lab circuits using NI ELVIS 3.0

Items Needed: Multimeter capable of measuring capacitance (Velleman model has Cap mounting insert), wire jumper kit, a resistor and capacitor (size to be determined later), oscilloscope probe, ELVIS Board

Figure 1. ELVIS Instrument Launcher (Programs -> National Instruments -> NI ELVIS 3.0 -> NI ELVIS)

Turn on ELVIS Board. There is a switch on the left side of the front panel and the right side of the rear of the device. Both must be on for the board to activate. When active, green lights will turn on to indicate the board is ready for use.

Open the following program

Programs -> National Instruments -> NI ELVIS 3.0 -> NI ELVIS

You should see the instrument launcher.

This is the computer interface to use the various instruments built into ELVIS. Today we will explore the Oscilloscope and the Function Generator. Open up both programs. The function generator can be run manually from ELVIS or virtually on the computer. For now, use the computer interface.

To use the function generator, find the rows on the lower left satellite breadboard that is listed as part of the function generator , and locate the function output row then put a wire into one of the holes and have it stick straight out of the breadboard. You will use the ground line that you used before for the DC voltage supply in the lower left portion of the satellite bread board. Place another wire sticking out of ground. Also place a third wire in the 5 Volt supply line. Get an oscilloscope probe with a BNC connection and attach it to channel A in the right side of the ELVIS front Panel. On the oscilloscope display, make your source is “BNC/Board CH A” Clip the alligator clip to your ground and touch the probe end to the wire going into 5V. Make sure your oscilloscope is on 2V/div. and the red slide setting on the probe is on 1x. Pay attention to the RMS (DC equivalent) voltage level under the oscilloscope display.

Figure 2. Oscilloscope Probe with BNC connection

What do you observe when you clip the probe onto the 5V line? What happens if you reverse the probe and the grounding clip on the 5V and grounding line? _______________ _____________The line on the oscilloscope jumps up to 5V __________The line drops down 5V ________________________________________________________________________________________________________________________________

Now make sure your function generator is active, put the grounding clip back on ground and the probe on the wire in the function generator’s row labeled “func_out.” (Use autoscale or play with the timebase and scale settings yourself to optimize the waveform). What do you observe? _____________________________________A sin wave appears on the oscilloscope. _____________________________________________________________________________________________________________________________________

Adjust the settings on the waveform generator to make different types of waves. Rescale the oscilloscope if necessary. If your wave is dancing back and forth, you can steady it with the Trigger on the Oscilloscope. In the trigger drop down menu for source, choose “Channel A” and the signal will lock and be steady.

Create a wave with amplitude of 200mV and frequency of 1kHz. What scaling (V/div and s/div) do you need in order to see at least 1 period on the screen and the entire Peak to peak amplitude of the wave? (if the wave is not centered on 0V, i.e. has a dc offset that you didn’t program, you can change to AC coupling to look at only the AC part of the wave)

__________________ vertical: scale 100 mV per division Horizontal: 500us per division __________

Take a screen shot (PRTSCN button) and paste picture of the 200mV 1kHz wave in the oscilloscope here. Be sure to crop the image down to just the plot and display settings.

Now try 2.5V and 15kHz. What scaling (V/div and s/div) do you need in order to see at least 1 period on the screen and the entire Peak to peak amplitude of the wave?

_______________Vertical: 1 V per division Horizontal: 10us per division _______________________________________________________________

Take a screen shot (PRTSCN button) and paste picture of the 2.5V 15kHz wave in the oscilloscope here. Be sure to crop the image down to just the plot and display settings.

Using the oscilloscope you can view multiple inputs at once, in this case 2 simultaneously. The source signal can come from the probe, Analog Channel Inputs (ACH0-ACH7), or internally the ELVIS software can link the virtual function generator and Oscilloscope.

For channel B, choose source “FGEN FUNC_OUT” and turn on the display so you can see both the probe and the source on the screen. This should display the output of the function generator directly on the oscilloscope without needing an external connection. If this does not work, just get another Probe and attach it to the front panel and connect it to the “Func_out” row on the satellite board. Make sure Channel A and Channel B have the same settings so you are looking at the same scale for each.

