The act of sensing the absence or the presence of a substance (object) with a non-contact or contact sensing device is known as presence sensing. The sensors generate an output signal (electrical) that can be utilized to control processes or equipment.

Limit switches are a category of sensing device that helps in detecting the presence and absence of objects. Mechanical limit switches refer to those switches that can be activated mechanically i.e. they consist of some kind of lever, arm, plunger, knob, etc. which is mechanically or physically activated. Other kinds of switches/sensors include light sensors, proximity sensors, etc.

As said earlier, these limit switches help in the sensing of objects in industrial applications. The device is named as 'limit switch' due to the operation it performs. As the target (object) comes in close contact with the switch’s operator, it moves the actuator to the limit where the electrical contacts change state. Because of this mechanical activity, the electrical contacts are either closed (in an open circuit) or opened (in a closed circuit). Capacitive proximity, photoelectric sensors, and inductive proximity carry out this same procedure through non-contact detection.

Let's have a look at some of the basic functions linked with limit switches.

• Counting
• Detecting Speed
• Detecting Absence or Presence
• Detecting Travel limit and Positioning
• Detecting Range of Movement
• When an unsafe condition forms up it breaks the live circuit.

Limit switches have found its use in many commercial and industrial applications which requires safety. Let’s check out some of its strengths as well as its weaknesses.

Strengths

• Limit switches can withstand several environments.
• It provides high accuracy, repeatability, and precision.
• It’s quite a good economic sensing solution.
• It’s not a big deal to switch high currents (approx. 10A).

Weaknesses

• The mechanical component used in it may wear out.
• It needs to make physical contact with an object to actuate.

Advantages of using Limit Switches

• It can operate multiple loads.
• It consumes less electrical energy.
• It can be utilized in nearly any industrial habitat.
• Loads can be switched with high inductance.
• It’s very much specific regarding repeatability and accuracy.

Disadvantages of Limit Switches

• These switches are by and large confined to hardware working at moderately low speeds.

Basic Limit Switch Design and Terminology

• Pretravel – It is the angle or the distance that the actuator must go through to trip the contacts.
• Operating Point – It is the position of the actuator where the contact break to the position of operation.
• Release point – It is the position of the actuator at which the contacts come back to their initial state.
• Differential – It is the length between contacts reset and contacts trip.
• Overtravel – It is the movement of the actuator past the contacts trip point.
• Initial Position – It is the position of the actuator when no external force is applied to it.
• Operating Force (Torque) – It is the amount of force needed to move the actuating element.

This was all we have regarding limit switches. Brands that manufacture them are Omron, Honeywell, and QUADRANT. Make sure to follow them using the links as provided.

View all the Limit Switches