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Sensors and detectors. How to use sensor and detectors (in robotics ) RACE PROJECT VIGO (SPAIN) September 26-29, 2012. Definitions (1). Sensor: a device for sensing a physical variable of a physical system or an environment

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sensors and detectors

Sensors and detectors

Howtousesensor and detectors (in robotics)


VIGO (SPAIN) September 26-29, 2012

definitions 1
Definitions (1)
  • Sensor: a device for sensing a physical variable of a physical system or an environment
  • A sensor is in most cases associated with electronic circuits (converter) to generate a conditioned, normalized, amplified electric signal
  • A sensor plus a converter form a transducer, a device which transforms energy from one type to another (in this specific case electric energy)
  • Sometimes the sensor reacts by generating an electric signal itself, so it can be considered a transducer
  • Definitions of sensors and transducers do not always agree, so the word “sensor” alone might be enough to indicate these types of devices
  • Sensors are what the robotsneedtoknow the world …
    • from
classifications 1 physical characteristic
Classifications 1 (physicalcharacteristic)
  • Primary (sensors/transducers)
    • Temperature
    • Light (photoelettric)
    • Strain gauge / Mechanicaltension
    • Magneticfield
    • Displacement (potenziometers)
  • Secondary (sensors/transducers)
    • Force, acceleration, pressure (based on strain gauge)
    • Displacement (based on photoelettric, magneticfield, capacitance, …)
    • Speed (based on displacement and time)
classifications 2 output electric signal
Classifications 2 (output electricsignal)
  • Analog
    • The output isanelectricsignalwhichvariescontinuouslyaccordingto the variationsof the physicalvariablesbeeingmeasured
  • Digital
    • The output isanelectricpulsesignalwhich can assume onlytwovalues: logical 0 and 1. The frequency or the code associatedwith the pulsesequencecarries the information about the physicalvariablesbeeingmeasured
classifications 3 energetic behavior
Classifications 3 (energeticbehavior)
  • Active
    • Theyprovideanelectricsignalwhich can bedirectlyprocessedwithoutfurtherconsumptionofenergy: forexample the photovoltaiccells and termocouples
  • Passive
    • The requireanelectricalgenerator in ordertotransduce the physicalvariable in anelectricsignal: forexample the potentiometer
specifications static and dynamic parameters
Specifications (static and dynamicparameters)
  • Transfer function (transcaratteristic)
  • Monotone function
  • Linearity
  • Offset
  • Operationrange
  • Hysteresis
  • Sensitivity
  • Resolution
  • Repeatibility
  • Stability
  • Responsetime (timecostant e bandwidth)
  • Input and output impedance
sensors in this presentation
Sensors (in thispresentation)
  • Thermoresistance, thermistor, PN junction, integratedsensor (temperature)
  • Photoresistor, photodiode, phototransistor (light)
  • Tachometer (angolar speed)
  • Encoder (differenttipesfordisplacement and speed)
temperature thermoresistance 1
Temperature - Thermoresistance (1)

Metallicconductorswith a known “resistance vs temperature caracteristic curve”.

The basicphysicalprincipleofthesedevicesisthat the electricconductivity (resistivity) decreases (increases) as the temperature increases. Thisholdstrueformaterialslikeplatinum, nickel, copper.

The valueof T is in 0C

If β and γ are smallcomparedto the valueofαthis relation can beconsideredlinear (forexampleplatinum)

Ifnotitmightbenecessarytoperform a linearization (forexamplefor nickel and copperfortemperaturesabove 1000C)

Thermoresistancehave a low sensitivity

temperature thermoresistance 2
Temperature - Thermoresistance (2)

Exampleof a temperature monitoring system from 00C to 3000C, output tensionbetween 0V and 10 V, based on PT100.



temperature thermistor ntc
Temperature - Thermistor NTC

Unipolar semiconductor material

The basicphysicalprincipleofthesedevicesisthat the electricconductivity (resistivity) of the pure semiconductor material increases (decreases) as the temperature increases.

NTC (Negative Temperature Coefficient); T is in 0K

Thermistors are very sensitive, but R isstrongly non linearwithrespectto T.

Withhighlydopedsemicobductor material itispossibletoobtain PTC type (Positive Temperature Coefficient) thermistors

temperature pn junction
Temperature - PN junction

In a directbias PN junctionwithcostantcurrent the directdiodetensiondecreasesby 2,5 mVwith the increaseof 10C of the temperature.

