by John Schop

One of the most powerful newer features of the RSLogix 5000 program is the ability to create Add-On Instructions. This allows a programmer to define an instruction that contains a commonly used function or algorithm (as a set of instructions), and use it as one instruction.

To illustrate how this works, I am going to create an instruction that operates a cylinder, and because I’m making an add-on instruction, I can use that same instruction to control any number of cylinders in my application

by John Schop

Have you ever lost data in a CLX processor, because you downloaded new code? Unfortunately, when you donwload a program to a ControlLogix processor, you also download the values of the tags (variables).

A solution to this problem that could be useful, is an Excel sheet that reads and writes values to the ControlLogix processor using the DDE/OPC capabilities of RSLinx.

In this article, I will show you how to create one of these sheets for your projects.

Here’s what you’ll need:

These are general guidelines for connecting, downloading and uploading from an S7-300 or S7-400 PLC. The following procedures were created using Siemens SIMATIC STEP 7 version 5.4 software.

by John Schop

For years now, Object Oriented Programming paradigm (or OOP) has been a commonly used programming practice, and has of course found its way into industrial automation as well.

by John Schop

I often find that using SFC's or Grafcets is the easiest way to design industrial automation systems. I have worked for several machine builders, and one of them had given the term 'SFC logic' another meaning. There was absolutely no process in their PLC logic that was not documented by an SFC or as I like to call it, a Grafcet. After some getting used to that, I absolutely loved the way it enabled me to program and troubleshoot complex machinery, and ever since, I've tried to use this method whenever I could.

Courtesy of: Inductive Automation

Water and Waste Water Plants Transform Using Web-Launched, Java-Based SCADA Software

Professionals in the water and waste water management field face a series of difficult challenges as they seek to stabilize and expand their service delivery capabilities, while at the same time meeting the regulatory reporting requirements of the state. As if that were not enough, they must accomplish this in the current economic environment facing local governments. Managers clearly need better ways of doing business and an economic model which will give them the functionality and scalability required at a price point that does not break the budget.

Implementing Sequential Function Chart Designs using Ladder Diagram Programming Language for Programmable Logic Controllers

by James McWhinnie
Napier University, Edinburgh, Scotland.

ABSTRACT

Sequential Function Charts (SFC’s) have long been established as a means of designing and implementing sequential control systems utilising programmable controllers. The Programming Standard IEC 61131-3 includes a graphical implementation of SFC’s in its suite of programming languages.

I couldn't find a complete listing of all the function blocks in the standard Siemens S7 Libraries so I made one myself. It helps me get a better overview of what is available. The complete listing is also available as an Excel spreadsheet so you can sort or adjust to your needs.

The Siemens S7 PLCs have five different timers in the regular instruction set yet it is missing a standard retentive on-delay timer. There is one called a Retentive On-Delay S5 Timer (S_ODTS) and its coil counterpart (SS) which provide a function to continue timing even when the timer is disabled. What we are looking for is something like Allen Bradley's RTO instruction that stops when disabled, retains the accumulator value and then starts where it left off when enabled again. This is very handy for keeping track of elapsed times.

Courtesy of: Inductive Automation

Weaving it all together with Web Technology

Bronco Wine Company, Ceres, CA (the producer of “Two-buck Chuck”) uses FactoryPMI for enterprisewide process monitoring, control, and troubleshooting. It was a business decision to use this technology, and is paying off handsomely for the Franzia family-owned business.