The symbol for a “normally open held closed” state indicates that the contact has been wired as a normally open contact, but when the circuit is put into its normal off state, part of the machine keeps the contact closed. The most common contact symbols show whether the device has normally open or normally closed limit switch contacts. Limit Switch ContactsĬontrol schematics for limit switches usually display a limit switch symbol to indicate the state of the switch contacts. Most switches are either maintained contact or momentary contact models. Limit switches can be installed into machinery as control instruments for standard operations or as emergency devices to prevent machinery malfunction. These switches can be used as pilot devices for magnetic starter control circuits, allowing them to start, stop, slow down, or accelerate the functions of an electric motor. The limit switch then regulates the electrical circuit that controls the machine and its moving parts. In most cases, a limit switch begins operating when a moving machine or a moving component of a machine makes contact with an actuator or operating lever that activates the switch. In addition, a limit switch’s electrical rating should be matched to the mechanical system loads that it will be controlling in order to avoid instrument failure. Due to the mechanical specifications and performance parameters of different machines, factors such as size, operational force, mounting method, and stroke rate are important characteristics in the installation and maintenance of limit switches. For repeat usage, the accuracy of the electrical switches needs to be reliable and their response rate should be prompt. Industrial machinery that undergoes automatic operations usually requires control switches that activate according to the movements involved in a machine’s performance.
The electrical terminals are connected to the switch contacts and enable wires to be joined to the switch through terminal screws. The switch body contains the switch contact mechanism whose state is controlled by the actuator. The actuator contains is connected to the operating head, whose linear, perpendicular, or rotary motion is then translated by the actuator to close or open the switch. The operating head is the part of the limit switch that comes in contact with the target.
WHAT DOES A VEX LIMIT SWITCH DO SERIES
Limit switches consist of an actuator with operating head, the switch body mechanism, and a series of electrical terminals that are used to connect the switch to the electrical circuit that it is controlling. Most limit switches are mechanical in their operation and contain heavy-duty contacts capable of switching higher currents than those of alternative proximity sensors. Hence, limit switches are contact sensors in contrast to these other types of proximity sensing devices. Similar devices, such as inductive or capacitive proximity sensors, or photoelectric sensors, can accomplish the same result without requiring contact with the object. Limit switches use the mechanical movement of the actuator plunger to control or change the electrical switch's state. When an object (sometimes called the target) comes in physical contact with the actuator, the actuator plunger’s movement results in the electrical contacts within the switch to either close (for a normally open circuit) or open (for a normally closed circuit) their electrical connection. How does a limit switch work?Ī standard limit switch used in industrial applications is an electromechanical device that consists of a mechanical actuator linked to a series of electrical contacts. It was at this point that the switch was engaged to control the limit of travel. The original use for limit switches, as implied by their name, was to define the limit or endpoint over which an object could travel before being stopped. Limit switches are used to automatically detect or sense the presence of an object or to monitor and indicate whether the movement limits of that object have been exceeded. Image credit: mofaez/ What are Limit Switches? Limit switches are contact switches used to detect objects and control machines.
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