ECE 1201 – Electronic Measurements and Circuits Laboratory

Experiment #1 -- Equipment Familiarization

No Prelab Plan required

The objective of this lab is to develop a basic familiarity with the equipment that will be used in this course and in succeeding lab courses. The equipment includes oscilloscopes, multimeters, signal generators, and power supplies.

OSCILLOSCOPE (or SCOPE): This is a device that can display the time variation of the voltage signal appearing at its input terminals or can be used to create and x-y display of voltage vs. voltage. A manual for the DS1102E oscilloscope can be from the Rigol site here. (Click on Documents).

MULTIMETERS: These devices measure various common resistances of components andvoltages or currents in circuits. Electrical resistance is measured in terms of , k, and M. AC voltages and currents are usually measured in terms of their RMS values. Voltage measurements are given in terms of mV or V, and currents are generally measured in terms of mA or A. A “Quick Guide” and a “User’s Guide” for the Rigol 3058 digital multimeter is found here. This meter can measure voltage, current and capacitance.

SIGNAL GENERATOR: These produce a voltage source in which different types of voltage signals (functions of time) can be generated. Sine waves, squares waves and triangular waves will be used during the semester. The Rigol DG 1022 Waveform Generator is capable of two independent outputs. A “Quick Guide” and a “User’s Guide for the Rigol 1022 Function Generator can be accessed from here.

POWER SUPPLY (dc voltage source): This device provides an approximately constant or DC voltage source. Any power supply will have a maximum current output. In general, a power supply or voltage source can be modeled by its Thevenin equivalent (ideal voltage source in series with a resistor). This implies that the output of the powersupply source will drop as more current is drawn from the supply. A manual for the Rigol DC 1308A Power supply may be downloaded from the Rigol sitehere (Click on Documents).

EXPERIMENT

Take a few minutes to study the devices and their connectors on your bench. Refer to any handouts of instructions for the equipment and, if necessary, to the equipment manuals. Several copies of each instrument manual are available in the laboratory. The lab instructor or TA will circulate around the lab to answer any questions. The equipment is quite user friendly and with a little "knob-twisting" you'll probably be able to figure out the controls without reference to the manuals. For this lab and all subsequent labs, answer all questionsin the formal lab report.

Procedure A: Here you should figure out how to use the most basic features of the equipment. The following procedures will help you to do this. Feel free to try lots of other experiments, but take care not to short the terminals of the power supply or of the function generator!

  1. Connect the power supply output (use the +6 output) to the terminals of the multimeter. Be sure that the multimeter is set to measure dc voltage. Vary the power supply voltage and observe the associated variation in meter reading.
  1. Connect the function generator (using a BNC T) to the oscilloscope and to the multimeter (voltage measurement terminals). Measure the root-mean-square (RMS) and average (DC) values of the voltage on both the oscilloscope and on the multimeter for the following waveforms: sinusoidal, triangular, and square wave. (Set frequency to 400 Hz) Set each of the waveforms for 1 V peak to peak, symmetric about zero volts. (You may have to adjust the offset on the signal generator). The signal generator is capable of two, simultaneous output waveforms. Figure out how to produce the proper output on Channel 1 of the signal generator. How do you measure the average value of the waveform on the multi-meter? How do you measure the rms value of the waveform on the multi-meter. Measure the rms values. Calculate (analytically) the RMS of each waveform to confirm that measured values match calculations. (You may have to look up the definition of RMS.) Vary the waveforms' amplitudes and observe the variation of measured voltage. You should observe these waveforms on the scope when you do these measurements. (This gives you a bit of a head start on part 3.)
  1. Connect the function generator (set to generate a sinusoid with about 2 V peak to peak [PP]) to channel 1 of the y inputs to the scope. Set up the scope to display this waveform by setting the trigger level to be at about the midpoint of the sinusoid. Then vary the frequency and amplitude of the waveform and observe the changes on the scope. Finally, vary the trigger level setting such that the displayed waveform appears to move horizontally on the scope display. Why must the trigger level be within the range of the waveform to get a stable display?
  1. Repeat these observations for the other waveforms: square wave, triangle wave, ramp, noise, and sinc (from the "arb" menu-choose arb., load, Builtin, Math, sinc). Notice that the sinc waveform requires you to more carefully set the trigger level to get a stable display -- Why is this so? Why can't you get a stable display of the noise signal?

Procedure B:


Measure the output resistance of the function generator (set for sinusoidal waves) with the following circuit:

You can do this by measuring the output voltage with and without the resistor R in the circuit. Be sure to explain clearly in your report the basic theory used to do this measurement. (Note: do not short the outputs of the function generator!)

Procedure C:

Set up the following circuit and measure the voltage across resistor R using the "A-B" feature of your scope. (Pick R and R1 such that the output resistance of the function generator R0 ≪ R + R1) The “A-B” feature allows you to display the difference between two voltages. This is particularly useful in such circuits since the scope's common is tied to AC ground. You could not measure the voltage across R with a single channel without severely affecting the circuit, since the ground in the circuit (i.e. the FG's common terminal) is often tied to the AC ground. The vertical scale on the A-B display can be adjusted. The A-B feature is accessed through the MATH menu.


Procedure D:

Use the scope into X-Y mode for the following observations.

(a) Place the same output of a function generator (sine wave at 1000 Hz) on both X and Y inputs, i.e. channels 1 and 2. Set volts/div the same for both X and Y axes, and adjust the signal amplitude and/or volts/div to fill most of the display. What do you see?Explain why it looks this way. Does the display change when an equal amplitude triangle wave is substituted for the sinusoid? Repeat your observations for frequencies of 100 Hz and 10 KHz. Do you see the same thing? Does the brightness of display vary significantly as the frequency is varied? What would you expect to see if you were using an analog scope? Would brightness change with frequency? (The scope in the lab is a digital scope.)

(b)Now invert one channel so that you have signals that are 180º out of phase (press “CH1” set “Invert” ON). How does inversion affect the display?

(c)Now place the two different outputs from the function generator on the X and Y inputs. Start with sine wave for both outputs of the function generator and try to set both generator frequencies to the same value, say 1000 Hz. (You are welcome to use other frequencies here – also, late night TV viewers may recognize a display seen in “The Outer Limits”) You will know you are getting close if the “chaotic” look of the display begins to resolve into a more slowly varying set of patterns. Characterize this set of patterns and explain why you see these. Hint: If the frequencies are not perfectly matching, does the relative phase between the two signals vary? (Press the Menu button in the Horizontal control section, select Time Base and choose X-Y)

(d)Now try the same experiment as in (c) with triangle waves. Why do you see a different basic pattern?

In your report make use of the scope capture program to record scope displays. Use equations (where appropriate) to characterize the results you’ve found. Also, make ample use of graphics in answering the various questions posed in these pages. Finally, speculate about what kinds of X--Y signals you could use to draw an upright equilateral triangle on the display.

Updated August 24, 2007

Updated January 8, 2008

Update July 25, 2011, January 4, 2012, Typo correction March 26, 2012

Updated January 2, 2018