Take a screen shot (PRTSCN button) and paste picture of the oscilloscope here. Be sure to crop the image down to just the plot and display settings so that your source selection can be seen and the signals are aligned.

Today you are going to use a capacitor to make a frequency filter. In the next chapter we will learn about the behavior of capacitors and why it can be used to filter out certain frequencies for sine waves.

Build a simple filter with your choice of R and C values, but you must choose values that have a cutoff frequency between 1000 and 10,000 Hz. Do the following calculations to choose values:

Figure 3. RC filter indicating where the input and output voltages are measured, cutoff frequency is a function of R and C.

Note: The cutoff frequency also represents a 3dB decrease from the maximum amplitude in a log scale, which is the same as 0.707 times the maximum amplitude on a linear scale.

Get a 0.01, 0.1 or 1 uF (micro Farad) capacitor. A Farad is the fundamental unit of capacitance. When doing calculations, pay attention to the Greek prefix for scale. For unit conversion, an Ohm*Farad = Second so 1/(Ohm*Farad) = Hertz (Hz) . The cutoff frequency is the point at which the filter reduced the signal to half of its unfiltered power. For an RC circuit like the one above, this value is (2*pi*R*C)^-1 .

Which capacitor value did you choose (use labeled value, not measured)? _____1 uF_____________

To get a cutoff frequency of 1000 Hz, what R value do you need (use 0.01, 0.1, or 1 uF for calculation)? ____________160 ohm________

To get a cutoff frequency of 10,000 Hz, what R value do you need (use 0.01, 0.1, or 1 uF for calculation)? ___________16 ohm_________

Choose a resistor that falls between these values that we have in the lab.

What value of R did you choose? ______100 ohm__________

What is the cutoff frequency for the filter you built using labeled values of R and C? _______________1590 Hz____________

Measure the actual capacitance of the capacitor with a Multimeter than can measure capacitance. Measure the Resistor too. What are the actual values? Not all multimeters measure capacitance. The Velleman Multimeters have a special attachment that slides into the slots labeled “Cx”, others that have a C(apacitance) or F(arads) can use normal alligator clip probes. Check near the banana plug jack to see which plugs are used for capacitance. Take the R and C measurements and record them.

C = _____1.1 uF_____

R= _______99.2____

What is the actual cutoff frequency using these values?

f= ________1458 ohms____

Now build the circuit:

ACH0+

ACH0- and ground

ACH1+ and Func_out

ACH1- and ground

Figure 4 RC Filter showing connections to be made on the ELVIS breadboard. The input voltage is measured by Analog Channel 1 (ACH1) and the output is measured by Analog Channel 0 (ACH0). To reduce the number of wires needed, R and C can be placed directly in ACH0 and ACH1.

Look for a device called a Bode (pronounced bo –day) Analyzer on the NI ELVIS instrument launcher. This instrument uses the analog input channels on the ELVIS board, ACH0 and ACH1. These are located in the upper left hand corner of the small satellite breadboard. The first row of four holes is the ACH0+ input; the next row is ACH0-. The next two rows are ACH1+ and ACH1-. On the Bode window brought up by the instrument launcher, it tells you at the top that ACH0 is to be attached to the output of the circuit, and ACH1 is the input to the filter which should also be connected to Func_out from the function generator. Connect ACH1+ and Func_out to Vin and ACH0+ to Vout. Attach ACH0- and ACH1- to ground. Run the Bode Plot. This device generates different frequencies sequentially and sends it into your circuit then measures the level of the signal that returns for each frequency. On a logarithmic scale it displays Power Out over Power In. A high signal means little or no loss. A low signal means that the filter did not allow that frequency to pass. Take a screen shot (PRTSCN button) and paste picture of Bode Plot here. Be sure to crop the image down to just the plot.

From this data in the graph does this filter allow low frequencies or high frequencies or pass?

___________________________________Low pass _____________________________________

Reverse the position of the resistor and capacitor in the circuit, so the capacitor is connected between Vin and Vout and Vout is designated across the resistor. Run the Bode plot again, how does reversing the components affect the circuit?

________________________________High Pass _____________________________________

Take a screen shot (PRTSCN button) and paste picture of Bode Plot with reversed components here. Be sure to crop the image down to just the plot.

When done, shut down computer and turn off ELVIS, and submit this assignment in blackboard.