Control Devices 211

“jog/off/run”

A three-position selector switch that allows a technician to choose between jogging a computer numerical control machine, turning the machine off, or running its part program. “Jog/off/run” selectors improve safety compared to “jog/run” selectors since they have an added “off” option.

“jog/run”

A two-position selector switch that allows a technician to choose between jogging a computer numerical control machine or running its part program. “Jog/run” selectors are common two-position selector switches.

actuated

Made to operate or run. Electrical contacts are actuated to open or close a circuit.

actuator

The part of a limit switch that comes into contact with an object and triggers the switch to perform an action. Limit switch actuators come in many different styles that are generally categorized as either rotary actuators or plunger actuators.

air compressors

A component that pressurizes ambient air. Air compressors are used in pneumatic systems and cooling systems.

amperage

The amount of current flowing through a circuit. Amperage is measured in amperes (A), or amps.

amperes

A. A unit of measurement that indicates the amount of current flowing in a circuit. Amperes are also called amps.

automatic input

A method of actuating a control device that occurs when it receives a signal from a sensor. Automatic input devices include pressure switches and temperature switches.

ball float

A round device that rests on the surface of a liquid. Ball floats are used in float switches to detect changes in liquid level.

bellows

A cylindrical device with several deep folds that allow it to expand or contract in response to pressure changes. Bellows are used in pressure switches at medium pressure levels.

bimetallic sensor

A temperature sensor made of two different types of metal that are bonded together. A bimetallic sensor, also known as a bimetallic strip, curls when heated because the two different metals expand at different rates.

bimetallic strip

A temperature sensor made of two different types of metal that are bonded together. A bimetallic strip, also known as a bimetallic sensor, curls when heated because the two different metals expand at different rates.

Bourdon tube

A semicircular tube that inflates and straightens out in response to pressure changes. Bourdon tubes used in pressure switches actuate contacts when they straighten out.

capacitive proximity switch

A proximity switch that actuates in response to changes in the dielectric constant of the sensor. Capacitive proximity switches use electrostatic sensing fields and can detect both conductive and nonconductive targets.

capillary tube sensor

A temperature sensor that uses a fluid-filled tube and temperature-sensitive fluid to detect changes in temperature. In a capillary tube sensor, the fluid in the tube expands and exerts pressure on a force collector.

chatter

Occasional unwanted vibration between components. Chatter in a pressure switch can be caused by using a deadband pressure range that is too small.

circuits

A controlled path for electrical current. Circuits include a power source, loads, and control devices.

coils

Wire that is wrapped around a magnetic core. Coils conduct electrical current and generate heat when energized.

cold junction

The end of a thermocouple that acts as a reference point and outputs a voltage signal. The cold junction is held at a constant temperature.

conductive

Able to act as a path for the flow of electricity. Conductive materials, which include many types of metals, form magnetic fields when energized.

contact block

The part of a pushbutton assembly that holds the contacts controlled by the operator. The most common type of contact block has one set of normally open (NO) contacts and one set of normally closed (NC) contacts.

contactors

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

contacts

A conductive metal part used in pairs that opens or closes a circuit by separating from or touching a matching part. Contacts close to allow current flow and open to prevent it.

control devices

A component that controls the flow of electricity in a circuit. Control devices determine when loads are energized or de-energized.

control relays

An electrical switch that controls one circuit by opening and closing the contacts in another circuit. Control relays can handle up to 10 amperes (A) of current.

conveyor belt

A moving strip of material used to transport parts and materials from one location to another. Conveyor belts often use limit switches to control their movement and detect objects.

current

The flow of electricity through a circuit. Current strength is called amperage and is measured in amperes (A), or amps.

deadband pressure

The difference between the upper set level and lower set level of a pressure switch. Deadband pressure describes the amount pressure must change before pressure switch contacts reset after actuation.

diaphragm

A flexible membrane that deflects in response to pressure changes. Diaphragms are attached to springs for use in pressure switches.

