Sensors Sensors andand

ElectricityElectricity

What is a Sensor?What is a Sensor?

A sensor is a device that:A sensor is a device that:1)1) MeasuresMeasures a physical quantity a physical quantity

2)2) Converts this measurement into a Converts this measurement into a readable signalreadable signal

Sensors can be found in many Sensors can be found in many everyday places – for example: everyday places – for example: home, car, schoolhome, car, school

Some Important Sensor Some Important Sensor PropertiesProperties

AccuracyAccuracy – Does the sensor give the – Does the sensor give the right value?right value? CalibrationCalibration- The process of adjusting a - The process of adjusting a

sensor’s output to correct it’s accuracysensor’s output to correct it’s accuracy SensitivitySensitivity- How much does the - How much does the

sensor output change as the quantity sensor output change as the quantity it is measuring changes?it is measuring changes? Ideally, a sensor will be Ideally, a sensor will be linearlinear

LinearityLinearitySenso

r O

utp

ut

Measured Property

Slope = Sensitivity

More Sensor PropertiesMore Sensor Properties

RepeatabilityRepeatability- Is the sensor reading - Is the sensor reading consistent from measurement to consistent from measurement to measurement?measurement?

RangeRange- What values can the sensor - What values can the sensor detectdetect

SpeedSpeed CostCost

TransducerTransducer

A transducer converts energy (either a A transducer converts energy (either a physical quantity or signal) into another physical quantity or signal) into another physical form.physical form.

Some examples:Some examples: An LED (light emitting diode)- Converts electricity An LED (light emitting diode)- Converts electricity

into lightinto light A microphone- Converts air pressure into electricityA microphone- Converts air pressure into electricity A weather vane- Converts wind direction into A weather vane- Converts wind direction into

positionposition Many transducers use electricity Many transducers use electricity

What Is What Is ElectricityElectricity??

A form of A form of energy made energy made up of moving up of moving electrons that electrons that can produce can produce light, heat, or light, heat, or motionmotion

ElectronsElectrons

Two types of charges: Two types of charges: Positive and NegativePositive and Negative

In an atom, positive In an atom, positive charge is confined to charge is confined to the nucleus, while the nucleus, while electrons are located electrons are located away from the nucleusaway from the nucleus

Sometimes electrons Sometimes electrons can be transferred can be transferred from one atom to from one atom to anotheranother

Electron(- charge)

Nucleus(+ charge)

Conductors and Conductors and InsulatorsInsulators

ConductorConductor Any material Any material that allows that allows electrons to electrons to move through itmove through it

Examples:Examples: Metals (esp. Metals (esp. copper)copper)

Your bodyYour body Sea waterSea water

InsulatorInsulator Materials that Materials that do not allow do not allow electric charges electric charges to flow freely to flow freely through themthrough them

Examples:Examples: WoodWood GlassGlass RubberRubber

SemimetalSemimetal (semiconductor)(semiconductor) Material whose Material whose conduction conduction properties properties change with change with conditionsconditions

Examples:Examples: SiliconSilicon Some ceramicsSome ceramics

VoltageVoltage

VoltageVoltage = = Electric Potential Electric Potential DifferenceDifference

Involveselectrons Has the

ability to make things happen

Measured between two points

-Voltages are measure in Volts (V)-Electronics can read voltages and send them to a computer

BatteryBattery In a battery, a In a battery, a chemical chemical

reactionreaction removes electrons removes electrons from the positive terminal from the positive terminal ((anodeanode) and brings them to the ) and brings them to the negative terminal (negative terminal (cathodecathode))

A voltage forms between the A voltage forms between the two terminalstwo terminals

Circuit Symbol: Circuit Symbol:

++ ++ +

- - - --

Ele

ctrons

Cathode

Anode

Cathode

CircuitsCircuits Circuits are paths along Circuits are paths along

which electricity moveswhich electricity moves

Voltage creates current, Voltage creates current, which provides energy for which provides energy for devicesdevices

Current is measured in Current is measured in Amperes (A)Amperes (A)

+

-

Electrons

Electrons

Circuit in a FlashlightCircuit in a Flashlight

ResistanceResistance

ResistanceResistance is a measure of how much is a measure of how much a device in a circuit resists current. It a device in a circuit resists current. It is measured in ohms (is measured in ohms (

Wires have zero resistanceWires have zero resistance

A A resistorresistor is a device whose only is a device whose only function is to provide a specific function is to provide a specific resistance.resistance.

Ohm’s LawOhm’s Law

V = I * RVoltage Current Resistance

The voltage drop across a device is equal to the current through the device times the resistance of the device

Ohm’s Law –FormsOhm’s Law –Forms

R = VI

I = VR

V = I * R

Ohms Law - UnitsOhms Law - Units

V = A *Volts Amperes Ohms

milliAmpere: 1 mA =

kiloOhm: 1 k =

V = I * RVOLTAGE CURRENT RESISTANCE

0.001 A

1000

Resistance in a CircuitResistance in a Circuit

2 10 V

I = VR

10 V2 = = 5 A

Resistors in SeriesResistors in Series

When two resistors are connected in series, it can be treated as one resistor, where the resistances are added together.

5 k 3 k

Total resistance = 8 k

Temperature SensorsTemperature Sensors

ThermometerThermometer Volume of a liquid changes with Volume of a liquid changes with

temperaturetemperature Bimetallic stripBimetallic strip

Angle changes with temperatureAngle changes with temperature

ThermistorThermistor

A thermistor is a resistor with a resistance that is strongly dependent on temperature

0 20 40 60 80 100

Celsius Temperature

Th

erm

isto

r R

es

ista

nc

e

Finally, a Question:Finally, a Question:

How can you use a thermistor to build a temperature sensor?