Proximity sensorA proximity sensor is a sensor able to detect the presence of nearby

objects without any physical contact.

INFRARED

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.

INDUCTIVE

CAPACITIVE

Types of PROXIMITY SENSOR

Capacitive

Inductive

Passive optical

Ultrasonic sensor

MAGNETIC

Magnetic Proximity Sensors

Magnetic proximity sensors are non-contact proximity

devices that are used to detect magnetic objects (e.g.

permanent magnets).

They sense the presence of a magnetic object,

commonly referred to as the target. The target,

characterized by its magnetic field, triggers the

switching process when it enters the detection range of

the sensor.

The switch may be a reed switch or the device could

operate due to inductive, variable reluctance,

magneto resistive or hall effect operating principles.

Sensors Specifications

Performance Criteria

• Rated operating distance is the critical distance at which switching takes place. It is important to choose a sensor that

will operate in the required sensing range. This could be

dictated by process requirements and mounting option.

• Repeatability is the distance within which the sensor repeatably switches. It is a measure of precision. Depending on

the application, precision could be an important design

criterion when selecting a sensor.

OPERATING PRINCIPLES FOR MAGNETIC SENSORS

• Contacts are well protected against dust, oxidization and corrosion due tothe hermetic glass bulb and inert gas; contacts are activated by means of amagnetic field rather than mechanical parts

• Special surface treatment of contacts assures long contact life• Maintenance free• Easy operation• Reduced size

Magnetic sensors are actuated by the presence of a permanent magnet.

Their operating principle is based on the use of reed con- tacts, whose thin

plates are hermetically sealed in a glass bulb with inert gas. The presences of

a magnetic field makes the thin

plates flex and touch each other causing an electrical contact. The plate’s

surface has been treated with a special material par- ticularly suitable for

low current or high inductive circuits. Magnetic sensors compared to

traditional mechanical switches have the

following advantage:

When using the NO (normally open) type the open reed contact closes as the magnet approaches. NO Magnetic sensors are twowires. When using the NO+NC type both NO (normally open) and NC (normally closed) functions are made available by means of a single glass bulb. NO+NC Magnetic sensors are supplied with three wires, one is in common, one is NO and one is NC

TYPICAL REED CONTACT PROTECTIONS

The lifespan of a magnetic sensor at low values of voltage and current depends on themechanical characteristics of the contact while for higher values the operating life depends upon the charectristics of load.

Magnetic Proximity SensorsExtremely small dimensions and high operating distances characterize these magnetic sensors in metallic case. To actuate sensor a magnetic is required.

Features:• High operating distance

• Threaded metallic case

• Protection degree of IP 67

• Hermetically sealed

• Compliant to the EMC directive

Dimensions: mm, 1" = 25.4 mm, 1 mm = .03937”

Table 1. Operating distances as a function of the magnetic unit(mm)

not to scale

4

Output NO NO/NCMagnetS3410 8 6S3411 20 17S3412 40 33

Output VA V A MODELNO 10 220 0.5 S3390 S3391 S3392 S3393

NO+NC 20 150 1 S3398 S3399 S3400 S3401Dimensions: mm1" = 25.4 mm1 mm = .03937”

Wiring

NO

Changeover, NO+NC

External Dimensions ∅ 6 mm M8 x1 M10 x 1 M12 x 1Operating Distance See Table 1Switching Frequency NO output = 230 Hz max/ NO+NC output = 250 Hz maxCase Nickel-Plated BrassProtection Degree IP 67Operating Temperature -25 to +100°C (-13 to +212°F)Output Connection Cable: 2 x 0.14 mm², L=2m

Rectangular Magnetic Proximity Sensors

To actuate sensor a magnetic is required.

Features:

•

•

•

•

High operating distance

Rectangular case

Protection degree of IP 67

Hermetically sealed

• Compliant to the EMC directive

CAPACITIVE

proximity sensor

Introduction

Capacitance is an electrical property which is created by applying

an electrical charge to two conductive objects with a gap between

them. The capacitance of a parallel plate capacitor is given by:

Where C is the capacitance, k is the permittivity of free

space constant, K is the dielectric constant of the material in the

gap, A is the area of the plates, and h is the distance between the

plates.

