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Proximity switch vs. limit switch - Differences and areas of application
In industrial automation and control technology, precise and reliable switching operations are essential. But which technology is right for your application? Mechanical limit switches offer robustness and ease of use, while non-contact proximity switches offer high precision and durability. This blog provides you with a detailed comparison of both systems, explains their operation, differences, and areas of application, and provides valuable insights into key parameters such as sensing range, switching hysteresis, and detection distance.
Switch vs. Sensor
A mechanical switch is a switching element that controls electrical current flow through physical contact of two conductive components. Actuation is mechanical, such as by pushing, pulling, rotating, or moving an object against the switch. The operation is based on direct contact between metal components that are closed or opened by mechanical motion. A physical impulse, such as actuating a lever or impacting an object, triggers the switching operation. Mechanical switches are characterized by their robustness and simple design and are resistant to electromagnetic interference. However, they are subject to a limited service life due to mechanical friction and wear. Typical applications are found in industrial and automation technology. For example, they are used as limit switches for limiting the position of machine components or as door contact switches in industrial environments.
A sensor is an electronic device that detects objects, movements, or physical changes and then outputs an electrical signal. Unlike mechanical switches, a sensor operates without contact and uses different physical principles, such as magnetic, capacitive, or optical sensing, depending on the design. The functionality is based on the analysis of environmental changes. The sensor responds to the approach or presence of an object, processes the signal, and outputs a switching pulse that can control downstream processes. Since no mechanical contacts are actuated, detection is wear-free. Sensors offer high precision and are particularly suitable for fast or sensitive applications. Typical applications include automation technology, such as inductive sensors for non-contact object detection. In our blog on sensor technology you will find further explanations on the selection and function of various sensor technologies.
The following example shows the use of a proximity sensor PSAM18 with an automated door. For more examples, check out our inCad-Library.
Types of Switches
Switches are available in different designs that meet different requirements depending on the application. All switches operate according to the same basic principle - switching a circuit by mechanical pressure. Pressure switch or Positioning switches reliably detect the position of an object, regardless of the material, shape, color, magnetism, or surface finish of the detected object. With direct physical contact, these switches provide precise and repeatable position monitoring – ideal for applications where absolute reliability is critical.
| Switch type | Signal point repeat accuracy *1 | Contact point, accuracy, service life *2 | Operating temp. range | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Compact |  |
0.003 mm | 3,000,000 cycles | 0...80 °C *3 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| High precision |  |
0.0005 mm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Standard |  |
0.005 mm | 10,000,000 cycles | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| With stop |  |
Up to 0.01 mm (except flat type) |
10,000,000 cycles | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| With plunger |  |
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| Heat resistant |  |
At ambient temp. up to 0.01 mm |
500,000 cycles | 0...200 °C | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Limit switch
A limit switch is used for position monitoring and is mechanically actuated by a moving object. Once the object reaches a certain position, it actuates the switch, causing the internal contacts to close or open and trigger an electrical signal. The switch consists of a robust housing, a spring mechanism, and a switching contact that is actuated by a lever, roller, or plunger.
Limit switches are often used in machines and conveyors to limit movement and for safety shutdown.
Application example: limit switch with DGSM switch cam
(1) = limit switch
The limit switch is actuated by the stop plate (switch cam) mounted on the linkage.
Pressure Contact Switch
A pressure contact switch reacts to mechanical pressure or a force. Once a certain pressure threshold is exceeded, the contacts close or open to allow or interrupt current flow. The switch usually consists of a housing with a spring mechanism and a simple contact system, and is activated by applying pressure (manually or mechanically). Pressure contact switches are often used as safety switches on machines or as push buttons in control systems.
Precision Pressure Contact Switch
A precision pressure contact switch is an advanced form of the traditional pressure contact switch. It is designed to switch at a very precisely defined pressure point. This is achieved through high-quality materials, precise manufacturing and special spring and contact systems. Precision pressure switches have high sensitivity and respond to small pressure changes with high repeatability. The defined switching point remains stable even with frequent actuation and under changing environmental conditions. Typical applications are precision measurement technology and automation technology.
Mechanical influencing variables and switching behavior of contact switches
The switching behavior of contact switches is not only determined by the electrical design, but also by mechanical influencing variables. Parameters such as pressure angle, contact speed, stroke, or impact energy determine whether a switch is reliable, accurate, and durable. Particularly in industrial applications where high cycle rates, varying loads or demanding environments are prevalent, understanding these mechanical characteristics is crucial for safe integration and trouble-free operation.
Pressure angle
The pressure angle describes the angle at which the actuating force acts on the switch - ideally axial, i.e. straight along the actuating axis. Side or oblique force (false load) may jam the switching mechanism, affect switching accuracy, or in the worst case, lead to total mechanical failure of the switch. The permissible direction of force is determined individually for each switch by the manufacturer and must be taken into account when designing the application to prevent malfunction and premature wear.
