Section-16 Scada Systems

Haward Technology Middle East 1Section 16

Process Control, Instrumentation and Safeguarding

Section 16

SCADA Systems



SCADA Systems

TOPICS

Basic Definitions

Levels of Hierarchy

SCADA Configuration



BASIC DEFINITIONSSCADA Systems



SCADA is the acronym for Supervisory Control And Data Acquisition.

In Europe, SCADA refers to a large-scale, distributed measurement and control system, while in the rest of the world SCADA may describe systems of any size or geographical distribution.

SCADA systems are typically used to perform data collection and control at the supervisory level. Some systems are called SCADA despite only performing data acquisition and not control.

BASIC DEFINITIONS

SCADA Systems



The supervisory control system is a system that is placed on top of a real-time control system to control a process that is external to the SCADA system (i.e. a computer, by itself, is not a SCADA system even though it controls its own power consumption and cooling).

This implies that the system is not critical to control the process in real time, as there is a separate or integrated real-time automated control system that can respond quickly enough to compensate for process changes within the time constants of the process.

BASIC DEFINITIONS

SCADA Systems



The term SCADA usually refers to centralized systems which monitor and control entire sites, or complexes of systems spread out over large areas (on the scale of kilometers or miles).

Most site control is performed automatically by remote terminal units ("RTUs") or by programmable logic controllers ("PLCs").

Host control functions are usually restricted to basic site overriding or supervisory level intervention.

BASIC DEFINITIONS

SCADA Systems



As an example, a PLC may control the flow of cooling water through part of an industrial process, but the SCADA system may allow operators to change the set points for the flow, and enable alarm conditions, such as loss of flow and high temperature, to be displayed and recorded.

The feedback control loop passes through the RTU or PLC, while the SCADA system monitors the overall performance of the loop

BASIC DEFINITIONS

SCADA Systems



BASIC DEFINITIONS

SCADA Systems



There is a fair degree of confusion between the definition of SCADA and process control systems.

SCADA has the perception of remote or distance operation.

The inevitable question is how far is far? Typically this means over a distance such that

the distance between the controlling location and the controlled location is so great that direct wire control is impractical (n.b. the communications link is a critical component of the system).

BASIC DEFINITIONS

SCADA Systems



BASIC DEFINITIONS

SCADA Systems



Data acquisition begins at the RTU or PLC level and includes meter readings and equipment status reports that are communicated to SCADA as required.

Data is then compiled and formatted in such a way that a control room operator using the HMI can make supervisory decisions to adjust or override normal RTU (PLC) controls.

Data may also be fed to a Historian, often built on a commodity Database Management System, to allow trending and other analytical auditing

BASIC DEFINITIONS

SCADA Systems



TYPICAL DATABASE MANAGEMENT SYSTEM

BASIC DEFINITIONS

SCADA Systems

SCADA(stand Alone)

SCADA(Redundant)

CorporateDatabase

Applications

CorporateE-mailSystem

CorporateWeb

Application

CitectSCADAReports

Web Client(Analysis & Reporting)

Excel Client(Analysis)

Custom Clients

Historian



Levels of

Hierarchy

SCADA Systems


Process Control, Instrumentation and SafeguardingSCADA Systems



LEVELS OF HIERARCHY

On a complex SCADA system, there are essentially 5 levels of hierarchy.

Field level instrumentation and control devices Marshalling terminals and RTU’s Communications systems The master station(s) The commercial data processing department computer system

SCADA Systems



1 Field Level and Instrumentation Devices

SCADA Systems



1 FIELD LEVEL AND INSTRUMENTATION DEVICES

SCADA Systems




SCADA Systems



The field mounted devices are no different from any other application.

In many cases, the process may be petrochemical, in which case, consideration must be given to intrinsic safety problems.

It would be logical to assume the “smart” devices would be adopted.

