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Electrical Measurement, Ohm’s Law, & Watt’s Law

Electrical Measurement, Ohm’s Law, & Watt’s Law. CVSD Electronics 1. Resistance. A measure of the opposition to the flow of electrons (current) through a material Unit of Measurement: Ohm (Ω) Symbol: R = Resistance. Current.

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Electrical Measurement, Ohm’s Law, & Watt’s Law

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  1. Electrical Measurement, Ohm’s Law, & Watt’s Law CVSD Electronics 1

  2. Resistance • A measure of the opposition to the flow of electrons (current) through a material • Unit of Measurement: • Ohm (Ω) • Symbol: • R = Resistance

  3. Current • A measure of the total amount of electrons flowing in a circuit in a given unit of time • Unit of Measurement: • Ampere (A) • Symbol: • I = Intensity

  4. Voltage • A measure of the Electromotive Force (EMF) or pressure that pushes electrons through a circuit • Unit of Measurement: • Volt (V) • Symbol: • E = Electromotive Force

  5. Power • A measurement of the rate of consuming energy, transferring energy, or doing work • Unit of Measurement: • Watt (W) • Symbol: • P

  6. Ohm’s Law • Describes the mathematical relationship between resistance, current, and voltage Voltage (E) = Amperage (I) x Resistance (R) • With two of these values, you can use Ohm’s Law to find the third (DIY Alarm Forum, 2006)

  7. Variations of Ohm’s Law • E = IxR • I = E/R • R = E/I

  8. Ohm’s Law Example • E = 24 VDC • I = ? • R = 12 Ω Calculations E=IR 24=Ix12 I = 24/12 I = 2 A

  9. Watt’s Law • Describes the mathematical relationship between power, current, and voltage Power (P) = Amperage (I) x Voltage (E) • With two of these values, you can use Watt’s Law to find the third

  10. Variations of Watt’s Law • P = IE • I = P/E • E = P/I

  11. Watt’s Law Example • P = 36 W • I = ? • E = 12 V Calculations P=IE 36=Ix12 I = 36/12 I = 3 W

  12. Combinations of Ohm’s and Watt’s Laws

  13. Measuring Resistance with the DMM • Must select Ohmmeter Range (Ω) • Pos (+) lead must be in Volt/ Ohm pin • Sat meter to proper range • Must wire in parallel with circuit • Power must be removed from the circuit

  14. Measuring Voltage with the DMM • Must select DC Voltage Range • Pos (+) lead must be in Volt/ Ohm pin • Set meter to proper range • Must wire in parallel with the circuit • Circuit must be have power

  15. Measuring Current with the DMM • Must select DC Current Range • Set meter to proper range. (meter can be damaged if not set to the proper range) • Must wire in series with the circuit • Circuit must be have power

  16. Measured Tolerance • Predicted values, and measured values may not always be exactly the same • There is unaccounted for resistance in the wires etc. • Applied voltage may fluctuate • Human error may disturb measurements • Components have tolerance (not always exact values) • As components change temperature, resistance may also change

  17. Review • State Ohm’s Law • State Watt’s Law • How is voltage measured? • How is resistance measured? • How is current Measured? • Why do predicted and calculated values differ?

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