Sensors and Electricity

1
Sensors andElectricity
2
What is a Sensor?

• A sensor is a device that
• Measures a physical quantity
• Converts this measurement into a readable signal
• Sensors can be found in many everyday places
  for example home, car, school

3
Some Important Sensor Properties

• Accuracy Does the sensor give the right value?
• Calibration- The process of adjusting a sensors
  output to correct its accuracy
• Sensitivity- How much does the sensor output
  change as the quantity it is measuring changes?
• Ideally, a sensor will be linear

4
Linearity
Slope Sensitivity
Sensor Output
Measured Property
5
More Sensor Properties

• Repeatability- Is the sensor reading consistent
  from measurement to measurement?
• Range- What values can the sensor detect
• Speed
• Cost

6
Transducer

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

7
What Is Electricity?

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

8
Electrons

• 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)
9
Conductors and Insulators

• Conductor
• Any material that allows electrons to move
  through it
• Examples
• Metals (esp. copper)
• Your body
• Sea water

• Insulator
• Materials that do not allow electric charges to
  flow freely through them
• Examples
• Wood
• Glass
• Rubber

• Semimetal
• (semiconductor)
• Material whose conduction properties change with
  conditions
• Examples
• Silicon
• Some ceramics

10
Voltage

• Voltage Electric Potential Difference

-Voltages are measure in Volts (V) -Electronics
can read voltages and send them to a computer
11
Battery

• In a battery, a chemical reaction removes
  electrons from the positive terminal (anode) and
  brings them to the negative terminal (cathode)
• A voltage forms between the two terminals
• Circuit Symbol

Cathode





Electrons
Cathode
-
-
-
-
-
Anode
12
Circuits

• Circuits are paths along which electricity moves
• Voltage creates current, which provides energy
  for devices
• Current is measured in Amperes (A)

-
13
Circuit in a Flashlight
14
Resistance

• 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.

15
Ohms Law
V I R
Resistance
Voltage
Current
The voltage drop across a device is equal to the
current through the device times the resistance
of the device
16
Ohms Law Forms
V I R
V
V
R
I
I
R
17
Ohms Law - Units
V I R
VOLTAGE
CURRENT
RESISTANCE
V A W
Volts
Ohms
Amperes
1 mA
0.001 A
milliAmpere
1 kW
1000 W
kiloOhm
18
Resistance in a Circuit
2 W
10 V
5 A
19
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
20
Temperature Sensors

• Thermometer
• Volume of a liquid changes with temperature

• Bimetallic strip
• Angle changes with temperature

21
Thermistor
A thermistor is a resistor with a resistance that
is strongly dependent on temperature
22
Finally, a Question
How can you use a thermistor to build a
temperature sensor?