This also assumes that a network system would be used at this level


SCADA Systems



SCADA System for Pipelines Showing Field Instruments


SCADA Systems

Main Control Room

SCADA

RTU

ComnSpike

RTU

OutletDock Valve

Dock Valve

ComnSpike

ComnSpike

ComnSpike

Dock Valve

RTU

P

T

O P

T

P

P

T

O



2 Remote Terminal Units

SCADA Systems



2 REMOTE TERMINAL UNIT

SCADA Systems

Commercial Data Processing System

Master station

Communication system


RTU’s

Field Level

Field devices (analog & digital Input/output)

Mainframe computerData processing system


Master station

Master station

Sub-Master station

Sub-Master station

Sub-Master station

Sub-Master station



TYPICAL REMOTE TERMINAL UNIT


SCADA Systems



The RTU provides an interface to the field analogue and digital signals situated at each site.

Sometimes referred to as a Remote Telemetry Unit, as its name implies, this device is a standalone data acquisition and control unit.

Generally microprocessor based.

The main function of an RTU, is to monitor and control equipment at some remote location from the central station.


SCADA Systems



Typical RTU modules include the following modules

Control processor and associated memory. Analogue I/O Digital I/O Counter inputs Communication interfaces Power supply RTU rack and enclosure


SCADA Systems




SCADA Systems



3 Communication Systems

SCADA Systems


Process Control, Instrumentation and SafeguardingSCADA Systems



3 COMMUNICATIONS SYSTEM

The communications systems provides the pathway for communications between the master and remote sites.

This communications system can be radio, telephone, microwave or satellite.

Specific protocols and error detection philosophies are used for efficient and optimum transfer of data.

SCADA Systems



4 Master Stations

SCADA Systems



4 MASTER STATIONS

SCADA SystemsCommercial Data Processing System

Master station



RTU’s

Field Level

Field devices (analog & digital Input/output)



Master station

Master station

Sub-Master station

Sub-Master station

Sub-Master station

Sub-Master station



The master station (and sub-masters) gather information from the various RTU’s and generally provide an operator interface for display of information and control of remote sites.

In large telemetry sites, sub-master sites gather information from remote sites and act as a relay back to the control master station.

4 MASTER STATIONS

SCADA Systems



A SCADA system includes a user interface, usually called Human Machine Interface (HMI).

The HMI of a SCADA system is where data is processed and presented to be viewed and monitored by a human operator.

This interface usually includes controls where the individual can interface with the SCADA system.

HMI's are an easy way to standardize the facilitation of monitoring multiple RTU's or PLC's (programmable logic controllers).

4 MASTER STATIONS

SCADA Systems



Usually RTU's or PLC's will run a pre programmed process, but monitoring each of them individually can be difficult, usually because they are spread out over the system.

Because RTU's and PLC's historically had no standardized method to display or present data to an operator, the SCADA system communicates with PLC's throughout the system network and processes information that is easily disseminated by the HMI.

4 MASTER STATIONS

SCADA Systems



HMI's can also be linked to a database, which can use data gathered from PLC's or RTU's to provide graphs on trends, logistic info, schematics for a specific sensor or machine or even make troubleshooting guides accessible.

In the last decade, practically all SCADA systems include an integrated HMI and PLC device making it extremely easy to run and monitor a SCADA system.

4 MASTER STATIONS

SCADA Systems



A TYPICAL SCADA APPLICATION

REMOTE TERMINAL UNITS

SCADA Systems

Oil TreatmentPlant

Oil Production

Wells

Oil Gathering

Field



5 Management Level

SCADA Systems



5 MANAGEMENT LEVEL

SCADA Systems



A SCADA system must continue to operate when field communications have failed.

The “ quality” of the data shown to the operator is an important part of the SCADA system operation.

SCADA systems often provide special “event” processing mechanisms to handle conditions which occur between data acquisitions periods.

5 MANAGEMENT LEVEL

SCADA Systems



SCADA Configuration

SCADA Systems



SCADA CONFIGURATION

SCADA Systems

Workstation

Workstation

RTU

RTU1

RTU2RTU N



SCADA CONFIGURATION

SCADA Systems

RTU1

RTU2

RTU3

RTU4

Server



SCADA CONFIGURATION

SCADA Systems



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Section-16 Scada Systems