Control Devices 211

actuate

To make a device or machine operate. Selector switches actuate contacts.

actuates

Makes a device operate or run. Pushbutton operators actuate electrical contacts.

actuator

The part of a limit switch that comes into contact with an object and triggers the switch. Limit switch actuators come in different styles: rotary levers, forks, plungers, flexible loops, and spring rods.

air compressors

A component that pressurizes ambient air. Air compressors direct pressurized air into pneumatic systems.

automatic control

A control device that runs independently of an operator. Automatic control devices receive signals from other devices that tell them when to start a process.

automatic inputs

A control device that is set to determine and manage each step in a process independently. Automatic inputs include pressure switches, flow switches, and temperature switches.

bellows

A cylindrical device with several deep folds that expand or contract in response to pressure. Bellows are usually used at medium pressure.

bimetallic sensor

Also known as a bimetallic strip, a sensor made of two unlike bonded metals that expand at different rates when heated. Bimetallic sensors provide a physical signal that the sensor converts into an electrical signal.

bimetallic strip

Also known as a bimetallic sensor, a sensor made of two unlike bonded metals that expand at different rates when heated. Bimetallic strips provide a physical signal that the sensor converts into an electrical signal.

capacitive proximity switches

A control device that is triggered when it detects either conductive or nonconductive substances. Capacitive proximity switches are able to detect both solid and liquid materials.

capillary tube sensor

A sensor that changes internal pressure when temperature changes. Capillary tube sensors use temperature sensitive liquid.

chatter

The occasional unwanted vibration between components. Chatter decreases machining productivity, negatively impacts surface quality, and increases tool wear.

circuit conditions

The different options that selector switches allow technicians to choose. Circuit conditions may include options such as "left/right," "up/down," "manual/automatic," and "on/off."

CNC machines

Computer numerical control machine. A machine controlled by a computer that performs a series of operations. CNC machines contain control devices such as switches to help them function safely.

coils

Wire that is wrapped around a magnetic core. Coils conduct electrical current in a circuit.

cold junction

The end of a thermocouple that provides a reference point. The cold junction is held at a constant temperature.

contact

A conductive metal part that opens or closes a circuit by separating from or touching a matching part. Contacts are components of electrical circuits.

contact blocks

Pushbutton components that hold contacts and are activated when pushbuttons are pressed. The most common contact block has one normally open (NO) and one normally closed (NC) contact.

contactor

A device that uses a small control current to energize or de-energize a load. Contactors can handle high amounts of current and are also combined with overload relays to create motor starters.

control devices

Any input device that controls the flow of current in a circuit. Control devices determine when loads are energized or de-energized.

control relay

An electrical switch that opens and closes a circuit. Relays can open or close one or many sets of contacts.

cooling lines

A passage through which cooling fluid is circulated. Cooling lines assist in maintaining the desired temperature in a system.

current

The flow of electricity through a circuit. Current in a circuit can be controlled by control devices.

deadband pressure

The amount of pressure that must change before pressure switch contacts reset after actuation. Deadband pressure is also referred to as differential pressure.

diaphragm

A spring-loaded valve mechanism that moves in response to variations in pressure in a pneumatic system. The diaphragm is a flexible membrane that responds to pressure changes.

digital multimeter

DMM. A device that can measure voltage, current, or resistance. A digital multimeter is the most versatile and common meter used today for electrical maintenance.

eddy currents

A magnetic current created by sensor vibration. Eddy currents flow out and around the head of a sensor.

electrical circuit

A controlled path that contains electrical current. Electrical circuits are controlled by control devices.

electrical control devices

A type of control device that senses the presence of an object without touching it. Electrical control devices include proximity switches and photoelectric switches.

emergency stops

E-stop. A switch or button that brings a machine to a safe, rapid stop. Emergency stops are often mushroom button operators.

extended button operator

A pushbutton operator whose button extends beyond its guard. Extended button operators are used in situations where accidental startup is not dangerous.

float

A device used in switches that floats on liquid. Floats rise or fall based on the level of the liquid.

flow switches

A switch that detects the movement of any fluid, such as liquid, gas, or air, in a system. Flow switches are commonly used in fluid pumps and air compressors.

