Transcript Sensors - SENSE

Sensors and
Electricity
What is a Sensor?
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A sensor is a device that:
1)
2)
Measures a physical quantity
Converts this measurement into a readable
signal
 Sensors can be found in many everyday
places – for example: home, car, school
Some Important Sensor Properties
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Accuracy – Does the sensor give the right
value?
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Calibration- The process of adjusting a
sensor’s output to correct it’s accuracy
Sensitivity- How much does the sensor
output change as the quantity it is
measuring changes?
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Ideally, a sensor will be linear
Sensor Output
Linearity
Slope = Sensitivity
Measured Property
More Sensor Properties
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Repeatability- Is the sensor reading
consistent from measurement to
measurement?
Range- What values can the sensor detect
Speed
Cost
Transducer
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A transducer converts energy (either a physical
quantity or signal) into another physical form.
Some examples:
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An LED (light emitting diode)- Converts electricity into
light
A microphone- Converts air pressure into electricity
A weather vane- Converts wind direction into position
Many transducers use electricity
What Is Electricity?
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A form of energy made
up of moving electrons
that can produce light,
heat, or motion
Electrons
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Two types of charges:
Positive and Negative
In an atom, positive
charge is confined to the
nucleus, while electrons
are located away from
the nucleus
Sometimes electrons can
be transferred from one
atom to another
Electron
(- charge)
Nucleus
(+ charge)
Conductors and
Insulators
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Conductor Semimetal
Insulator
Any material  (semiconductor)
that allows  Material whose
electrons to conduction
move through properties
it
change with
Examples:
conditions

 Metals (esp.
 Examples:
copper)
 Silicon
 Your body
 Some ceramics
 Sea water
Materials that
do not allow
electric charges
to flow freely
through them
Examples:
 Wood
 Glass
 Rubber
Voltage
Voltage = Electric Potential Difference
Involves
electrons
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
Battery
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In a battery, a chemical reaction
removes electrons from the positive
terminal (anode) and brings them
to the negative terminal (cathode)
Cathode
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Circuit Symbol:
Electrons
A voltage forms between the two
terminals
Cathode
+++
+ +
- - - - Anode
Circuits
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Circuits are paths along
which electricity moves
Electrons
Voltage creates current,
which provides energy for
devices
+
-
Current is measured in
Amperes (A)
Electrons
Circuit in a Flashlight
Resistance
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Resistance is a measure of how much a
device in a circuit resists current. It is
measured in ohms (W)
Wires have zero resistance
A resistor is a device whose only function
is to provide a specific resistance.
Ohm’s Law
V=I*R
Voltage
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 –Forms
V=I*R
V
R=
I
V
I=
R
Ohms Law - Units
V=I*R
V=A*W
VOLTAGE
Volts
milliAmpere:
kiloOhm:
CURRENT
Amperes
RESISTANCE
Ohms
1 mA = 0.001 A
1 kW = 1000 W
Resistance in a Circuit
2W
10 V
V
10 V
I=
=
=5A
2W
R
Resistors in Series
When two resistors are connected in series, it can
be treated as one resistor, where the resistances
are added together.
5 kW
3 kW
Total resistance = 8 kW
Temperature Sensors
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Thermometer
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Volume of a liquid changes with temperature
Bimetallic strip
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Angle changes with temperature
Thermistor
Thermistor Resistance
A thermistor is a resistor with a resistance
that is strongly dependent on temperature
0
20
40
60
80
Celsius Temperature
100
Finally, a Question:
How can you use a
thermistor to build a
temperature sensor?