# Basic Programming 250

This class will teach you the basics of PLC programming using ladder logic. The class will identify common PLC commands and describe how those commands can be used to program a controller.

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## Class Details

Class Name:
Basic Programming 250
Version:
1.0
Difficulty:
Intermediate
Number of Lessons:
15
Spanish

## Class Outline

• Objectives
• Using PLCs
• Line Diagrams
• Proprietary Programming
• Programming Components
• Internal Relays
• Programming Devices
• Input Instructions
• Other Common Instructions
• Shorthand Programming
• Programming Limitations
• Power Flow
• Latching Contacts
• One Shots
• Summary

## Objectives

• Describe the use of PLCs.
• Define line diagrams.
• Explain proprietary programming.
• Distinguish between programming components and physical devices.
• Describe internal relays.
• Describe programming devices.
• Identify common PLC input instructions.
• Describe other common PLC instructions.
• Describe shorthand programming methods.
• Describe some limitations in PLC programming.
• Describe logical continuity in PLC systems.
• Describe latching contacts.
• Describe one shots.

## Glossary

Vocabulary Term Definition
concurrent parallel processing The conceptually simultaneous execution of more than one sequential program on a computer or network of computers.
contacts Conductive metal parts in an electrical circuit that open or close the circuit by coming in contact with or separating from each other.
count down counter Decreases the current value by an increment of 1 every time an input transitions from FALSE to TRUE. Count down counters should always start counting at the preset value.
count up counter Increases the current value by an increment of 1 every time an input transitions from FALSE to TRUE. Count up counters are started from zero and continue counting until the accumulated value matches the preset value.
designator The label given to each element in ladder diagrams, used to reference that element throughout the program.
examine if closed A PLC input instruction that is true if its addressed bit is ON and false if it is OFF. The same instruction as examine on.
examine if open A PLC input instruction that is true if its addressed bit is OFF and false if it is ON. The same instruction as examine off.
examine off A PLC input instruction that is true if its addressed bit is OFF and false if it is ON. The same instruction as examine if open.
examine on A PLC input instruction that is true if its addressed bit is ON and false if it is OFF. The same instruction as examine if closed.
function block A graphical PLC programming language that allows for both sequential and parallel processing. Function block diagrams are starting to replace ladder logic in higher level PLCs.
hand-held programmer A PLC programming device that combines a display screen and keypad all in one unit. Specially assigned keys allow you to enter program instructions and changes, and navigate and troubleshoot the PLC system.
internal relay Software relays that can be used with ladder logic programs to perform logical operations. Internal relays are represented digitally within a PLC's memory.
ladder logic A method for drawing electrical logic schematics. Ladder logic is now most often used to program PLCs.
latched contact A contact that keeps the output energized even once the input signal is removed.
line diagram A diagram that shows the logic of an electrical circuit or system using standard symbols. Also known as a ladder diagram because the diagram appears as individual lines or "rungs" connected between two vertical lines.
logical continuity The way that PLC programming logic allows power to flow. PLC logical continuity always reads a program from left to right.
memory The ability of a circuit to store a charge and keep the load energized even after the signal is removed.
mnemonic An instruction that is presented in a short, easy-to-remember form.
momentary contact A contact that returns to its original position immediately after sending a signal.
network A group of connected logic elements used to perform a specific function.
one shot A series of ladder instructions that energizes an output for one scan only.
one shot rising A one shot instruction that is triggered when the programmed input transitions from OFF to ON.
output energize The most common PLC output symbol. Using this symbol signals the PLC to energize, or turn on, the output.
personal computer A small, single-user computer. Also known as a PC.
programmable logic controller A processor driven device that uses logic-based software to provide electrical control to machines and devices.
programming component Any component of a PLC software ladder program. Programming components do not physically exist but are representations used by the PLC software.
programming device A device, usually a personal computer, used to enter instructions into the PLC. Some programming devices are small enough to fit in your hand.
programming language A set of symbols and rules used to represent information to a processor so that it can understand and apply instructions.
proprietary Designed by a specific company for use only with its own systems.
register A group of bit data used to store information in a PLC's memory.
rising edge The point at which an AC signal wave transitions from low to high.
rung The horizontal programming lines in ladder logic. Each rung controls one output.
sequential Doing one and only one step at a time, followed by the next step in a logical order.
shorthand programming A programming method that saves time by using mnemonic names for instructions rather than having to search for the graphic symbols.
timer off delay A delay timer that immediately closes contacts when the control coil is energized, then waits for a predetermined amount of time to open them after power is removed from the coil.
timer on delay A timer that waits to turn on the output after receiving an ON signal from the input.
troubleshooting The systematic elimination of the various parts of a system, circuit, or process to locate a malfunctioning part.
vertical contact A contact that bridges a parallel path, shown up and down instead of left and right, on a line diagram. PLC programs cannot use vertical contacts.