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Unit 2

Unit 2. Basic Instruments and Measurements. There are two styles of meters. DIGITAL. ANALOG. ANALOG METER. Uses a moving coil meter , a pointer, and a scale. DIGITAL METER. The digital meter circuits change or convert the analog quantity into a digital form.

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Unit 2

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  1. Unit 2 Basic Instruments and Measurements

  2. There are two styles of meters. DIGITAL ANALOG

  3. ANALOG METER • Uses a moving coil meter, a pointer, and a scale.

  4. DIGITAL METER • The digital meter circuits change or convert the analog quantity into a digital form. • Digital meters are easy to read. • Their measurements are more accurate. • May be an auto-range meter. • A disadvantage is, they are powered by a battery.

  5. Types of electrical meters • VOLTMETER • AMMETER • OHMMETER

  6. AC meters are notpolarized. • Why? • AC is changing polarity 60 times a second.

  7. Some meters are POLARIZED • Which means that we must pay attention to the direction the electrons are flowing in the circuit. • Electrons flow from a negative point to a positive point.

  8. DC meters are polarized (you must pay attention to the direction that the electrons are flowing)

  9. Ammeter • Measures current, the amount of electrons flowing in a conductor. • Measures in units called AMPS. • Ammeters are connected in series to the load being measured.

  10. USING THE AMMETER • Set the Function to DCA. • Set the Range to highest value. (500mA) • Turn on power to meter, check the needle to see if it is on Zero, if not adjust to Zero. • Open the circuit, close the circuit with the meter. This gets the meter in series with load. • A DC ammeter must be connected in the correct polarity. • You must choose the correct scale. • Take the reading Students must know these steps!

  11. Ammeter in series with lamp Electron flow

  12. Voltmeter • Measures voltage, the force that pushes the electrons. • Measures in units called VOLTS. • Voltmeters are connected in a parallel connection to the load being measured.

  13. USING THE VOLTMETER Students must know these steps! • Set the Function to DCV • Set the Range to just above the source voltage. • A DC voltmeter must be connected in the correct polarity. • Is always connected in parallel to the load or device being tested. (place the black test lead on the negative side of the load and the red test lead on the positive side of the load.) • You must choose the correct scale. • Take the reading

  14. Voltmeter in parallel to the load Electron flow

  15. Ohmmeter • Measures resistance, the opposition to the flow of current. • Measures in units called OHMS. • Are connected in a parallel connection to the circuit or load.

  16. USING THE OHMMETER • Should never have any voltage or current applied to it, serious damage could happen. • Set the Function to Ohm’s • Set the Range to Rx10 or Rx100 (for most of the readings taken in this class) • To get an accurate measurement an ohmmeter must be "ZEROED" before using. • Zero the meter to the left side of the scale using the zero adjustment knob. • Zero the meter to the right side of scale. To zero the meter you short the leads together and turn the ohms adjustment knob till the needle is on the 0 of the Ohms scale. (the right side of the scale) • Connect to the meter leads in parallel to the load.

  17. Connecting the Ohmmeter Notice there is not any voltage at the source The Ohmmeter is connected in parallel to the load.

  18. You first zero the to the zero on the left side

  19. Then zero on the right side of the scale Shorting the leads together

  20. Multimeter • The most common multimeter is called a VOM meter.

  21. A VOM meter will measure. • Volts • Ohms • Milliamps - a small unit of amperage (.001)

  22. READING THE SCALE OF A METER • Just like a clock’s numbers can represent a different amounts of time, the numbers on the scale of a meter can represent different amounts.

  23. If a meter is not zeroed it will give a falsereading

  24. Continuity test are commonly done with an Ohmmeter • Continuity means a wire or conductor has a continuous path for electrons to flow from one end to the other.

  25. Clamp-on meter • Clamp-on meters are generally used to measure AC current and voltage • They do not have to hook directly to the circuit • They clamp around a single conductor and pick up the magnetic field around the wire.

  26. Pic Clamp on meter

  27. The End

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