Showing posts from April, 2015

PLC Analog IO Troubleshooting Tips

When commissioning or troubleshooting PLC inputs and outputs (IO), the analog signals are often the most difficult.  First, analog IO almost always has to be scaled to convert the raw signal to useful process values.  Also, there are many wiring and external device (sensor/actuator) configurations. Here are some simple guidelines for troubleshooting and working with Analog IO.  Although these guidelines are intended to help you think about the process of troubleshooting, this process will surely catch any specific issues you encounter.
Inside the PLC: 1. Ensure the IO channels are properly configured Most PLCs try to make it easy to configure analog IO hardware.  There are often selection boxes for the many signal types:  Voltage / current / resistance.   4 wire / 2 wire.  In the Allen Bradley RSLogix500 IO configuration at #3 below, for example, you can select an input type for each channel. Double-check your analog IO channel settings and make sure they match the sensor or actuator w…

Source Code Protection in Studio 5000 Logix Designer

While working with a customer on a recent RSLogix 5000 project (now called Studio 5000), there was a need to protect some proprietary source code. In this particular case, DMC had developed a custom Add-On Instruction (AOI) to be used within the project that contained some unique logic that the client wished to protect. This is incredibly easy to do. Rockwell provides an easy tool for this that comes prepackaged with RSLogix.  Since protecting intellectual property or touchy algorithms while opening up some of the code for modification or troubleshooting is pretty common, I thought I'd share some of the info I found and provide a few easy steps to locking down your code. Incidentally, while I'll walk you through configuring an AOI for source protection, you can use the same approach to protect routines as well. Note that all of the information below can be found in various forms in two useful documents published by Rockwell Automation that I would highly recommend you downloa…

Siemens vs Allen-Bradley: Function Blocks

iemens and Rockwell Automation are two giants competing in industrial automation technology today.  Rockwell (aka Allen-Bradley) seems to be more popular in the US market, but Siemens has a larger international customer base.  A cursory Google search will reveal that there is no lack of debate among automation professionals over which one is preferred. On the higher end of their PLC lines, the programming environments to use are:   Siemens - Step 7 Simatic Manager for S7-300 and 400 level PLCsAllen-Bradley (AB) - RSLogix 5000 for the Control Logix and Compact Logix PLCs As someone who uses both platforms regularly, I would like to compare one of the key differences between them - function blocks.
What's a function block? Siemens uses the term Function Block (FB) for program routines that can have internal memory, as opposed to Function Calls (FC) that have only temporary internal memory.  Function blocks are a fundamental concept in the Siemens platform, which give them a signific…

Process Automation Handbook (PDF)

Book Description
To be an effective engineer in process automation requires knowledge of a range of disciplines: chemical engineering, instrumentation, electrical engineering, control theory, mathematics, computing and management. Other books in these areas are generic and few are oriented towards the needs of the chemical and process industry. Process Automation Handbook distills into a single coherent handbook all the essentials of process automation at a depth sufficient for most practical purposes. The knowledge needed to cope with the majority of process control and automation situations is focused on. In doing so, a number of balances have been struck between theory and practice, classical and modern, technology and technique, information and understanding. The reader is referred to more specialised texts after receiving a thorough grounding of each topic. Process Automation Handbook will be of value to engineers actively concerned with process control and automatio…

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Siemens LOGO!Soft Comfort 8.0.0

Siemens AG , a global company in electronics and electrical engineering, and operates in the industry, energy and healthcare sectors, has announced the new release of LOGO!Soft Comfort 8.0, is software for programming simple Siemens LOGO! PLCs. Programming is done in one of two graphical programming languages - FBD (Function Block Diagram) or LAD (Ladder Diagram). Simulation and online monitoring is available. Suitable for use in small automation applications such as lighting, heating, ventilation, gate control etc.

Important new features:

- Graphical reference functions
- Status table including saving on PC (CSV format)
- Enhanced diagnostic options
- Improved commentaries
- Improved alignment of function blocks
- Import / export of port names
- Replacement of function blocks
- Virtual keyboard for message texts
- Astronomical clock with configurable on/off delay
- Macro (user-defined function) including commentaries, port name, password and parameter transfer
- Offline network si…

PLC programming cables for several brands

Most PLC's can be programmed from a PC via a serial cable. Unfortunately, many of these cables have a non standard layout. De cables shown here can be bought from the regular sales channels, but it is often much cheaper to solder them yourself.
Siemens PLC's Most programming of Siemens S5 PLC's is done using a special RS232 to TTY converter. The S7 series are programmed using a RS232 to MPI bus converter. The easiest thing to do is buy these special cables from your local Siemens supplier. The operator terminals however can be programmed using a normal serial cable. The following cable can be used to program the OP series of operator displays.
Programming cable for OPxx display series Idec / Izumi PLC's Idec / Izumi PLC series FA2, FA2J and FA3J all require a special communication adaptor for programming. This communication link adaptor (CLA) is a small box that converts the RS232 electrical signals into a compatible level for the PLC. The cable to connect the PC t…