# Logic and Line Diagrams 220

This class will teach you the basic rules for line diagrams and their common elements. You will also learn how line diagrams are put together and how they are referenced.

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## Class Details

Class Name:
Logic and Line Diagrams 220
Description:
This class will teach you the basic rules for line diagrams and their common elements. You will also learn how line diagrams are put together and how they are referenced.
Version:
1.0
Difficulty:
Intermediate
Number of Lessons:
15
Spanish
Related 2.0 Class:
Logic and Line Diagrams 312

## Class Outline

• Objectives
• What Is a Line Diagram?
• Rules for Line Diagrams
• Control Devices
• Line Numbers
• Cross-Referencing
• Wire and Terminal Numbers
• Mechanically Connected Contacts
• Control Circuit Steps
• Logic Functions
• AND and OR
• NAND and NOR
• Memory
• Troubleshooting
• Summary

## Objectives

• Define line diagram.
• Describe the rules for line diagrams.
• Describe control devices.
• Describe line numbers in diagrams.
• Explain how line diagrams cross-reference contacts.
• Identify wire and terminal numbers on a line diagram.
• Describe methods used to show mechanically connected contacts on line diagrams.
• Identify the steps of a control circuit.
• Describe logic functions in control circuits.
• Distinguish between AND and OR circuit logic.
• Distinguish between NAND and NOR circuit logic.
• Describe troubleshooting in control circuits.

## Certifications

MSSC
• MSSC Maintenance Awareness

## Glossary

Vocabulary Term Definition
action The third step of a control circuit. Actions are the physical work performed as loads are energized.
AND A type of circuit logic where both normally open control devices must be closed to energize the load. Control devices are connected in series in AND logic.
automatic signal A type of signal that is sent when an input device detects a change in conditions such as flow, pressure, or temperature.
auxiliary contact An additional motor starter contact used to provide memory to control circuits. When energized, the motor starter closes the auxiliary contact, maintaining a closed circuit.
control device Any input device that controls the flow of current in a circuit. Control devices determine when loads are energized or de-energized.
counter A device that keeps track of the number of entering inputs and provides an output when a preset count is reached. Counters also usually display the counted value.
cross-reference number The numbers on the right side of a line diagram that reference contacts in other circuit lines that electrically connect the load in the referenced line. Numbers that cross-reference normally closed contacts are underlined.
dashed line method A method of cross-referencing mechanically connected contacts that operate together but on different lines of the diagram. The dashed line method is used on simple diagrams when the contacts are close together.
decision The second step of a control circuit. Decisions are based on the signals received and the logical functions designed in the circuit.
digital multimeter A device that can measure voltage, current, or resistance. A multimeter is the most versatile and common meter used today.
dual palm buttons Two separate buttons that must be pressed simultaneously in order to power stamping presses. This is an example of AND logic.
hard-wired Having physical connections that are designed to act the same way over and over.
ladder diagram Another name for a line diagram, due to its resemblance to a ladder. In this sense, each circuit line is a "rung" of the ladder.
limit switch A mechanical input that requires physical contact of the object with the switch actuator.
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.
line number The sequential numbers running down the left side of a line diagram. Each line, or rung, of the line diagram has its own number.
load Any device that converts electrical energy to motion, heat, light, or sound. A motor starter coil and a pilot light are both examples of loads.
logic function The sequence of operations performed by a circuit. Logic functions such as AND and OR follow a set, predictable pattern.
manual signal A type of signal that you send to a circuit through physical action. Flipping a light switch or pressing a pushbutton are manual signals.
mechanical signal A type of signal that is sent through the mechanical motion of a machine. A gear contacting a limit switch is an example of a mechanical signal.
memory The ability of a circuit to store a charge and keep the load energized even after the signal is removed.
momentary contact A contact that returns to its original position immediately after sending a signal.
motor starter An electrically operated switch that uses magnetic induction to provide the startup current for a motor.
NAND A type of circuit logic where both normally closed control devices must be opened to de-energize the load. Control devices are connected in parallel in NAND logic.
NOR A type of circuit logic where only one normally closed control device must be opened to de-energize the load. Control devices are connected in series in NOR logic.
normally closed An electrical contact that regularly allows electricity to flow.
normally closed contact An electrical contact that regularly allows electricity to flow until it is signaled to open.
normally open An electrical contact that rarely allows electricity to flow.
NOT A type of circuit logic that uses normally closed contacts.
numerical cross-reference method A method of cross-referencing mechanically connected contacts that operate together but on different lines of the diagram. The numerical cross-reference method is used on complex diagrams when the connected contacts are several lines apart.
OR A type of circuit logic where only one normally open control device must be closed to energize the load. Control devices are connected in parallel in OR logic.
overload contact A normally closed contact placed in series between a load and the neutral line of a circuit. Overload contacts open only when an overload condition is present.
pushbutton A manual control device that opens or closes a circuit when pressed. Pushbuttons can be normally open or normally closed.
relay A device that controls one electrical circuit by opening and closing contacts in another circuit.
signal The first step of a control circuit. Signals are inputs that change the condition of a circuit.
specification A description of the essential physical and technical properties of a machine. Specs are the principle indicator of machine capability.
switch A control device that can make or break a circuit by closing or opening. A switch can be either manual, mechanical, or automatic.
terminal number A number assigned by a manufacturer to a device's contact points. Terminal numbers help identify the connection points in a circuit.
tie-down method Connecting one probe of a DMM to the neutral side of a circuit and moving the other probe systematically along the sections of a circuit to find the malfunctioning part.
timer A device that delays the signal sent by a control device to a load for a preset amount of time.
troubleshooting The systematic elimination of the various parts of a system, circuit, or process to locate a malfunctioning part.
wire number A reference point on a line diagram used to keep track of the different wires that connect the components in the circuit. Wire numbers are circled and start with 1 from the top left of the diagram.