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PLC Safety and Reliability

What is a commonly overlooked safety and reliability area that affects the entire facility?


I'll give you a clue; it has the letters "PLC" in it. Yes, you probably guessed what it is by now, the Programmable Logic Controller. And even more so is the next technological advancement to the PLC, the PAC (Process Automation Controller), but I'll talk about that a little later. It is not the PLC it's self that is the problem as they are highly reliable devices, it is how we work with PLCs that makes our systems so much less reliable.


The PLC controls just about every machine, in every industry, in every country, yet is the last item that plant maintenance and engineering do reliability analysis on. If the reliability issues related to PLCs are even addressed at all. What is even more surprising and even less known, is that the PLC also controls most of the world's infrastructure. The PLC controls most of the world's power, water, traffic lights, trains, elevators, big building's HVAC and much less critical equipment like boilers, bridges, tunnels, hospital incinerators, combines, car crushers, etc.



Better safety and reliability in your car than in your machine...

The PLC is like your car's "Brain Box" (Electronic Control Unit - ECU), in the respect that it is an out sight-out of mind little black box, until the car breaks down.  The difference being when your car's ECU indicates a problem, you have a technician trained and certified on that unit work with it. When a machine or other PLC controlled system indicates a problem, most have an electrician or engineer with little training on that specific PLC work on it. There are other differences too.  An ECU typically affects one piece of equipment that typically cost less than $40k. A PLC typically affects one or many machines, each costing $100k to millions of dollars. But more importantly an ECU affects the reliability of one machine (car) and the safety of one person. A PLC can affect the reliability and safety of many machines and many people.


So, how is Safety and Reliability, put at risk when working with PLCs?


The above four causes of safety and reliability risks associated with PLCs are in order of importance. The number one cause of risk while working with a PLC, is lack of proper training. Because technology in manufacturing and other related industries evolve almost as quickly as the computer industry, text book training alone is not enough to qualify an individual to work with PLCs. (Especially since the textbooks are out of date by the time they get printed anyway. :>) But more importantly, safety and reliability policies and procedures must be incorporated in to the training. These safety and reliability procedures must also be incorporated into company policy. Company policy must dictate only those "properly trained" be allowed to work with the PLCs and that each year employees be retrained and qualified to avoid complacency and keep up with technology advancements. With PLCs, lack of security was a rare cause of safety and reliability risk in the past. But with more networking of PLCs to other devices the risk has been steadily increasing. With the evolution of the newest controller, the PAC, the risk is climbing exponentially.


PLC safety


Those seasoned vets in our industry know specifying and design of both PLCs them selves as well as the automated equipment cover safety quite adequately. We also realize during the commissioning phase, working with the PLCs and automated equipment safety risk increase considerably. Especially in the area of working with PLCs/PACs. But what most of the industry has neglected, working with PLCs/PACs safely for the other 90% of the automation equipment lifecycle.


Another very important PLC safety point is made with the chart above. While the pie chart shows modifications and MRO are only 35% of the picture, what is does not take in to account is the life of the equipment or automation control system. When you look at the linear chart below it, you see that 35% MRO and occasional modifications of the machine/ system continue on for 10-25 years of the lifecycle of the equipment. Another way to view it is 35% times 90% of the lifecycle of the equipment! All a sudden, that 35% becomes an astronomical amount of risk being neglected over the life of the equipment!


Safety and reliability get worse with new technology ...

With PACs (Process Automation Controllers), all four categories of risk to safety and reliability have been greatly increased. Mostly due to the fact it is new technology and lack of training. But equally so because of the way the PAC is designed. The PLC is designed to mimic electrical circuits and for the electrician to work with. The PAC is designed to combine the PLC with motion control and other technologies, including computer programming. Companies are hard processed to find electricians who also have a degree in computer programming, or computer programmers who also know PLCs.

Complacency is not really an issue with the relatively new PAC, as most find it over complex and confusing. But security greatly increases because of the ever growing use of Ethernet and even the internet to access PACs. Maintenance and engineering are not as likely to know and take computer communication security steps and procedures. As IT personnel are not as likely to understand the concept and reality that a PAC on their network breached, is not as simple as just backing up the program. Breaches in PAC/PLC security don't just crash a program; they can crash a machine causing damage to real world man or machine!

Oh the stories I can tell.


So my advice to companies, get annual PLC training that includes safety and reliability. Just as importantly, get policy and procedures that include PLCs/PACs.

I would also highly recommend you read the article "Managing PLCs in your Facility"


About the Author:
Don Fitchett is President of Business Industrial Network (BIN), an industrial training company specializing in PLC training. Don has held that position for over 20 years and has been in the industrial training industry for over 28 years.