Published: 08 Jul
TMAZTZ supply professional and honest service.
If you're like most people, the terms limit switch and actuator probably mean very little to you. However, it's important to understand the functions of the products you buy, so we're going to walk you through the concept of limit switches in actuators, and explain why they're beneficial.
A limit switch does just what the name implies: it stops an actuator at a certain stroke length. This saves gears from being stripped as it prevents the actuator from breaking whatever it's pushing. This also serves to protect users from injury.
Limit switches are more effective than current overloads and sensing, as these methods will eventually still strip the gears since they are coming to a hard stop.
There are a few different types of limit switches.
These switches break the connection externally through the use of a mechanical button or lever. When either the actuator or the object it's controlling hit this button or lever, the limit switch will break the connection and stop the actuator.
Much in the same way as an external switch, an internal limit switch is activated by a small strip of plastic inside the actuator, which breaks the connection as soon as it's triggered.
Internal switches can be very small (some are called micro-switches), and since they're mounted internally, there's very little risk of external forces interfering. Plus, no wiring is required from the installer.
All of TecHome's actuators come equipped with this sort of internal micro-switch, mounted on both retracted and extended ends of the actuator.
There is a third option for setting actuator limits in addition to these switches: using the TH717+ Smart Controller to set artificial limits by working in conjunction with the hall sensors.
The user can set this artificial limit at whatever number of pulses from the hall sensor they choose. Once that limit is reached, the TH717+ Smart Controller will trigger the artificial limit.
This type of limit is highly customizable; it can be set at any length and is highly accurate for any application.
Setting artificial limits with the TH717+ also allows you to set a 'dynamic' limit switch (or a current limit), meaning power to the actuator will be cut when a certain current or force is applied. This function is especially useful for applications like opening windows, or any other where human intervention could occur.
Though every type of limit switch has its practical uses for safety and preventing damage, setting artificial limit switches with the TH717+ Smart Controller does the job more efficiently than any other.
Contact us at +61 (0)7 , or reach out to with any questions!
Detecting the presence or absence of an object using a contact or noncontact detecting device is possible using a simple switch. Once the object is detected then these devices will generate an electrical signal that is used to control different types of equipment and also processes in different industries. One such is a limit switch. It has also become an essential part of the control and sensing community of different sectors like construction, industrial, commercial, agriculture, and transportation. So thousands of limit switches are used in different types of construction or agriculture machinery, industrial equipment & control systems around the world. So this article discusses an overview of a limit switch ' working with applications.
Limit switch definition is an electromechanical switch that operates by any physical force or the movement of a machine. These switches are very helpful in detecting the absence or presence of an object, counting, detecting speed, detecting movement range, travel limit, positioning, etc. These switches include three terminals NO (Normally Open), NC (Normally Open) & Common.
The controlling of this switch can be done by different factors like temperature, position, and pressure. This switch is mainly designed to operate only once a fixed limit is achieved, and it is generally activated through contact by using an object like a cam. The limit switch symbol is shown below.
The construction of a limit switch can be done by using different components like an actuator, cover, built-in switch, and a switch case.
The actuator is an essential part of the limit switch which comes in contact physically with the object. The connection of an actuator within this switch can be done by connecting to an operating head which translates a linear, rotary otherwise perpendicular motion to control the electrical contacts of the switch.
Connect the cover once you have connected the outside connection cable to the built-in switch terminal. To seal the connection between the switch case and the cover, rubber packaging is used.
The built-in switch can directly switch ON/OFF by using its snap-action mechanism. The exterior force reverses the variable spring & shifts the moving contact from the upper NO contact & to the lower NC contact.
The switch case of the limiter switch encloses for safety. These cases are designed with resin or metal to enhance mechanical strength. At the bottom of this switch, a special connector can be connected to the opening of the conduit to protect the outside cable connection into position and to form a protecting seal for the inside components.
A limit switch can be made out of many different materials depending on its application. For example, limit switches used in elevators are usually made out of stainless steel so they won't rust when exposed to water from humidity in an enclosed space like an elevator shaft or shaftway between floors. Limit switches used in industrial applications where there might be hazardous chemicals may also be made out of stainless steel with copper contacts (instead of silver) because copper doesn't corrode like silver does when exposed.
A limit switch working principle is similar to a sensor to identify the presence & absence of an object. This switch can be triggered mechanically by communicating with other substances. When the object contacts the actuator of the switch, then it moves eventually to the boundary of the actuator wherever the location of the contact changes. Most of these switches are mechanical in their operation & include heavy-duty contacts which are capable of switching high current.
This switch can be arranged in your furnace's supply plenum. So this switch reads the plenum's temperature & waits until it gets hot properly. Once the plenum achieves a specific temperature, then this switch transmits a signal to the air handler to start running & transmitting warm air to your home. The limit switch commonly operates at an upper limit of 160°F and a lower limit of 130°F.
Want more information on tm? Feel free to contact us.
Pressure switches mainly rely on the pressure of water to perform all the work. The change in the pressure will trigger the switch. The water pressure will move up through the diaphragm which pushes against a spring & piston, which in turn contacts will be opened or closed.
