Vocabulary Term Definition

ActuatorThe part of a limit switch that transfers the mechanical force of the moving part to the electrical contacts.

Air CompressorA component that pressurizes ambient air and directs it into a pneumatic system.

Automatic InputA type of control device that is set to automatically control each step in a process. Pressure switches, flow switches, and temperature switches are types of automatic inputs.

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

Bimetallic SensorA sensor with two unlike metals bonded together. The metals expand at different rates when heated, providing a physical signal that the sensor converts into an electrical signal.

Capacitive Proximity Switches

Switches that are triggered when they detect either conductive or nonconductive substances.

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

ChatterThe occasional unwanted vibration between components. Chatter decreases productivity and can cause wear.

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

ContactA conductive part in an electrical circuit attached to a switch that opens or closes a circuit by coming in contact with or separating from the main conductor.

Contact BlockThe part of a pushbutton that holds the contacts and is activated when the pushbutton is pressed. The most common pushbutton contact block has one NO and one NC contact.

ContactorA device that uses a small control current to energize or de-energize a load.

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

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

Deadband PressureThe amount of pressure that must be removed before pressure switch contacts reset after the actuation level has been reached. Deadband pressure is also referred to as differential pressure.

DiaphragmA deflecting mechanism that moves when reacting to pressure. Diaphragms are usually used at low pressure.

Eddy CurrentA magnetic current created by sensor vibration that flows out and around the sensor head.

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

Vocabulary Term Definition

Extended Button OperatorA type of pushbutton operator that extends beyond the guard ring. An extended button operator is used when accidental startup is not hazardous.

FloatA device used in switches that floats on liquid. The float raises or lowers based on the level of the liquid.

Flow SwitchesSwitches that detect 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.

Fluid Pump A mechanical device used to move liquids in a hydraulic system.

Flush Button OperatorA type of operator that has a guard ring around it to prevent accidental startup.

Fork Lever ActuatorA type of actuator that is moved by one of its two roller arms. Fork lever actuators can detect movement in two directions.

Guard RingA device around a pushbutton operator that prevents an individual from accidentally pressing the button.

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

Hydraulic Power created by the motion and pressure of fluids.

Inductive Proximity Switches Switches that are triggered when they detect a conductive substance.

Legend PlateThe part of a switch that has the written function of the switch's operation. A legend plate often includes the words "start," "stop," "jog," "on," or "off."

Level SwitchesSwitches that detect 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.

Lever ActuatorA type of actuator that works through a lever connected to the shaft of a limit switch.

Light SourceA beam of light received by a photosensor used to trigger photoelectric switches.

Limit SwitchesSwitches that detect the presence or absence of an object by physically touching it. Limit switches have a variety of actuators that come into contact with an object.

Main Control StationA control panel on a machine that consists of the main pushbuttons and switches that turn the machine on and off and control various other functions.

Manual InputA type of control device that requires an individual to manually press a button or turn a switch. Pushbuttons and selector switches are types of manual inputs.

Mechanical DevicesA type of control device that physically contacts an object. Mechanical devices include limit switches, flow switches, and level switches.

Mechanical InputA type of control device that must touch an object in order to detect it. A limit switch is a type of mechanical input.

Vocabulary Term Definition

Mechanical Level SwitchA type of level switch that uses a float that triggers electrical contacts when the liquid reaches a set height.

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

Mushroom Button OperatorA type of pushbutton operator that hangs over the guard in a mushroom shape. A mushroom button operator is easy to press and is used for emergency stops.

OperatorThe 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.

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

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

PhotosensorA type of sensor that detects the presence of an object through the use of a beam of light.

PistonA rod inside a cylinder that is moved by hydraulic or pneumatic pressure. Pistons are used at high pressure.

PneumaticPower created by the motion and control of gas, often air, under pressure.

PressureThe amount of force exerted on a surface divided by the area of the surface. Pressure is typically expressed in pounds per square inch (psi).

Pressure SwitchesSwitches that detect a certain amount of force and activate electrical contacts when the force is reached. Pressure switches have different sensing devices that detect pressure changes.

Proximity SwitchesSwitches that use 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.

Push Roller Actuator A type of actuator that moves directly forward into the limit switch.

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

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

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

Resistor A device used in circuits to limit current flow.

Selector SwitchesSwitches that can be turned to different positions to make a connection with the contacts in that particular position.

SensorA device that detects a change in a physical stimulus and turns it into a signal that can be measured or recorded. All sensors are control devices, but not all control devices are sensors.

Solenoid An output device that converts electrical energy into linear mechanical

Vocabulary Term Definition

force.

Stop PlateA 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.

Switch A device that opens and closes a circuit.

Temperature SwitchesSwitches that react to different heat intensities and activate electrical contacts when the temperature rises or drops below a set level. Temperature switches are often used in heating and cooling systems.

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

ThermocoupleA 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 SelectorA 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 SelectorA selector switch that allows you to select one of two circuit conditions. Common two-position selector switches are on/off and forward/reverse.

Wobble Stick ActuatorA type of actuator that works through any movement into the switch except a direct pull.