Limit Switches and Proximity Sensors 231
Limit Switches and Proximity Sensors introduces users to commonly used manufacturing sensors that detect the presence or absence of an object. Limit switches are mechanical sensors that require physical contact to be actuated. There are many variations of limit switches, including different operating mechanisms and environmental classifications. Proximity sensors, including inductive, capacitive, and Hall Effect sensors, do not require physical contact because they use an electronic or magnetic sensing field. These devices have different advantages and disadvantages and are used for various applications.
Limit switches and proximity sensors are widely used for automated systems in all types of industries. They are used to control speed and motion as well as detect, count, position, and divert parts. After taking this class, users will understand the function, application, and installation considerations for commonly used limit switches and proximity sensors.
Number of Lessons 23
- The Role of Sensors
- Limit Switches
- Limit Switch Classifications
- Parts of a Limit Switch
- Limit Switch Basics Review
- Limit Switch Actuators: Rotary
- Limit Switch Actuators: Plunger
- Limit Switch Operation
- Limit Switch Selection and Installation
- Specialized Limit Switch Applications
- Limit Switches Review
- Proximity Sensors
- Inductive Proximity Sensors
- Capacitive Proximity Sensors
- Inductive and Capacitive Proximity Sensor Review
- Shielded and Non-Shielded Proximity Sensors
- Proximity Sensor Range
- Proximity Sensor Installation
- Proximity Sensor Review
- Other Proximity Sensors
- Hall Effect Sensors
- Hall Effect Sensor Actuation
- Other Proximity Sensors Review
- Describe sensors.
- Describe limit switches.
- Describe different limit switch classifications.
- Describe the parts of a limit switch.
- Distinguish between types of rotary actuators.
- Distinguish between types of plunger actuators.
- Describe limit switch operation.
- Describe considerations for limit switch selection and installation.
- Describe specialized limit switches.
- Describe proximity sensors.
- Describe inductive proximity sensors.
- Describe capacitive proximity sensors.
- Distinguish between shielded and non-shielded proximity sensors.
- Describe factors that affect the sensing range of proximity sensors.
- Describe proper installation of proximity sensors.
- Describe other types of proximity sensors.
- Describe Hall Effect sensors.
- Describe how Hall Effect sensors work.
A limit switch component that contacts an object and triggers the switch to perform an action. Limit switch actuators include bumper arms, rotary levers, forks, plungers, flexible loops, and spring rods.
Capable of moving or being moved. Adjustable roller lever actuators are less durable than fixed roller lever actuators, but more applications can use them.
Connected to the surrounding area. Ambient sounds are sounds that occur in the normal course of events for a particular space.
The direction from which one object moves toward another. The approach of the target affects how operators should set a sensing range.
Performed by machines or computers with little human interaction. A process that is automated relies on sensors to ensure quality control, trigger machine action, and count parts, among other processes.
A target approaching the face of a proximity sensor at a 90° direction of travel. An axial approach may cause the target to contact the sensor.
A force that is exerted at a 90° angle. Axial forces, such as those created by an object being set down on an actuator, can activate limit switches with plunger actuators.
A digitally readable code that conveys information about an object using a specific sequence of linear bars. Barcodes can be read using optical scanners.
A non-plug-in limit switch component that houses the contacts and electrical circuitry. The body will need to be replaced if either its electrical contacts or circuitry malfunction or wear.
capacitive proximity sensors
A type of proximity sensor that detects a target based on changes in an electrostatic field. Capacitive proximity sensors can detect targets made of any material with a higher dielectric constant than air.
A component of a capacitive proximity sensor consisting of two metal plates that store electrical charges. The capacitor of a capacitive proximity sensor has a specific dielectric constant.
A completely enclosed electrical path. Circuits usually include a source, path, load, and control.
A completely enclosed path for electricity. Circuits usually include a source, path, load, and control.
The component of an inductive proximity sensor that consists of an electrically conductive material wrapped around a ferrite core. The coil is responsible for generating and shaping the electromagnetic field.
The makeup of an object, liquid, or other substance. The composition of an object determines how the sensing field for a proximity sensor should be set in order to detect that object.
Easily transfers or transits. Copper wire is conductive of electricity and heat.