flow switches

A switch that detects the movement of any fluid, such as liquid, gas, or air, in a system. Flow switches are commonly used in fluid pumps and compressors.

fluid pumps

A mechanical device that is used to move liquids or gases. Fluid pumps are used in hydraulic and pneumatic systems.

flush button operator

A pushbutton operator that has a guard ring that sits at the same level as the operator. Flush button operators are used in situations where accidental startup is dangerous.

guard ring

The piece of circular material surrounding a flush button operator. Guard rings prevent unintentional starting of an operation or machine.

hot junction

The end of a thermocouple that measures temperature. The hot junction is exposed to the elements.

hydraulic

A system that uses liquids to transmit power. Hydraulic systems rely on fluid force to run different systems.

indicator light

A device that lights up to signal something. Indicator lights may flash when normally open (NO) contacts close.

inductive proximity switches

A control device that is triggered when it detects a conductive substance. Inductive proximity switches operate using eddy currents.

inputs

A device that enters in and contributes to a process. Inputs are a type of control device.

jog/off/run

A common circuit condition that lets a technician run a machine intermittently, power it down, or run it consistently. "Jog/off/run" is a common circuit condition on a three-position selector switch.

jog/run

Circuit conditions that allow a technician to make a machine function intermittently or consistently. The "jog/run" choice of conditions is the most common set of conditions on a two-position selector switch.

legend plate

The part of a switch that displays the function of the switch's operation. Legend plates surround pushbuttons.

level switches

A device that detects the height of a liquid or solid in a tank or another type of vessel. The most common type of level switch is the mechanical level switch.

light source

A device that emits beam of light received by a photosensor. Light sources are used to trigger photoelectric sensors.

limit switch actuator

The part of a limit switch that contacts an object and triggers the switch to perform an action. Limit switch actuators come in two different categories: rotary and plunger.

limit switches

A switch that detects the presence an object by physically touching it. Limit switches have a variety of actuators that come into contact with an object.

load

A device that converts electricity into light, heat, or mechanical motion. Loads are components of electrical circuits.

lower set level

The minimum level at which a technician has set a pressure switch to operate. Once pressure has reached the lower set level, contacts will close or open and remain in that condition until pressure rises.

manual control

A control device that requires an operator to activate or deactivate it. Manual control devices include pushbuttons.

manual inputs

A control device that requires individuals to press a button or turn a switch. Manual inputs include pushbuttons and selector switches.

mechanical control

A device that must make physical contact with an object to operate. Mechanical control devices include limit switches.

mechanical control devices

A device that physically contacts objects. Mechanical control devices include limit switches, flow switches, and level switches.

mechanical inputs

A control device that must touch an object in order to detect it. Mechanical inputs include limit switches.

mechanical level switch

A device that uses a float to trigger electrical contacts. Mechanical level switches are used to detect liquid levels when they reach a set height.

motor starter

An electrically operated switch that uses magnetic induction to provide the startup current for a motor.

mushroom button operator

A pushbutton operator that extends beyond its guard. Mushroom button operators have large, rounded heads and can be easily accessed.

NC contacts

Normally closed contacts. Electrical devices that allow electricity to flow. When an NC contacts open, electricity stops flowing.

NO contacts

Normally open contacts. Electrical devices that prevent electricity from flowing. When NO contacts close, electricity starts flowing.

normally closed

NC. An electrical contact that allows electricity to flow. If an NC contact opens, electricity stops flowing.

normally open

NO. An electrical contact that does not allow electricity to flow. If an NO contact closes, a circuit may be formed.

operator

The part of a switch that is pressed, pulled, or turned by an individual operating the circuit. Operators come in a variety of styles and sizes.

output

An activity or result of a process. Outputs triggered by contacts closing can range from the flashing of an indicator light to the sounding of a warning bell.

paddle

A hinged actuator used in many types of flow switches. The flow of fluid deflects the paddle, actuating the flow switch contacts.

photoelectric sensors

A control device, also known as a photoelectric switch, that detects the presence of an object through the use of a beam of light. When the beam of light is interrupted, the sensor sends a signal through the circuit that affects the operation of the machine in a specific way.

photoelectric switches

A control device, also known as a photoelectric sensor, that detects the presence of an object through the use of a beam of light. When the beam of light is interrupted, the switch sends a signal through the circuit that affects the operation of the machine in a specific way.

