1. Sensors and Electricity

2. What is a Sensor? A sensor is a device that: A sensor is a device that: 1) Measures a physical quantity 2) 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? Accuracy – Does the sensor give the right value? Calibration- The process of adjusting a sensor’s output to correct it’s accuracy 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? Sensitivity- How much does the sensor output change as the quantity it is measuring changes? Ideally, a sensor will be linear Ideally, a sensor will be linear

4. Linearity Sensor Output Measured Property Slope = Sensitivity

5. More Sensor Properties Repeatability- Is the sensor reading consistent from measurement to measurement? Repeatability- Is the sensor reading consistent from measurement to measurement? Range- What values can the sensor detect Range- What values can the sensor detect Speed Speed Cost Cost

6. Transducer A transducer converts energy (either a physical quantity or signal) into another physical form. A transducer converts energy (either a physical quantity or signal) into another physical form. Some examples: Some examples: An LED (light emitting diode)- Converts electricity into light An LED (light emitting diode)- Converts electricity into light A microphone- Converts air pressure into electricity A microphone- Converts air pressure into electricity A weather vane- Converts wind direction into position A weather vane- Converts wind direction into position Many transducers use electricity Many transducers use electricity

7. What Is Electricity? A form of energy made up of moving electrons that can produce light, heat, or motion 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 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 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 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 Any material that allows electrons to move through it Examples: Examples: Metals (esp. copper) Metals (esp. copper) Your body Your body Sea water Sea waterInsulator Materials that do not allow electric charges to flow freely through them Materials that do not allow electric charges to flow freely through them Examples: Examples: Wood Glass RubberSemimetal (semiconductor) (semiconductor) Material whose conduction properties change with conditions Material whose conduction properties change with conditions Examples: Examples: Silicon Silicon Some ceramics Some ceramics

10. 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

11. Battery In a battery, a chemical reaction removes electrons from the positive terminal (anode) and brings them to the negative terminal (cathode) 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 A voltage forms between the two terminals Circuit Symbol: Circuit Symbol: +++ ++ ----- Electrons Cathode Anode Cathode

12. Circuits Circuits are paths along which electricity moves Circuits are paths along which electricity moves Voltage creates current, which provides energy for devices Voltage creates current, which provides energy for devices Current is measured in Amperes (A) Current is measured in Amperes (A) + - Electrons

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 (  Resistance is a measure of how much a device in a circuit resists current. It is measured in ohms (  Wires have zero resistance Wires have zero resistance A resistor is a device whose only function is to provide a specific resistance. A resistor is a device whose only function is to provide a specific resistance.

15. 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

16. Ohm’s Law –Forms R = V I I = V R V = I * R

17. Ohms Law - Units V = A *  Volts Amperes Ohms milliAmpere: 1 mA = kiloOhm: 1 k  = V = I * R VOLTAGECURRENTRESISTANCE 0.001 A 1000 

18. Resistance in a Circuit 2  10 V I = V R 10 V 2  = = 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 k  3 k  Total resistance = 8 k 

20. Temperature Sensors Thermometer Thermometer Volume of a liquid changes with temperature Volume of a liquid changes with temperature Bimetallic strip Bimetallic strip Angle changes with temperature 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?