SENSORS k.saideep

What is a sensor A sensor is a detector which converts a physical quantity into a signal which can be read by an observer or electronic instrument For example consider a thermometer which converts the temperature of the body into expansion and contraction of the mercury in thermometer or consider a thermocouple which converts the difference of the temperature at the junction into the electrical voltage

WHAT IS THE PRINCIPLE INVOLVED IN THE THERMO COUPLE AND TELL ME ONE PRACTICAL APPLICATION OF THIS SENSOR AND ON WHAT PRINCIPLE DOES THE THERMOCOUPLE WORK?

CLASSIFICATION OF SENSORS BASED ON TOUCH: SIMPLE TOUCH : The presence or absence of object COMPLEX TOUCH : The presence of object plus some information regarding it’s size and shape BASED ON CONTACT: LIMIT SWITCH: contact detection of object PROXIMITY: Non-contact detection of object

How to make a simple touch sensor? using simple 555 timer: By connecting a 555 timer in mono stable mode a simple touch sensor circuit sensor can be made The time period(T) of the wave form is calculated as: T=1.1*R*C R=value of resistor connected between +VCC and 6 and 7 pin of timer C=value of capacitor connected between –VCC and 6 and 7 pin of timer

Circuit for mono stable mode? Circuit explanation: In this circuit when input voltage at trigger terminal is one-third of supply voltage an output pulse is produced at the output terminal of timer whose time period is adjusted by varying resistor and capacitor values

Complex touch sensor TACTILE SENSOR: The tactile sensor is a coordinated group of touch sensors Due to some of it’s qualities like coordination has given it a industrial importance There are many types of tactile sensors based on what property it depends upon like resistance , force, capacitive etc.

LIMIT SWITCH: It is a pressure sensor It is generally employed with pressure sensitive mechanical arm which is used to protect the mechanical arms from being damaged

APPLICATION CIRCUIT FOR limit switch for robotic arm In case of robotic arm this limit switch is connected to robotic arm and when it touches a obstacle the switch automatically closes and output is pulled low(similar in working of limit switch)

PROXIMITY SENSOR Types of proximity sensors 1.Inductive proximity sensor 2.capacitive proximity sensor 3.semiconductor displacement sensor 4.IR proximity sensor 5.Ultrasonic sensor

INDUCTIVE PROXIMITY SENSOR There is oscillator , detector and output circuit in this sensor The oscillator produces the radio frequency magnetic field which is shaped by the ferrite rod present inside it and makes it to focus at sensor face . when a metallic target comes near the sensor face the magnetic field gets disturbed and the amplitude of RF wave decreases and this change in amplitude is detected by detector and useful work is done by it based on it’s functionality

DIAGRAMATIC REPRESENTATION:

CAPACITIVE PROXIMITY SENSOR It also consists of oscillator , detector and output circuit Consider one plate of capacitor connected to switch via a lead and other face of the capacitor as target and the dielectric space is sensor consists of above mentioned circuits when switch is closed under normal condition a voltage is induced across capacitor and based on distance between plates some amount of charge is induced.

And when the lead connected to the switch is moved up or down then their will be movement of capacitor plate(assumed) and their will be difference in the voltage between plates and this change is observed by detector circuit and corresponding action is done according to the detector circuitry

What is the practical application of this sensors?

Semiconductor displacement sensor As the name indicates it has a semiconductor (LED) and it senses displacement of object It internally consists position sensitive detector(PSD) When the light from light emitting diode is reflected from target it falls on PSD forming a beam spot As the target moves the position of beam on PSD moves and the displacement of object can easily be found by the displacement of beam.

What is the practical application of this sensors?

IR PROXIMITY SENSOR It majorly consists of IR 417 and IR LED(which acts as transmitter) The connections are made as:

Working of the circuit The anode of LED is connected to fourth terminal of IR417 and cathode is connected to first terminal of IR417 and in turn connected to +ve terminal of battery Care must be taken such that only illumination from target element only must reach the IR417 but not the direct illumination from led which can be done by facing IRLED in downward direction.

