Proximity sensor

A PROXIMITY SENSOR is a sensor able to detect the presence of nearby objects without any physical

contact.

A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared,

for instance), and looks for changes in the field or return signal. The object being sensed is often referred

to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For

example, a capacitive or photoelectric sensor might be suitable for a plastic target; an inductive proximity

sensor always requires a metal target.

The maximum distance that this sensor can detect is defined "nominal range". Some sensors have

adjustments of the nominal range or means to report a graduated detection distance.

Proximity sensors can have a high reliability and long functional life because of the absence of

mechanical parts and lack of physical contact between sensor and the sensed object.

Proximity sensors are also used in machine vibration monitoring to measure the variation in distance

between a shaft and its support bearing. This is common in large steam turbines, compressors, and

motors that use sleeve-type bearings.

International Electro technical Commission (IEC) 60947-5-2 defines the technical details of proximity

sensors.

A proximity sensor adjusted to a very short range is often used as a touch switch.

A proximity sensor is divided in two halves and if the two halves move away from each other, then a

signal is activated.

A proximity sensor can be used in windows, and when the window opens an alarm is activated.

Types of sensors

Capacitive

Capacitive displacement sensor

Doppler effect (sensor based on effect)

Eddy-current

Inductive

Laser rangefinder

Magnetic, including Magnetic proximity fuse

Passive optical (such as charge-coupled devices)

Passive thermal infrared

Photocell (reflective)

Radar

Reflection of ionising radiation

Sonar (typically active or passive)

Applications

Parktronic, car bumpers that sense distance to nearby cars for parking

Ground proximity warning system for aviation safety

Vibration measurements of rotating shafts in machinery [1]

Top dead centre (TDC)/camshaft sensor in reciprocating engines.

Sheets break sensing in paper machine.

Anti-aircraft warfare

Mobile phones

Roller Coasters

Conveyor systems

Touch screens on mobile devices that come in close proximity with the face

Descriptionhttp://www.engineershandbook.com/Components/proximitysensors.htm

Proximity - Spatial Presence

Proximity Sensors

1. Inductive Proximity Sensors

Inductive proximity sensors are widely used in the modern high speed process control environment for the detection, positioning and counting of ferrous and non-ferrous metal objects. Due to the method of construction and superior performance of inductive sensors, they are increasingly used to replace the traditional limit switch, thus upgrading speed and reliability of existing machinery.

Principle of Operation

Inductive proximity sensors respond to ferrous and non - ferrous metal objects. They will also detect metal through a layer of non - metal material. An inductive sensor consists of an oscillator circuit (ie. the sensing part) and an output circuit including a switching device (eg. transistor or thyristor), all housed in a resin encapsulated body. An essential part of the oscillator circuit is the inductance coil creating a magnetic field in front of the sensing face. When the magnetic field is disturbed, the output circuit responds by either closing the output switch (normally open version type NO) or by opening the output switch (normally closed version type NC).

Proximity - Spatial Presence

Turck Proximity Sensors

Proximity Sensors

1. Inductive Proximity Sensors

Inductive proximity sensors are widely used in the modern high speed process control environment for the detection, positioning and counting of ferrous and non-ferrous metal objects. Due to the method of construction and superior performance of inductive sensors, they are increasingly used to replace the traditional limit switch, thus upgrading speed and reliability of existing machinery.

Principle of Operation

Inductive proximity sensors respond to ferrous and non - ferrous metal objects. They will also detect metal through a layer of non - metal material. An inductive sensor consists of an oscillator circuit (ie. the sensing part) and an output circuit including a switching device (eg. transistor or thyristor), all housed in a resin encapsulated body. An essential part of the oscillator circuit is the inductance coil creating a magnetic field in front of the sensing face. When the magnetic field is disturbed, the output circuit responds by either closing the output switch (normally open version type NO) or by opening the output switch (normally closed version type NC).

1. Capacitive sensors are often successfully used in applications which cannot be solved with other sensing techniques. Capacitive sensors respond to a change in the dielectric medium surrounding the active face and can thus be tuned to sense almost any substance. Capacitive sensors can, also, sense a substance through a layer of glass, plastic or thin carton.

Some typical applications for capacitive sensors are:

1. Level control of non-conductive liquids (oil, alcohol, fuel).2. Level control of granular substances (flour, wheat, sugar).3. Sensing substances through a protective layer (eg. glass).

