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Limit Switches and Actuators: What They Are and The Benefits They Provide

Published: 08 Jul 2019

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.

Limit switches are an important part of many linear actuators, as they help control where the actuator stops. This helps protect the actuator, the object it is moving, and the people using the system.

What Is a Limit Switch in an Actuator?

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.

In simple terms, a limit switch tells the actuator, “stop here.” This is useful when the actuator is opening a window, lifting a panel, moving a roof system, or pushing and pulling any object that needs to stop at a safe point.

Why Are Limit Switches Important?

Limit switches help an actuator move in a safe and controlled way. Without them, an actuator may continue trying to move even after it reaches the end of its stroke. This can put extra pressure on the motor, gears, brackets and the object being moved.

A limit switch can help:

Stop the actuator at the right point
Protect the actuator from damage
Reduce stress on gears and moving parts
Prevent damage to the object being pushed or pulled
Make the application safer for users
Support smoother actuator operation

This is especially important in applications such as opening windows, opening roofs, hatches, vents, panels, and other automation systems where movement needs to be controlled properly.

How Does a Limit Switch Actuator Work?

A limit switch actuator works by breaking the electrical connection when the actuator reaches a set point.

When the actuator extends or retracts, the limit switch is triggered once the actuator reaches the end of its set movement. Once the switch is triggered, power is stopped in that direction, and the actuator stops moving.

This helps stop over-travel and reduces the risk of damage.

There are a few different types of limit switches.

External Limit Switch

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 hits this button or lever, the limit switch will break the connection and stop the actuator.

External limit switches are useful when you need the actuator to stop at a custom position. They can be placed where the actuator or moving object will touch them during operation.

They are often used when the actuator does not need to travel its full stroke, or when the stopping point depends on the setup around it.

Internal Limit Switch

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, and some are called micro-switches. 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.

This means the actuator can stop safely when it reaches full extension or full retraction.

Micro Switches in Actuators

A micro-switch is a small type of limit switch that is commonly used inside an actuator. It is compact, reliable, and useful where there is limited space inside the actuator body.

Because micro-switches are mounted inside the actuator, they are protected from most outside interference. This makes them a practical option for many electric linear actuator applications.

If you are choosing an actuator for a project, it is worth understanding whether the actuator has internal limit switches, external limit switch options, or controller-based stopping options.

Why Choose Artificial Limits?

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.

Where Are Limit Switch Actuators Used?

Limit switch actuators can be used in many different applications where controlled movement is required. They are useful anywhere the actuator needs to stop at a certain point instead of continuing to push or pull.

Common uses include:

Opening and closing windows
Moving roof systems
Lifting panels or hatches
Adjusting vents
Moving machinery parts
Supporting agricultural equipment
Controlling automation systems
Preventing over-travel in custom applications

For example, in window automation, a limit switch can help stop the actuator once the window reaches the correct open or closed position. In a roof or hatch system, it can help prevent the actuator from pushing past the safe stopping point.

Limit Switches vs Current Overload Sensing

Current overload sensing can help protect an actuator, but it is not always the best way to stop movement.

Current overload usually reacts when the actuator is already under pressure. This means the actuator may have already reached a hard stop before the power is cut. Over time, this can still place strain on the gears and moving parts.

A limit switch is different because it stops the actuator at a set point. This can help avoid repeated hard stops and give the actuator a smoother, safer stopping point.

In some applications, both methods may be useful. For example, internal limit switches can control the end of travel, while a smart controller can help with artificial limits or current limits.

Choosing the Right Limit Switch Setup

The right option depends on how you plan to use the actuator.

If the actuator only needs to stop at full extension and full retraction, an actuator with internal limit switches may be enough.

If the actuator needs to stop at a custom position, an external limit switch or artificial limit may be a better option.

If the actuator is used in an application where people may interact with the moving object, a current limit or dynamic limit can add another layer of protection.

You should also consider where the actuator will be used. If it will be used outside, in wet areas, or in dusty conditions, it is important to choose a suitable actuator. You can learn more about this in TecHome’s guide to linear actuator IP ratings.

Do You Need More Than One Actuator?

Some applications need two actuators to move at the same time. This is common when lifting a larger panel, hatch, platform or roof section where both sides need to stay level.

In this case, you may need actuator synchronisation. This helps two actuators move together instead of one moving faster than the other.

TecHome has explained this in more detail in the blog on dual synchronisation.

Need Help Choosing the Right Actuator?

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 accurately for many applications.

The best option will depend on your stroke length, load, stopping position, controller setup and where the actuator will be used.

If you’re not sure which actuator or controller you need, TecHome can help. You can view our range of linear actuators or send your project details through our actuator enquiry form.

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