Capacitive sensor

The capacitive sensor, consists of a target

plate and a second plate known as the

sensor head. These two plates are

separated by an air gap of thickness h

and form the two terminals of a capacitor.

Capacitive sensor

The guard ring

essentially moves the

distorted edges of the

electric field to the

outer edge of the

guard, significantly

improving the uniformity

of the electric field over

the sensor area and

extending its linearity.

Capacitive sensor

Sensitivity

It is clear that the capacitance impedance Zc is linear in h and that

methods of measuring ∆Zc will permit extremely simple plates to act

as a sensor to measure the displacement ∆h.

Cylindrical sensor heads are linear and is valid provided that

0<h<D/4 where D is the diameter of the sensor head. Fringing in the

electric field produces nonlinearities if h >D/4. The linear range can

be extended to h=D/2 if a guard ring surrounds the sensor.

The sensitivity of the probe is given by :

Sensitivity

Sensitivity can be improved by reducing the area of the probe, however

the range of the probe is limited by linearity to about D/2.

Low frequency improves sensitivity but limits frequency response of the

instrument.

It is also important to note that the frequency of the ac power supply must

remain constant to maintain a stable calibration constant.

Advantages

It is non-contacting and can be used with any target material.

The sensor is extremely rugged and can be subjected to high shock loads

and intense vibratory environments.

Can be used at high temperature.

Sensitivity remains constant over a wide range of temperature.

Industrial application

Typical capacitive sensor construction shows two plates: one

connects to the oscillator (sensor electrodes), and the other is the

object being sensed, which is detected within the electrical field.

Industrial application

Capacitive proximity sensors can detect objects composed of a wide

variety of materials. Here, a capacitive sensor detects the contents of a

box.

Industrial application

A capacitive sensor functions like a typical capacitor. The metal plate in

the end of the sensor electrically connects to the oscillator, and the object

to be sensed acts as the second plate. When this sensor receives power,

the oscillator detects the external capacitance between the target and

the internal sensor plate. This arrangement completes the circuit and

provides the necessary feedback path for the output circuit to evaluate.

Capacitive sensors can detect many different kinds of objects. For

example, solids, liquids, or granular targets are all detectable (including

metals, water, wood, and plastic).

Inductance proximity sensors

Inductive proximity sensors operate under the electrical principle of

inductance. Inductance is the phenomenon where a fluctuating

current, which by definition has a magnetic component, induces an

electromotive force (emf) in a target object.

these are best used when your application calls for metallic target

sensing with a range that is within an inch of the sensing surface.

An inductive proximity sensor has four elements: coil, oscillator, trigger

circuit, and an output. The oscillator is an inductive capacitive tuned

circuit that creates a radio frequency. The electromagnetic field

produced by the oscillator is emitted from the coil away from the

face of the sensor. The circuit has just enough feedback from the

field to keep the oscillator going. When a metal target enters the

field, eddy currents circulate within the target. This causes a load on

the sensor, decreasing the amplitude of the electromagnetic field. As

the target approaches the sensor, the eddy currents increases,

increasing the load on the oscillator and further decreasing the

amplitude of the field.

The trigger circuit monitors the oscillator’s amplitude and at a

predetermined level switches the output state of the sensor from its

normal condition (on or off). As the target moves away from the

sensor, the oscillator’s amplitude increases. At a predetermined level

the trigger switches the output state of the sensor back to its normal

condition (on or off).

Eddy current sensor

An eddy current sensor measures distance between the sensor head and

an electrically conducting surface.sensor operation is based on eddy

currents that are induced at the conducting surface as magnetic flux lines

from the sensor intersect with the surface of the conducting material.

The magnetic flux lines are generated by the active coil in the sensor,which

is driven at a very high frequency(1 MHz).

The magnitude of the eddy current produced at the surface of the

conducting material is a function of the distance between the active coil

and the surface.the eddy currents increase as the distance decreases.