The fact that capacitive sensors respond to most substances, necessitates some care during the installation, adjustment and long term operation of the sensor. The sensitivity of capacitive sensors is affected by the moisture content and the density of the substance to be sensed. Deposits of excessive dust and dirt on or around the sensing face of the sensor, cause erratic response and hence the sensor may require periodic cleaning if used in a polluting environment.

Principle of Operation

Turck Proximity Sensors

Capacitive sensors respond to any substance with a high dielectric constant (water, oil, fuel, sugar, paper) without necessarily making physical contact. They are less suitable for polystyrene and similar low density substances. Operation is based on an internal oscillator with two capacitive plate-electrodes, tuned to respond when a substance approaches the sensing face. When the target is sensed, the output switch will either close to activate a load for a normally open option or the switch will open to de-activate the load for a normally closed option. The LED will illuminate when the output switch closes.

2. Photoelectric or Opto-electronic Sensors

Photoelectric sensors offer non-contact sensing of almost any substance or object up to a range of 10 meters. Photoelectric sensors consist of a light source (usually an LED, light emitting diode, in either infrared or visible light spectrum) and a detector (photodiode). Due to the high intensity infra-red energy beam, these sensors have major advantages over other opto-electronic systems when employed in dusty enviroments. With their focused beam and long range, opto-electronic sensors are increasingly used in applications where other sensing techniques are lacking in sensing distance or accuracy.

Photoelectric sensors are available in a variety of modes including:

Infrared Proximity (Diffuse Reflective)

Proximity type photoelectric sensors detect the light reflected by the target itself. Proximity photoelectric sensors are preferable for general purpose sensing applications, particularly where the detected object is only accessible from one direction.

Transmitted Beam (Thru-beam)

Transmitted beam photoelectric sensors use separate infrared transmitters and receivers. Objects passing between the two parts interrupt the infrared beam, causing the receiver to output a signal.

Retroreflective (Reflex)

Retroreflective photoelectric sensors operate by sensing the light beam that is reflected back from a target reflector. As with thru beam models, objects which interrupt the beam activate an electronic output.

Polarized Retroreflective (Polarized Reflex)

Polarized retroreflective sensors work like normal retroreflective sensors but use a polarizing filter in front of the transmitter and receiver optics. These filters are designed so that shiny objects are reliably detected.

Fiber Optic

Fiber optic sensors use fiber optic cable to conduct light from the LED to the sensing area, and another cable to return light from the sensing area to the receiver. By using fiber optic cables, the electronics can be protected from hostile environments such as temperature extremes and harsh chemicals. Fiber optics also allow sensing in extremely confined spaces.

Background Rejection

STI's background rejection sensors use a special arrangement of two sensing zones: the near-field zone is where objects can be detected, the far-field zone is where objects cannot be detected. There is an extremely sharp cut-off between these zones. The cut-off range is adjustable. These sensors are ideal for applications where background objects need to be ignored.

3. Ultrasonic sensors

Ultrasonic sensor utilize the reflection of high frequency (20KHz) sound waves to detect parts or distances to the parts. The two basic ultrasonic sensor types are:

1. Electrostatic - Uses capacitive effects for longer range sensing and wider bandwidth with more sensitivity.

2. Piezoelectric - These rugged and inexpensive sensors operate by a charge displacement during the strain in crystal lattices.

In general, ultrasonic sensors are the best choice for transparent targets. They can detect a sheet of transparent plastic film as easily as a wooden pallet.

http://www.sensorcentral.com/photoelectric/proximity01.php

Proximity Sensors/Operating Principle/Type

Outline

A proximity sensor can detect metal targets approaching the sensor, without physical contact with the target. Proximity sensors are

roughly classified into the following three types according to the operating principle: the high-frequency oscillation type using

electromagnetic induction, the magnetic type using a magnet, and the capacitance type using the change of capacitance.

KEYENCE proximity sensors are of the high-frequency oscillation type.

Features

Non-contact detection, eliminating damage to sensor head and target.

Non-contact output, ensuring long service life.

Stable detection even in harsh environments exposed to water or oil

splash.

High response speed.

 

Operating Principle of High-frequency Oscillation Type Proximity Sensor

Operating principle of general sensor

 

A high-frequency magnetic field is generated by coil L in the oscillation

circuit. When a target approaches the magnetic field, an induction

current (eddy current) flows in the target due to electromagnetic

induction. As the target approaches the sensor, the induction current

flow increases, which causes the load on the oscillation circuit to

increase. Then, oscillation attenuates or stops. The sensor detects this

change in the oscillation status with the amplitude detecting circuit, and

outputs a detection signal.