Contact speed
The contact speed indicates the speed at which the object hits and actuates the switch. Too high a speed can overload the contact mechanism, while too slow movements make the switching process unstable. Therefore, when selecting, ensure that the switch is suitable for the planned speed of movement of the process.
Total stroke
The total stroke is the maximum travel of the actuator from the starting point to the mechanical stop. It defines the total clearance the switch can accommodate before it is mechanically blocked. It is important that the detected objects do not collide with the switch housing when actuated, unless they are special switches with integrated stops. If there is a risk of collision, a separate mechanical stop should be provided in the system to relieve the load on the switch. It is essential to check the impact resistance of such switches with stops to avoid mechanical overload and associated damage.
Application example: Contact switch with stop
(1) = Workpiece
(2) = Stop
tr = stroke (travel)
Switching travel and operating point
The switching travel is the part of the stroke in which the electrical switching actually occurs. The operating point lies within this path and marks the exact moment at which the switch switches. These two parameters are important to know the exact position of the switching pulse in the motion sequence and to correctly integrate the switch into the process.
Contact force
The contact force is the force necessary to safely close the electrical contacts. It provides stable contact without bouncing, which is critical for reliable signal flow. The selection of the switch must take into account the correct contact force to ensure both safe switching operations and adequate operating force in the process.
Impact Energy
The maximum impact energy or Impact energy indicates how much kinetic energy can be absorbed by the switch without damaging it. Particularly with fast-moving machine components, it is important that this energy is below the load limit of the switch to avoid mechanical damage and downtime.
horizontal impact
An object hits the switch at a certain speed (v).
Calculation of kin. energy Ekin
E_{kin} = \frac{1}{2} \times m \times v^{2}
free fall
In vertical free fall, an object falls from a certain height (h) onto the switch.
Calculation of kin. energy Ekin
E_{kin} = m \times g \times h
• Ekin = kinetic energy (J) • m = weight (kg) • v - speed (m/s) • h - drop height (m)
• Gravitational acceleration (9.8 m/s2)
Maximum static load
The maximum static load describes the maximum force that can be applied to the actuator continuously when depressed. If the load exceeds this value, deformation or damage to the switch may occur. This parameter is important if a continuous load is applied to the switch after actuation, such as for fixed positions in machines.
Contact Logic
The contact logic of a switch determines how it operates in the circuit and is divided into two basic types: NC (Normally Closed) and NO (Normally Open).
An NC contact (also called a normally closed contact) ensures that the circuit is closed at rest. Only when the switch is activated will the contact open and interrupt the current flow. This principle is often used for safety functions because the circuit remains open automatically in the event of a switch failure or a cable break.
A NO contact (also called a normally open contact) behaves in the opposite way: The circuit remains open when idle. Only by actuating the switch do the contacts close and enable the current flow. This logic is typically used for normal control tasks where current flow is enabled only when needed.
Safety precautions when installing and using switches
When using switches in industrial applications, care must be taken to ensure proper design, wiring, and assembly to avoid accidents, damage to machinery, or hazards to persons.
A major risk is that excessive heat, smoke, or even fire can damage the circuit. This can occur when switches are operated outside their rated values, e.g., when the allowable currents, life cycles, or environmental conditions are exceeded. Likewise, there is a danger if cables and connectors are used beyond their maximum current capacity or laid near heat-producing components. In particular, in safety-critical applications where switch failure could result in serious injury or machine damage, additional measures are required. This includes, for example, redundant circuits or safety devices such as emergency stop circuits in order to be able to intervene reliably in the event of a fault.
During installation, certain precautions must also be observed to avoid mechanical damage to the switch or the connection cables. This includes correctly routing cables, preventing damage from sharp-edged components, and mechanically fixing the switch to prevent unwanted movement or loosening.
When wiring electrical equipment, the correct connection to the power supply, proper grounding, and proper handling of inductive loads must be followed. Even for switches with an integrated LED display, the circuits must be wired in accordance with the manufacturer's instructions to prevent malfunctions or overloads.
Types of sensors
There are also different types of sensors that are used depending on the application and requirements. Two commonly used sensors are the proximity sensor and the spacer sensor. Although both sensors can detect objects, they differ significantly in their function, range and measurement options.
Proximity Switches
A proximity sensor, or proximity switch, detects the presence of an object in its immediate vicinity without the need for physical contact. The sensor outputs a signal as soon as an object is detected within a defined detection range. However, it does not measure the exact distance, only whether an object is in range or not. Proximity sensors detect objects without contact, i.e. they react to physical changes such as electromagnetic fields (inductive), capacitive field differences or light reflections (optical). They usually give a simple yes-no signal for the detection or Non-detection of objects.