Changes in the eddy currents are sensed with an

impedance(inductance) bridge.two coils in the sensor are used for

two arms of the bridge. The other two arms are housed in the

associated electronic package.

The first coil in the sensor is the active coil and the second coil is

inactive or balance coil.active coil changes inductance with target

movement which is wired into the active arm of the bridge.thw

second coil is wired into an opposing arm of the same bridge,where it

serves as a compensating coil and cancel the effects of temperature

change.

The output from the impedance bridge is demodulated and

becomes the analog signal,which is linearly proportional to distance

between the sensor and the target.

The sensitivity of the sensor is dependent on the target material,with

higher sensitivity associated with higher conductivity materials.

Thus eddy current sensors are high output devices if the specimen is

non magnetic and from the graph it says that the sensitivity

decreases significantly if the specimen material is magnetic.

For aluminium the sensitivity is typically 100mV/mil(4mV/mm).

For non conducting,poorly conduting or magnetic materials,it is

possible to bond a thin film of aluminium foil to the surface of the target

at the location of the sensor to improve the sensitivity.the thickness of

the foil can be little as 0.7mm.

The effect of temperature on the output of the eddy current sensor is

small. The sensing head with with dual coils is temperature

compensated,however a small error can be produced by

temperature changes in the target material,since resistivity of the

target materil is a function of temperature.

So while measuring output we should even take care of sensitivity.

The range of eddy current sensor is controlled by the diameters of the

coils,with the larger sensors exhibiting the larger ranges.the range to

diameter is usually about 0.25.

linearity is typically better than 0.05 percent

Eddy-Current Sensor Advantages

Compared to other noncontact sensing technologies such as optical,

laser, and capacitive, high-performance eddy-current sensors have

some distinct advantages.

Tolerance of dirty environments

Not sensitive to material in the gap between the probe and target

Less expensive and much smaller than laser interferometers

Less expensive than capacitive sensors

Eddy-Current sensors are not a good choice in these conditions:

Extremely high resolution (capacitive sensors are ideal)

Large gap between sensor and target is required (optical and laser

are better)

The Eddy Current Sensor

Precision eddy current noncontact measuring systems have been used for

more than 30 years for displacement, vibration, thickness, alignment,

dimensioning, and parts sorting applications. All these can be classified as

variations on displacement because in each case the parameter being

measured is the distance from the target to the sensor. The differences lie in

the interpretation and implementation of the displacement data.

The fact that eddy current sensors do not require contact for measuring

displacement is quiet important.as a result of this feature,they are often

used in transducer systems for automatic control of dimensions in

fabrication process.

They are also applied extensively to determine thickness of organic

coatings that are non-conducting.

Ultrasonic Sensors

Ultrasonic sensors are based on measuring the properties of

sound waves with frequency above the human audible

range.

Systems typically use a transducer which generates

sound waves in the ultrasonic range, above 18 kHz, by

turning electrical energy into sound, then upon receiving

the echo turn the sound waves into electrical energy

which can be measured.

Ultrasonic sensors are non-intrusive in that they do not

require physical contact with their target, and can

detect certain clear or shiny targets otherwise obscured to some vision-based sensors.

Active Sensors

Active ultrasound sensors emit sound waves from quartz-crystal

transducers. The waves strike objects within the field of detection and

as long as there are no movement the waves are not disrupted.

However, when movement occurs the sound wave is disrupted and is

reflected back to the system’s receiver.

Passive Ultrasonic Motion Sensors

Passive sensors operate on the principle of sounds such as breaking glass or metal striking metal to trigger alarms.

These sounds produce waves detected by the sensors

that, like the active sensors, relay them to electronic

control units to determine if the sound wave pattern falls

within established normal parameters.

Benefits of High Frequency

Uninterrupted coverage

Electronically adjustable reach

Detection through glass, wood, walls etc.

“Invisible” sensor that can be integrated in lights

Can be concealed behind trim panels

Uninterrupted signal propagation

Good quality of detection, even in long rooms, stairwells etc.

