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Introduction to the Multimeter

VIEWS: 57 PAGES: 26

									            DC Circuits Lab
                               Professor Ahmadi

                                       ECE 002




George Washington University
Objectives
 Constructing a Series Circuit
    Ohm‟s Law Review
    Breadboard Overview
    DC Power Supply Review


 Measuring the D.C. Voltage in the Series Circuit
    Multimeter Overview




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Today we will build this series circuit
                                      Series Circuit From Lecture
       I = ? Amps                     Determine the current

                                      Use Ohm‟s Law:

      3V       R = 1K Ω                     V      =I   x R

                                           3V      =I   x 1000    Ω

                                                   Solve for I:

                                      I=3V / 1000 Ω = 3milliAmps
                0V

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How to Build the Circuit

          I = 3mA                     We need 5 components
                                         1) A 1K Ohm Resistor (Ask your
                                            GTA for these materials)
     3V      R = 1K Ω                    2) Breadboard
                                         3) DC Voltage Source
                                         4) 2 sets of Banana Clip to mini-
                                            grabber wires




                0V

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The Breadboard
           The breadboard is building
            circuits quickly without the
            need for soldering

           You can plug resistors and
            wires right into the board




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The Breadboard
           The 5 holes in each row are wired
            together underneath the breadboard
            The rows themselves are not wired
             together
            The rows do not connect over the bridge
 BRIDGE




           The columns between the blue and
            red bars are connected vertically
            We typically use these as „power rails‟
            The left side we use for positive voltage
            The right side we use for negative voltage


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Setting up the breadboard

          Plug 1 end of the 1K resistor in the
           top row, on the left side of the
           bridge

          Plug the other end of the resistor
           into the top row, on the right side of
           the bridge




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Setting Up the DC Power Supply

 This DC Power supply is
  capable of generating
  voltages from -25V to 25V.

 For this lab, we will be
  using the 6V supply
  terminals.

 First, press the Power
  Button to turn it on.




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Setting Up the DC Power Supply

 Press Output On/Off once to
  turn on the output.

 Press the +6V button to tell
  the power supply that we
  want to alter the output
  from the 6V terminals.

 Once done, your screen
  should look the same as it
  does on this slide.




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Setting Up the DC Power Supply
                                                              Press this arrow to
 Use the dial to increase the          This is the digit         Select the
  display value to 3 volts as          we want to adjust         desired digit
  shown.

 Note: You can safely ignore
  the value of the right most
  digit for this experiment.

 Once you have reached 3V,
  Press Output On/Off once to
  turn the output OFF while
  you hook up the circuit.
                                                               Rotate this dial to
                                                            alter the output value.


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Connecting the Power Supply to your
Circuit
 Plug the „banana‟ end of
  your cables into the 6V
  terminals of your power
  supply

 Connect the mini-grabber
  ends of the cables around
  your 1K resistor on the
  breadboard

 After attaching the mini-
  grabbers to your circuit,
  press the Output On/Off to
  apply 3 Volts across your 1K
  resistor

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Measuring the Voltage Across the
Resistor…Using the Multimeter




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What is a Multimeter?
 A tool capable of measuring a variety of different quantities.

 Possible Measurements
   Current (Amperes)
   Resistance (Ohms)
   Voltage (Volts)




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How is the Multimeter different
than the Oscilloscope?
        Multimeter                                     Oscilloscope
 Numerical Output Displayed              Graphical Output Displayed
 Represents a complete                   Shows how a signal changes
  signal with a single value.              over time
 Measures voltage, current               Many only display voltage
  and resistance.




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Explanation of Controls
Setting up the multimeter for various measurements.




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Taking measurements with the
Multimeter
             First, we connect our wires.
 One wire is always
  connected to the black
  terminal. This is called the
  common terminal.

 The red terminal is used
  when measuring voltage,
  resistance and small
  currents.
                                              TO DO: Using another set
 The white terminal is used
                                              of banana to mini-grabber
  when measuring large
  currents.                                   cables, connect the
                                              banana end to the red &
                                              black terminals
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Taking measurements with the
Multimeter
 Next, we turn it on and select the item to measure.

