action |
The third step of a control circuit. Actions are the physical work a circuit performs as loads are energized. |
AND |
A type of circuit logic where two normally open contacts are connected in series. With AND logic, both contacts must be closed to energize the load. |
automatic signal |
A circuit input sent when a device detects a change in conditions. Automatic signals are sent by flow, pressure, and temperature switches. |
auxiliary contact |
A motor starter contact used to provide memory to control circuits. Auxiliary contacts close when a motor starter is energized, and they stay closed until another signal opens them. |
circuit lines |
The parallel horizontal paths in a line diagram on which circuit components appear. Circuit lines stretch between the live power line, L1, and the neutral return power line, L2. |
circuits |
A controlled path for electricity. A circuit includes a source, path, load, and control. |
contacts |
Connecting points between two conductors that allow electricity to flow when they are closed. Contacts prevent the flow of electricity when open. |
control circuits |
An electrical system that uses control devices to determine when loads are energized or de-energized by controlling current flow. Control circuits usually carry lower voltages than power circuits. |
control device |
An input device that controls the flow of current in a circuit. Control devices determine when loads are energized or de-energized. |
control relays |
CR. An electrically controlled mechanical device that controls one circuit by opening and closing contacts in another circuit. Control relays often use electromagnetic coils to open and close contacts. |
cross-reference number |
A number that identifies other circuit lines that electrically connect to the load in the referenced line. Cross-reference numbers appear on the right side of a line diagram. |
cross-referencing |
The practice of referring from one part of a diagram to another. Cross-referencing helps identify contacts in a line diagram. |
dashed line method |
A technique used to cross-reference mechanically connected contacts by drawing a dashed line between them. The dashed line method is used on simple diagrams when the contacts are located near each other on the diagram. |
decision |
The second step of a control circuit. Decisions are based on the received signals and the logic functions in a circuit. |
diagrams |
A drawing that illustrates the parts or operation of something. Motor diagrams use pictures and symbols to represent motor components. |
digital multimeter |
DMM. A device that can measure voltage, current, or resistance. A digital multimeter is used to troubleshoot a circuit with the tie-down method. |
dual palm buttons |
A device with two separate buttons that must be pressed simultaneously in order to power a stamping press. Dual palm buttons use AND logic. |
flow switch |
A switch that actuates automatically when it senses the movement of fluids. Flow switches sense the movement of air or liquid in a duct or pipe. |
hard-wired |
Having wires that are physically connected to other devices or wires so as to consistently function the same way. Hard-wired circuits perform the same tasks over and over again. |
ladder diagrams |
An electrical print that shows the logic of an electrical circuit or system using standard symbols. Ladder diagrams are also known as line diagrams. |
lead |
A conductive device within a circuit or device to which other components can be attached. A lead has either a negative or positive charge. |
limit switch |
A switch that detects the presence or absence of an object. Limit switches operate mechanically. |
line diagram |
An electrical print that shows the logic of an electrical circuit or system using standard symbols. Line diagrams are also known as ladder diagrams. |
line number |
A number that identifies a circuit line in a line diagram. Line numbers run sequentially down the left side of a line diagram. |
load |
A device that converts electrical energy to motion, heat, light, or sound. Loads include motors and pilot lights. |
logic |
The reasoning behind the functioning of something. The logic of a circuit comprises all the principles required to understand electrical circuitry. |
logic function |
A sequence of operations that a circuit performs. Logic functions follow a set, predictable pattern. |
manual signal |
A circuit input sent by physical action. Manual signals are sent by light switches and pushbuttons. |
mechanical signal |
A circuit input sent by the mechanical motion of a machine. A mechanical signal is sent by a gear contacting a limit switch. |
memory |
The ability of a circuit to store a signal and keep the load energized even after the signal is removed. Memory circuits use auxiliary contacts. |
momentary contact |
A contact that returns to its original position immediately after sending a signal. Momentary contacts close when a pushbutton is depressed but open as soon as it returns to its original position. |
motor starter |
An electrically operated switch that starts a motor when actuated. Motor starters use magnetic induction to provide the startup current for a motor. |
NAND |