A specification that describes what electrical setups are appropriate for a given limit switch. Contact ratings are based on the switch's electrical capacity and determined by the manufacturer, the International Electrotechnical Commission (IEC), and the National Electrical Manufacturers Association (NEMA).
A damaging, unwanted material or substance, such as dust or water, that causes wear to machine components. Contaminants can cause premature wear in the head or body of a limit switch.
A manual or automatic mechanism used to manage dynamic manufacturing processes by adjusting or maintaining physical variables such as velocity or positioning. Control systems often use proximity sensors to trigger actions based on the presence or absence of an object or material.
A device used to move items from one location to another. A conveyor belt's speed and direction of movement can be controlled using a sensor.
A ductile reddish metal that is thermally and electrically conductive. Copper is often used as the wire in the coil of an inductive proximity sensor.
Having the ability to erode or damage other materials. Corrosive substances can damage machine parts not rated to withstand them.
Interference between two sensors when one sensor unintentionally picks up the signal of another sensor. Cross-talk can cause poor sensor performance or false activation.
The flow of electricity. Current is measured in amperes or amps (A).
A device made of hard or tough material used to remove metal from a workpiece. Cutting tools include cutting inserts for the lathe and milling cutters.
The change in the directional flow of an electric current. Electricity cycles in alternating current (AC) but not in direct current (DC).
To lessen in intensity or shrink in size. Eddy currents have a dampening effect on the electromagnetic field of an inductive proximity sensor.
Flawed or unusable. A defective part can fail in a real-world application and should, therefore, be removed from production before it can leave the manufacturing facility.
Pushes or moves downward. Plunger-style actuators are activated when the weight or force of an object depresses the actuator.
An electrical circuit in an inductive proximity sensor that detects the size of the electromagnetic field. A detector is set to trigger the output circuit when an electromagnetic field shrinks to a specific size.
The distance from one edge of a circle to the opposite edge passing through the center. The diameter of a proximity sensor's face helps determine optimal target size.
The measure of how much electrical energy a material or object can store. Capacitive sensors can sense objects with dielectric constants greater than air, which has a dielectric constant of 1.2.
A device that increases the intensity of any source of voltage. A differential amplifier is essential to a Hall Effect sensor because the sensors produce too little voltage to reliably trigger the output function on their own.
The distance between the operating position and the release point. Differential travel indicates how long it takes for the contacts to fully reset to their initial open-or-closed state.
Changing an object's course of direction. Diverting defective parts from a production line ensures they do not leave the manufacturing facility.
An electromagnetic current generated when a metal object enters an electromagnetic field. Eddy currents cause a dampening, or shrinking, of the original electromagnetic field.
The amount and type of electricity a limit switch can safely and effectively process during its inactive and active states. Electrical capacity is a key consideration in assessing if a limit switch will fit a specific application.
A conductive device that opens or closes a circuit by either making contact with or separating from the main conductor. Electrical contacts are moved by a limit switch to complete or interrupt a circuit and perform a desired action.
An area of force that contains magnetic and electrical energy. Electromagnetic fields can be generated by running electricity through a wire wrapped around a ferrite core.
A negatively charged particle that orbits the nucleus of an atom. Electrons move between atoms to cause electrical flow.
The area of potential electrical force surrounding an object. The electrostatic field is used by capacitive proximity sensors to detect nearby objects.
E-stop. A switch that brings a machine to a safe and rapid stop. Emergency stops are important safety features that can be found on safety-cable pull switches or mounted on their own.
A condition of (or in) the surrounding area that can cause a manufacturing device to malfunction. Environmental hazards for limit switches include temperature fluctuations, humidity, and flying debris.
The flat sensing area at the end of the coil or capacitor. The face of the proximity sensor is always left uncovered by the metal sensor enclosure.
A catastrophic malfunction that prevents a component from operating correctly. Failure of limit switches can occur through normal wear and tear but also if the switch is subjected to excessive force or contamination.
A distinguishing characteristic that performs a function of a part. Features can be assessed by sensors to ensure parts meet specifications.
A ceramic compound that contains large amounts of iron. Ferrite is often used to make the core of the coil for inductive proximity sensors.
A metal in which iron is the main ingredient. Ferrous metals, including steel and cast iron, are the most commonly used commercial metal.
Set permanently in place. Fixed roller lever actuators have better durability than adjustable roller lever actuators, but fewer applications can use them.