photoelectric switches

A switch that uses a light beam to detect the presence of an object without touching it. Photoelectric switches can detect lightweight objects, heavy objects, or objects that are too hot.

photosensor

A control device that detects light. Photosensors detect the presence of an object using a beam of light.

piston

A piece of metal that moves up and down inside a hollow cylinder in response to a pressure change in pneumatic and hydraulic systems. Pistons may be used to transfer motion to brake components.

plunger actuators

A limit switch actuator in the form of a button that is depressed to activate the switch. Plunger actuators come in three basic styles.

pneumatic

A system that uses gases to transmit power. Pneumatic systems rely on gas to run a system.

power source

A device that generates electricity. Power sources are components of electrical circuits.

pressure sensing devices

A control device that is designed to detect a range of pressures in motor control systems. Pressure sensing devices include diaphragms, bellows, and pistons.

pressure switches

A device that detects a certain amount of force and activates electrical contacts when the force is reached. Pressure switches have different sensing devices that detect pressure changes.

pressure switches

A switch that detects a certain amount of force and activates electrical contacts when the force is reached. Pressure switches have different sensing devices that detect pressure changes.

proximity sensors

A control device, also called a proximity switch, that uses an electronic sensing field to sense the presence of an object without touching it. Proximity sensors can detect the presence of almost any liquid or solid.

proximity switches

A control device, also called a proximity sensor, that uses an electronic sensing field to sense the presence of an object without touching it. Proximity switches can detect the presence of almost any liquid or solid.

proximity switches

A switch that uses an electronic sensing field to sense the presence of an object without touching it. Proximity switches can detect the presence of almost any liquid or solid.

pushbutton

A manual control device that opens or closes a circuit when pressed. Pushbuttons can be normally open or normally closed.

pushbuttons

Manual control devices that open or close a circuit when pressed. Pushbuttons can be normally open or normally closed.

receiver

A mechanism designed to receive light. When receivers do not receive light from the photosensor, an object or person is in its path.

relay

An electrically controlled mechanical device that controls one circuit by opening or closing contacts in another circuit. Relays can open or close one or many sets of contacts.

resistance

The opposition to current flow. Electricity flows in the path of least resistance.

resistor

A device that restricts current flow. Resistors produce work, such as heat or light.

rotary actuators

A limit switch actuator with a handle that directs force in a circular motion. Rotary actuators come in a range of styles and sizes to be used in a variety of applications.

selector switch

A device that can be turned to different positions to make a connection with contacts in that particular position. Selector switches allow technicians to operate machines under different conditions.

selector switches

A switch that can be turned to different positions to make connections with the contacts in that particular position. Selector switches can allow technicians to operate machines under different conditions.

short

A circuit where current takes a shorter, unintended path between two conductors. Shorts, also known as short circuits, cause excess current flow.

stop plate

A metal guard plate connected to a limit switch that prevents damage to the switch. Stop plates keep limit switches from being forced beyond their travel limit.

surface grinder

A machine that uses a rotating wheel to wear away precise amounts of a flat workpiece surface. Surface grinders rely on limit switches to keep them from being damaged.

switch

A control device that can make or break a circuit by closing or opening. Switches can be manual, mechanical, or automatic.

temperature switches

A switch that reacts to different heat intensities and activates electrical contacts when the temperature rises above or drops below a set level. Temperature switches are often used in heating and cooling systems.

thermistor

A resistor that is temperature sensitive. As the temperature changes, the resistance of a thermistor changes.

thermocouple

A temperature sensor that measures heat at a hot junction and outputs voltage at a cold junction. Thermocouples output voltage that is proportional to the measured temperature.

three-position selector

A selector switch that allows you to select one of three circuit conditions. The third position is usually "off," as in "forward/reverse/off."

two-position selector

A selector switch that allows a technician to select one of two circuit conditions. Common two-position selector switches are "on/off" and "forward/reverse."

upper set level

The maximum level at which a technician has set a pressure switch to operate. Once pressure has reached the upper set level, contacts will close or open and remain in that condition until pressure falls.

workpiece

A part that is worked on during manufacturing processes. Workpieces may be subjected to cutting, welding, forming, or other operations.