In the broadest sense, a limit switch is an electromechanical device designed to detect the presence or absence of another physical object, usually a piece of machinery that moves or travels.
Perhaps one of the best ways to understand limit switches at a high level is through the many applications they have in the real world.
- Detect when a car or garage door is open or closed.
- Detect when a door to a vehicle is not fully closed (safety interlock Limit switch)
- Detect when a mechanical device passes the limit of its travel. The switch then trips arresting the motion and preventing the device from doing any damage.
- Detecting the presence or absence of an operator. (Dead man’s switch)
- Detect that a computer printer head is in the right position for printing.
- Used by CNC machines in manufacturing to identify maximum limits for machine parts or to provide a known reference point for incremental motions.
The list of possible uses is really as endless as your imagination but you get the idea. Too look at some of the many Limit Switches CPI offers, look at our Sealed Limit Switch page on our website.
Limit Switch Design Considerations
The basic design of a robust limit switch has certain primary considerations that designers must be familiar with to understand performance capability in their application and to select from the many types of switches available.
Electrical Rating – Current through the switch is a key parameter that affects all other performance characteristics, including electromechanical endurance and performance at temperature limits.
Circuit Type – Most limit switches can be made in standard circuit options such as normally open/closed, and SPST or SPDT. Maintained or momentary switch contact is another key factor in the design.
Actuator Style – The actuator can be a simple as a straight metal lever, or a roller or ball type. Angles can be varied to create customized travel distances which affect the lifetime and performance characteristics of the switch. They can be designed to offer tactile feedback when humans operate them manually.
Duty Cycle – How often will your switch turn on and off? One a week? Twice a second? Extreme requirements here will dramatically affect your other switch design choices as you trade off durability with operation.
Mounting and Packaging – Limit switches can be made with a wide variety of mounting options which allow them to be placed in common and uncommon ways. They can be made entirely waterproof for deployment under exceedingly wet or even underwater operation.
Types of Mechanical Limit Switches
Many Mechanical limit switches are the push-button variety. When something comes in contact with the limit switch, the switch depresses to complete the electrical circuit. As the object moves away from the limit switch, spring pressure opens the switch, turning off the circuit.
Standardized limit switches are manufactured with a variety of operator types including most commonly; lever, roller, plunger, and pushbutton limit switch types.
CPI has designed and assembled robust electromechanical limit switches for over 60 years in its facility in East Hanover New Jersey. If you have a question about a custom application for one of our switches, we encourage you to call us today.