NI Elvis Virtual Instrumentation And Prototyping Board

Transcription

1 NI Elvis Virtual Instrumentation And Prototyping Board Objectives: a) Become familiar with NI Elvis hardware ( breadboard ) and software b) Learn resistor color codes c) Learn how to use Digital Multimeter to read voltage, current, resistance, and capacitance d) Learn to build circuits on breadboard e) Build a voltage divider f) Learn to use oscilloscope to test RC circuit g) Learn to use impedance analyzer h) Learn to use Gain/Phase (Bode) plot to analyze RC circuits (understand concepts of gain and phase with respect to A-C signals) MEASUREMENT OF THE CIRCUIT COMPONENT VALUES Objective: To measure the resistances and capacitances of the given electronic components. Use the handheld Multimeter or the Virtual DMM (Digital Multimeter) found in NI Elvis software. The virtual meter is connected to NI Elvis Prototyping Box. 1

2 Apparatus required: Resistors, capacitors, NI Elvis Procedure: Launch the NI ELVIS Instrument Launcher (shown above) and select Digital Multimeter. Use the DMM [Ω] to measure the resistor R and then use DMM[C] to measure the capacitor C. Observations: Resistor R = Capacitor C= Ω µf 2

3 BUILDING VOLTAGE DIVIDER CIRCUIT ON THE NI ELVIS PROTOBOARD Objective: To become familiar with building circuits on a Breadboard, and measuring voltages and currents with a Digital Multimeter. The Breadboard below, is used to assemble electronic components and connect them to test voltages. The horizontal rows of holes (green) are connected electrically. These rows are used to connect two or more circuit elements or wires. A single circuit element (e.g. a resistor) must be inserted as shown (or go across a divider column). Otherwise it will be shorted out. Build the following circuit on the Breadboard. Measure the voltage drop (IN PARALLEL) across each resistor. Note results. Measure circuit current flow with DMM ammeter. (NOTE: ammeter must be in SERIES with circuit, unlike a voltage measurement). Note results 3

4 TESTING A RC SERIES CIRCUIT WITH THE FUNCTION GENERATOR AND OSCILLOSCOPE Objective: To become familiar with the operation of an oscilloscope and function generator. Open up the Virtual Function Generator, on your monitor, as shown below. The FGEN creates a test signal to test the response (output) of a given circuit. Frequency and amplitude of the A-C signal may be changed. Open up the oscilloscope on your monitor, as shown: 4

5 We will be building the following series RC circuit on the Breadboard. The Input signal will be monitored with a pair of wires on Oscilloscope channel ACH1, while the output signal (across resistor) will be monitored with a pair of wires on Oscilloscope channel ACH0. Change the frequency of FGEN signal, and note change in amplitude of output signal. WHY? Measurement of Component and Circuit Impedance Z 5

6 1. Objective: To measure the component and the circuit impedance z of a simple series RC circuit. 2. Apparatus: NI Elvis set up capacitor and resistor. 3. Theory: For a resistor, the impedance is the same as the DC resistance. It can be represented on a 2- D plot as a line along the X axis often called the real component. For a capacitor, the impedance (or more specifically the reactance) X c is imaginary, depends on the frequency and can be represented as a line along the Y axis of a 2-D plot.it is called the imaginary component. Mathematically, the reactance of a capacitor is represented by: X c 1 j c Where is the angular frequency (measured in radians/sec) and j is a symbol used to represent an imaginary number. The impedance of a RC circuit in series is the sum of these 2 components where r is the resistive (real) component and X c is the reactive (imaginary component. Z R X R 1 c j c This can also be represented as a phasor vector on a polar plot with: Magnitude = (R 2 + X c2 ) and Phase tan -1 (X c /R) A resistor has a phasor along the real (X) axis. A capacitor has a phasor along the negative imaginary(y)axis. Recall from complex algebra that 1/j= -j. Open up the Impedance analyzer on your monitor, as shown: 6

7 We will be using the RC circuit as before, except we will not need the Function Generator or Osciloscope. This is because the Impedance analyzer furnishes its own test signal. The test leads come from the current terminals on the front of the NI Elvis protoyping box. If you test the capacitor only, you will get a RED vector along the negative imaginary axis. Change frequency and note how length (magnitude) of impedance vector changes. WHY? Now test the resistor only. You will notice a GREEN vector on the positive real axis, its length corresponding to the value of the resistor. Now change frequency of test signal. Note vector does not change length. WHY? Finally, test the overall impedance of resistor and capacitor together. Note the total impedance is the YELLOW vector sum of the capacitance vector and resistance vector. 7

8 The Gain/phase Bode Plot of the RC Circuit Objective: To understand the input / output characteristics of a simple series RC circuit as a sweep (spectrum) of frequencies is input across the circuit. To understand the concept of signal gain. Open the Bode Analyzer on your monitor, as shown: We will be using the same connections as part 7-C, below. Set the start frequency at 10 Hz and the stop frequency at Hz. Hit the run button. You should get a Bode plot similar to the one below. This is a simple High-pass filter (across the resistor). A High-pass filter passes high frequencies but attenuates low frequencies. CAN YOU EXPLAIN WHY? If you change output leads across capacitor instead, you will have a simple Lo-pass filter 8

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10 Discussion of Results: a)record the values of a resistor and a capacitor measured with a Digital Multimeter. Explain how a DMM works and why you need one b)record voltage and current measurements from circuit that you built on breadboard. Show photos of your circuit. Explain how to measure current and voltage in a parallel and series circuit. c)explain how a simple series R-C circuit can be a simple Hi-pass filter. Take a screenshot of wave forms on oscilloscope at high and low input frequencies. Explain the waveforms. d)explain how the impedance analyzer measures pure resistance, pure capacitance, and the combination of both. Take a screenshot. Explain how impedance differs from resistance. e)explain what a Bode plot is. What is gain? Take a screenshot and explain what is being presented in the graph. 10