RATINGS OF IR417 Sno. rating MIN MAX 1. VCC 4.5V 5.5V 2. illumination 100 50,000 3. output voltage 0 VCC-1.5 4. temperature -10 70

FORCE SENSORS There are two types of force sensors 1.strain gauge sensors 2.piezo electric transducer Strain gauge sensors: It basically works on relation of resistance of conductor with respect to length and area of conductor

PIEZOELECTRIC TRANSDUCER When a mechanical force is applied on piezo electric crystal a corresponding voltage is developed There is also inverse piezoelectric effect where the electric potential is applied across the plates of crystal it causes the deformation of crystal

Encoders Encoder is a digital optical device which converts motion into sequence of digital pulses By counting a single bit or by decoding a set of bits relative motion is converted into set of digital pulses. They can be of linear or rotary type

ABSOLUTE LINEAR ENCODERS It’s principle is that it gives a digital pulse as output based on the scanner position on linear scale which consist of opaque and transparent gratings

ABSOLUTE ROTATORY ENCODER The rotary encoder is similar to linear encoder expect that the scale is in circular form Generally gray code scanning is preferred rather than traditional binary code scanning in linear encoder

MAGNETIC SENSORS 1.Reed sensors 2.Hall effect sensors In both the cases this sensors performs switching action when magnetic field is applied What is industrial application of hall effect and normal application of reed sensors?

Reed sensors

GAS SENSORS There are many types of gas sensors whose working varies based on the gas which is detected by them like ethanol , methanol etc. MQ2 - Flammable Gas & Smoke MQ3 - Alcohol MQ4 - Methane MQ6 - LPG / Iso Butane / Propane MQ7 - Carbon Monoxide MQ9 - Carbon Monoxide & Flammable Gas Ethanol sensor: The sensor gives an output current in response to ethanol in breathed air.

Internal of sensor In this there are 6 pins -two pins are present in the heating system present in the tube -four pins are used for giving input or taking output and it is industrial grade

Working of sensor: Basically this sensor consists of aluminium tube which is surrounded by silicon and a the center there is a electrode made of aurum in which heating element is present When heating coil is heated the sno2 ceramics becomes semiconductor and releases the electrons and when the alchol is breathed in and reaches aurum electrode and alchol gives out acetic acid and more amount of current is produced

When there is change in alcohol content in breath corresponding change in output current takes place .

Connections(sample circuit): The heating coil terminals are connected to power terminal and ground terminal The pin A is connected to the power terminal via heating element and pin B is connected to microcontroller or aurdino and between this terminal and ground a resistor whose value is between 100K and 470K for getting more accurate values

TEMPERATURE SEN of 10mv/SOR The sensor has a sensitivity of 10mv/˚c . It means for every increase or decrease or increase in 1 degree centigrade of temperature there is increase or decrease by 10mv Use a conversion factor that is the reciprocal, that is 100˚C/V.

The general equation used to convert output voltage to temperature is: Temperature ( oC) = Vout * (100 oC/V) So if  Vout  is  1V , then, Temperature = 100 oC * The output voltage varies linearly with temperature.

ULTRASONIC SENSORS Ultrasonic sensors (also known as transceivers when they both send and receive) 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

PIN DIAGRAM

PIN DESCRIPTION Sno. Name type rating 1. Ground pin input 0V 2. Input pin input 5V 3. Signal pin input/output It covers a range of 2CM to 3M

THEORY OF OPERATION: The PING))) sensor detects objects by emitting a short ultrasonic burst and then "listening" for the echo. Under control of a host microcontroller (trigger pulse), the sensor emits a short 40 kHz (ultrasonic) burst. This burst travels through the air at about 1130 feet per second, hits an object and then bounces back to the sensor. The PING))) sensor provides an output pulse to the host that will terminate when the echo is detected, hence the width of this pulse corresponds to the distance to the target.

Conclusion(Yes/No) Whether sensor calculations are predetermined in all cases? Whether sensors are used for controlling something only? Whether all transducers are sensors? If yes are no why?