of this new control signal is determined by control unit.

Example of automatic control system - room temperature automatic control system

Controlled variables are temperature, pressure and humidity inside the room. Object of automatic control – climate in the room. Controlled variables may vary due to various disturbing influences (rain, snow, increase or decrease of outside temperature and other weather changes). Sensors measure these changes for a certain period of time. Then sensor transmits information to the control unit, which compares the new values of temperature, pressure and humidity with the required and sends a signal to the executive unit which generates the control affect for climate change.

Executive unit contains a variety of devices to change the values of parameters, such as - air conditioning, heating or cooling air, humidifier and air compressor for pressure support.

Дата добавления: 2014-01-11