Views: 41 Author: China Micro Switch Manufacturer Publish Time: 2020-08-28 Origin: https://www.unionwells.com/
The Basics of Limit Switches
It has been discovered that there are lots of people who don’t understand what limit switches are all about. In case you are handling any electrical project, it is very important to know what these forms of switches can help you achieve over a given period of time. This helps such project to realize its goals without any struggle. For instance, there are lots of confusing aspects of limit switches that people are yet to clearly understand. A problem like this can deprive you of experiencing the benefits that they have got to offer.
Have you been wondering what limit switches are? Do you know that these switches are special and can help your device or appliances work effectively once used the right way? In case there are lots of things that seem confusing to you about them, there is no doubt that you have come to the right place. The major aim of this post is to help you understand everything about limit switches. It will be explaining the A-Z about these switches and how they have been playing their roles in helping devices as well as appliances work in the past.
What is a limit switch?
These are switches which have been designed to sense or detect an object (presence) automatically. The primary aim for such detection is to find out whether the object has exceeded its limit or not. You can see that such is the primary reason why it is called limit switch - to define the endpoint or limit of an object. In simple terms, it has been designed to detect the distance that an object can travel up to before its getting stopped. Furthermore, it can be seen that limit switches exist to monitor how far objects can travel before having them (the objects) interrupted.
It is also important to note that such detection or monitoring process happens via physical contact. The actuator is moved by an object which brings about closing or opening of the contacts. This is basically what limit switches have been designed to carry out in devices and appliances they are used in.
Uses of limit switches
In case you don’t know, these switches have lots of uses that any system can benefit from. It is the reason why most companies are including them in their products more than ever before. Some of these uses will be highlighted and briefly explained below:
Stopping rod length
This is one of the uses of a limit switch. When rods are being cut, there are measurements which are always expected to be followed. Without out a limit switch, it becomes difficult for a machine to get the job done excellently. This is because it tends to stop at the right measurement before such rods will be cut. This is why rods are cut in a standard and accurate way.
Switching off/on loading systems
Limit switches have crucial role in ensuring that loading systems work as expected without any need for fear of under-pressure or over-pressure. The loaded pallet has to reach a particular level or set point in order to avoid breakdown which can be very costly to fix in the long run. It is the duty of a limit switch to regulate such loading systems. It will detect or monitor when the set point has been reached or exceeded.
Controlling washing machines
Washing machines are using limit switches more than ever before. This is usually to automate some processes in order to ensure optimal function which could not have been possible. Limit switches determine when these appliances/devices will start or stop depending on whether load is unbalanced or not.
Have you see how those containment doors usually function in terms of closing automatically? Without the use of limit switches in having them operated, they will close much faster. It is the presence of these switches that makes them close very slow to avoid any form of confusion or accident.
Advantages of limit switches
It is true that there are other switches which can carry out the functions of a limit switch. However, limit switches seem to have more advantages and benefits as compared to what conventional switches offer users. This is why they are considered to be one of the best when it comes to monitoring how objects operate. Some their advantages/benefits are listed below:
1 - They are easy to install
This is probably one of the most notable benefits of limit switches as compared to conventional forms of switches you will come across in the market. They have been built in such a way that anyone can understand how they are used without any technical knowledge or experience. All you have to do is understand its various components in order to ensure a successful installation process.
2 - High level of flexibility and compatibility
The use of limit switches in industrial settings wasn’t that popular in the past as most companies prefer using other forms of switches to control their activities. However, all of these are beginning to change as they have been discovered to be very flexible. This means they can fit into any industrial setting without any complication. The goal is always to ensure efficiency and effectiveness is achieved.
3 - High level of accuracy
This is another reason why limit switches have proven to be very popular amongst various industries. They have been designed to monitor how objects move with great degree of accuracy. This means they determine when objects move and stop without any mistake.
4 - Low power consumption
Most companies are constantly looking for ways to use appliances/devices which consume low power. This is to ensure their cost of electricity is reduced drastically. Limit switches have been known to consume low power. This is why they are included in most of the modern devices and applications. In case you are handling an electrical project, the ability of a limit switch to consume low amount of power makes it a perfect option to explore.