The exactvalueof the tensionfor a given temperature dependsupon the valueof the costantcurrentof the diode.

A smallsignaljunctiondiodelike 1N914 or 1N4148 can beeasilyusedas a temperature sensor.



temperature ic ad590 1
Temperature - IC AD590 (1)


Deviceswhichembed the sensor plus the circuitstonormalize, linearize, amplify the signal, in otherwords a “transducer”.

The integrated T sensors are based on the lineardipendencebetween VD e T of the directbiascostantcurrentdiode (seeprevouspage). The junctionis the BE junctionof a BJT transistor

AD590: high impedencecurrent generatori

T is in 0K; K isμA/0K

The generatedcurrentisdirectlyproportionalto the absolute T value

It can belocated far from the measurementinstrument (itworkswithcurrent) and itisnotverysensitivtonoise

It can show scale and offset errors

The output currentsignalisconvertedtotensiomthrough a resistance plus a I/V converter (forexamplebased on OpAmp)

light sensor photoresistor 1
Light sensor – Photoresistor (1)
  • Devices in which the information associatedto light isconverted in variationofresistance: resistivitydecreases (conductivityincreases) as the light increases
  • Madewith N typesemiconductore materiale (not a PN junction)
  • Thoughness, low priced, sensitivity
  • They can dissipatehighvaluesofpower (forexampletocontrolrelays)
  • Limitedbandwidth
light sensor photodiode 1
Light sensor – Photodiode (1)
  • When a reversedbiased PN junctionisilluminated the total reverse currentisgivenby the sum of the typical revers current plus a componentproportionalto the luminousflux
  • Thesedevices are very fast and are highlyusedasdetectors in telecommunicationsystemsbased on fiberoptics
speed tachometer generator 1
Speed-Tachometergenerator (1)

The tachometer generator (dynamo) is a small generator that produces an output voltage that is very accurately determined by its operating speed

speed incremental encoder 1
Speed - Incremental encoder (1)

Devicewhichmeasures the angolar displacementof a shaft in ordertogetinformationsabout the angularspeed (forexampleof a motor)

Itismadeby a rotary disc and a Led/fototransistor system.

On the circumferenceof the disc a set ofholeshasbeen set all at the samedistance on from the other.

When the disc rotates the light beameitherisinterrupted (no hole and bjt in cut-off mode) or goesthroughfrom the led to the phototransistor (precenceof the hole and bjt in saturation mode).

The phototransistorgenerates a trainpulse, onepulseforeachholecrossedby the light beam.

From the numberofpulsesitispossibletodetermine the angulardisplacement and, in relation totime, the angularspeed

With the incremental encoder itispossibletomeasure the speed, butitisnotpossibletodetermine the rotational direction

speed incremental encoder 3
Speed - Incremental encoder (3)

Two/threephasesincremental encoder todetermine the rotational direction

speed incremental encoder 4
Speed - Incremental encoder (4)

Two/threephasesincremental encoder

speed absolute encoder 1
Speed – Absolute encoder (1)

Usedtodetermine the shaftangular position.

Eachcombinationofholesiscoded so toprovide the angular position of the disc.

Normally the Gray code isused in ordertoprevent the transmissionoferrors

WithsimplecombinatoryExorcircuititispossibletoconvertGray code in natualbinary code

motor control with encoder 1
Motor controlwith encoder (1)

Analogcontrol system

motor control with encoder 2
Motor controlwith encoder (2)

Digitalcontrol system

sensors society of robots
Sensors(Society ofrobots)
  • Sensorsspecificforrobotics: Society ofrobots
sensors in robotics applications
Sensors in robotics & applications
  • Accelerometer
  • Color Sensors
  • DigitalCompass
  • Encoder (Slot, Rotary, Linear)
  • InfraredEmitter/Detector
  • Load and TorqueSensors
  • Mercury Tilt Switch
  • Photoresistor
  • Robot Computer Vision
  • SharpIRRangefinder
  • Sonar
  • Tactile Bumper Switch
sensors in robotics applications1
Sensors in robotics & applications
  • Accelerometer
  • Color Sensors
  • DigitalCompass
  • Encoder (Slot, Rotary, Linear)
  • InfraredEmitter/Detector
  • Load and TorqueSensors
  • Mercury Tilt Switch
  • Photoresistor
  • Robot Computer Vision
  • SharpIRRangefinder
  • Sonar
  • Tactile Bumper Switch
robot for the contest
Robot for the contest
  • Ideasfor the final meeting