Dick Morley and the Story of the PLC

It’s been a few months since Dick Morley passed away. While a younger generation of engineers may be unfamiliar with Morley’s work, those that work in production environments are most certainly beneficiaries of his invention of the Programmable Logic Controller (PLC).

The PLC was first introduced in 1968 while Morley worked at Bedford Associates. The first model produced was designated “084” – a number corresponding with the company’s 84th project. With its ability to operate as a Modular Digital Controller the product’s name was soon improved with the change to “Modicon”.  Ultimately the product would spawn an entire industry of digital control solutions and it would play an instrumental role in improving the safety and profitability of manufacturing facilities worldwide.

Given his role as technical lead Morley is widely seen as the “Father of the PLC”. To understand what that means to the process control industry, it’s worth considering what the PLC is, how it’s used, and why it’s important:

What’s a PLC?

Simply put, the PLC is an industrial computer that intakes data, applies pre-programmed logic, then outputs a command. PLCs are typically programmed using the ladder logic programming language. This programming language is very simple and easy to understand, allowing for rapid deployment and upkeep. Flexibility was a key factor when Morley was inventing the PLC. While Proportional Integral Derivative (PID) logic is often used the PLC has the ability to apply other logic as well.  This in addition to its modular design allows the PLC to be operated in almost any process.

How is the PLC Used?

Since PLCs are designed to be modular they can be used in almost every aspect of process control. PLCs are sometimes confused with Distributed Control Systems (DCS) controllers because both are a type of controller. A key difference between the two is linked to their application. While a DCS supervises the control of an entire plant, a PLC’s responsibility is typically limited to the regulation of an individual process. In many cases, the PLC is used in conjunction with a DCS. The PLC will make quick simple changes whereas the DCS will manage more complex, plant-wide adjustments.

What Makes the PLC So Important?

The PLC was arguably the technology that kicked-off the 3rd industrial revolution. This achievement alone is worthy of recognition. However, the PLC isn’t just recent history as it remains a widely used technology that is continually improving manufacturing automation. The PLC’s reliable and flexible make-up allows it to be used in almost any application and in almost any environment. With a reaction time of 1/10th of a second, the PLC allows for quick and efficient process control.


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