A type of circuit logic where two normally closed contacts are connected in parallel. In NAND logic, both contacts must be opened to de-energize the load. |
NC |
Normally closed. An electrical contact that generally allows electricity to flow. An NC contact symbol has parallel lines with a diagonal line crossing them. |
NO |
Normally open. An electrical contact that does not generally allow electricity to flow. An NO contact symbol has parallel lines with an opening between them. |
NOR |
A type of circuit logic where two normally closed contacts are connected in series. In NOR logic, only one contact must be opened to de-energize the load. |
normally closed |
NC. An electrical contact that generally allows electricity to flow. A normally closed contact symbol has parallel lines with a diagonal line crossing them. |
normally open |
NO. An electrical contact that does not generally allow electricity to flow. A normally open contact symbol has parallel lines with an opening between them. |
NOT |
A type of circuit logic that uses normally closed contacts. NOT logic functions are either NAND or NOR. |
numerical cross-reference method |
A technique used to cross-reference mechanically connected contacts by indicating associated contacts' line numbers and pointing toward the lines. 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 two normally open contacts are connected in parallel. With OR logic, only one contact must be closed to energize the load. |
overload condition |
A situation in which current exceeds recommended levels. Overload conditions can cause devices to overheat. |
overload contacts |
OL. A normally closed contact that opens only when an overload condition is present. Overload contacts are sometimes placed in series between a load and the neutral line of a circuit. |
overload relay |
A control relay that protects a motor from overheating due to overload conditions in the machinery. Overload relays connect to contacts that open when overload conditions are detected. |
parallel |
An electrical route that has multiple paths. Parallel circuit lines in line diagrams each have their own number. |
pilot lights |
A type of indicator light found on machines. Pilot lights typically indicate when a device is energized or operating. |
pressure switch |
A switch that actuates automatically when it senses changes in pressure. Pressure switches are used in pneumatic and hydraulic systems. |
pushbuttons |
A manual control device that opens or closes a circuit when pressed. Pushbuttons can be normally open or normally closed, like other switches. |
rails |
The vertical paths in a line diagram that represent a circuit's power supply. The rails consist of L1, the live power line, and L2, the neutral return power line. |
series |
An electrical route that has only one path. Series connections in line diagrams may have multiple control devices but not multiple loads. |
signal |
The first step of a control circuit. Signals are inputs that change the condition of a circuit. |
specifications |
A description of the essential physical and technical properties of a circuit or a device. Specifications are sometimes called specs. |
stamping presses |
A machine tool that moves up and down continuously to cut and shape sheet metal using a die set. Stamping presses often require dual palm buttons for starting. |
switches |
A control device that opens and closes contacts in a circuit. Switches can operate manually, mechanically, or automatically. |
symbols |
A sign or mark that represents something else. Symbols are often used to represent components in diagrams. |
temperature switch |
A switch that actuates automatically when it senses changes in temperature. Temperature switches are often used in heating and cooling systems. |
terminal |
A connecting point in a circuit where a wire can be attached to connect a component. Terminals are either negative or positive. |
terminal block |
A device that joins wires or cables. Terminal blocks typically snap into a metal rail or are mounted on the panel of a control enclosure. |
terminal number |
A number assigned to a contact point of a component to help identify the connection points in a circuit. Terminal numbers are assigned by the manufacturer of a device or by the engineer of a terminal block. |
thermostat |
A device that regulates temperature. A thermostat can be controlled manually or automatically. |
tie-down method |
A process of troubleshooting a circuit with a digital multimeter (DMM). The tie-down method works by connecting one lead of a DMM to the neutral line of a circuit and systematically moving the other lead along the circuit to find the malfunctioning part. |
troubleshooting |
The systematic elimination of the various components of a system, circuit, or process to locate a malfunctioning part. Troubleshooting a motor circuit often involves using electrical diagrams as a guide to find the problem area. |
voltage |
The electrical pressure or potential that pushes electrons through a conductor. Voltage is measured in volts (V) and is also called electromotive force. |
wire number |
A number that identifies a specific wire in a line diagram to indicate how components are connected. Wire numbers start with 1 on the top left of a diagram and may be circled on older diagrams. |