 Choose from:                             TO DO: Since we want to
   Current                                measure the voltage
   Resistance                             across our 1K ohm resistor,
                                           press the Voltage button
   Voltage




  Power
  Button


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Taking measurements with the
Multimeter
 Now, we select our scale.

 Either select a scale appropriate for your measurement or choose AUTO
  and let the multimeter select the appropriate scale for you.

 Measuring the voltage from across the 1K resistor (~3V), you wouldn‟t
  want to choose 200mV (much too small) or 200V (much too large).
  Instead, the 2V selection is more suitable.




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Taking measurements with the
Multimeter
 While your circuit is
  attached to the power
  supply…

 Attach the minigrabber end
  around the 1K resistor

 Press the “POWER” button
  on the multimeter and take
  a reading!!




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Building & Verifying Series Circuit #2
                                    Resistors connected by only
                                     1 terminal, back-to-back,
      R1 = 1KΩ                       are considered to be in
                                     „series‟
                                    Ohm‟s Law States:
      3V     R2 = 1KΩ
                                   V(R1) = 1.5mA x 1K Ω = 1.5V

                                   V(R2) = 1.5mA x 1K Ω = 1.5V
                                    We are now going to build
                                     the circuit, and verify the
                 0V                  voltage drops…

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Setting up the breadboard

          Turn off the 3V supply and disconnect
           the cables

          Disconnect the cables to the
           minigrabbers to the multimeter

          Obtain a 2nd 1K resistor
          Plug one end of the resistor into a
           hole in the same row as the end of
           the other resistor

          Plug the other end into a hole in
           another rowUniversity
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Taking measurements with the
Multimeter
 Set the Power Supply to 3V

 Attach the power supply
  leads as follows

 Measure the voltage across
  each resistor with the
  multimeter




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Resistors in Parallel
                                     Resistors connected at 2
                                      terminals, sharing the same
                                      node on each side, are
                                      considered to be in
                                      „parallel‟
      3V
                                     The voltage is the same on
                                      both branches of the circuit

                                     The current will split!
           R1 = 1K Ω R2 = 1K Ω
                                     It is now up to you to build
                                      this circuit and verify the
                 0V                   voltages
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      Including a Diode In the Circuit
                                                      We‟ll use LEDs (Light
                                                       Emitting Diodes) for our
                                                       circuits.

                                                      Unlike resisters, the two diode
                    3V                                 leads (wires) must be
                                        R1 = 1KΩ       connected in the correct way.
                                                      The longer lead (anode)
                                                       should be connect so that
                                                       current flows through it and to
                                                       the shorter lead (cathode).

                                 0V
 Note: In some diodes, a stripe is used to indicate the cathode lead. Round diodes often have a
  flat side, indicating the cathode.
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Your Turn
1) Build the parallel circuit (in the last slide) and measure the
   voltage across it
   Using Ohm‟s Law, what is the current through each resistor?
   What is the total current in the circuit?
   Show your TA your circuit, measurements, and calculations

2) In your parallel circuit, change one of the 1K resistors to a 2K
   resistor
   Measure the voltage across each resistor
   Use Ohm‟s law to determine the current through each resistor
   Show your TA…

3) Rebuild the two resistor series circuit…
     Change one of the 1K resistors to a 2K resistor
     Measure the voltage across each resistor
     Use Ohm‟s law to determine the current through each resistor
     Show your TA…

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Your Turn
4) Build a circuit with a diode in series with a 1K resistor
    Using Ohm‟s Law, what is the current through the resistor?
   What is the total current in the circuit?
   Show your TA your circuit, measurements, and calculations
   Reverse the anode and cathode connections of the diode and
    observe the results.

5) Build a circuit with a diode in series with 2 parallel 1K resistors
   Measure the voltage across each resistor
   Use Ohm‟s law to determine the current through each resistor
   Show your TA…

6) Don‟t forget the HW!




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