by Mike Stanley

Created on: August 03, 2009

Computers have transformed almost every aspect of our lives in recent years. Increasingly they are used to help us in banking, buying, and paying our bills. In industry, computers have a much more expanded role as they are used for all that plus controlling the processes that earn them a paycheck.

Instrumentation is used to control processes in chemical, power, and most manufacturing plants. Instruments are placed in these processes to measure temperatures, stress, density, weight, volume, flow, and much more. The readings from these instruments have to be collected and used to control those processes, and before computers it was done with manual controls. Someone had to read the gauges and adjust valves and switches to maintain the process in the desired way. This method requires more manpower, and is subject to a larger degree of error. In manufacturing, error is your worst enemy.

To help reduce error, electronic control systems were created. These control systems could operate with much less interaction from people, and also able to maintain a finer degree of control by introducing feedback controls. By taking the feedback from a sensor, the controller could adjust the valves and electrical signals to keep the process under control. However, even with this new semi-automated system, some interaction was still required, and setting up the control system was complicated. In larger plants and factories, setting up a control system could take a long time even with a team of specially trained technicians and engineers.

The answer to this was to eliminate the middleman. By running all the sensors and controls to a special card in a computer, all the sensors could be read in one place, and that input used to control the actuators for valves, switches, relays, and other controls. By mapping out how the circuit will work on a computer, the process is made much simpler. Instead using long runs of complex wiring to link sensors, controls, and controllers, the computer uses software to decide how the sensors effects the controls. Because the software can be easily changed on the fly without the need to move physical wiring, changes can be made to the control systems much easier. This helps to save time and money in setting up the systems initially and also later if the process has to be changed.

With computers, the process can be monitored in a more graphical way as well. Monitors can be used to show tank levels, boiler temperatures, and flow rates in a way that people associate with more readily. By interfacing a touch screen monitor with the computer, you can not only display the information for the operators, but also give them a fast and easy way to control the process if necessary. With touch screens, the operator can simply touch the tank level graphic, and set a new level. The control system will then make the needed changes to adjust to the new level.

It's easy to see how much more control computers give us over instrumentation control systems. It helps to reduce stress on both the process controls, and the operators overseeing the process. There are many implementations of virtual instrumentation, but the goal is usually the same; higher production and lower overhead.

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