 

Aluminum Proximity Sensor

Generally, the frequency of high-frequency, oscillation type proximity sensors tend to change when a nonferrous metal is placed

near it. The aluminum proximity sensor detects any changes in oscillating frequency.

Type

Classification by configuration

Standard configuration Features

Self-contained proximity sensor

Readily operative by adding DC power supply.

Separate/In-cable amplifierCompact sensor headLong-detecting distance

Glossary

Shielded type Non-shield type

The sensing coil is encased in a metal-shielding.This type is less affected by surrounding metal, and can be embedded in a metal base.

The sensing coil is not metal-shielded.This type provides a longer detecting distance, compared to a shielded type of the same size.This type is easily affected by surrounding meta, and therefore no object other than the target must be present around the tip of the sensor head.

Term Explanation of Proximity Sensors/Reading Characteristics Data

Term Explanation of Proximity Sensors

Detecting distance

 

The distance from the detecting surface of a sensor head to the point where a standard

target approaching the sensor head is first detected.

Maximum operating distance (ES Series):

The maximum obtainable operating distance, disregarding accuracy.

Hysteresis

 

The difference between the reset distance and the detecting distance using a standard

target. The reset distance refers to the distance from the detecting surface of a sensor

head to the point at which the sensor resets for subsequent detection.

Standard target

 

A target determined as standard according to shape, size, and material, that is used to

obtain the specifications of a sensor.

Repeatabillty

 

The detecting distance tolerance range when a standard target is subjected to repeated

detection under set conditions.

Response frequency

 

A sensor's maximum number of ON/OFF operations per second when repeatedly

detecting standard targets aligned on a wheel, as shown.

Temperature fluctuation

 

The effect of ambient temperature, within the rated operating range, on the detecting

distance of a sensor, represented by the percentage of change from the detecting

distance obtained at +23ºC.

N.O. and N.C. output modes

N.O. (normally open) output mode

The operating mode that permits the sensor to output an ON signal when a target

enters the detecting range.

N.C. (normally closed) output mode

The operating mode that permits the sensor to output an ON signal when a target

goes out of the detecting range.

Reading Characteristics Data

Detecting range

 

This graph shows the variations in detecting points of the target (defined in each graph) measured by moving the target parallel to the sensor head.

*The ES Series is equipped with a sensitivity adjustment trimmer located on the amplifier unit, that can be used to change the detecting distance.The data in this chart was obtained with the trimmer set at 100% and 50% of the maximum stable detecting distance.

 

Residual voltage  

 

This graph shows the effect of the load current on the residual voltage output.

 

Detecting distance vs. size and material of target

 

This graph shows the effect of the size of a square metal target (t=1 mm t=0.04") on the detecting distance.

*For the ES Series, the data obtained at 100% of the maximum stable detecting distance is provided.

Leakage current

 

This graph shows the effect of the supply voltage on the leakage current for the DC 2-wire type proximity sensors. This graph is used to adjust the quantity of leakage current to the appropriate level in order for the load to operate and reset properly.

Type of metal and detecting distance

 

The detecting distance varies according to target material. The charts show the

percentage of detecting distance for common materials when iron is 100%.

However, as the rate varies depending on the sensor model, refer to the

characteristics chart "Detecting distance vs. size and material of target" for each

model. Note that metal-plated targets will affect the detecting distance.

 

Detecting distance vs. target thickness

ex)EX-18M:KEYENCE products  In general, when a target of nonferrous metal such as copper or aluminum is

approximately 0.01- mm 0.0004" thick, it has a detecting distance similar to that of

a target of ferrous metal.

Connections

Parallel connection (OR logic circuit) and serial connection(AND logic circuit)

Example:AND logic circuit for EV Series AC 2-wire type proximity sensors

For serial connection follow the guidelines given below:

Supply voltage: 85 to 240 VAC

Number of connected sensor units: 3

max.

*If sensors do not operate stably, provide each with a 500 k to 10 MΩ resistor in parallel. This will stabilize the voltage and allow the

sensors to operate stably.

Example:OR logic circuit for EV Series AC 2-wire type proximity sensors

*Do not connect in this manner when 2 or more sensors are activated simultaneously. The total leakage current produced by "n"

number of proximity sensors connected in parallel is "n" times greater than that with a single sensor.

*Reference by KEYENCE products

OR logic circuit and AND logic circuit with ES Series

OR logic circuit AND logic circuit

ES-32DCIn OR logic circuits, the desired number of amplifier units can be used if the leakage current produced by the amplifiers does not disturb the load current.

0.1 mA x number of connected units < Load current

ES-32DCIn AND logic circuits, set the mode selector switch to position B and connect the external relay as N.C. 

