The Ultimate Buyer's Guide for Purchasing What Triggers a Limit Switch?

Limit Switch is a type of sensor that identifies presence and absence. The limit switch can be mounted into remote locations so that it is moved by an object aside from using a human operator. UNIONWELLS, china micro switch limit switch manufacturer company that produces and supplies different types of custom switches. Visit UNIONWELLS now to know more information. 

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How does a Limit Switch Work?

Limit switches have many functions, including the following: 

• Detecting the presence or absence
• Identifies the range of movement and counting
• Detecting the positioning & travel limit
• Breaking a live circuit in case of the apparent unsafe condition
• Detecting the speed

Different types of Limit Switch

The common limit switch types are the following:

• Heavy-Duty Precision Oil Tight (Type C limit switch)

This type of limit switch is commonly used due to its long mechanical and electrical life span. It is easily installed and has a straightforward wiring arrangement, which makes this type recommended to be used in an industrial setting.

• Heavy-Duty Oil-Tight and Foundry (Type T) 

This type is more upgraded than the type C limit switch. It can withstand high trip and reset forces, and at the same time can handle operating sequences that Type C can’t handle. This limit switch type is also commonly used in foundries and mills.

• Snap Switches

Snap switches are used to trigger as soon as the mechanism attached to the switch has moved a predetermined distance, regardless of the speed at which the moving part travels. It is commonly used in applications that require only basic contact parameters, which can work with or without an operator. Snap switches are best used in machines that have short movements or a slow rate of operation.

• Gravity Return 

Like what the name implies, this type mostly relies on gravity to reset its contact switches by exerting a force on a lever arm and usually works with a low level of torque. There are different types of gravity return switches, which includes spring return, roller-type, lever type, top push, and maintained contact designs. Gravity Return is usually used in production lines and operations with small components.

• Miniature Enclosed Reed

Last but not the least, this type of limit switch is smaller and less expensive compared to the mentioned types above. Miniature enclosed reed contains a contact array featuring a hermetically sealed reed, which makes this type suited for applications that require a high level of contact reliability.

Different Uses of a limit switch

The use of a limit switch can either activate (turn on) or deactivate (turn off) an electrical circuit. Most limit switches are used in industrial companies and household appliances.

• Use of a limit switch in Industrial companies 

In industrial companies, limit switches to shut off when an action exceeds its travel or position. An example would be when a robot malfunction occurred- the limit switch will shut down the power to the movement control.

• Use of limit switch in the home. 

You can see a limit switch at work when you open and closes a refrigerator. The limit switch limits the light by turning it off when you close the refrigerator, then the light operates on when you open the refrigerator. This is also the same when it comes to washing machines. When you open the top lid, the agitator stops its motion. The limit switch that sets just under the top frame cover, removes the control voltage from the circuit and stops the operation during the mid-cycle. This type of use for a limit switch is also known as a safety limit.

By Casey Storer

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Limit switches have practically limitless applications in regulating crane operation to prevent potential incidents. For instance, when ropes come out of groove or in preventing two trolleys from impacting on the same bridge structure.

In addition, a limit switch keeps a crane from lifting loads above rated capacity. Another kind of limit switch prevents a hoist from reaching the upper block and rope drum. Yet another type protects motors from overheating.

Without overhead crane limit switches, the potential for harm is quite high. For this reason, each limit switch should be inspected and maintained regularly.

Check limit switches daily

As they open or close electrical circuits, limit switches wear out over time. To monitor wear and replace switches before they fail, limit switches should be checked daily before a crane is used.

Konecranes has conducted extensive research to determine how many uses a limit switch is physically capable of performing. This provides essential information for developing inspection and maintenance programs.

Know how a limit switch works

Knowing how a limit switch works is important for understanding how the crane works and how these established set points keep the crane operating safely and efficiently.

In some cases, there may be multiple limit switches associated with a crane operation such as crane travel or hoist motion. The first switch will signal that the end of the safe travel limit is approaching and slows the crane motion. A subsequent switch will indicate that the end of the safe travel distance has been reached and stops the motion.

Hoisting motions may be served by several limit switches, which provide set points for safety and reliability. An initial limit switch will slow the hoist before it reaches the stop limitation. Slowing the hoist prior to reaching the limit decreases mechanical wear, as the hoist is traveling below maximum speed when the brakes set.

The “up” stop limit switch provides a safe position for the hoist to stop motion for safe travel motions and standby positions.

The ultimate limit

An additional limit beyond the stop limit—typically called the “ultimate limit”—prevents the hoist block from impacting the drum. The ultimate limit acts as a safeguard in the event the stop limit fails or is set improperly.

This extra limit prevents two-blocking—that is, when the hook block contacts the drum hoisting machinery. Two-blocking is one of the most dangerous incidents involving cranes, as it can snap wire ropes and cause dropped loads and other catastrophic accidents.

After being tripped, the ultimate limit may require a manual reset. This involves resetting a wedge component or lever so that an inspection can be carried out to determine why the crane reached this position and did not stop at the up stop limit position.

Limit switches can also be used for travel motions, providing consistent and predictable motion limitations without impact at end stops. In automated environments, lasers or encoders track positions of crane movements, and limit switches provide consistent calibration points to insure values being used are accurate for safety and reliable production.

Konecranes uses limit switches to calibrate Sway Control height and other critical measures of repeated accuracy to control real-world position.

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