PLC Simulator

PLCdev is your home for quality simulators for Programmable Logic Controllers from Allen Bradley, GE Fanuc, Siemens, Modicon, Mitsubishi, Omron, Automation Direct and anything else you're using. We specialize in making PLC test boards to simulate your control environment so that you can debug your programs on your desk or in the field. And if that wasn't enough we offer educational materials, articles and tips for the novice to the advanced programmer. We invite you to register so that you can receive timely updates to PLCdev. Thanks for coming and visit again soon!

A Siemens S7-300 Trainer

PLC demonstration units are an essential tool for maintenance and engineering.

An Allen Bradley SLC-500 Trainer

Here's a good example of our PLC simulators used on an Allen Bradley SLC-500 trainer.  I built this unit for a customer that does automation training.  This concept is easily adaptable so if you're interested in something like this then feel free to contact me.

Selecting the Right PLC for your Personality

OK, maybe someday I'll seriously write an article on how to choose a PLC. For now though you'll have to make do with the PLC Personality Quiz. It's the fortune cookie of PLC marketing. Smile

Book Review: Programmable Logic Controllers by Frank Petruzella

cover of Book Review: Programmable Logic Controllers by Frank PetruzellaProgrammable Logic Controllers

author: Frank Petruzella
ASIN or ISBN-10: 0078298520
binding: Hardcover
amazon price: $253.59 USD

I really like this book.  The text discusses PLCs in a general sense even though the examples and exercises use the Allen Bradley line of PLC-5, SLC-500 and ControlLogix PLCs extensively.  So if you are student seeking to gain a good working knowledge of one of the most popular PLCs on the market then this is your book.  It deals very thoroughly in a basic and intermediate level, touching on some advanced concepts as well.  Some nice extra material not found in other books is chapter 13 on PLC Installation Practices, Editing and Troubleshooting.    The b

Modbus FAQ


1. What is MODBUS?

MODBUS is a commonly used industrial communications protocol. It allows the exchange of data between PLCs and computers. It was originally designed for Modicon (Schneider Electric) PLCs but has become widely used by many PLC manufacturers and industrial networks.

2. Why would I use MODBUS?

MODBUS is a common means of gathering data from many different sources for viewing operations, archiving and troubleshooting from a central remote location. It is widely used and a fairly simple protocol. Depending on the application a newer protocol may have more advantage.

An Interview with Mike Kraft

I'm a big fan of the retro-encabulator spoof so it was a great surprise to have the actor in the video, Mike Kraft, respond to my plea for more information.

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How PLCs Work

A programmable logic controller is a specialized computer used to control machines and processes.  It therefore shares common terms with typical PCs like central processing unit, memory, software and communications.  Unlike a personal computer though the PLC is designed to survive in a rugged industrial atmosphere and to be very flexible in how it interfaces with inputs and outputs to the real world.

The components that make a PLC work can be divided into three core areas.

  • The power supply and rack
  • The central processing unit (CPU)
  • The input/output (I/O) section

PLCs come in many shapes and sizes.  They can be so small as to fit in your shirt pocket while more involved controls systems require large PLC racks.  Smaller PLCs (a.k.a. “bricks”) are typically designed with fixed I/O points.  For our consideration, we’ll look at the more modular rack based systems.  It’s called “modular” because the rack can accept many different types of I/O modules that simply slide into the rack and plug in.

Book Review: Programmable Controllers by L.A. and E.A. Bryan

cover of Book Review: Programmable Controllers by L.A. and E.A. BryanProgrammable Controllers: Theory and Implementation

author: L. A. Bryan
E. A. Bryan
ASIN or ISBN-10: 0826913008
binding: Paperback
list price: $110.00 USD
amazon price: $110.00

Programmable Controllers by L.A. Bryan and E.A. Bryan has been around for several years (first published in 1988) and is now in a second edition (1996). Its longevity is due to it's well written style, clear organization and it's generic nature which covers many PLCs. It's a book that targets an intermediate beginner level. So it's not a "PLC for dummies" book yet it might leave the advanced PLC programmer wanting more.

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Time Engineers


Time Engineers

Time Engineers is a really cool looking game that teaches kids fundamentals in engineering. It's aimed at middle and high school ages even though it looks entertaining (and maybe even educational) for adult engineers. The basis of the game is to unlock the time travel machine and go back to help cultures in the past with their engineering problems.  For instance you could help the Egyptians build the pyramids or design a draw bridge in Medieval France.


The thing that really tickled my fancy is the first two exercises involve principles that I've included in my PLC tutorial.   The first hurdle involves the time traveler having to use decimal to binary conversion to open up the door to the machine.  After that, a series of switches must be set using Boolean functions like AND, OR and NOT to power up the time machine.

I love educational software like this.


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The Decision Makers: AND, OR and NOT

Life is full of decisions. What is true for us is also true of PLCs. We gather information (input) and based on that we make choices that determine our output. All though I've always found computers to be quite a bit more logical then human beings.

For an example of how we use logic in everyday life consider these statements:

  • If Tommy OR Bob want to play basketball then I'll play too.
  • It's 6 o'clock AND I'm NOT hungry therefore I'm going to keep playing.
  • If Mom comes out AND orders me inside OR it get's dark then I'll stop playing.

Now these are pretty simple decisions especially if you're a ten year old boy.  You'll notice that they all involve three types of comparisions: AND, OR and NOT.  Now we could get more complex but all that we'd be doing is using these simple building blocks.

In the world of automation these types of TRUE or FALSE conditions come down to a device being ON or OFF, CLOSED or OPEN, PRESENT or ABSENT, 24 VOLTS or 0 VOLTS.  In the PLC it all boils down to our now familiar binary system of a 1 or a 0.  Typically having a bit ON represents a TRUE condition while OFF is FALSE.  This is abitrary though as it may make more sense to use what is called failsafe logic and have an ON bit as a FALSE condition.