ES-12ACIn OR logic circuits, the desired number of amplifier units can be used if the leakage current produced by the amplifiers does not disturb the load current.

ES-12ACIn AND logic circuits, the number of amplifier units used must not exceed 10.

0.2 mA x number of connected units < Load current

ES-11AC/21ACIn OR logic circuits, the desired number of amplifier units can be used if the leakage current produced by the amplifiers does not disturb the load current.

0.2 mA x number of connected units < Load current

ES-11AC/21ACIn AND logic circuits, the number of amplifier units used must not exceed 10.

Hints on Correct Use/General Notes

Hints on Correct Use

Cable disconnection alarm output(ES-32DC)

 

The alarm output will be triggered when the sensor head cable becomes disconnected or

if it is wired incorrectly, notifying the operator of a malfunction.

*It is recommended that the ES-32DC unit be connected to a self-holding circuit, otherwise alarm output may be intermittently output in the early stages of wire breakage.

Ensuring horizontal positioning accuracy

 

For the ES Series, repeatability data is provided only for the direction perpendicular to the

detecting surface of the sensor head. If the same level of accuracy is required horizontally,

adjust the sensitivity adjustment trimmer to achieve the detection conditions as shown here.

2-wire proximity sensors

Residual voltage

The impedance of the 2-wire-type proximity sensor's circuit, when output is ON, produces a voltage which is the difference of the

voltage across the 2 wires connected to it (V1, 0 V). This means that the voltage across the load (V2) is equal to the supply voltage

minus V1 (V2 = Vs - V1). Make sure that V2 is greater than the operating voltage of the load. (Refer to the Characteristics chart

"Residual voltage".)

Effects of leakage current

With a 2-wire proximity sensor, a small amount of current flows (leakage current) to keep the circuit operating even when the sensor

is turned OFF. (Refer to graph "Leakage current characteristics".)

Because of this current, a low voltage remains on the load, sometimes preventing the load from properly resetting. Before operation,

check that the residual voltage is lower than the reset voltage of the load.

When the load current is low

When the load current is less than 5 mA, connect a bleeder resistor to give the sensor 5 mA or more load current. Make sure the

residual voltage is less than the reset voltage of the load.

General Notes

Interference

When 2 or more proximity sensors of the same model are closely installed side-by-side, the high-frequency magnetic fields of one

sensor may disturb the other sensor's operation. This phenomenon is called interference.

 

Eliminating interference

Use a proximity sensor that can be switched to an alternate frequency (EM Series).

Use interference suppression function. --- ES-M1, M2

Provide the proximity sensor with an interference prevention adaptor.(ES Series)

Allow sufficient distance between sensors to prevent interference. (For further information, refer to the section "Hints on correct

use" for each model.)

Use sencors of different models. (Contact KEYENCE for details.)

Surrounding metal  

When embedding a proximity sensor in a metal base, provide the distances specified for

each model to minimize interference from the surrounding metal. For details, refer to the

section "Hints on correct use" for each model.

 

Miscellaneous

When using a commercially available switching regulator, ground its chassis grounding and earth grounding terminals.

Isolate sensor wiring from power lines and highvoltage lines; otherwise, the sensor may malfunction due to noise interference.

Loads (lamps, motors, etc.) having a rush current 10 times greater than the rated current will damage or break the output circuit.

For such loads, use external relays with a sufficient rated capacity. Also, to protect sensors from surge due to the counter-

electromotive force of a relay coil, use relays with a surge-absorber.

Proximity Sensor Products

Amplifier-in-Cable Small Proximity SensorEM Series

Amplifier-in-Cable Compact Proximity Sensor

Ultra-small sensor head

Amplifier and operation indicator built into cable.

Strong, flexible cable IP-67 waterproof housing

 Price Inquiry

 2D CAD Data

 3D CAD Data

 Catalog

 Instruction Manuals

Self-Contained Proximity SensorEZ/EV Series

Self-contained Proximity Sensor

Compact sensor head.

Visible output indicator built into sensor.

Flexible cable joint IP-67-rated housing

 Price Inquiry

 2D CAD Data

 3D CAD Data

 Catalog

 Instruction Manuals

Long-distance Separate-amplifier Proximity SensorsES Series

Long-distance Separate-amplifier Proximity Sensors

Detecting distance twice that of conventional sensors

Detecting distance is easily adjustable

Wide range of sensor head types available.

Built-in alarm output

 Price Inquiry

 2D CAD Data

 3D CAD Data

 Catalog

 Instruction Manuals

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