Control and automation communication systems have traditionally been proprietary and closed. The current trend is that technologies allowing industrial components to merge with computer networks are becoming less expensive. This fact, coupled with the explosion of the Internet and its technologies, is revealing new innovative solutions for control and monitoring systems. The power of the Internet in monitoring and troubleshooting cannot be overstated. Internet-compliant communications are going to be the basis for future automation solutions.
Background on TCP/IP and the Internet.
The Internet is a conglomeration of networks throughout the world that forms a vehicle to exchange information between authorized participating machines. Intranets, on the other hand, are localized enterprise-wide networks of a smaller scope than the Internet. They use the same protocol suite, however. A company has full control over its own intranet and can assign network classes as needed. The use of company-wide intranets is growing rapidly. Intranets are a solid and uniform standard that simplifies a company networks because the setup and protocols are standard. In addition, tools, software, and utilities that function on the Internet can be used on an intranet.
The primary protocol for information exchange with the Internet or intranets is TCP/IP. TCP — Transmission Control Protocol — formats information to be transferred and adds header information and error checking to the stream of data. A lower level protocol called IP — Internet Protocol — routes the transferred information from one address to another. IP adds its own header and checksum to ensure the proper machine receives that information. TCP and IP work in conjunction, allowing computers to share resources across a network. The Internet and intranets are designed so that if links or sections fail, IP can route around them. Redundant routes lead to tremendous network reliability.
TCP/IP is a standard and essential element of wide area networking. Ethernet accepts messages from TCP/IP, adds a header and a checksum, and transmits a packet on the physical network.
The advantages of having a PLC on the Internet.
The centerpiece of contemporary automation is the programmable logic controller. Having the ability to remotely interface with a PLC holds many advantages. A key advantage is the ability to directly access the PLC program and configuration from a central or remote location. Consider, for a moment, the utility of having a centralized computer on the plant floor that accesses the programs of every PLC in a process. Then, consider the even greater utility of being able to connect to these PLCs remotely using the Internet.
Such connectivity is the hallmark of easier system start-up. After mounting and terminating control panels, checking I/O, and configuring the PLC, the technician loads initial program in the PLC. Suppose a plant has several identical processes. After starting the program and then modifying it to correct errors, the technician must then load the program in the other panels. That is relatively easy. But, if the programs are similar, but not identical, the technician must now spend more time to modify the program several times and load the different copies in the appropriate PLCs.
Doesn't it stand to reason that if the technician had a central computer that could switch from one PLC to the next through its software, the programs could be loaded in less time and with greater efficiency? The truth is that it is possible to completely implement and start-up a PLC program over the Internet, saving a lot of re-work time.
There is benefit in monitoring a PLC program during the start-up and testing phase. Being able to select and monitor different PLC programs from the one location is useful.
Centralized start-up monitoring gives the added convenience of allowing you to locate the computer in an office where schematics and other resources are easily accessible. Imagine being able to monitor a program from a desktop computer while seeking telephone support for a problem. It also means PLCs and office computers run simultaneously on the same hub.
Possibly the most beneficial advantage the Internet offers is the ability to connect a off-site expert with the PLC. Saving travel costs and time, the expert guides the technician through problem areas remotely and views the PLC program directly. Often, analyzing the PLC program reveals errors in the electrical control panel itself. This type of remote support saves time and money during both start-up and after a control system is in operation. If you cannot observe a control system from hundreds of miles away in the company's headquarters, you are at a competitive disadvantage.
Direct interface to PLC programs allows one to view or modify the programs. Multiple users may simultaneously view the same PLC. Human-machine interface packages or other applications operate normally while viewing or monitoring the program. Better grades of PLC allow 32 or more simultaneous connections.
What does this multi-user feature suggest about improved training for instrument technicians? New technicians benefit from viewing the program remotely as it is implemented and modified. Allowing multiple outside experts to view and evaluate a program leads to quicker and more complete solutions. Use of the Internet or intranet in combination with a TCP/IP-compliant PLC communications module makes this connectivity possible.
Network security is a concern at many companies, especially when control systems may be in jeopardy. To address this concern, state-of-the-art PLC programming software has built-in program and configuration security. In this scheme, several levels of security provide the ability to view the program, copy it, load a new program, change or manipulate the current program, and full access rights.