ADVANCED SENSOR

BYSUBHAJIT KARMAKAR 3rd year, A.E.I.E

HALDIA INSTITUTE OF HALDIA INSTITUTE OF TECHNOLOGYTECHNOLOGY

Contents Of The Topic

Introduction Analog & Digital Sensors Position Sensors Temperature Sensor Light Sensor Motion Sensor Conclusion Bibliography

Let us know something about sensors…

• Devices which perform an input function are commonly called Sensors because they "sense" a physical change in some characteristic that changes in response to some excitation, for example heat or force and covert that into an electrical signal. Devices which perform an output function are generally called Actuators and are used to control some external device, for example movement.

Analogue & Digital Sensors

Analogue Sensor

Analogue Sensors produce a continuous output signal or

voltage which is generally proportional to the quantity being measured.

Physical quantities such as Temperature, Speed, Pressure, Dis-

placement, Strain etc are all analogue quantities as they tend to be

continuous in nature.

Analogue sensors tend to produce output signals that are changing

smoothly and continuously which are very small in value so some form

of amplification is required. Then circuits which measure analogue signals

usually have a slow response and/or low accuracy.

Digital Sensor

Digital Sensors produce a discrete output signal or voltage

that is a digital representation of the quantity being

measured. Digital sensors produce a Binary output signal

in the form of a logic "1" or a logic "0“. This means then

that a digital signal only produces discrete values which

may be outputted as “bit” or “byte”.

Compared to analogue signals, digital signals or quantities

have very high accuracies and can be both measured and "sampled" at a very high clock speed.

Position SensorAs their name implies, these types of sensors provide

a "position“ feedback. One method of

determining a position, is to use either distance

which could be the distance between two points

such as the distance travelled or moved away

from some fixed point, or by "rotation“.

PotentiometerThe most commonly used of all the "Position Sensors", is the

 potentiometer because it is an inexpensive and easy to use position

sensor. Potentiometer is a simple device used to measure the EMF,

TPD, internal resistance of a cell.

Inductive Position Sensor One type of positional sensor that does not suffer from

mechanical wear problems is the "Linear Variable Differential

Transformer“or LVDT for short. This is an inductive type

position sensor which works on the same principle as the AC

transformer that is used to measure movement.

Inductive Proximity SensorAnother type of inductive sensor in common use is the

  Inductive Proximity Sensor also called an Eddy current

sensor. While they do not actually measure displacement

or angular rotation they are mainly used to detect the

presence of an object in front of them or within a close

proximity

Temperature Sensor Temperature Sensors measure the amount of heat energy or even coldness that is generated by

an object or system, and can "sense" or detect any physical change to that temperature producing

either an analogue or digital output.

Temperature sensors consist of two basic physical types:-

1) Contact Temperature Sensor:- These types of temperature sensor are required to be in physical contact with the object being sensed and use conduction to monitor changes in temperature

2) Non-contact Temperature Sensor:- These types of temperature sensor use convection and radiation to monitor changes in temperature.

Thermostat

The Thermostat is a contact type electro-mechanical

temperature sensor or switch, that basically consists of two

different metals such as nickel, copper, tungsten or aluminum

etc, that are bonded together to form a Bi-metallic strip.

Thermister

The Thermistor is another type of temperature sensor, whose name is a

combination of the words THERM-ally sensitive res-ISTOR. A thermistor

is a type of resistor which changes its physical resistance with changes in

temperature.

Resistive Temperature Detector(RTD)Resistance Temperature Detectors (RTDs) are temperature

sensors that contain a resistor that changes resistance value

as its temperature changes following a positive slope

(resistance increases when temperature is increasing). 

LEAD WIRE CONFIGURATION OF RTD

Thermocouple

Thermocouple is by far the most commonly used type

of all the temperature sensing devices due to its simplicity,

ease of use and their speed of response to changes in

temperature, due mainly to their small size.

Thermocouples also have the widest temperature range

of all the temperature sensors from below -200oC to well

over 2000oC.

 It is based on Seebeck's principle that, thermocouples can only measure temperature

differences and need a known reference temperature to yield the abolute readings.

The change in material EMF with respect to a change in temperature is called the

Seebeck coefficient

Light Sensor The light sensor is a passive devices that convert this "light energy" whether visible or in the

infrared parts of the spectrum into an electrical signal output. Light sensors are more commonly

known as "Photoelectric Devices" or "Photo Sensors" because the convert light energy into

electricity.

Light Sensors are classified in four types:

Photo Emissive Cells- :- These are photo devices

which release free electrons from a light sensitive material

such as cesium when struck by a photon of sufficient energy.

Photo Conductive Cells- These photo devices vary their

electrical resistance when subjected to light. Photoconductivity results from

light hitting a semiconductor material which controls the current flow through

it.

Photo Voltaic Cells These photo devices generate an emf

in proportion to the radiant light energy received and is similar in effect to photoconductivity. Light energy falls on to two semi- conductor materials sandwiched together creating a voltage.

Photo Junction Devices- These photo devices are

mainly true semiconductor devices such as the photodiode or

photo-transistor which use light to control the flow of electrons

andholes across their PN-junction.

Light Dependent Resistor

As its name implies, the Light Dependant Resistor (LDR) is made from a

piece of exposed semiconductor material such as cadmium sulphide that

changes its electrical resistance from several thousand Ohms in the dark to

only a few hundred Ohms when light falls upon it by creating hole-

electron pairs in the material.

Also, photo resistive cells have a long response

time requiring manyseconds to respond to a

change in the light intensity.

Phototransistor

An alternative photo-junction device to the photodiode is

the Phototransistor which is basically a photodiode with

amplification. The Phototransistor light sensor has its collector-

base PN-junction reverse biased exposing it to the radiant light

source

Photo-Darlington Photo Darlington transistors use a second bipolar NPN transistor to

provide additional amplification or when higher sensitivity of a

photo detector is required due to low light levels or selective

sensitivity, but its response is slower than that of an ordinary NPN

phototransistor.

Motion Sensor A motion detector is a device for motion detection. That is, it is a device that contains a

physical mechanism or electronic sensor that quantifies motion that can be either integrated

With time or connected to other devices that alert the user of the presence of a moving object

within the field of view.

An electronic motion detector contains a motion sensor that transforms the detection of motion

into an electric signal. This can be achieved by measuring optical or acoustical changes in the

field of view

An occupancy sensor is a motion detector that is integrated

with a timing device. It senses when motion has stopped

for a specified time period in order to trigger a light

extinguishing signal.

Passive Infrared Sensor:-

A Passive Infrared sensor (PIR sensor) is an electronic

device that measures infrared (IR) light radiating from objects in

Its field of view. PIR sensors are often used in the construction

of PIR-based motion detectors. Apparent motion is detected

when an infrared source with one temperature, such as a human,

passes in front of an infrared source with another temperature,

such as a wall.

Ultrasonic Sensor

Ultrasonic sensors  work on a principle similar

to radar or sonar which evaluate attributes of a target by

interpreting the echoes from radio or sound waves respectively.

Ultrasonic sensors generate high frequency sound waves and

evaluate the echo which is received back by the sensor. Sensors

calculate the time interval between sending the signal and

receiving the echo to determine the distance to an object

Conclusion• There are many other advance sensor in the world which are able to perform

difference actions. Here are very examples of them but we can apply them into many other applications

Bibliography http://www.wikipedia.org

http://www.advancedsensors.co.uk

http://www.sensors-research.com

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=610263

Jeffrey Cole & Steven Dubowsky, The Application of Advanced Robotics and Sensor

Technologies.