Limit switches utilize the actuator plunger's mechanical movement to change or control the condition of the electrical switch.
In general, there are Two Types of Limit switches
Mechanical ' These switches are controlled by a physical movement (typically using a lever). This often makes them suitable for delicate equipment because they don't require any power to operate. However, they can be more prone to wear and tear than electronic versions.
Electronic ' Electronic limit switches are powered by batteries or mains electricity and use sensors to detect when an object crosses a certain point.
A limit switch can be activated by several types of mechanisms: magnetic, mechanical and optical. Magnetic limit switches are activated by magnets located near them. Mechanical limit switches are activated by physical contact with a lever or other object that moves when the actuator comes into close proximity with it. Optical limit switches use light-emitting diodes (LEDs) and photoelectric cells to detect when an object has come within a certain distance of them
The circuit diagram of the limit switch is shown below. This circuit can be built with a 12V battery, 3.5V, 10mA of green color LED, 3.5V, 10mA of red color LED, and 850 ohms resistor. The connections of this circuit can be done like the following.
The positive terminal of the battery is connected to the common terminal of the switch through a resistor. Here resistor is connected in series with the common terminal and the battery's positive terminal.
Both the LED's negative terminals are connected directly to the battery negative terminal. Connect the green color LED's positive terminal to the NO terminal of the switch and the red color LED's negative terminal to the NC terminal of the switch.
The above switch works in two conditions which are discussed below like when the switch is OFF and the switch is ON.
Once the switch is turned OFF, the NC terminal of the switch is connected to the common terminal whereas the NO terminal of the switch is detached from the common terminal. As a result, the RED color LED gets the supply & it will turn ON whereas the green color LED will be turned OFF.
Once the switch is turned ON, the NO terminal of the switch is connected to the common terminal whereas the NC terminal of the switch is detached from the common terminal. As a result, the Green color LED gets the supply & it will be turned ON whereas the red color LED will be turned OFF.
The difference between limit switch and proximity switch includes the following.
Limit Switch
Proximity Switch
The limit switch works by using a physical response to function as ON and OFF. The proximity switch works under the responses of the sensor.This switch needs either a machine or a manually operated switch to change the current flow. In this switch, the sensor detects the object in the specified range to change the current flow.
These are contact switches. These are non-contact switches. Its working life is shorter because of the internal contacts. Its working life is longer. These switches are used for the detection of positions in only one direction. These switches are used to detect two-way positions, These switches use two wires. These switches use more wires as compared to the limit switch.
There are different types of limit switches available in the market which are discussed below.
These switches include a roller on the tip of the lever. Once an object is there the roller will activate radially. Here the main use of a roller is to remove a high level of friction & reduce the power required to control the limit switch. Similarly, when there is no object then the lever will come back to its original position because of a spring mechanism fixed within the switch's body. These switches are most frequently used in the industrial sector.
These switches are similar to a typical standard roller level switch except for one function which is the capacity to alter the roller's height. So this gives adjustment once the limit switch is fixed within the place. Here, the adjustment range can be changed through the limit switch when it is 2 millimeters to 6 centimeters distance. Generally, these switches are applicable where the object they are sensing may move slightly.
These switches are available in different sizes and shapes. So, the most frequently used type is the roller type. This switch is mainly used whenever the pressure is not applied directly to the head of plungers at 90 degrees. The Roller plunger changes some of the pressure from non-perpendicular to perpendicular after that it can be used to trigger or disable the plunger. These switches will trigger once something pushes downward on the plunger's end.
This switch includes a rounded tip which is triggered once it gets perpendicular energy that is provided to the end part of the plunger. In this switch, the main function of the rounded tip is to provide a larger detection region on the head of the switch. Here head types can come in different sizes & shapes.
These switches include a thin and long rod that is triggered once it notices presence. These switches have a spring mechanism inside so when the object is detached then the lever will come back to its original position. Here, the rod length ranges from 1 centimeter to above 10 centimeters. These switches are normally applicable in non-heavy-duty applications.
These switches are approximately the same as typical rod lever limit switches but they can trigger in a 360º region. They seem practically identical in appearance to rod lever type.
These limit switches are applicable where the application features an axis or hinge. Once an axis or hinge turns, the switch will activate. These types of switches are used on door hinges & also on any application that includes a turning axis.
These types of limit switches are available with a lanyard or hook on the tip of the body of the switch. A pull cord or cable is connected to the hook & triggers the switch once the cable is pulled. This switch includes a spring-loaded lever that activates when it is pulled.
Generally, these switches are mainly used on security devices like a pull cord on a conveyor. When somebody needs to stop the conveyor in an emergency then they can drag the pull cord. These are normally very simple to install & set up.
There are many reasons to fail limit switch including the following.
The advantages of the limit switch include the following.
The disadvantages of the limit switch include the following.
The applications of the limit switch include the following.
Thus, this is all about an overview of a limit switch with working, types, and its applications. Some of the industries which use limit switches are; manufacturing, material handling, packing and distribution of food and beverage, metals, control cabinets, commercial, and many more. Here is a question for you, what is a proximity switch?
Are you interested in learning more about toggle switch working? Contact us today to secure an expert consultation!