5 - Its high level of versatility
When it comes to versatility, limit switches are proving to be a viable option which is why industrial companies are making use of them more than ever before. Do you know that these switches can be used in switching up multiple loads? Are you aware that a functionality or feature such as this can help reduce the stress of having to get every load controlled by one specific switch? This can simply be interpreted as being able to use a single limit switch in controlling the functionalities of various loads.
6 - Durability
Limit switches are highly durable. In other words, they have been designed to withstand conditions that are considered very harsh without experiencing any breakdown. They are also very reliable as proven in the past. A typical example of this is their heavy-duty contacts. These can be used in switching current which are of higher levels without any need for secondary relay control being utilized.
With limit switches being included in an electrical appliance, you don’t have to worry about it breaking down or not functioning as expected. This is because despite its simple nature, it can over-deliver even far beyond your expectations.
How do limit switches work?
Although the use of limit switches is becoming very popular around the world, it is fair enough to conclude that there are lots of people who do not understand how it has been designed to function or work. This is a very important step that you must not forget since it can help you know whether limit switches are perfect for your project or not.
The details below will be explaining in details how these switches work when installed in appliances or devices. The reason why you need to understand this aspect is that it can go a long way in determining whether a limit switch will be used optimally or not.
The first thing you have to understand is that presence sensing entails the process of having an object presence detected. This happens through two means which are non-contact or contact sensing tool/device. It is the sensors which are responsible for the production of electrical output signals to aid the control of equipment. Just as said above, these explanations are what define a typical limit switch. It is important to note that limit switches are similar to sensor. In other words, they carry out similar function as a sensor. This is because they play the role of absence and presence detection. Some switches can be mechanically activated.
This means they have either plunger, knob, lever or arm through which activation takes place. For these switches to work as expected, there has to be contact between their actuator and the object. It is through this process that the actuator is moved to its limits whereby it becomes possible for contacts to change state. It should also be noted that sensor switches have different types like electrical switches, light sensors, proximity sensors and others.
It is the contact between the object and switch actuator which brings about changes. It is the movement of the actuator which will determine whether the contacts of such switch will be opened or closed. Limit switches can either be normally open or normally closed. These switches are used in addressing problems when it comes to motor control, manufacturing, packaging, consumer and safety applications. This simply means that it is very possible for a limit switch to be connected as “normally open” or “normally closed”.
Once used in any machine travel, limit switches can be maintaining a position of normally closed (NC) or normally open (NO). As a matter of fact, every limit switch can operate in either of 4 ways. These are normally closed, normally open, held down or held open. However, most switches you will come across in the markets today are usually normally closed or normally open. They determine the point at which there will be flow of electricity or circuit breakage.
Through these contacts, it becomes possible for them to detect speed, travel limit, motion range, of objects. This will determine whether the flow of circuit will be interrupted or not.
Types of limit switches
There is no doubt that this post wouldn’t come to an end without helping you understand the various types of limit switches you can find in markets. A knowledge such as this can help your buying decision to a great extent. In case you do not know, limit switches are of different types. The details below will explain more about them.
1 - Rotary limit switches
The functionalities and features of these switches are majorly based on shaft (rotating). They become activated once the shaft has reached a given set point. These switches carry out detection and activation through rotational movements. Simply put, their activities involve rotational motion. For any equipment to be controlled using this switch, there is always the rotating shaft.
The above picture is a typical example of a rotary limit switch. This is characterized by the rotating shaft which extends through their rear and front as you can see. Activation only becomes possible when the set angle or amount of rotations/revolutions has been reached.
2 - Linear limit switches
Unlike rotary switches which have been explained above, linear limit switches depend on linear motion to function as expected. Their most popular use is ensuring that linear actuators motion is limited. Linear actuators are what they are used together with in order for desired results to be achieved.
The picture above is a clear example of how a linear limit switch actually looks like.
3 - Windmill switches
These forms of limit switches are much more complicated than what have been listed above. With them, operations can take place in 2 different directions. Also, they are characterized by multiple positions as well as switches. That is to say, they have the ability to make rotation take place in various positions.
