Unformatted text preview:

LIMIT SWITCHESIntroductionBasic ComponentsBasic Components (contd.)Type-1 Nonplug-in HousingType-2 Plug-in HousingMore on Plug-in HousingActuator FunctionSide Rotary ActuationLever arm types that can be used with Side Rotary Actuation switch.Side or Top Push ActuationSide and Top Push Actuator ExamplesWobble Stick/Cat Whisker ActuationActuation of Wobble Stick Limit SwitchClassification of ContactsClassification of Contacts (contd.)Snap Action ContactsSnap Action Contact MovementSlow Make and Break ContactsSlow Make and Break Contact MovementDirect Opening Action ContactsDirect Opening Action Contacts (contd.)Contact Operating CharacteristicsContact Operating Characteristics (contd.)Mechanical Advantages of Limit SwitchesElectrical Advantages of Limit SwitchesDisadvantages of Limit SwitchesTypical ApplicationsPosition VerificationWoodworkingCounting and Parts DetectionReferenceRef: Fundamentals of Sensing, Rockwell Automation / Allen BradleyLIMIT SWITCHESByBharath RamaswamyDepartment of Electrical & Computer EngineeringUtah State UniversityECE 5320: MechatronicsECE 5320: MechatronicsRef: Fundamentals of Sensing, Rockwell Automation / Allen BradleyIntroduction•A limit switch is an electromechanical device that consists of an actuator mechanically linked to a set of contacts.•When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection.•It can determine the presence or absence of an object. It was first used to define the limit of travel of an object; hence the name "Limit Switch."Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleyBasic Components•Actuator: The portion of the switch that comes in contact with the object being sensed.•Head: It houses the mechanism that translates actuator movement into contact movement. When the actuator is moved as intended, the mechanism operates the switch contacts.•Contact Block: It houses the electrical contact elements of the switch. It typically contains either two or four contact pairs.Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleyBasic Components (contd.)•Terminal Block: The terminal block contains the screw terminations. This is where the electrical (wire) connection between the switch and the rest of the control circuit is made.•Switch Body: The switch body houses the contact block in a plug-in switch. It and terminal block in the nonplug-in switch.•Base: The base houses the terminal block in a plug-in switch. Nonplug-in switches do not have a separate base.Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleyType-1 Nonplug-in Housing•They are box shaped with a separate cover.•Seals between the head, body, and cover are maintained by an O-ring and a flat gasket.Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleyType-2 Plug-in Housing•Developed to ease replacement of the switch if needed.•Plug-in housing splits in half to allow access to the terminal block for wiring.•A set of stabs in the switch body “plugs” into sockets in the base to make electrical connections between the contact block and the terminal block.Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleyMore on Plug-in Housing•An O-ring provides the seal between the operating head and the switch cover while a custom-cut gasket guards the switch body against entry of oil, dust, water, and coolants.•Design benefits of the plug-in housing:–Installation without removal of the cover–No moving parts located in base–Reduced downtime because head and body can be replaced quickly without disturbing wiring in base.Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleyActuator Function•When there is no force or torque applied to the actuator it is in the unactuated, free or rest position. •The position to which the actuator must be moved in order to operate the contacts is called the trip point or operating position. •When the motion of the actuator is reversed, the position at which the contacts return to their original state is called the reset point or releasing position. •Common actuator types:–Side Rotary–Side or Top Push–Wobble Stick or Cat WhiskerRef: Fundamentals of Sensing, Rockwell Automation / Allen BradleySide Rotary Actuation•A side rotary actuator is a shaft protruding from the side of a limit switch head that operates the switch contacts when rotated. •It can move in a clockwise and/or a counterclockwise direction and is designed for either uni- or bi-directional operation of the contacts. •A lever arm is typically affixed to the shaft, allowing passing objects to activate the switch by pushing on the lever.Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleyLever arm types that can be used with Side Rotary Actuation switch.Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleySide or Top Push Actuation•A short rod (button) on the side or top of a limit switch head that operates the switch contacts when depressed.•Usually designed with a spring return mechanism that returns to its original position when the actuating force is removed. •A few side push designs employ rods that have no spring return and must be pushed in the opposite direction to reset the contacts.Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleySide and Top Push Actuator ExamplesRef: Fundamentals of Sensing, Rockwell Automation / Allen BradleyWobble Stick/Cat Whisker Actuation•A wobble stick or cat whisker actuator is a long narrow rod on the top of a limit switch head which operates the switch contacts when deflected from the vertical position. •Wobble sticks are typically nylon rods, while cat whiskers are made of flexible wire. •They are capable of operating in any direction (movement similar to a joystick) and return to their original position when the actuating force is removed.Ref: Fundamentals of Sensing, Rockwell Automation / Allen BradleyActuation of Wobble Stick Limit SwitchRef: Fundamentals of Sensing, Rockwell Automation / Allen BradleyClassification of Contacts•Maintained vs. Momentary Contacts –The contacts of a limit switch change state when a predetermined force or torque is applied to the actuator. –A spring return (momentary) switch returns its contacts to their original position when the operating force is removed. –The contacts of a maintained switch remain in the actuated position until force or torque is applied in


View Full Document

USU ECE 5320 - LIMIT SWITCHES

Documents in this Course
PH Sensor

PH Sensor

17 pages

Load more
Download LIMIT SWITCHES
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view LIMIT SWITCHES and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view LIMIT SWITCHES 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?