Industrial Control Systems in a Nutshell

Eyal Leshem


The nitroglycerin plant,  that Alfred Nobel, inventor of dynamite, built in 1870 was probably the most dangerous factory in the world at  the time. To produce the nitroglycerin required to make dynamite, the reaction had to be kept below 22°C. Otherwise it could get out of control and cause a catastrophe. So the inventor placed a  worker whose job was to stare at a huge thermometer and make sure the temperature remained below the threshold. If necessary, this watchman could stop the reaction completely by opening and closing some valves, flooding the system with coolant or air, and in extreme cases dumping the tank, taking cover, and yelling to let the others know that disaster was imminent. However, Nobel was concerned that his watchman would be so bored he’d fall asleep, endangering his life’s work and employees. Nobel, ever the inventor, came up with an idea to keep his watchman awake. It was a one-legged stool that the watchman could perch on, but if he nodded off he’d lose his balance and be wakened by the fall. With all due respect to this early control system, it was, you will agree, inherently precarious, and the feeling was shared by a visitor to the plant in 1897: “Your life depends at every moment upon a thermometer and a man on a one legged stool”.

150 years after the one-legged-stool, no modern plant would conceivably entrust its manufacturing precision, efficiency, and safety to the alertness of a bored worker balancing on a wobbly stool. Industrial process control is a task requiring unfailingly professional planning, and is diametrically opposed to improvisational decision-making. A process plant control system is a lot like the human nervous system. Just like a human body, modern plants have thousands of sensors. To implement process control in plants, we must first be able to measure a large variety of parameters (e.g. pressure, temperature, pH, conductivity, flow rate). We no longer need a gigantic thermometer, because our sensors are smaller, much more accurate, and can monitor many more physical and chemical parameters. Like a nerve signals, communication systems can transmit information using electrical signals from smart sensors to a central controller that collates the information, makes the necessary calculations, and tunes the system accordingly. The controller, if you will, is the brain at the center of this nervous system.

Smart process control makes manufacturing safe, accurate, and uninterrupted, saving enormously in human resources. But that is not the only benefit; plants with inadequately maintained control systems waste a fortune on energy unawares. Lacking or inadequate systems will run motors at a higher capacity than is actually necessary and heat or cool more that you need. For example, in the absence of correct calibration management, heating water a mere 2 degrees hotter than a water-intensive process actually requires can cost hundreds of thousands annually. Add to the financial burden of unnecessary energy expenditure and accelerated wear, the harm our environment suffers from superfluous heating and unnecessary fuel consumption, multiply this by the number of plants run this way and you will have a measure of the national cost to our environment. A good control system is one that operates motors efficiently, heats and cools accurately, and runs manufacturing processes economically, in an environmentally responsible way.

*The author is head of systems and engineering in the Meptagon Group

Meptagon Group designs, installs, develops control systems, integrates, and trades in process industry instruments and equipment.