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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
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
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
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
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
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