A device that holds a tool, workpiece, or manufacturing component in place. Fixtures often hold limit switches in position during a manufacturing operation.
Having the ability to ignite easily and start a fire. Flammable materials must be insulated from the electricity in a limit switch to prevent sparking that can cause fire.
Set level, even, or in line with another object. Shielded proximity sensors can be set flush with mounting components because the shielding protects the sensor from interference.
A type of rotary actuator consisting of a V-shaped lever with a rotating wheel at each end. Forked-roller levers allow for increased application flexibility because they can be set to activate two distinct actions depending on which handle is moved.
The initial position of the actuator when no object or force is acting on it. The free position is usually where an actuator will be located for the first step of limit switch operation.
A force that resists motion between two objects that are in contact with each other. Excessive friction can increase the wear rates on mechanical parts, such as limit switches.
A circular toothed component that engages, rotates, and transmits power to another circular toothed component when rotated. Gear motion and speed can be monitored and controlled by a Hall Effect sensor.
A specialized limit switch that has no spring return mechanism and uses the weight of the lever arm to reset the contacts. A gravity-return switch is often used in applications where it is only exposed to low-force activation.
The creation of voltage in a semiconductor through the perpendicular exposure of a magnetic field. The Hall Effect is the basis for the operation of Hall Effect sensors.
Hall Effect sensor
A type of proximity sensor that generates voltage to trigger an action in response to a magnetic field. Hall Effect sensors require a setup that exposes a sensor to a magnetic field or fluctuations in a magnetic field.
A thin plate of semiconductive material that induces the Hall Effect in a Hall Effect sensor when exposed to a magnetic field. Hall elements are usually made of silicon.
hazardous-location limit switches
A limit switch designed for use in environments where it may be exposed to particularly dangerous conditions, such as corrosive chemicals or explosions. Hazardous-location switches are constructed with sturdy materials and use encapsulated contacts.
A limit switch component that holds the actuator. The head of a limit switch adjusts to position the actuator in a number of different places depending on the application.
The amount of water vapor in the air. Environments with high humidity can allow water to get into a limit switch and reduce its service life if it is not rated to handle large amounts of water vapor.
International Electrotechnical Commission. An organization that governs electrical equipment standards in countries other than the United States. The IEC provides a range of information about sensors, including recommended applications and durability and safety ratings.
A shock that occurs when two or more objects suddenly collide. Impact forces caused by debris striking a limit switch can shorten the operating life of the switch.
inductive proximity sensor
A type of proximity sensor that uses an electromagnetic field to detect metal targets. Inductive proximity sensors are more accurate than other proximity sensors but can only be used with metal targets.
IR sensors. A type of proximity sensor that uses changes in heat to detect a target. Infrared sensors are very inexpensive but have limited application due to small sensing ranges and light sensitivity.
The disruption of the normal functioning of an electrical device due to the presence of another device that produces electricity or magnetic fields. Interference can cause a proximity sensor to malfunction.
International Electrotechnical Commission
IEC. An organization that governs electrical equipment standards in countries other than the United States. The International Electrotechnical Commission provides a range of information about sensors, including recommended applications and durability and safety ratings.
To stick or become wedged. High-volume production lines may jam, which can be prevented by using flexible spring-rod actuators.
A small, specially shaped piece of metal or plastic used to open a lock or activate a machine. A key inserted into a slot activates a safety-guard limit switch.
An area used for scientific research. Laboratories are often used in manufacturing settings to create compounds that will enhance parts and part creation processes.
A target approaching a proximity sensor that is traveling in a plane parallel to the face of the sensor. The lateral approach diminishes the possibility of contact between the target and sensor.
A force that moves to the side of an object. Lateral forces, such as those created by an object passing over another object, can activate limit switches with lever-plunger or roller-plunger actuators.
A type of plunger actuator consisting of a thin strip of metal over a pushbutton. Lever-plunger actuators can be triggered through lateral force as well as axial force.
A device, usually a long piece of metal, that pivots on a fixed point to transfer motion. Levers are used as actuators in some types of limit switches.
limit switch enclosure
A physical barrier that surrounds a limit switch and protects it from damage. Limit switch enclosures are rated by the level of protection they provide.
