1

• Introduction
• SCS (Function, Definition, Architecture, Challenge, Network)
• SCS, DCS, SCADA & PLC
• Examples
• Applications

Supervisory Control Systems

Abdulhamid Al Hamoud

Tuesday, February 21, 2012

abdulhamidalhamoud@gmail.com

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Introduction

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Hardware, Software, & User Development

HS1

Introduction

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WHY SCS

S8

S32

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WHY SCS

S33

What is the problem?

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WHY SCS

S32

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SCS Key Function

Monitoring Functions

Detection

Follow

Diagnosis

Control Functions

Control

Recovery

Emergency

Supervision Function

Decision

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SCS Definition

There is no standard definition for optimal, therefore it can be adjusted to the specific demands of a certain situation (e.g. time, costs, energy costs, environmental load, etc.)

Supervisory Control System, coordinates the tasks that need to be executed in order to fulfill the manufacturing requests, in such a way that the formulated specifications and conditions are satisfied.

PLC Programmable Logic Controller

DCS Distributed Control System

SCADA Supervisory Control and Data Acquisition

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Main figure of SCS could be

S27 & 29

An illustration to the Supervisory Control System

1. Controller
2. Resource controllers
3. Field System Components

task coordination

task execution

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Form of SCS

all supervisors are coupled with each other by parallel operation composition

S25

Distributed supervision

With distributed supervision, the control problem is divided into sub problems.

Distributed supervision >>

The control problem is divided into sub problems.

Next slide

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S41

Form of SCS

So different systems are executed and work at the same time.

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D12

Form of SCS

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SCS Architecture

Network

Database

Bulk

Memory

Security

Data Acquisition

Display

Batch Sequencing

Interface Components

Storage & Backup

Control

Process

Work

station

Asset Management

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SCS Architecture

Typical SCS consists of the following

1. Control Unit (Main, Local, Field, Web)

2. Computer(Data Server, Management, General Purpose, Engineer, Operator, Mobile)

3. Bulk Memory Unit

4. Database Management (include Documentation)

5. Data Acquisition Unit (collecting and organized component history record)

6. Asset Management

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SCS Architecture

8. Display (Central, Operator, Maintains, Local, Field, Web)

9. Network (Data Highway, Modbus, Routers, Center, Local, Field, Globe)

10. Interface Components (I/O, Other System)

11. Protection and Security

12. Storage and Backup

7. Batch Sequencing Unit

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Distributed Control Triangle

16

• Time-delay or Loss of Data

SCS Challenge

Based on Ashby’s law of requisite variety,

combination of the following is necessary

• Resource abundance,

• Plural intelligent agents,

• Freedom of communication

• Better response to changes in their environment

• Interaction between these factors leads to increased complexity of the situation

• Heavy traffic

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Network

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Network Components

• Fieldbus Network

• To link sensors and other devices to a PLC or other controller

• To eliminate the need for point-to-point wiring

• Sensors communicate by using a specific protocol

• Messages sent uniquely identify each of the sensors

• Control Network

• Connects a supervisory control level to a lower-level control

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Network Components

• Communications Routers

• Transfer messages between two networks

• Connect a LAN to a WAN,

• Connect MTUs and RTUs to a long-distance network medium for Supervisory control communication

• Modbus

• High level Protocol for industrial networks

• It is a messaging structure developed by Modicon in 1979.

• Used to Provide client/server communication between devices connected to different types of buses or networks. 

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Network Components

• Firewalls

• Monitor and control communication packets

• Use predefined filtering policies

• Useful in managing SCS network segregation strategies

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Device Net

DeviceNet is a standardized network that enables intelligent control of field devices and improves system productivity

Network Components

DeviceNet is a field network that easily performs mutual connections between control devices, such as PLCs, computers, and sensors, as well as data devices, such as barcode readers.

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SCS Challenge

S17

The SCS action mostly based on the detection by the sensor

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Field Devices

Smart Sensors

It includes an inner computing device, which can be configured to perform specific functions.

It includes a microprocessor that conditions the signals before transmission to the control network.

It filters out unwanted noise and compensates for errors before sending the data

Some sensors can be custom programmed to produce alerts on their own when critical limits are reached.

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Field Devices

Actuators

Smart Actuator : an actuator that combines sensor and control capabilities in a single device.