Distance Sensors
A distance sensor measures the exact distance between the sensor and an object. Unlike the proximity sensor, it outputs a continuous measurement signal indicating the actual value of the distance. This allows for more precise measurement of distances within a defined measuring range. Spacer sensors thus measure continuously using technologies such as They use ultrasound or laser. They either output an analog signal (proportional to distance) or a digital signal with measured values. As an alternative for precise distance measurements that are occasionally required, dial indicators are also suitable, which are discussed in detail in the article Dial gauges - Types and Properties.
Proximity Switch Operating Principles
Proximity switches or Proximity sensors are used in many industrial applications. Depending on the measurement principle and application, there are different types of sensors that react to different physical effects. Four common types are presented below.
Inductive sensors
An inductive sensor detects metallic objects by altering an electromagnetic field. A high-frequency magnetic field is generated in the sensor. As a conductive (metallic) object approaches this field, a so-called eddy current is created, which changes the magnetic field. This change is detected by the sensor and triggers a switching signal.
Capacitive sensors
Capacitive sensors operate on the basis of electrical fields. They detect objects by changing the electrical capacitance between two electrodes. When an object approaches the sensor, it changes the electrical field, resulting in a measurable change in capacitance. This triggers a switching signal. Capacitive sensors are suitable for the detection of both metallic and non-metallic materials. Capacitive proximity switches are ideal for level control of liquids or bulk materials.
Optical Sensors
Optical sensors, in particular laser sensors, work with light beams. A transmitter (laser or LED) emits a beam of light that is reflected by an object. A receiver detects the reflected light and evaluates the change in light intensity or the time difference to generate a switching signal. Optical sensors work with precision, accurately detecting objects, distances, and even the smallest details. Optical proximity switches are often used in automated manufacturing and packaging technology, such as monitoring moving components.
Acoustic Sensors
Acoustic sensors, usually ultrasonic sensors, emit high-frequency sound waves (above the human hearing range). These waves are reflected by objects and received again by the sensor. The sensor calculates the distance based on the time of the sound (time-of-flight principle) between emitting and receiving the signal. Acoustic sensors operate independently of material, i.e., they can detect solid, liquid, and even transparent objects.
Proximity Switch Design and Function
Proximity switches consist of several electronic components that enable non-contact detection of objects or physical changes. Their design varies by sensor type, but follows a similar basic principle.
A sensing element detects a physical quantity, a signal processing system evaluates it, and a switching output passes the signal to downstream controllers. Depending on the technology, different sensing mechanisms are used, which determine the sensor’s performance and applications.
A central point in the selection and integration of a proximity switch is the spatial detection of objects, which is defined by three essential parameters:
• Sensing range
• Blind area
• Detection distance
Inductive sensor
S = Inductive sensor
(1) = Object in the stable detection range
(2) = Object in the unstable sensing area
(3) = Object outside the sensing distance
Optical sensor
S = Optical sensor
(1) = Object in the detection area
(2) = Object in the blind area
(3) = Object outside the detection distance
α = sensor angle
Detection range, blind range, and detection distance
The sensing range of a proximity switch describes the maximum range in which an object can be reliably detected. This value varies by sensor type and technology and indicates the distance up to which object detection is possible.
The blind area is the immediate area in front of or next to the sensor where no reliable sensing takes place. Particularly with ultrasonic and optical sensors, this area is caused by the necessary signal processing, which means that objects that are too close to the sensor cannot be registered.
The detection distance defines the specific distance at which the sensor safely detects an object and outputs a switching signal.
Hysteresis and switching points for proximity switches
For proximity switches, the switching points determine when and how the sensor outputs a signal when an object moves in or out of the sensing range.
The switch point On defines the exact moment or distance at which the sensor detects an object and switches to the detection state. If the object exceeds this threshold, the sensor outputs a switching signal.
The switch point Off, on the other hand, marks the distance at which the sensor no longer detects the object and returns to the undetected state. This point is usually farther away than the switch point On.
The distance between these two points, i.e., between switch point On and switch point Off, is called switching hysteresis. This hysteresis is deliberately intended to prevent the sensor from switching between the states On and Off continuously during small movements of the object or during disturbances such as vibration or noise. The hysteresis thus ensures a stable and reliable switching process by creating a defined range in which the sensor does not make a status change even though the object is near the switching threshold.
Proximity Switch Accessories
For the effective use of proximity switches, a variety of tools and accessories are available to improve the mounting, alignment, and performance of the sensors. This includes, but is not limited to, workpiece detection devices specifically designed to accurately position and reliably detect objects. They are instrumental in increasing the accuracy of object detection in automated manufacturing processes. Sensor holders are another central accessory, which allow for stable attachment and flexible alignment of proximity switches. Using angle plates, angle consoles or special mounting systems, as presented in the article Angle Plates and Angle Brackets – Overview & Fields of Application, sensors can be precisely aligned and fixed to the respective object or process. In addition, sensor rails, switch cams, or sensor plates are also used in practice, which further simplify the integration of proximity switches into complex systems. These elements facilitate precise positioning, fine-tuning of the sensors and increase flexibility as requirements change.
