It has been roughly 50 years since Dick Morely created the first programmable controller, and while the demise of the PLC has been predicted many times, it is still here with us.
As the control industry has evolved in the “age of electronics” PLCs have changed dramatically. One of the subtle problems of electronics is that chip manufacturing changes every 2-3 years. Obsolescence of some parts can be as short as six months for products that are not widely accepted. This means that semiconductor life cycles are much shorter than equipment life cycles in the industrial world. Control system companies have traditionally managed product cycles of 5-10 years. So when key semiconductor components become obsolete, major control systems can become obsolete as well.
Manufacturing plant operations are assets that operate for even longer periods based on market conditions and capital investment. Bottling plants for beer, for example, have to be planned on 10-30 year investment cycles, or longer. Cost of equipment in large plants is a critical issue, and as controls and machinery migrate over time, effort needs to be put into maintenance and planned improvements to keep product costs competitive.
If a piece of equipment has provided 10-20 years of service with little or low maintenance, count your blessings, and don’t wait for equipment to fail. Check with the original equipment manufacturer to see if critical repair parts are available. If not, maybe the OEM has a program to upgrade the controls to meet current standards. At least, find out if there are suggested substitutions or service recommendations that will keep the machine working.
In machines that use electric motors and controls, issues of obsolescence can get complicated quickly. Machines that process a filament or web of material require precision torque motors that in the past would have been brush dc type motors and control. In systems 100-500 horsepower, such as are found in dockside loaders and other types of crane, brush dc motors and drives were very common because ac motor slip typically could not be controlled at low speeds.
Today, closed loop vector drives can operate at low speed with full control down to zero RPM, and since these systems use standard ac motors, they are much lower cost and more readily available than a comparable dc system. So when the question of obsolescence comes up, sometimes the “ripple effect” is to cause changes all the way through the system. Old motors that work perfectly well may have to be considered for replacement, because the older technology is difficult, expensive and time consuming to repair. Any motor failure could result in catastrophic down time. Any drive failure means the machine is down and may not be repairable.
Check to see what the age of equipment is in your plant operations. Find the oldest controls and see what the availability of repair parts is. You might be surprised to find out that some of the controls in your plant have aged out and become obsolete.