Features and Functions of SCADA systems

Here we discuss about different Features and Functions of SCADA systems used in industrial automation control systems.

Functions of SCADA systems

The below are the detailed SCADA functions as follows.

(a) Dynamic process Graphic –

It should resemble the process mimic. SCADA should have good library of symbols so that develop the mimic as per required. When operator sees the screen he should know what’s going in plant.

By this feature, graphics develop which can resemble the plant. The graphics can include Reactors, valves, pumps, agitators, conveyors as well as other equipment and machinery used in the plant. The status of the equipment running / stopped can be shown using different colures / animation.

Typically the SCADA software will have many ready to use symbols for proper representation which can be used in any type of industry.

(b) Alarm summery & Alarm history -

A SCADA system must be able to detect, display, and log alarms and events. When there are problems the SCADA system must notify the operators to take corrective action.

Alarms and event must be recorded so that engineers and programmers can review the alarms to determine what caused the alarm and prevent them happening again. More complicated expressions can be developed by creating derived parameters on which status or limit checking is then performed.

The alarms are logically handled centrally, i.e. the information only exists in one place and all users see the same status, and multiple alarm priority levels are supported. Every plant needs proper monitoring and control of the process parameters.

Alarms represent warnings of process conditions that could cause problems, and require an operator response. Generally alarms are implemented by using the lamps or hooters in field but in SCADA it can be represented using animation. In many SCADA software, four type of alarm limits are used ie HI, HIHI, LOW, LOW LOW

© Real time trend & Historical time trend -

The trends play very important role in the process operation. If batch fails or the plant trips then historical trend data used and do the analysis. Better look of the representing parameters through the trends in graphical form.

The trend plots the value with reference to the time. Real-time data will plot the real-time value for fixed period of time while historical data will have historical data stored value which can be viewed on demand.

Depending upon the storing capacity of the hard-disk one can specify the no of days the data can be stored. Some SCADA software show real-time and historical trends in single graphics while fewer use separate tools.

(d) Security (Application Security)

Allocate certain facilities or features to the operator, process people, engineering dept & maintenance dept. for example operators should only operate the system, not be able change the application.

The engineers should access to changing the application developed. Every SCADA software has various levels of security for securing the application by avoiding unauthorized access.

Depending upon the access level given the operator / engineers is allowed to do the task. In most of the cases, operators are allowed only to operate the plant while maintenance engineers can do the application modifications. The security can be given for individual as well as for groups.

(e) Data base connectivity

In manufacturing units go for Enterprise Resource Planning (ERP) or Management Information System (MIR).One can produce reports using SQL type queries to the archive, RTDB or logs. Although it is sometimes possible to embed EXCEL charts in the report.

Facilities exist to be automatically generated, print and archive reports. It is important to download the real-time information to the MIS.

In this case the database connectivity is must. Much SCADA software doesn’t have their own database. Hence for storage and reporting they use third party database like MS Access or SQL.

(f) Device connectivity

There are hundreds of automation hardware manufacturer like Modicon, Siemens, Allen Bradley, Yokogawa, ABB. There are own communication protocol. SCADA s/w should have connectivity to the different hardware used in automation. It should not happen that for Modicon buy one software & for Siemens another one.

The software like Aspic or Wonderware has connectivity to almost all hardware used in Automation. Every control hardware has its own communication protocol for communicating with different hardware / software.

Some of the leading communication protocol include Modbus, Profibus, Ethernet, Dh +, DH 485, Device net, Control net. The SCADA software needs device driver software for communication with PLC or other control hardware.

More the driver software available better is the device connectivity. Most of the SCADA software used in the industry have connectivity with most of the leading control system.

(g) Scripts

The majority of the products allow actions to be automatically triggered by events. Scripting languages provided by the SCADA products allow these actions to be defined.

The concepts of receipts is supported, whereby a particular system configuration can be saved to a file and then re-loaded at a later date. Sequencing is also supported; it is possible to execute a more complex sequence of actions on one or more devices.

Sequences may also react to external events. Script is a way of writing logic in SCADA software. Every SCADA software has its own instructions and way of writing program. One can develop complex applications.

The functions can create to suit the process requirement execution. Various types of scripts make project execution simpler for programmer.

(h) Recipe management

It is an additional feature. Most of the plants are manufacturing multi products. When Different product to manufacture, then recipe of that particular get loaded. The same plant for manufacturing different product range.

For example an oil blending plant can manufacture power oil, transformer oil, automobile oil. It is the facility used for maintains various recipes of different products and implement it on the process. The recipe can be stored in a single server and it can be fetched by any client server from any area to run the process.

(i) Networking

In an application, we have to use more than one SCADA software / operator stations. This can be achieved by taking the SCADA node on network. Ethernet TCP/IP is commonly used for networking.

(j) Data Acquisition-

SCADA must be able to read data from PLCs and other hardware and then to analyze and graphically present that data to the user. SCADA systems must be able to read and write multiple sources of data.

(k) Operator Interface –

A SCADA system collects all of the information about a process. The SCADA systems then need to display this data to the operator so that they can comprehend what is going on with the process.