1 introduction scs

8/8/2019 1 Introduction SCS

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Sistem

Kendali

Sekuensial

M. Arrofiq, Ph.D.

2010


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Final Mark

It is arranged by three components as follow

- Quis, 20%

- Mid term, 30%- Final Exam., 50%

Feel free to discuss


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1. Michael Whitt

For almost any project, there will be threetypes of control:

- Discrete,

- Continuous, and

- Sequential 1)


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Sequential control is crucial in many control applications,

as in chemical batch processes. A sequential controlprocedure can be represented graphically by e.g. one of

the following two methods:

A State diagram, also denoted a State machine

A Sequential function chart (SFC)

State diagrams and SFC are quite similar, as they have the

same basic elements:

States with actions to be executed when the state is

active

Transitions from one active state to another taking

place if the transition condition is logically true.


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State diagram

Fig. 1 Elements of state diagrams: States and transitions


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A state diagram represents a state machine. A state machine has anumber of states. Each state is either active or passive. Only onestate is active at a time.

The state machine always starts in a particular state defined as theinitial state, and it ends (stops) after the final state..

Associated with a state are one or more actions. An action may be acontrol action executed by a controller. Actions may be listed as

indicated below:

State 1 actions:

Action 1: Valve V1 is open

Action 2: Motor M1 runs

State 2 actions:Action 1: Valve V1 is closed

Action 2: Heater H1 is on


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Fig.2 Action box listing actions of a state

The actions for a given state can be listed in a box attached

to the state symbol. However, the diagram may then

become overloaded by symbols. Therefore, in morecomprehensive state diagrams.


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Transitions brings the state machine from one state to another. A transitioncan go only from an active state which is presently active. A transition takesplace only if its transition condition is TRUE. Transition conditions are in theform of logical expressions having value either TRUE or FALSE and may belisted as indicated below:

Transition T_Init_1: Button_start = ON.

Transition T_1_2: L1 > Level_High;

where Transition T_1_2 means the transition from state S1 to state S2. Atransition condition may be written directly in the state diagram. For

example, the expression

T_Init_1: Button_start = ON

A transition may take place unconditionally, that is, it takes placeimmediately after the actions of the presently active state have beenaccomplished. Such unconditional transitions are named default transitions.

The transition condition of an unconditional (or default) transition haspermanent value TRUE, and it may be expressed as indicated below:

T_3_4: Default

or

T_3_4: TRUE


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Sequential function charts (SFCs)

Sequential function charts (SFCs) are similar to State diagrams. One small

difference is that a transition condition is indicated by a small line in thetransition path from one state to another. And, typically, the states are

denoted steps, which are represented by rectangles, see Figure 3.

Fig. 3 Elements of a Sequential Function Chart (SFC)


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Figure 4 shows a simple batch process which is to be controlled by

sequential control. The tank is filled with water. The water is then heated

and stirred, and finally the heated water is discharged from the tank.

Fig. 4 Elements of a Sequential Function Chart (SFC)


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The control signals are

- u_valve_in (boolean, i.e. having value TRUE or FALSE, or ON or OFF)

u_valve_out (boolean)

u_motor (boolean)

u_heat (continuous having any value between 0% and 100%)

The measurements are

Temperature T of the water in the tank

Level h of the water in the tank

Figure 5 shows an overall block diagram of the control system defining setpoints(specified values), control signals, and measurements.

Fig. 5 Block diagram of control system for example


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Figure 6 shows a SFC (Sequential Function Chart) defining the control task.

Fig. 6 Sequential Function Chart (SFC) defining the control


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The state diagram defining the sequential control of the batch process usingthe State diagram toolkit of LabVIEW

Fig. 7 State diagram


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Programmable Logic Controller, PLC

OMRON Mitsubishi Siemens

Fig.8

Snapshot of PLCs


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Nowadays, programmable logic controller (PLC) has becomesworkhorse of factory automation. It provides several advantagescompared to the relay logic systems such as smaller dimension,

capable of communicating with other system etc. With the growingof industrial automation, there is still available potential market forPLC.

PLC is a microprocessor-based controller designed to perform a certaintask. The capability of PLC can be classified into several groups i.e.

micro, small, medium, large and very large PLC. The above groupsare different from each other based on the number of input outputpoints, program memory and functional block.

The operation sequence of PLC in executing a program is slightlydifferent from a computer or a microcontroller. In general, there arethree basic operation sequences on PLC i.e. input scan, logic solve

and output scan.


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The advantages of PLC over Relays

Easily programmed and reprogrammed

Easily maintained and repaired

Capable of operation in a plant environment

Smaller than relay equivalent

Capable of communicating with central data collectionsystem

Cost-competitive with solid-state and relay logic system


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Operation on PLC

Fig.9

Block Diagram of a PLC


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Fig. 10 Block Diagram of a PLC


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PLC Scan Time

Fig. 11 PLC scan time


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The time taken by logic solve depends on the number of instructioncomposed the program. The more the instruction the more the timetaken. But the PLC executes the instruction very fast. Input scan and

output scan takes time more than logic solve. This is because thePLC does communicate with I/O module and may be, some of theI/O module includes slower parts. The design of PLC programshould consider the operation sequences to produce a properprogram.

The development of PLC programming includes improved graphicaluser interface (GUI), high level language such as Basic and C andcommunication over high speed Ethernet network. So thecommunication between PLC and other devices connected on thenetwork is possible.

Another side of development makes it possible to have an attractive

and user friendly system. An interfacing between system andoperator can be realized using programmable terminal which couldbe a combination between the touch panel and the liquid crystaldisplay (LCD). Using these devices, it is easier to monitor, controland manage minor maintenance of the system.


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22Fig. 12 Industrial automation


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It is time to watch video

Movie 2

Movie 1


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Thank you

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1 introduction scs

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