The Basics of Limit Switches: Beginners’ Course


The first thing to note about limit switches is that they are electromechanical devices. This means that they operate on both electrical energy and energy due to motion (mechanical energy). The simplest way to define limit switch is that they are electromechanical switches that carry out specific functions and operate as a particular object moves or is identified.

A mechanism very similar to this is that of the toilet float valve. As the tank fills up with water, the float is raised and it keeps rising until it reaches a level high enough to stop water from entering into the tank.

Application of Limit Switches

There are several ways limit switches can be applied and several functions they can perform. For instance, let’s say you own a truck that evacuates refuse, you want to make sure that each time you load the bed is secure and down before you start driving off. A limit switch can totally help you out here. A position limit switch and a button actuator can be automated such that when the bed has been let down properly, the button is pressed down and this activates an indicator light or sound close to you, letting you know that all is good and you can drive off. A position limit switch as shown below is used for these sorts of operation.

Position Limit Switch

Another way limit switches can be applied is in the automation of doors. Again, let’s assume you have a motored roll-up door and you’d like to automate it such that the motor stops when the door has been totally opened. As in the case above, a position limit switch can be of great help. The adjustable arm of the position switch will be linked to a pivot point which would also be connected to a switch. Once the door is opened up till its full height, the roller of the limit switch is touched and it starts to rotate. Once this happens, a switch is activated and the motor shuts off. In place of the roller, the switch can be activated using a plunger or button. It all depends on your preferences.

Other Types of Limit Switches

Apart from the Position Limit Switch, there are several other limit switches currently in use in modern times. The type of limit switch you use is dependent on the type of task you want to perform or problem you want to solve.

  • Rotary Gear Limit Switch

Oscar Rotary Gear Limit Switch

One more time, we would assume you have a rotational motor and you’d like to automate it to stop working or shut down after rotating for a set number of times. As the shaft on the limit switch turns, the motor turns. This is because the shaft is in contact with the motor through gears or sprockets. The limit switch, itself is made up of some gears and a series of cam. The number of gears inside the switch determines how many times the motor would rotate. As the gears in the switch and the motor turn, they rotate until they achieve the maximum number of turns.  Once this happens, the cam in the limit switch activates an electromechanical switch which turns off the motor.

These sorts of limit switch have several applications such as windmills, wind turbines, boat lifts, etc.

  • Proximity Limit Switch

A proximity limit switch is used to detect and indicate when a little bit of metal is present in an environment or material. It does this using a magnetic field which is able to detect when a disruption, usually due to the presence of a metallic object has occurred.

  • Windmill Limit Switch

The windmill switch is a little more complex and can operate in more than one direction, working with several positions and switches.

Travel Chart of an Activated Windmill Switch

A common application of the windmill switch is seen in gantry and bridge cranes, as shown in the image below. As seen, the crane can move to and fro (or front and back) over the length of the beam overhead. As it moves across the beam, a position limit switch can be used to determine and indicate its relative position.

Image of a Gantry Crane

  • Reed Limit Switch

A reed limit switch is used to indicate the presence of a magnetic field, and in some cases, determine how close it is to a magnet.

As you’ve already discovered, limit switches perform a wide range of functions and have varying sizes, modes of operation and applications. Hopefully, this piece has been very useful in helping you understand them better.

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