Learning PLCs: hardware vs. software background?

Albert LaFrance

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Mar 2012
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Falls Church, VA
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As someone who's learning about PLCs (just for fun at this point), I follow the various threads posted by other beginners, and have been wondering how someone's prior knowledge affects their learning approach, and what challenges and advantages it brings to their effort.

Specifically, I'm thinking of the differences between people who have a hard-wired controls background, versus those who come from the computer programming field.

For example, many of the practices taught to beginning programmers in languages like C++ and Java apply directly to PLC work; things like understanding and documenting the requirements thoroughly before starting to code, using comments to explain your program, giving your variables meaningful names. And a programmer will readily understand the concept of the PLC scan as a "DO loop" control structure and perhaps, more abstractly, see a ladder rung with PLC input contacts as an "event handler".

On the other hand, the hard-wired controls designer/technician has major advantages in reading ladder diagrams, understanding the characteristics of the real-world equipment and processes being controlled, and having an awareness that any input can change at any time.
 
I reckon controls background is best. Learn how things work first, interlocks, safety considerations, physical constraints of mechanical and electrical hardware devices. Fine to be able to write a pile of fancy code in C++ that no one in the factory can understand or something but if you do not understand the machine/process disaster is only a step away.
 
when I went to school we had ONE 'COMPUTER' (FYI I am 10 years younger than BoBB) this computer was a Paper tape reading terminal @ 300 Baud.
we learned 'BASIC'
so I had a litle knowledge in logical thinking - however I was one of the best Chess Players in the school.
- so my LOGICAL thinking existed.
I left school and started a 4 year apprenticeship as an Electrician.
for those years and the years following I learnt Machinery control.
(most electricians in Australia wire houses - I have not done this)
so for 36 years I have been working with control systems.
Before I started in PLC's controls were principly done with Relay Logic.
At the end of the day you need to know how a machine is wired.
And be able to follow a logical process.
When interviewing for future apprentices I ask
- what types of games do they play?
- role playing - logical thinking (chess etc)
is the type I need to hear
- So I know I can teach them and they will learn.
 
When interviewing for future apprentices I ask
- what types of games do they play?
- role playing - logical thinking (chess etc)
is the type I need to hear
- So I know I can teach them and they will learn.

thats awesome. i think i will adopt this method as well in the future. i too enjoy chess. altho i wouldnt say i was the best... lol
 
I got thrashed playing chess some years ago, by a 16 y/o.
He is now a Professor of medicine - Makes sence
 

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