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Disclaimer: This document is written in the hope that you can utilize for your own education to gain knowledge of PLC systems (should you decide to utilize this document). Although I believe the information in this document to be accurate, it is YOUR responsibility to verify this information before implementing it in any way, especially when damage to personnel or equipment could result. By continuing to read this document, you agree to hold no one who writes, modifies, or distributes this document liable in any way (even negligence). Due to the wide variety of plant applications, some of the examples in this document may be prohibited at your location, or could cause damage to equipment, or harm personnel.

Author: Ricky Bryce (Montgomery County, IL)

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Glossary

Addressing:

Bit: Smallest unit of information the PLC can process– ON or OFF

Word: 32 Bits for Double Integer

Hardware:

Input module: Reads the STATUS of field devices

Output module: CONTROLS field devices

Discrete module: Reads or controls devices which only have 2 states:

on or off

Analog Module: Reads or controls devices which have a range

such as 0 to 10 volts or 4 to 20 milliamps

Power Supply: Provides control power to modules on the backplane

Chassis: The physical device that modules are plugged into.

Local Chassis: The chassis where the processor resides.

Processor: The 'Brain' of the PLC which contains the machine program.

Troubleshooting Tools:

Cross Referencing:

Allows the troubleshooter to quickly navigate through the

program by listing all locations in ladder logic where a

particular address is located.

Usually the troubleshooter will cross reference a false condition on a

rung of logic to find the output that will turn the referenced bit on.

You can Access Cross Referencing by right clicking a particular address. (Note: You must be on the address, not the instruction)

Custom Data Monitor Utility:

Allows the troubleshooter to gather data from various

memory locations onto one screen for easy troubleshooting. For

example: One can create a custom data monitor for the failure of

a particular motor. Next time the motor fails, the troubleshooter

can simply look down the list of conditions that must be met, and

see in real time which condition is causing the failure.

The custom data monitor utility has to be installed as a separate tool.

Since the CDM utility is not built into RSLogix, you must have RSLinx activated.

RSLinx Lite will not work with the CDM utility.

Force:

Simulates real world jumpers. Use care while performing a force.

You must understand fully how a force is going to affect your system.

In most cases, only addresses starting with an I: or an O: can be forced.

To force an input or output, you can right click on the address in logic,

then choose force on or force off. After the force is installed, forces

can then be enabled from the online toolbar.

Trending:

Trending acts somewhat like a 'software chart recorder', and allows you

to track an analog signal over time.

Communication terminology:

RSLinx: This is the communication server. If RSLinx is not set up properly, RSLogix will not communicate to the processor.

Driver: Allows RSLinx to communicate with a particular hardware device. The

most common drivers are the DF1 driver to communicate with

Channel 0, and the PCMK driver for a laptop to communicate to

Channel 1A for station 5. Configure drivers by clicking

communication on the menu bar.

RSWho: A graphical screen which will display what devices RSLinx has

established communication with. Access RSWho by clicking

communication on the menu bar. Then click on the name of

the driver you wish to use for communication. The right hand

side of the screen will reveal devices the driver has communication

with.

RSLogix: The software which allows you to troubleshoot or program a processor.

Online: Actively communicating with the processor (ladder spinning)

Download: If a program was changed offline, it must be downloaded (

or sent to) the processor. When downloading the processor must

be in program or remote program mode. A good way to download

once RSLinx is properly set up is to click COMMS on the menu bar, and

then go to Who Active. Click the driver name, highlight your processor, then click DOWNLOAD.

Memory Layout:

Tags: A section of the processor's memory that stores information. You can

also think of tag elements as variables. For example: The

memory location “MainTorque” could store a drive torque value.

There are two scopes of tags: Program tags which are local to the

program they Reside in, and Controller Scoped tags which are

global. You can access the Program Tag database by double clicking program tags just above the MainRoutine of each program.

Controller tags can by accessed at the top of the Controller organizer window.

Tasks: A section of the processor's memory which holds programs.

Programs hold Routines. Each controller can have multiple tasks with multiple programs in each task. Each of these programs can then have multiple routines.

Atomic Data Types:

BOOL 1-bit boolean 0 = cleared 1 = set

SINT 1-byte integer -128 to 127

INT 2-byte integer -32,768 to 32,767

DINT 4-byte integer -2,147,483,648 to 2,147,483,647

REAL 4-byte floating-point number -3.402823E38 to -1.1754944E-38