Some of the places you will usually find these types of switches are gantry cranes as well as bridge cranes. They will enable such cranes to move back and forth. In the picture below, you will notice how the crane tends to move across such beam. This function is made possible by a windmill switch. You will also notice that these limit switches are used in heavy-duty applications unlike the other ones explained above.
4 - Reed switches
Most people are yet to discover that a reed switch is one of the forms of limit switches. Reed switches have been known to make use of magnetic interactions when it comes to closing and opening their contacts. In every electrical switch, there are always two contacts. Once a button is pushed, these will be joined together thereby allowing the flow of current. Once your hand is released from the button, the contacts will return to their default or resting state.
In the case of a reed switch, ferromagnetic material are what the contacts have been made from. They are coated with metals like ruthenium or rhodium to ensure high level of durability. In most reed switches, you will always find two contacts. However, one is usually non-magnetic while the other will be ferromagnetic.
Reed switches are commonly found in phones and laptops. Have you ever seen those phones whereby as you flip them closed, their lights get turned off automatically? Also, once you have them opened, their lights will be turned on automatically. It is also the same for other devices like e-book readers. What usually happens is that whenever such phone is opened, the magnet and reed switch will be apart/separated. This is a process whereby power will flow into such phone thereby having it turned on. On the other hand, once the phone is closed, the magnet and reed switch will contact each other. This will have the lights turned off.
One thing you have to always understand about reed switches is that they are used in most household devices and appliances than imagined. This makes them one of the most popular forms of limit switches.
5 - Proximity switches
These switches are existing to show whether a metal is maintaining a particular position or not. They may not sound popular but such does not mean they are not common especially in the manufacturing setting. For instance, you will find them in security systems, robotics, and manufacturing equipment. In a nutshell, it is a switch which is based on detecting of desired or expected position.
What is difference between proximity sensor and proximity switch?
It is important to note that there is a difference between proximity switch and proximity sensor. For instance, the latter does not need to make any physical contact before actuation can be said to have occurred. Proximity switches do not operate or function like that. The truth is that although both tend to work in a similar manner, they are slightly different. Proximity switches are the best options to explore when it comes to environments that are harsh. This is because of how they have been designed to function.
Contact types of limit switches
It is true that limit switches can either be normally opened or normally closed. However, it is crucial to understand that their functionalities go beyond such explanation. There are 3 different contact types you need to understand about limit switches. These are:
1 - Momentary contact
In this case, the switch will remain closed or open as a result of actuation. In a situation such as this, a switch which is normally open will likely close as a result of actuation. It will reopen again once such condition stops or ceases.
2 - Maintained contact
In this instance, contacts are maintained even when there does not seem to be any process of actuation. The situation or condition or contacts do not change despite the actuation having stopped. In order have the contacts reset, mechanical action will be required.
3 - Positive opening
This can also be known as positive breaking. In this case, contacts are likely to remain/stay in such activated position despite the occurrence of mechanical problem or failure. You will usually find these forms of switches in those critical safety applications. This is because they tend to offer a much higher level of reliability as compared to the other contact types which have been explained above.
Some limit switch terminologies you should know and understand
When it comes to understand limit switches, there are lots of things or factors involved. Most of the time you may be tempted to focus on observing how such switches function in order to understand everything about their features and functionalities. Although these can be very helpful, there is no doubt that you can fall short when it comes to having proper understanding about limit switches.
There are lots of terminologies associated with limit switches. Understanding these will definitely help to know how they have been designed to function in various applications. Below are some of them.
1 - Pretravel
This is probably one of the most common terms you will hear when it comes to basic switches. The problem is that people don’t understand what it means. It simply refers to that distance which the actuator will have to pass through in order for the contacts to be tripped. Also, it can be seen as the angle or distance traveled by the actuator to an operating position from free position. At this point, it is important to note that every plunger has a maximum distance to travel. It is crucial to ask or find out before deciding to purchase a limit switch. This helps to ensure you have purchased something that can meet your needs.
