Programmable Logic Controllers (PLC) Series – History, Definition and Advantages

Simulan natin ang bagong serye ka-Pinoy Instru, tungkol sa Programmable Logic Controllers o PLC.

PLC concept was first introduced in 1968 when manufacturing industry realized that complicated relay based machine control systems are costly, difficult to maintain and modify. Dick Morley’s Bedford Associates, proposed the idea of a digital controller that is capable of operating in an industrial environment, able to be maintained by technicians and plant engineers and reusable or probably… scalable.

In 1969, the first PLC was used and introduced to General Motors and was called Modicon 084, derived from MOdular DIgital COntroller.

Image of Modicon 184, probably the upgraded version of the Modicon 084.

Modicon 084 was a success and served as the benchmark of innovation of successor products. Since then, innovation upon innovations have been non-stop until today’s modern PLC systems.

According to International Electrotechnical Commission (IEC), A Programmable Logic Controller is:

A digitally operating electronic system, designed for use in an industrial environment, which uses a programmable memory for the internal storage of user-oriented instructions for implementing specific functions such as logic, sequencing, timing, counting and arithmetic, to control  through digital or analog inputs and outputs, various types of machines or processes. Both the PLC and its peripherals are designed so that they can be easily integrated into an industrial  control system and easily used in all their intended functions”

Digitally Operating device; Similar to computers operates by converting analog to binary signals.
Industrial Environment; Non-Stop operation, dust, dirt, moisture, water, oil, corrosion. temperature among others – A PLC shall be offer a certain amount of tolerance to operate under the presence of those conditions.
Programmable Memory; A memory that can be modified with the use of a software or an external device to execute a logic.
Internal Components; PLCs have built in timers, relays, counters – eliminating the need of physical versions of the mentioned devices.
Integration; PLCs can be integrated to almost any HMI and SCADA, reporting systems, and even communicate with another PLC.

1. Flexibility;
A single PLC may be used to run different machines. Regardless if the machine’s function are typical or not.
2. Error Correction / Modification; Back in the relay logic systems, machine problems or modifications is hard to implement. Imagine modifying a system with tangled brittle wires – without a reference or updated diagram. Not to exaggerate but modification shall be done in a short period of time. With PLCs, majority of the work is in the modification of the internal instruction (program). In some cases, external wires do not require modification.
3. Cost Reduction; Since PLCs have internal timers, counters and relays, these basic components can now be eliminated from the list of items to purchase and from the panel design. In effect, a significant space can also be saved thus, reducing panel size.
4. Pilot Testing; PLCs can be programmed while waiting for the arrival of other electrical components. Nowadays, PLCs come with a simulator – allowing program testing even without the actual PLC. This saves a lot of engineering manhours and prevents commissioning problems.
5. Visual Observation; Troubleshooting a relay logic system require lots of imagination and circuit analysis. With a PLC, the program can be viewed online with the PLC programming software to analyze the actual state of your instruction – how is it working or why it is not working.

Some may find initial investment cost of PLCs too expensive. Complex and large control systems may tend to require a large amount to implement. The cost may be intimidating that one may decide to use a conventional control instead. However, imagine in the long run, the returns of the PLC advantages. Those are like guarantees of a faster investment return. Also, PLC systems are not rocket Science. Most of the time, process problems are caused by external peripherals, not by the PLC.  In other situations, some don’t even bother to touch the device. Those limit us to experience the PLC advantages. What is needed? A training program for those selected personnel to handle a PLC system.

Do you have something to share with regards to the topic? I want to hear from you! Leave your comments and thoughts and let’s share knowledge.

image sources: google images


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