Industrial Control and Automation: Continuous Systems and Automatic Regulation - Prof. Bit, Apuntes de Automatización Industrial

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THEME 3_1_

Continuous systems

What have we done so far in class?

We made industrial automation, we used tools to monitor the development and deployment of the correct sequence. We have the necessary GRAFCET techniques, performing sequential drivers (sequencers) based on PLCs or relays. We have had to learn sensors (passive switches, inductive, capacitive, optical, etc.). Pre-actuators (electromagnets, relays, ...) and actuators (motors, pneumatic and hydraulic cylinders, heaters, fans, etc.). We have also had to learn how to connect electrically these elements (part of command and maneuver) and some European standards (such as the stop pushbuttons shall be normally closed, that a stop should disconnect whole automation or only outputs).

PLC and relays, as controllers, are basically receiving digital signals, binary, on/off, and give binary signals also kind of on/off (open relay, closed relay, motor running or stopped, cylinder forward or cylinder back, etc.). We need items that can be proportional, operating with quantities intermediate between on and off (there are what we call "analog"). We do not try to open or close a valve to open it but more or less, it will not connect or disconnect a heater but to make him more or less flow, etc. It is true that we can make PLC also because incorporating the possibility of working with analog signals, both input and output, and this will allow us to take advantage of automation expertise to incorporate them into the automatic regulation.

AUTOMATIC REGULATION IN CIiA

Automatic Regulation =

Continuous Systems

Servo-systems

Automatic Control

Control Engineering

Control

Automation

What is its purpose?

To replace human

operators to make any

physical task.

Sources, Literature

(some authors)

• (^) Lewis
• (^) Ogata
• (^) Dorf
• (^) Kuo

Process:

Operation is carried out with a system or set of systems. System is often confusing process and without it being very important. Ex.: A washing machine is a system of movement of clothing (drum) plus a water intake system (a solenoid) and output (pump) and a programmer who must act sequence for each system. All these elements working together are a system that washes clothes.

Input Variables:

These are the signals that enter the system and used to establish what systems are expected to do. Set points are input variables that express what value are expected to have output variables.

Output Variables:

Are system output signals and are the final purpose of the

system (what we are expected the system to do). Its

measurement informs controller.

Sensors:

Devices that measure the output variables of the system.

Disturbance Variables:

These signals cause a deviation of the output variables

regarding what the system is expected to do. Ex.: marine

currents that deflect the path of a ship or a water leak from

a tank to keep a certain level.

Manual control

Automatic control

Automatic control

with PLC as controller

Continuous control and discrete control :

There are two types of control depending on whether calculate input variables to the process at all instants of time (continuous in time, continuously), or only do so at certain moments (discrete in time, only sometimes).

Digital control (or logical) and analog control:

If the controller acts on the entry process with specific (usually binary) is a digital control. Doing a continuum of values (infinite reals, ) between the minimum and maximum range of input values, is an analog control. Normally, Continuous control = Analog control Discrete control = Digital control

Sensor Process Actuator Controller

Steam cooker Valve:

When the pressure inside the pot

exceeds the resistance offered by

the valve steam valve out, slowly at

first and then more forcefully,

causing the characteristic whistle. If

the pressure falls below that valve

does act, it ceases to spin.

The valve controller acts carried out

a continuous control action (always

acts, not certain moments) and

analog (acting for all the pressures

that exceed the performance of the

valve).

EXAMPLE

EXAMPLE

Steam cooker Valve:

It is never as simple as it seems!

Models: It is unwise to use real systems to see how they respond to a control action, it is much more practical to draw a model (mathematical almost always) and operate it from a computer or manually to see how it would behave the reality. This forces us to have models to make simulations fear. The methodologies of systems theory is not yet fully established, however, there is a very general Idea consists in obtaining behavioral models of systems to control or regulate.