2 - Operating Point
This simply means the point which limit switch operates. It can also be seen as a position maintained by the actuator to ensure contacts snap. Operating point is the stage whereby a limit switch starts working as it has been built to do. The point whereby operating point is established is known as biasing in the field of engineering.
3 - Release Point
Once there is an operating point as explained above, there is likely to be a point of release. This is the stage whereby contacts return to their normal or default state. It is that position the actuator maintains once the contacts have returned back to their original state. For instance, when a limit switch is in operation, it means a device is being monitored or detected to ensure it functions as expected. At some point contacts will come together thereby allowing current to flow. A situation when there is breakage of circuit, it means the actuator has returned to its release point.
4 - Differential
Differential simply means distance which exists between contacts reset and contact trip. The distance in this case is usually measured in degrees. Most people believe that differential is a term that is only associated with pressure switches. This is not true as you will also find such in limit switches. Do not forget that contacts reset is existing to make a limit switch return to its default state of normally closed.
5 - Over travel
This is a situation whereby an actuator has gone beyond its original or default setpoint. It can also be seen as when the actuator has moved beyond the trip points (contacts).
6 - Initial position
It is that original positioned maintained by the actuator before any external force can be applied. It is also a point whereby zero amount of force has been applied to the actuator. At this point, the limit switch will maintain its default position.
7 - Operating force
This is also known as torque. For an actuating element to be moved, a particular type of force is required. This is called operating force. It is that force which is responsible for moving an actuating element to a particular direction.
8 - Minimum return force
This type of force can also be called torque just like the operating force explained above. As mentioned, the actuating element will move once operating force is applied to it. In order to have it returned to the original or default state, minimum return force will have to be applied. It is therefore safe to conclude that minimum return force is the complete opposite of operating force.
9 - Total travel
This is the highest distance that an actuating element has been able to travel. It is not recommended for such element to travel beyond the set or expected distance in order to avoid any problem of malfunction.
10 - Repeat accuracy
Switches usually have a way of repeating various operations over and over again. The ability to do this is what is called repeat accuracy. It is not only common with limit switches as you will also find such in other types of switches like pressure switches, sensor switchers, detector switches, and others. When this happens, they tend to do it with a very high degree of accuracy.
What you need to understand about actuators in limit switches
There is something most people do not know about actuators, this is the fact that they are one of the most important components in limit switches. Trying to ignore little details about them can come back to haunt you more than expected. For instance, it is through the actuator that the application will experience a breakage of circuit or flow of current.
This is why you need to understand how it has been built to function. Also, know that your choice of actuator is very important. There are various factors that usually come into play when this is about to be chosen. The major ones are size and shape of the machine which is being used in having the limit switch tripped.
Reasons for actuator failure
There are lots of factors which can be responsible for this problem. Even though it is becoming rampant, most people are struggling to understand what could have gone wrong. With a failed or faulty actuator, it becomes very difficult for your limit switch to work at its best.
1 - Incorrect installation
Although limit switches are easy to install, you can get the process wrong once the right steps are not followed. When this happen, the actuator is at risk of failing when used. A problem such as this can be easily corrected. All you have to do is get the switch reinstalled from start again.
2 - Incorrect voltage
The problem of incorrect voltage can also make your actuator fail at will when expected to work. When there is incorrect power or control voltage, the fuse will likely get damaged. This can also adversely affect your actuator.
3 - Excessive loading
Limit switches are meant to monitor set points in order to know the right time when machines can work. It is important to know that there is a maximum amount of load a switch can carry. Once the load exceeds such amount, its actuator will likely be damaged. This is why you need to always check the application which such limit switch is to be installed in.
4 - Poor application maintenance
This is another common cause of actuator failure while working. When your appliance isn’t maintained as expected, the limit switch actuator may become victim. It can be affected from working effectively. This is why it is recommended that applications should be constantly checked for damaged parts/components.
Apart from the above faults which an actuator can experience, others could be incorrect power phasing, power board failure, disconnected or fused wire, engaged torque switch, undersized actuator, too much condensation, clogged actuator filter, and more.