A mechanical sensor that requires physical contact to detect the presence or absence of an object. Limit switches use an actuator to make or break an electrical connection that performs an action, such as turning a light on or off.
The amount of force or pressure placed on a component or system. The load an actuator can withstand without breaking helps determine the applications for which it is best suited.
A type of rotary actuator consisting of an adjustable wire or nylon coil that attaches to a limit switch head. Loop actuators must be attached to the object that triggers the switch.
A power-driven device that performs some manufacturing operation. Machine tools include metal-cutting machines, stamping machines, and plastic injection machines.
A force of attraction that surrounds magnets and electrical devices. Magnetic fields can cause interference with nearby electrical devices, such as inductive or capacitive proximity sensors.
The area of force or influence around a magnetic object that attracts or repels other magnetic fields. Magnetic fields are used to trigger the voltage that activates Hall Effect sensors.
Remaining in position until acted upon by a force or object. Limit switches with maintained actuation will remain either active or inactive until an object or force moves them into the opposite state.
The failure of a component or part to operate in the correct and expected fashion. A malfunction can be a result of improper installation or the presence of contaminants.
A machining process that uses a tool to remove metal from a workpiece. Metal-cutting processes include drilling, turning, and milling.
A minuscule device that conducts electricity and transfers data. Microchips are used in an array of electronics and can be smaller than can be seen with the human eye.
Automatically returning to its initial position. Limit switches with momentary actuation are spring-loaded to return to their free position once an object or force is no longer applied to the actuator.
To attach or fix an object in a specific position. Operators must mount a limit switch so that it is stable and protected from environmental hazards, such as flying debris.
National Electrical Manufacturers Association
NEMA. An organization that sets standards for electrical equipment used in the United States. The National Electrical Manufacturers Association provides a range of information about sensors, including recommended applications and durability and safety ratings.
National Electrical Manufacturers Association. An organization that sets standards for electrical equipment used in the United States. NEMA provides a range of information about sensors, including recommended applications and durability and safety ratings.
A specialized limit switch with two sets of electrical contacts that are activated depending on what direction an object contacts the actuator. A neutral-position switch activates one set of contacts when an object moves the actuator clockwise and activates the other set of contacts when an object moves the actuator counterclockwise.
A metal that does not contain a significant amount of iron. Nonferrous metals include aluminum, copper, and gold.
A limit switch configuration where a single enclosure contains all the internal switch components. A non-plug-in design provides more damage protection than the plug-in design, but it makes replacing and repairing the limit switch more difficult.
non-shielded proximity sensors
A proximity sensor with a coil or capacitor exposed due to a lack of metal enclosure. Non-shielded proximity sensors have greater sensing distances than shielded sensors, but are more susceptible to damage and wear.
NC. An electrical contact that is set in a position that allows current flow. A normally closed contact will enable a circuit to perform its function unless it is opened.
NO. An electrical contact that is set in a position that prevents current flow. A normally open contact will keep a circuit from performing its function until it is closed.
A strong and flexible type of plastic. Nylon is often used to make the loop on loop actuators.
The distance between an operating sensor and its target. Operating distances for some sensors range from less than an inch to hundreds of feet.
The position of the actuator where the contacts open or close. The operating position is the point at which the actuator activates the limit switch to perform its intended function.
A person trained to run a specific machine. Operators are responsible for helping ensure that a machining process runs properly, efficiently, and safely.
An electronic device that recognizes specially created codes, such as barcodes, and turns them into information that can be understood by a computer. Optical scanners are complex sensors.
An electronic circuit that produces fluctuating electric currents. Oscillators are used in inductive proximity sensors to create an electromagnetic field that will react to the presence of a metal target.
A circuit in an inductive proximity sensor that is activated by the detector and causes the sensor to perform its designed function, such as shutting down a machine. The output circuit remains active until the detector senses that the electromagnetic field returned to its original size.
The distance an actuator moves beyond the operating point. Overtravel provides space to ensure that the contacts have been opened or closed.
Two objects that come together at a 90° angle. The magnetic field must be perpendicular to the Hall element to trigger the Hall Effect sensor.
photoelectric proximity sensors
A type of proximity sensor that detects a target through changes in light. Photoelectric proximity sensors have excellent range compared with inductive and capacitive proximity sensors.
