ELEC 243 Lab

Experiment 3.1

Voltage and Waveform Measurements

Components

Microphone

Part 1: Basic A/D Conversion

Step 1:

Connect the cable from the DAQ card to J3-1 on the rightmost interface module. It should look like this:

Step 2:

Plug your BNC-banana adapter into the 6V supply terminals.

Note There is a bump on one side of the adapter to denote which prong is connected to ground. Be sure to plug this prong into the black terminal of the power supply.

Step 3:

Using a BNC patch cable, connect the 6 V supply output to J1-3.

Step 4:

Strip both ends of a 16 cm length of wire and connect J1-3 to A/D channel 0 as shown in the following diagram. The numbers below the connector symbols ( $\includegraphics[scale=0.400000]{conn_symh.ps}$ ) are the pin numbers on the interface connector socket strip. $\includegraphics[scale=0.500000]{ckt4.1.1.ps}$

Note that, as with the function generator and oscilloscope, the ground connection to the DAQ card is made automatically. We will not show the DAQ card ground in subsequent drawings.

Step 5:

Load the "Basic ADC" program from the Start menu by following the path: Programs -> ELEC 243 -> Basic ADC. It should look like this:

Labview programs are called Virtual Instruments (or VIs for short).

Step 6:

Start the instrument by selecting Run from the Operate menu, or by pressing the run button (the small arrow just below the menu bar), or by pressing CTRL-R on the keyboard with the cursor over the panel.

Vary the power supply voltage and verify that the displayed value changes. Measure the voltage with your Fluke DMM and see how the values compare.

Step 7:

Move the BNC patch cable from the 6 V supply to the function generator 50Ω Output. With a second BNC patch cable, connect CH 1 of the oscilloscope to J1-1. Strip a short piece of wire and connect the function generator output (on J1-3) to the oscilloscope input (on J1-1).

Step 8:

Verify that you have the following circuit: $\includegraphics[scale=0.500000]{ckt4.1.2.ps}$

Step 9:

Using the oscilloscope, adjust the function generator to produce a 5 V p-p, 0.5 Hz sine wave. An easy way to do this is to first select the 1 kHz range, set the amplitude to 5 V p-p and the frequency to 500 Hz, then switch to the 1 Hz range. Observe the signal on the Basic ADC display.

Step 10:

Increase the frequency to 1 Hz. Note that due to the reduced number of samples per cycle, the sinusoidal shape of the waveform is less smoothly defined.

Step 11:

Increase the freqency to 10.00 Hz. Observe the resulting display.

Question 1:

Explain why a 10 Hz sine wave, when sampled 10 times per second, appears as a nearly constant (DC) value on the A/D display. What would an 11 Hz sine wave look like under the same conditions?

Step 12:

Increase the sample rate to 100 samples per second by entering "100" into the Samples/Second field and pressing the Enter key. Observe the resulting display.

Step 13:

Stop the Basic ADC program by pressing the red STOP button.

Note Strange things can happen if two VIs are running simultaneously. Always make sure that all other VIs have been stopped before starting a new one.

Part 2: A Digital DMM/Oscilloscope

In the previous part we used a fairly straightforward process to sample, digitize, and display analog voltage values. Although this gives satisfactory results for low frequency signals, it's clear we need to be careful when measuring higher frequency signals. In this part we will look at a much more sophisticated VI which combines the functionality of the DMM and the analog oscilloscope, and adds a few extra features

Step 1:
Load the "DMM-Scope" program from the Start menu by following the path: Programs -> ELEC 243 -> DMM-Scope.

Step 2:
Set the function generator to produce a 100 Hz, 2 V p-p sine wave.

Step 3:
Start the DMM-Scope VI.

Step 4:
Adjust the Volts/Div and Time/Div controls to give a satisfactory display.

Step 5:
The fields in the lower left portion of the panel are the DMM function. These give the DC and AC voltage of the displayed signal. Do the values display correspond to what you measure with the scope and DMM?

Step 6:
The bottom field in the DMM section displays the frequency of the signal. Compare the value displayed here with the setting on the function generator.

Step 7:
Experiment with the controls and different function generator waveforms. Are there any situations in which the digital and analog give significantly different measurements? If so, describe carefully.

Step 8:
Reduce the function generator amplitude to minimum. Plug the microphone into J1-4 and connect it to A/D channel 4 (pin 4 to pin 46 on the interface connector strip).

Step 9:
On the DMM-Scope panel, set the controls as follows:

A/D Channel = 4
Volts/Div = 0.005
Time/Div = 1 ms
Triggering = Norm

Step 10:
Speak into the microphone and observe the resulting display, adjusting the controls if necessary. If musical talent is available, sing, whistle, play, or otherwise produce the note "A" and note the displayed frequency value.

Question 2:
Compare the utility of the digital DMM-Scope with that of the conventional instruments. Briefly discuss the advantages and disadvantages of each. Suggest a few situations where one or the other might be most appropriate.

Step 11:
Unplug the microphone and return it to the cart.


Step 1:		Load the "DMM-Scope" program from the Start menu by following the path: Programs -> ELEC 243 -> DMM-Scope.
Step 2:		Set the function generator to produce a 100 Hz, 2 V p-p sine wave.
Step 3:		Start the DMM-Scope VI.
Step 4:		Adjust the `Volts/Div` and `Time/Div` controls to give a satisfactory display.
Step 5:		The fields in the lower left portion of the panel are the DMM function. These give the DC and AC voltage of the displayed signal. Do the values display correspond to what you measure with the scope and DMM?
Step 6:		The bottom field in the DMM section displays the frequency of the signal. Compare the value displayed here with the setting on the function generator.
Step 7:		Experiment with the controls and different function generator waveforms. Are there any situations in which the digital and analog give significantly different measurements? If so, describe carefully.
Step 8:		Reduce the function generator amplitude to minimum. Plug the microphone into J1-4 and connect it to A/D channel 4 (pin 4 to pin 46 on the interface connector strip).
Step 9:		On the DMM-Scope panel, set the controls as follows: A/D Channel = 4 Volts/Div = 0.005 Time/Div = 1 ms Triggering = Norm
Step 10:		Speak into the microphone and observe the resulting display, adjusting the controls if necessary. If musical talent is available, sing, whistle, play, or otherwise produce the note "A" and note the displayed frequency value.
Question 2:		Compare the utility of the digital DMM-Scope with that of the conventional instruments. Briefly discuss the advantages and disadvantages of each. Suggest a few situations where one or the other might be most appropriate.
Step 11:		Unplug the microphone and return it to the cart.