dielectric constant

A value that represents how much electrical energy a material or object can store. Capacitive proximity sensors can detect any object with a dielectric constant greater than 1.2, which is the dielectric constant of air.

digital multimeter

DMM. An electrical instrument that can measure voltage, current, and resistance. A digital multimeter is an important tool for troubleshooting circuits.

eddy currents

A swirling electrical current generated when a conductive object enters an electromagnetic field. Eddy currents cause a dampening, or shrinking, of the original electromagnetic field.

electrical control devices

A device that actuates contacts without the need for physical contact or moving parts. Electrical control devices include proximity switches and solid-state pressure switches.

electromagnetic field

An area of force in and around an energized conductor that exhibits magnetic and electrical properties. Electromagnetic fields are used by inductive proximity switches.

electrostatic field

An area of potential electrical force surrounding an object. Electrostatic fields are used by capacitive proximity switches.

emergency stops

E-stops. A control device that brings a machine to a safe, rapid stop. Emergency stops are often pushbuttons with mushroom button operators.

extended button operator

A pushbutton operator that is taller than its guard. Extended button operators are used when accidental startup is not dangerous.

fire suppression sprinklers

An automated network of pipes, valves, and/or nozzles designed to prevent the spread of fire. Fire suppression sprinklers automatically deliver water or other extinguishing substances to areas where flames are present.

float switch

A level switch that uses a ball float to detect the level of liquid in a tank. Float switches are often used in sump pump systems.

flow switches

An automatic control device that actuates in response to changes in fluid movement. 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 is the same height as its guard ring. Flush button operators are used when accidental machine startup is dangerous.

force collector

A mechanism that is deflected or displaced a proportional amount in response to applied pressure. Force collectors, such as diaphragms and bellows, are used to measure pressure and actuate pressure switches.

frequency

A measurement of the number of times a waveform repeats in one second. Frequency is measured in hertz (Hz).

guard ring

A circular component that surrounds a pushbutton operator. Guard rings prevent unintentional starting of an operation or machine.

heat pumps

A device that uses mechanical energy to transfer thermal energy from a colder area to a warmer area. Heat pumps can be used to provide both heating and cooling.

hot junction

The end of a thermocouple that is exposed to different temperatures. The temperature of the hot junction determines the voltage the thermocouple outputs.

hydraulic

Powered by pressurized liquid. Hydraulic systems rely on pressure switches for many functions.

indicator light

A device that illuminates to signal a change in conditions. Indicator lights may be used to signal a desired condition has been reached.

inductive proximity switch

A proximity switch that actuates in response to disturbances in the sensing field caused by eddy currents. Inductive proximity switches use electromagnetic sensing fields and can only detect conductive targets.

infrared

IR. Invisible light energy with a wavelength slightly longer than visible red light. Infrared light is emitted by heated objects.

input

The method used to actuate a control device. Inputs for control devices can be manual, mechanical, or automatic.

jogging

Moving a machine component manually through the use of machine controls such as buttons or a handle. Jogging allows a technician to carefully position components using small, precise movements.

laser

A device that generates an intense beam of light that can be precisely aimed and controlled. Laser beams are used in some photoelectric proximity switches.

legend plate

A flat component with labels that identify the functions of a control device. Legend plates typically surround the operators of manual input devices like pushbuttons and selector switches.

level switches

An automatic control device that actuates when it detects certain levels of substances inside a container. Level switches such as the float switch are often used to detect the level of liquid in tanks.

limit switches

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

load

A component that converts electricity into light, heat, or mechanical motion. Loads include light bulbs and motors.

manual input

A method of actuating a control device that requires physical contact with a person. Manual input devices include pushbuttons and selector switches.

mechanical control devices

A device with moving parts that physically change position to actuate contacts. Mechanical control devices include pushbuttons, limit switches, flow switches, and level switches.

mechanical input

A method of actuating a control device that requires it to make physical contact with an object. Mechanical input devices include limit switches.

motor starter

A device that provides the startup current for a motor. A motor starter consists of a contactor combined with an overload relay.

mushroom button operator

A pushbutton operator that is both wider and taller than its base. Mushroom button operators have large, rounded heads that are easy to access.