Based on the above, it can be seen that there are lots of problems which can affect an actuator and prevent it from functioning optimally. It is all about running a check on yours and finding out what could have gone wrong with it. Actuators are like the brain in limit switches. Therefore, they should not be ignored in any way.
Limitations of limit switch
In order to improve your buying decision about limit switch, there are some certain things to understand. This is the fact that it usually has some limitations. Although these may not pose a threat in terms of how they are used provided you follow the instructions of its manufacturer, it is still very important you understand such limitations.
1 - The low speed equipment limitation
This is one of the most notable limitations of limit switches. They do not function in applications that require high speed to function. In such situations, you will notice they cannot monitor or detect how objects tend to move effectively. However, if you have an application or equipment with low speed, there is no doubt that limit switch installation will be very ideal. It can make all the difference in such scenario.
2 - The direct contact limitation
Do you know that limit switches have been designed in a particular way that there has to be contact with objects? Anything short of this means that they won’t function or work as expected. Therefore, if you are searching for a switch that will monitor how an object moves without any physical contact being made, it is highly recommended to look beyond what limit a switch can offer.
There are other ways that limit switches can prove to be useful but not in this regards. Trying to use it without any direct contact will only bring about frustration since there won’t be any changes in terms of normally closed or normally open contact.
3 - Wear out problem
Apart from limit switches, the problem of wear and tear will always affect every kind of switch in the market. This means it is a general issue and not only associated with limit switches. It is only natural that with the passage of time, the components of a limit switch will likely be affected by effects of depreciation. This will hinder their level of effectiveness.
The best decision to take here is ensuring that you are always carrying out regular maintenance routine on the application. The same can also be said of the limit switch. Components which require replacement shouldn’t be monitored closely since they can fail at any given point in time. These could be operating head/actuator, receptacle/terminals, and other parts of the body. An exercise such as this can help you overcome the problem of wear and tear with ease.
Top Tips to buy the best limit switches
When it comes to purchasing a limit switch that can be installed in an application, there are lots of variables or factors which have to be taken into serious consideration. In order to ensure you do not make the wrong decision, the details below have been put together to help you out in the best way possible.
Consider your needs
Before purchasing a limit switch, it is important to always take your needs into consideration. For instance, there have been instances when people are not supposed to purchase limit switches. Instead, what is required is some other device to monitor how their devices/applications function. However, due to wrong analyses and projections, they ended up purchasing limit switches. A decision like this can only bring about regret. Just as explained above, limit switches have some limitations that make them ineffective in different circumstances. It will be better to purchase a switch that can ensure your goals are achieved.
Even in the case when a limit switch is required, it is also very important to check properly before deciding on which one to purchase. This is because there are different types of limit switches like rotary switches, proximity switches, linear switches and more. These have different features and functionalities. In other words, they are unique in terms of what they can offer when installed in applications. It is the reason why you need to check which one can fit into your project without any compromise.
It is true that most sellers will want to convince you about how they have some of the best limit switches that can meet your needs. The earlier you know that this is a trap to collect your hard-earned money, the better. You have to learn how to do research online about sellers before reaching a decision on whom to patronize. For instance, consider buyer reviews about such type of limit switch before reaching any conclusion.
Also, you can research about whether a seller has been meeting needs over the years. When a seller is trusted, you won’t have problem of whether the limit switch purchased will be of high quality or not. This is one tip you should not take for granted since there are lots of fraudulent sellers of limit switches in the market today.
It does not really matter whether a limit switch is of the highest as such will not be of any good especially when your budget is not enough. This is why you have to always consider its price in comparison to your budget. The trick here is trying to find a limit switch that fits into your budget. You can decide to make comparisons of the prices of various sellers in order to find out the most favorable.
One of the benefits of this method is that it makes various options available that you can choose from. Do not make the mistake of settling down for the first seller of limit switches you will come across. This is because there are always other sellers that may even offer better prices/deals. Patience is the key here since you will be required to do lots of research. If you have to contact a seller in order to make some requests about discounts, do not hesitate.
In summary of the above, it can be seen that there are lots of details or facts about limit switches which you need to know before making any buying decision in the first place. Just ensure to go through each and every one of them in order to ensure proper understanding and better decision making.