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Sensors and Electricity

Learn about sensors and electricity, including what sensors are, their properties, types of transducers, the basics of electricity, conductors and insulators, voltage, circuits, resistance, Ohm's Law, and temperature sensors like thermistors.

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Sensors and Electricity

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  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 sensor’s output to correct it’s 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. 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 Electrons Electron (- charge) Nucleus (+ charge)

  9. 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 Conductors and Insulators Semimetal • (semiconductor) • Material whose conduction properties change with conditions • Examples: • Silicon • Some ceramics

  10. Measured between two points Involves electrons Has the ability to make things happen 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. Electrons Electrons 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. Ohm’s 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. Ohm’s 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 10 V 2 W V 10 V I = = = 5 A R 2 W

  19. Total resistance = 8 kW 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?

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