NC

Normally closed. A set of electrical contacts that generally allows electricity to flow. NC contacts typically open to de-energize a circuit.

NO

Normally open. A set of electrical contacts that generally does not allow electricity to flow. NO contacts typically close to energize a circuit.

nonconductive

Unable to act as a path for the flow of electricity. Nonconductive materials include plastic, glass, and wood.

normally closed

NC. A set of electrical contacts that generally allows electricity to flow. Normally closed contacts typically open to de-energize a circuit.

normally open

NO. A set of electrical contacts that generally does not allow electricity to flow. Normally open contacts typically close to energize a circuit.

open circuit fault

A type of electrical fault that prevents current from flowing through a circuit. Open circuit faults are often caused by broken wires or malfunctioning switches.

operators

The part of a manual control device that is pressed, pulled, or turned by an individual to acuate its contacts. Operators come in a variety of styles and sizes.

outputs

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

overload relay

A control relay used to prevent a motor from overheating by de-energizing it if overload conditions occur. Overload relays are combined with contactors to form motor starters.

paddle

A device used to detect changes in the flow of liquid. Moving liquid displaces the paddle and activates contacts in a flow switch.

photoelectric proximity switch

A proximity switch that uses changes in light to detect the presence of an object. Photoelectric proximity switches use a phototransmitter to emit a beam of light directed at a photoreceiver.

photoreceiver

The component of a photoelectric switch that detects light energy. The photoreceiver may be in a separate unit or enclosed in the same unit as the phototransmitter.

phototransmitter

The component of a photoelectric switch that emits a beam of light. The phototransmitter may be in a separate unit or enclosed in the same unit as the photoreceiver.

piston

A metal rod that moves up and down inside a hollow cylinder in response to pressure changes. Pistons are used in pressure switches at high pressure levels.

plunger actuators

A limit switch actuator in the form of a button that is depressed to activate contacts. Plunger actuators come in a variety of styles, the most common of which is the standard plunger actuator.

pneumatic

Powered by pressurized gas. Pneumatic systems rely on pressure switches for many functions.

power source

A component that provides electricity to a circuit. Power sources include batteries and generators.

pressure switches

An automatic control device that actuates when it detects a specified level of pressure. Pressure switches are commonly used in hydraulic and pneumatic systems.

pressure transducer

An electromechanical pressure switch that uses a force collector and solid-state components to output signals in response to changing pressure. A typical pressure transducer uses a diaphragm bonded to semiconductor strain gauges.

proximity sensors

A non-contact sensing device that detects the presence of an object based on electrical signals. Proximity sensors include inductive, capacitive, photoelectric, and ultrasonic sensors, among others.

proximity switches

An automatic electrical control device that uses electrical signals to detect the presence of an object and trigger outputs. Proximity switches can detect the presence, or absence, of almost any liquid or solid without touching it.

pushbuttons

A manual control device that opens or closes a circuit when pressed. Pushbuttons have an operator that opens or closes contacts in an attached contact block.

relays

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

resistance

The opposition to current flow. Changes in resistance levels can be used to send electrical signals that activate switches.

resistor

A device that opposes and restricts current flow. Resistors convert current into work, such as heat or light.

rotary actuators

A limit switch actuator in the form of a lever that directs force in a circular motion to activate contacts. Rotary actuators come in a range of styles, the most common of which is the standard roller lever.

sail

A device used to detect changes in the flow of gas, such as air. Moving air displaces the sail and activates contacts in a flow switch.

selector switches

A manual input control device that can be turned to different positions to operate the contacts in each particular position. The different positions of a selector switch correspond to different circuit conditions.