A rod inside a cylinder that is moved by hydraulic or pneumatic pressure. Piston movement may be monitored or controlled by a Hall Effect sensor.
A limit switch configuration where the switch is divided into discrete, easy to replace parts. The plug-in design separates the switch into three parts: the operating head, the switch body, and the receptacle.
A category of limit switch actuators consisting of a button that activates electrical contact when pressed. Plunger actuators come in three basic styles.
A pushbutton that can be depressed by an object. Plungers are activated when a force presses down, or axially, on it.
The device or component that supplies electricity to another device. Power inputs include electrical connections and batteries.
precision limit switches
A limit switch designed for applications that require repeatable, exact accuracy. Precision limit switches are small and inexpensive but have shorter service lives than other types of limit switches.
The distance an actuator travels between the free position and the operating position. Pretravel can be adjusted depending on the needs of a specific operation.
A manufacturing system in which materials are passed through a series of processes in order to create a finished product. A production line can be automated through the use of sensors, computers, and machines that operate largely without human input.
A solid-state device that uses an electronic sensing field to detect the presence of an object. Proximity sensors can sense the presence, or absence, of an object without making physical contact.
radio-frequency identification sensors
RFID sensors. A type of proximity sensor that detects a target through communication between the sensor and an embedded computer chip. Radio-frequency identification sensors can precisely identify any object but require that each target be separately tagged with a chip.
Cycling between inactive and active many times in a short time frame. Rapid switching occurs when a switch activates around 120 times in a minute.
The plug-in limit switch component that holds the electrical wiring. A receptacle is mounted on a fixture or machine and does not require any adjusting when replacing a head or switch body.
To be set back inside or embedded within another object. Shielded sensors can be recessed into external metal shielding when mounted but non-shielded sensors cannot.
The device in a Hall Effect sensor that ensures a steady flow of current. A regulator prevents unwanted deactivations or activations in a Hall Effect sensor.
The position of the actuator where the contacts return to their initial open-or-closed state. The release point marks when the limit switch is no longer activated.
To return to an original setting or position. A limit switch actuator typically resets once it is no longer in contact with an object.
revolutions per minute
rpm. A unit of measurement that indicates the number of complete rotations made by a circular or cylindrical object in one minute. Revolutions per minute can be monitored or controlled by a Hall Effect sensor.
Firmly placed. Rigidly mounting a limit switch helps to prevent damage from machine vibration.
An automated manufacturing device designed to replicate the movement of a human arm. Robotic arms can perform many of the same tasks as human operators only with greater precision, speed, and efficiency.
A machine tool, often with articulated joints and gripping capabilities, that can be programmed to precisely perform a variety of complicated, repetitive tasks. Robots are used to assemble parts, weld joints, position components, among many other manufacturing tasks.
A type of rotary actuator consisting of a thin, cylindrical metal shaft that extends out from a limit switch head. Rod actuators are longer and narrower than other types of rotary actuators.
A rotating wheel that facilitates an object's movement as it contacts a limit switch actuator. Rollers can be used with both rotary and plunger actuators.
A type of plunger actuator consisting of a rotating wheel on top of a pushbutton. Roller-plunger actuators can be triggered by an axial or lateral force.
A category of limit switch actuators consisting of a lever that rotates to activate electrical contacts. Rotary actuators come in a range of styles and sizes to fit an array of applications.
The speed at which an object revolves around an axis or center line. Rotational speed can be measured and monitored by a proximity sensor.
safety-cable pull switches
A specialized limit switch that stops machinery in the event of an emergency when an operator pulls, pushes, or cuts the cable. A safety-cable pull switch is exclusively used as a hazard-control measure.
A specialized limit switch that the operator activates by inserting a uniquely shaped key into a slot. A safety-guard switch can ensure that a machine will not run until all safety measures are in place.
A material that has more electrical conductivity than an insulator but less conductivity than a conductor. Semiconductors include silicon.
An area of force generated by a device to detect the presence and properties of an object. Sensing fields used for proximity sensors include electromagnetic fields, for inductive proximity sensors, and electrostatic fields, for capacitive proximity sensors.
A substance, force, or other means through which a device detects an object. Sensing mediums used by proximity sensors include light, sound, electromagnetic fields, and electrostatic fields.