1. Cause action or mechanical motion

2. Motivate or incite action

The motor and mechanism that moves the head assembly on a disk drive or an arm of a robot is called an actuator.

Are mechanisms that cause a device to be on/off, adjusted, or moved.

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SCS, DCS, SCADA, & PLC

2. Each of these SCS or DCS "controller/card" devices will be individually programmed.

1. Typical SCS or DCS systems will have several controllers in a chassis and the I/O wiring associated with each individual controller connected directly.

3. The SCS or DCS has a high level of integration between the controller, HMI, and historical database.

4. An operator can use a SCS or DCS terminal (computer) to monitor and operate the machinery.

5. The SCS or DCS terminal has the features to acquire production data and store it in a database.

6. The PLC was developed as a replacement for many relays.

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SCS, DCS, SCADA, & PLC

8. The PLC deals mainly with digital (1 or 0). For example, it gives a permission for a valve to totally open or totally close.

9. The SCS or DCS deals with analog (1%..…100%) it can give the valve a permission to open 50% or 30% as the controller wants. As a result, it is preferred for a large plant that has both analog and digital signals.

10. The SCS or DCS is process oriented, while SCADA is data acquisition oriented.

11. The SCS or DCS is process driven, while SCADA is event driven.

12. The SCS or DCS relies on the ability to obtain an immediate view of the current state of the system at any time.

7. The DCS was developed as a replacement or to manage the PID controllers.

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SCS, DCS, SCADA, & PLC

14. The SCS or DCS is useful in any project with a large number of variables that can be automated.

15. The PLC can act as an individual distributed control system in a SCS or DCS.

16. However if the PLC goes down, the system will follow.

17. In contrast, with SCS or DCS, if a single controller goes down, the system will not necessarily follow.

13. The SCS or DCS may employ one or several workstations and can be configured at the workstation, or by an off-line personal computer.

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SCS, DCS, SCADA, & PLC

• Database

In Summary, the main differences between SCS or DCS & PLC are:

• Control Philosophy

• Number of I/O’s that can be connected

• Scanning time

• Communication

• History

• HMI is an integral part of SCS or DCS, while for the PLC, there was no HMI to start with

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Cementing the relationship between DCS and PLC

DCS & PLC

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SCS Challenge

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SCS Challenge

S28

Dashed means uncontrollable

S29

​

No states are allowed to be reached, that are in violation with the formulated specifications

of the system.

• No states are allowed to be reached, from which no final state (i.e. marker state) can be

reached. Therefore, deadlock and livelock states should be avoided

Controllability, Reachability and Blocking

State 8 is not allowed to be reached since it is in violation with the formulated specifications.

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SCS Challenge

Controllability, Reachability and Blocking

Each state that can be reached by transitions from the initial state is called reachable.

Blocking can be divided into two groups, deadlock and livelock.

Blocking should be avoided

Livelock is a case where a group of states is reached from which it is not possible to reach a marker state

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SCS Challenge

supervisor meets certain criteria

S28

Controllability, Reachability and Blocking

The controllability criterion means that all states which are not allowed, have to be avoided.

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HMI & Display

Example

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Example

HMI & Display

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Example

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Example

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SCADA systems at the Water utilities in Illinois, Houston

Example SCADA using PLC

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Example

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Example

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Example

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Example

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Example

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Examples

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Applications

• Electric Power Generation, Transmission and Distribution

• Water and Sewage

• Buildings, Facilities and Environments

• Manufacturing

• Mass Transit

• Traffic Signals

• Gas & Oil Refining

• Petrochemicals

• Food & Beverage Manufacturing

• Cement Production

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Objective

• Controllability, Reachability and Blocking

• Explain the difference between the PLC, DCS and SCS.

• Describe the main elements or components of the SCS.

• Explain the smart sensor and smart actuator.

• Explain some of the SCS Challenge such as:

​

• Ashby’s law

• Difference between centralized control and distributed control

• Device Net Feature

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Exam review will be on

Thursday, March 1, 2012

Exam will be on

Tuesday , March 6, 2012

​

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Top Type Sensors

Liquid Level

Discrete Liquid Level Sensor

D-PK-SENSR-12003.00001

Provides a discrete contact closure when liquid levels fall below parameters. Contains a dry reed switch encapsulated within a stem. Supports N/O and N/C alarm contacts.

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Introduction

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Challenge

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Challenge

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