semiconductor

A material that has more electrical conductivity than an insulator but less conductivity than a conductor. Semiconductors are used in many solid-state devices, including strain gauges.

sensing field

The area around a sensor that exhibits certain properties used to detect objects. Sensing fields used by proximity switches include electromagnetic fields and electrostatic fields.

short circuit fault

A type of electrical fault that causes current to flow along an unintended path between two conductors. Short circuit faults can be caused by damaged insulation, unintentional contact between conductors, or water coming into contact with circuits.

solid-state

A device that functions purely electronically and contains no moving parts. Solid-state devices operate on electrical signals rather than physical movement.

solid-state pressure switch

An electrical pressure switch that uses semiconductor strain gauges to measure pressure and output signals. In solid-state pressure switches, changing pressure changes electrical resistance.

sound waves

A vibration, or disturbance, of matter caused by the movement of energy. Ultrasonic proximity switches use high-frequency sound waves to detect the position of an object.

standard plunger actuator

A plunger limit switch actuator that consists of a simple depressible button on the top, bottom, or side of a limit switch. Standard plunger actuators are the most common type of plunger actuator.

standard roller lever

A rotary limit switch actuator that consists of a single lever with a rotating wheel at its end. Standard roller levers are the most common type of rotary actuator.

stop plate

A flat metal guard mounted to a plunger-type limit switch that prevents the actuator from moving beyond its travel limit. Stop plates help prevent limit switches from being damaged.

strain gauges

A device that uses changing electrical resistance to measure the amount of strain within an object. Strain gauges are used in solid-state pressure switches and pressure transducers.

sump pump systems

A group of components used to collect liquid in a low-lying reservoir and move it to a different location. Sump pump systems use level switches that activate the pump when they detect certain levels of liquid.

surface grinders

A machine tool that uses a rotating wheel to wear away precise amounts of a flat workpiece surface. Surface grinders with reciprocating tables use limit switches to control table movement.

switches

A control device that opens or closes contacts to make or break a circuit. Switches can be manual, mechanical, or automatic.

table

The part of a surface grinder that directly or indirectly supports the workpiece. Movement of the table can be controlled by a limit switch.

temperature switches

An automatic control device that actuates when it detects specified temperature levels. Temperature switches are often used in heating and cooling systems.

thermal dispersion flow switch

A solid-state control device that uses two temperature sensors to detect flowing fluid. A thermal dispersion flow switch has one sensor that provides a reference temperature and another sensor that is heated and whose temperature falls as flow rate increases.

thermistor

A resistor whose electrical resistance changes in response to temperature changes. The resistance of a thermistor typically decreases and allows more current through as temperature increases.

thermocouple

A temperature sensor that outputs a temperature-dependent voltage at one end in response to temperature changes at the opposite end. Thermocouples expose the hot junction to different temperatures and output voltage at the cold junction.

three-position selector switch

A selector switch that allows a technician to choose between three circuit conditions. Three-position selector switches are often similar to two-position selector switches but usually include an “off” position to increase safety.

transducer

A device that converts one form of energy, such as electricity, into another, such as mechanical motion. Ultrasonic proximity switches use transducers to produce sound waves and convert sound into electrical signals.

transistors

An electrical device that amplifies electrical signals or switches current on and off. Transistors are used in solid-state control devices.

troubleshooting

The systematic elimination of the various parts of a malfunctioning system, circuit, or process to locate the source of the problem. Troubleshooting an electrical circuit often involves using a digital multimeter (DMM).

two-position selector switch

A selector switch that allows a technician to choose between two circuit conditions. Common two-position selector switches include “on/off” and “forward/reverse.”

ultrasonic proximity switch

A proximity switch that detects objects by sending out a series of high-frequency sound bursts and interpreting the sound that is returned to it. Ultrasonic proximity switches use sound waves that are beyond the range of normal human hearing.

voltage

The electrical force or pressure that forces current to flow in a circuit. Voltage is measured in volts (V).

workpiece

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