Click here to enlarge imageOver the past 20 years PLCs, digital and paper chart recorders, PC Cards and various other types of solutions were developed and used to collect, display and store process data, but it was the advancement of computers that helped drive the development of new protocols. SCADA packages that allow many different types of protocols to communicate with the same client software were developed.
For example, Modbus was and still is commonly used in plant automation for communication with PLCs and SCADA systems. Modbus has been convenient as it has allowed the manufacturer to provide equipment with a protocol that any systems integrator could use to develop their own software or driver. This type of technology was a way for plants to tie all equipment to a central controller where process data could be collected and provided to a recorder or control room computer.
Another technological achievement in the 1980s was the development of new protocols that different development packages could use to collect data through software. These industry standard protocols, such as DDE, could be used by developers to create software drivers for their equipment. These drivers could then be used by integrators to bring data to their SCADA systems, thus eliminating the need to develop a driver themselves.
This made it easier for the systems integrator to tie the data tags to charts, data points, and historical logs, but it did require the need to know how to define those tags. These tag definitions were provided by the manufacturer in documentation which could sometimes makes things difficult if the definitions were lost or if many tags needed to be defined.
A few years later another software driver, similar to DDE, was developed to eliminate this problem. OPC or OLE for Process Control was created with the idea of allowing item tags to be defined by the manufacturer and provided in a group directory format. These grouped tags could then be browsed and selected by a client system without having to know how those tags were defined. OPC provided ease of use, but developing the server could be difficult as it required knowledge of some advanced programming techniques.
In the last decade, computer networks rapidly became more important in plant automation as price and ease of operation allowed plant operators and engineers the ability to collect and monitor process data remotely. With software drivers or servers, such as DDE and OPC, water plants could collect vital data remotely and then view the results over the network.
Today
With the development of new programming languages, the Internet is being used to monitor and display process data. This was initially cumbersome and visually unappealing as connection speeds were slow and programming languages were not entirely accepted by all of the standard internet browsers.
As JAVA and XML becomes more widely used by internet developers and with the popularity of the internet increasing, new ideas for monitoring are a reality. Solutions are being created that use new communication protocols (Lonworks) and industrial PC's (Web Servers) to control and display automation data using standard web browsers. These applications, when placed on a network or on the internet, can be accessed by any plant employee with proper password security.
Web pages are being created with charts, visual controls, and data display to allow the user to monitor in a familiar environment. Using a browser is convenient as data tags are already configured and security for individual items and pages can be controlled by the administrator.