A device that detects the presence or absence of an object, or certain properties of that object, and provides feedback. Common sensor applications include detecting, counting, positioning, and diverting parts on a production line and preventing the unsafe operation of a machine.
The length of time a device is expected to operate before needing replacement. The service life of a limit switch depends on several factors, but the limit switch manufacturer provides basic expectations in written part specifications.
shielded proximity sensors
A proximity sensor with protective metal casing that extends around the coil or capacitor. Shielded proximity sensors have more sensitive, but smaller, electromagnetic or electrostatic fields than non-shielded proximity sensors.
A protective device that shelters a component on one or more sides. Shielding provides protection from flying debris and other impacts for limit switches and proximity sensors and, for proximity sensors, can change the size and shape of their sensing field.
The jarring impact caused by sudden shaking or collision. Repeated shock can damage limit switches over time.
A circuit where current takes a shorter, unintended path between two conductors. Short circuits are caused when the insulation, or protective coating, of two conductors is worn or damaged.
A nonmetallic material that acts as a semiconductor. Silicon is often used to make the Hall element in a Hall Effect sensor.
A electronic device that functions by means of dense components that do not move. Solid-state devices are extremely precise and have long service lives.
A flexible device used to control motion, apply force, and store energy. A spring attaches a spring-rod actuator to a limit switch head.
A component inside a mechanical device involving a coil of wire. Spring-return mechanisms automatically pull a movable device back to its original position, such as returning an actuator to its default position on a limit switch.
A type of rotary actuator consisting of a long, thin, metal cylinder with a flexible spring at its base that attaches it to a limit switch head. Spring-rod actuators can rotate in any direction without breaking.
An established policy on a particular practice or method. The standards related to limit switch design and function are set by nationally and internationally recognized organizations, such as the National Electrical Manufacturers Association (NEMA) and International Electrotechnical Commission (IEC).
standard industrial limit switches
A limit switch designed for use in a typical industrial environment. Standard industrial limit switches are the most commonly used limit switches.
standard plunger actuator
The most common type of plunger actuator. Standard plunger actuators have a simple pushbutton design that can only be activated by an object depressing the pushbutton.
standard roller lever
A type of rotary actuator consisting of a lever with a rotating wheel at its end. Standard roller levers are the most common type of rotary actuator.
A plug-in limit switch component that holds the electrical contacts. A switch body can be easily removed and replaced when its electrical contacts wear or malfunction.
The object or property that a sensor detects. Targets for proximity sensors can be nearly any form of solid or liquid.
Pulled tight. Taut cables are sometimes attached to safety-cable pull switches so that an operator pushing or pulling the cable activates the switch in an emergency.
Similarly shaped protrusions from an object. The teeth on a gear transfer motion from one gear to another by meshing together.
A metal-cutting operation during which a lathe rotates a workpiece while a cutting tool moves along the workpiece. Turning is usually used to shape cylindrical objects.
A specialized limit switch with two sets of electrical contacts that are activated depending on the degree of actuator rotation. A two-step switch can also be activated by an object applying force from either direction.
ultrasonic proximity sensors
A type of proximity sensor that detects a target by sending out series of high-frequency sound bursts and interpreting the sound that is returned to it. Ultrasonic proximity sensors are extremely precise and can be used with almost any type of material.
Rapid shaking. Vibration is usually caused by a machine setup that is not rigid enough and can cause limit switches or limit switch components to shake out of place.
A type of proximity sensor that detects a target through the use of a camera. Visual sensors can identify specific features of a target but require powerful and often expensive computers to accurately interpret the data they gather.
A measurement that indicates electrical pressure or potential. Voltage is measured in volts (V).
A device that measures voltage. The voltmeter triggers the output function in a Hall Effect sensor when it senses a set change, either an increase or decrease, in voltage.
The gradual deterioration of a component over time due to friction or the presence of a contaminant. Wear occurs naturally over time, but premature wear can occur if a component is left unprotected from contaminants or operated incorrectly.
welding power source
A device that generates or funnels electricity for a welding operation. Welding power sources can generate large magnetic fields that interfere with the performance of inductive or capacitive proximity sensors.
Raw material that is subjected to various machining processes in order to create a finished part. A workpiece can be subjected to a combination of metal cutting, welding, forming, and other operations.