ABSTRACT

This article describes about SCADA system (Supervisory Control And Data Acquisition) and SCADA System components

SCOPE

Scope of this document is limited to describing SCADA and its features.  Design details about each system will not be covered in this document.

INTRODUCTION

SCADA expansion is Supervisory Control And Data Acquisition. As the name suggests, it has both data acquisition and control feature in the SCADA System. It is used in the remote monitoring and tracking of plant devices such as Sensors. The SCADA system can be used in Oil & Gas pipe line monitoring, Energy distribution, Water and Waste water management, Traffic Monitor etc..

SCADA Usage in Oil & Gas Industry:

     SCADA usage in Oil industry is through the pipeline, monitoring and controlling of various pump satiation parameters and sensors. Each pump station will have various sensors like Temperature, Pressure, Valve status, motor sensors across the pipeline. From these sensors the parameters  to me monitored like Input Temperature, Input Pressure, Output Pressure, Valve Status,  Motor speed, Volume etc.. These parameters can be read using sensors installed at the pump stations. These sensors are in turn connected to either PLCs (Programmable Logic Controllers) or directly connected to RTUs (Remote Telemetry Units). A communication channel available between SCADA Master station and RTU where in the modems at Master station and RTU communicate and exchange the information. LAN can be used where ever LAN network is available and can use TCP/IP protocol. SCADA master station communicates/polls frequently to the RTU and converts the received data into readable format. The RTU sends both analog and digital signals. This data is in turn transferred to the MMI Stations for presentation like plant schematic, current trend of values, Historic trend of values, Alarm, event view etc.

    SCADA can be used to control the plant by giving the commands like Valve close, Valve open, motor start, motor stop etc.. Only authorized personnel can use the SCADA Control feature.

SCADA Components:

• SCADA Server (Master Station/Standby Station)
• Remote Telemetry Units (RTUs)
• Communication channel from SCADA Server to RTU
• Ethernet communication channel
• Man Machine Interface (MMI)/Human Machine Interface (HMI)
• Internet
• Mobile MMI
• Wireless communication Channel for Mobile MMI
   

SCADA System Architecture:

SCADA Master Station

     SCADA Master status contains dual servers. Each master status is connected in dual Redundant Ethernet. The purpose of duel connection is to recover when one system fails, other system will take over immediately. SCADA Servers repeatedly poll the RTUs which can be on serial communication link or in network. The received data will be updated in the local server and will broadcast the data to the MMIs. The functionalities of the SCADA Server is

• To poll the RTU/IEDs/PLCs
• Convert/parse the data received from the remote devices
• Store the data in the local database
• Broadcast the data to the servers
• Generate Historic Trends and send the Historic data to the clients when required
• Generate Current Trends and send the Current trend data when required
• Receive Alarm and Event information from RTUs
• Event Management / Alarm Management
• User Management
• Interface to 3rd Party software

Man Machine Interface (MMI)/Human Machine Interface (HMI)

     MMI/HMI is a Graphical User Interface for the SCADA System. The users use HMI for monitoring and control of SCADA system. The MMI presents Historical Trend View, Current Trend View, Alarm View, Event view, System control, facility to create the plant information, facility to add RTU information etc

Remote Telemetry Unit (RTU)

     Remote Telemetry Unit is a device that will be installed across the remote locations and connected to the remote sensors or IEDs. SCADA Master server keep on polling the RTU for the information. RTU fetches the information from Remote Sensors and sends the data to the SCADA Server.

Programmable Logic Controllers (PLCs)

     PLCs are works on ladder logic which can be programmed by user and used as field devices. These can be used by RTUs for fetching the remote data

Web Based SCADA

Traditional SCADA system used to stick to master station and communication to RTUs using radio or LAN connection. The usage is limited the users sitting and using the MMI/HMI workstations for monitoring and controlling at the same fixed location. With the advent of Internet and acceptance of standard HTTP protocol for Internet access, the same features can be extended in browser based MMI/HMI. Standard browsers like Microsoft Internet Explorer, Google Chrome, Firefox etc.. can be used to connect to the SCADA Web server. SCADA Web Server will have interface with SCADA Server for fetching the required information to the client. Standard web servers like Apache, IIS etc.. can be used as SCADA Web Servers. This can be used in intranet.

The same can be extended to internet where in SCADA details can be browsed in Internet. Since the SCADA is exposed to the external world, Security is a major concern and needs to be addressed before deploying SCADA in Internet.

SCADA in Mobiles

With the support for WAP Browsers in mobiles, SCADA network can be extended to display some important parameters and browse the same in the WAP Browser. SCADA Web server should support MML script for sending the response in MML for WAP Browsers in secured browsing.

Smart phones/PDAs has increased the connectivity and screen resolution where in a thick client can be developed (Mobile MMI/HMI). Similar features as mentioned in HMI(truncated due to limitation of the mobile) can be used in Mobile MMI. The advantages of Mobile MMI is its availability Anywhere (where ever the mobile connection is available) Site engineers can keep track of plant details where ever they are. In smartphones, mini browsers have the capability to render XHTML content. So, thin clients can be developed to browse the pages available in SCADA Web server. Security feature should be enabled in the browsers for viewing the SCADA pages.

Standard Protocols

Legacy SCADA systems used to use proprietary protocols to communicate between SCADA servers and RTUs. It leads to increase in development, maintenance cost and no interoperability. Standards have been evolved like IEC, DNP3, Modbus etc.. for communication between SCADA and RTU/PLC/IEDs

Security:

Security is an important feature in the SCADA system and ignored in the legacy SCADA system since the installation was in isolated physical location. With the introduction of Internet/Intranet and Mobile SCADA, more stringent measures should be taken to protect the SCADA systems from the hackers. Each system should have secured access.