It's no longer enough to run circuits to a PLC or process loop controller. Today, customers expect you to work with control system software to give them turnkey results.
Electrical work is increasingly moving into areas where software skills are essential. We all know these skills are critical for project management, estimating, and accounting. But, that's not all. The work itself is becoming software-centric.
A decade ago, electricians working with industrial controls dealt primarily with physical wiring and discrete control (e.g., switches and contactors). Today, industrial customers expect you to deal with data cables and virtual control.
Processes move at high speed, with high precision, and at high volume. To stay competitive, plants are shifting to control and communication systems that rely on networked components. This means fewer wires to run. Networks link operator interfaces, input/output (I/O) modules, programmable logic controller (PLCs), and PCs. Those PCs run data-gathering and control programs often set up in off-the-shelf software. Graphical programming interfaces enable staff engineers or technicians to move objects around the screen to model the system and create the data structures necessary for gathering and analyzing data, as well as making control decisions.
While there isn't nearly as much wiring involved, contractors who can learn to work with software will have plenty to do. The network and various components on it, including the client and server computers, still need software installation and configuration. If you can add this business to the wiring jobs, you will see a net gain in revenue. Let's take a look at what kind of software we're talking about.
The operating system (OS) manages how the Central Processor Unit (CPU) operates, where it puts incoming data, how it schedules tasks, where it sends the results of its decisions, and so on. Standard OSs, such as DOS, UNIX, and Windows, exist wherever standard microprocessors can run them. UNIX is common in industrial systems. Like DOS, it's command-driven, and like DOS, Graphical User Interfaces (GUIs) are available for it. As for performance, UNIX is the "high end" of common operating systems, while DOS is at the low-end. Windows New Technology (NT) and Windows 2000 (true Windows Oss) are in the middle.
The most popular GUIs for DOS are DeskView (an older system), Window 95, and Window 98. However, DOS is not robust or stable enough to drive these newer GUIs in critical processes. NT has a lower cost of ownership than either DOS or UNIX, which helps it make inroads that DOS never did and displace UNIX in many circumstances. Although NT is not as powerful, robust, or stable as UNIX, it is a vast improvement over DOS. Microsoft's Windows CE, originally developed in response to the Palm Pilot and other Personal Digital Assistants, is now showing up on production floors; but in small, limited-resource devices.
Installing an OS amounts to launching a program that copies a collection of files to the hard drive of a PC. Among those files are programs such as standard device drivers, which allow the CPU to communicate with peripheral devices like keyboards, disk drives, and displays. The program that installs the OS also sets up the necessary links between the various driver and utility programs within the OS. Installing NT on an individual computer is extremely simple, but when you get involved in network issues it can become thorny.
Once you've installed the OSs in the individual computers, you must establish network connectivity. Networks often have several layers. At the lowest level is the bus that links I/O components to the controller. This controller is typically a PLC that reads inputs and sets outputs. A variety of semi-standard I/O buses are in wide use. The protocols that determine data communication on these I/O buses are for the most part fairly simple, and the drivers that run them need little help from software. All you have to do is make sure the devices connected on the bus have the built-in drivers to communicate. Some configuration work may be necessary, too: setting DIP or rotary switches, entering parameters with a keypad, or downloading them over the bus.
In some modern systems, I/O buses integrate into Local Area Networks (LANs). The latest push is to integrate the data and control LANs into corporate-wide Wide Area Networks (WANs) for full vertical integration between management and production. LANs and WANs require software to implement the complex protocols that define how the system packages, addresses, and sends data. The software also defines how data interact with control and application programs. You must load this software on the PC server that manages the network.
In a sense, network software is another kind of OS, providing the communication functionality between components rather than within them. Early LANs relied on proprietary software, unique to a manufacturer, so only that manufacturer's components could communicate on the network. The move toward standardization has led to "open networks." Now, components from different manufacturers include the same drivers and can run the same network software, so they can communicate; at least in theory. In practice, full interconnectivity on open networks is still an unrealized goal.
Before a control network can do anything, the servers typically need database software. They also need the operation and application programs that set up and coordinate the operation programs. That's a lot of software to load (or in the case of the operation programs, create). Electricians who move into the controls field in modern plants find themselves heavily involved.
One of the most common types of application programs allows you to create a sequential control program for a PLC. The major PLC manufacturers provide application programs that allow you to address inputs and outputs, graphically arrange ladder logic rungs, and input parameters to function blocks.
The application programs also handle the conversion of the ladder logic program to a form the PLC can understand, and provide functions like downloading the control program to the PLC, debugging, accessing data tables, and monitoring real time operation. Most of these PLC-oriented application programs run on standard PC platforms. They can run on a client or server, and the resulting control program can download to the target PLC over the network or from disk.
Application programs provide their own Human-Machine Interface (HMI) for programming. They also let you set up the HMI that the equipment operator will see. As part of creating the operator HMI, you establish system security with passwords and access hierarchies that limit the possibility of unauthorized access to data or control programs.
Other application programs allow you to model integrated data acquisition (DAQ) systems. You do this by choosing appropriate objects from a graphical library to represent system components or subsystems. For each object, you create data structures to handle the information reported by the components or subsystems, and set up the automated reporting, alarm, and data analysis functions. The application program then creates and executes the DAQ program you defined.
Application programs that set up Supervisory Control and Data Acquisition (SCADA) systems go a step further. They not only let you set up functions to gather, report, and analyze data, but they also oversee the activities of the system controllers. They let you start and stop the controllers, reset their control parameters, and tell them which control programs to run.
An integrated, hierarchical, networked system has many advantages. Controllers can still handle time-critical routines that can't tolerate variable network data transmission rates. Along with security measures, the software allows improved maintenance record-keeping and diagnostic routines for the smart devices connected on the network.
The main advantage, however, is the flexibility provided by openness. When your customer needs a configuration change, you can usually accommodate the changes in software. Add another client or server PC, extend the network, and then run the user-friendly application software to modify system operation.
In earlier systems, you might have needed to scrap a mainframe because there was no way to expand its capacity or nobody in-house knew how to write the code for it.
Easier application software, running on standard operating platforms with agreed-upon connectivity standards, allows users to create ever more powerful and flexible data and control programs. The effect is to lubricate industrial production. If you stay current with the developments in industrial software and apply them appropriately, you will maintain a competitive edge.
Coleman and Bowden are developmental instructors for PRIMEDIA Workplace Learning, Chattanooga, Tenn.