Extremely fast detection of the smallest of movements

Operates irrespective of ambient temperature and temperature

of objects

Reach, twilight threshold and light ‘ON’ duration can be set to suit

individual needs

Applications

a)Bottle Counting on Drink Filling Machines

Thru-beam sensors

Individual detection of conveyed bottles is normally too fast for

sensing by ultrasonic sensors. The bottles pass the sensor too

quickly and the gaps between the bottles are often too small.

For this reason, ultrasonic thru-beam sensors are particularly

suitable for bottle counting.

The use of hot steam and chemicals for machine cleaning in

these applications requires ultrasonic thru-beam sensors with a

high degree of chemical resistance.

Even in areas with strong steam generation, reliable detection

of bottles is guaranteed with ultrasonic thru-beam sensors.

b) Vehicle Detection in Barrier Systems

In car parking lots and parking garages, entry is controlled using

barrier systems. The barrier must not be lowered when there is a

vehicle underneath. Ultrasonic sensors are particularly suitable

for controlling this process. They detect objects regardless of

vehicle type or color and monitor the entire area below the

barrier.

When mounting and aligning the sensors, ensure that the

devices are installed at a sufficient distance from the ground (if

necessary, angled slightly upwards)

Optical Proximity

Sensors

Working Principle

An optical proximity sensor offers non-contact sensing of

almost any object up to a range of 10 meters. It includes a

light source, (usually an LED in either infrared or visible light

spectrum) and a detector (photodiode). The light source

generates light of a frequency that the light sensor is best able

to detect, and that is not likely to be generated by other

nearby sources. Infra-red light is used in most optical sensors. To make the light sensing system more foolproof, most optical

proximity sensor light sources pulse the infra-red light on and

off at a fixed frequency.

Due to the high intensity infra-red energy beam, these sensors

have major advantages over other opto-electronic systems when employed in dusty enviroments.

There are two main types of Optical Proximity Sensors :

1) Beam Type

2) Retro Reflective Type

Name Advantages Disadvantages

Beam Type

•Most accurate

•Longest sensing

range

•Very reliable

•Must install at two

points on system:

emitter and receiver

•Costly - must

purchase both

emitter and receiver

Reflective Type

• Slightly less

accurate than

through-beam

•Very reliable

•Must install at two

points on system:

sensor and reflector

•Sensing range less

than beam type

Effective in Dusty/ noisy enviroments

Uses focused beam

Long range

Higher sensing distance compared to Inductive and

capacitive type sensors

Immune to visible light interference

Drawbacks

Interference

Cost

Pb in fog/smoke/nontransparent materials

Advantages

Lift door mechanisms

Pipeline monitoring, wind turbine blade monitoring, fuel tank

and ship hull monitoring, power line monitoring etc.

Component positioning sensing in Electronic industry

Security and safety applications in presses

Colour sensing applications

Counting of bottles/containers in factories etc.

General Applications

proximity sensor for

neurovascular bundle detection during dental

implant surgery

The basic implant procedure involves using a drill to create

an osteotomy in the bone where a titanium screw is

placed. A dental prosthesis is then placed onto the frame

of the titanium screw. The success of these procedures is

dependent on the anchorage by the formation of bony

tissue around the implant, such that implant shows no mobility when loaded.

Dental implant surgery is done by using combined near infrared absorption (NIR) and optical coherence

tomography (OCT) techniques. These have different

sensitivity to the proximity of optical contrast from

neurovascular bundles.

Implant depth is determined by the

surgeon when drilling the channel in

the mandible. The depth when drilling

a dental implant channel within the

mandible is limited by the risk of

breaching the mandibular canal that

contains a neurovascular bundle

including the inferior alveolar nerve

(IAN), which is the mental nerve

providing sensory enervation to the

lower lips and chin.

Loss of sensation in the anterior

mandible, such as numbness to the

lower lip and chin, can occur due to

the disruption of the IAN.

The reported incidence of nerve

injury from implant placement is as

high as 44%, with 73% of dentists

encountering neurosensory

impairment within their practice.

The medical complications that could be avoided by using this

device are

(i) Vertical bone grafting

(ii) Nerve lateralization (moving the nerve out of the jaw) which

causes a high risk of nerve injury and sometimes permanent

damage.

Thank you !