ABSTRACT

This document describes about the design considerations for integrating  SCADA (Supervisory Control And Data Acquisition) with WAP (Wireless Access Protocol) technologies and WWW (World Wide Web).

SCOPE

Scope of this document is limited to describing integration of SCADA, WAP and WWW.  Design details about each system will not be covered in this document.

INTRODUCTION

What is WWW?

The Internet World Wide Web (WWW) architecture provides a very flexible and powerful programming model. Applications and content are presented in standard data formats, and are browsed by applications known as web browsers.  The web browser is a networked application, i.e. it sends  requests for named data objects to a network server and the network server responds with the data encoded using the standard formats.

The WWW standards specify many of the mechanisms necessary to build a general-purpose application environment,

• Standard naming model – All servers and content on the WWW are named with an Internet-standard Uniform Resource Locator(URL)
• Content typing – All content on the WWW is given a specific type thereby allowing web browsers to correctly process the content based on its type
• Standard content formats – All web browsers support a set of standard formats. These include the HyperText Markup Language (HTML), Scripting languages JavaScript, vbscript, and a large number of other formats
• Standard Protocols – Standard networking protocols allow any web browser to communicate with any web server. The most commonly used protocol on the WWW is the HyperText Transport Protocol (HTTP), operating on top of the TCP/IP protocol suite.

This infrastructure allows users to easily reach a large number of third-party applications and content services. It also allows application developers to easily create applications and content services for a large community of clients.

What is SCADA?

SCADA is Supervisory Control and Data Acquisition System. As the name suggests, the main purpose is to acquire the remote data, present in user understandable formant and give controls to the remote devices like stop, start etc.. SCADA can be used in Oil, Gas, Water, Waste Water, Automation and energy monitoring systems. This system will have Master station, MMI/HMI and RTU. The RTUs will be located at remote places where the data/control should be taken. At Master Station, the SCADA servers will be running and continuously polling the RTUs to gather the information. After gathering the information, it will be passed to HMI/MMI for presentation. The Master status consists of various modules like Historical Management System, Trend Management System, Log Management System, Alarm Management System etc.. The HMI/MMI is used to display the remote locations schematic, display alarms, display trends (current trend, historical trend and logs) and generating the reports. The RTU is the remote interface to the Remote device like, Valves, Motors etc in the Oil Industry. The master status polls the RTU to get the information about the status, current values etc.., The RTU will contact remote device and pass the information to SCADA.

What is WAP?

The WAP programming model is the WWW programming model with a few enhancements. Adopting WWW programming model provides several benefits to the application developer community, including a familiar programming model, a proven architecture, and the ability to leverage existing tools (e.g. We servers, XML tools etc..). Optimizations and extensions have been made in order to match the characteristics of the wireless environment. Wherever possible, existing standards have been adopted or have been used as the starting point for the WAP technology.  WAP provides two services viz. Pull services and Push services. In pull services, User gives the request and fetches the response from web through WAP proxy. In the Push services, Origin Server/Push Initiator initiates the connection and sends the push message to the mobile device. It may be email notification, stock price or news service.

Limitations in Traditional SCADA

Following are the limitations in traditional SCADA system

1. Limited to standard number of MMI/HMI
2. Platform dependent client software
3. Dependency software should be installed before use of scada
4. Work area is restricted to the place where HMI/MMI is installed
5. Continuous monitoring is required

Web SCADA
In WebSCADA, WebServer will be placed before the SCADA system. Any client which is in the network can access the WebSCADA through Web server using the HTML browsers. The fetched contents will be rendered in the Browsers. Any browser that supports HTML rendering can be used to browse the SCADA system. SCADA server can send alert messages, reports etc to the specified users through mail server. Browser is independent of platform and can be viewed the SCADA information on any platform. For security reasons, the web server can be enabled through HTTPS protocol.

Advantages with Web SCADA
Following are the advantages with WebSCADA

1. Can be access from any where in the world
2. Installation of client software is minimal
3. Platform independent  clients
4. Can be viewed by any body who is authorized.
5. End to End security is available through HTTPS(from web browser to Web server)