The objectives of this experiment are to provide the student with an opportunity to
· Become familiar with an oscilloscope, function generator, and digital multimeter.
· Observe and describe different signals.
· Develop Lab Notebook skills.
The following materials are needed to complete this experiment.
· Dual beam oscilloscope.
· Function generator.
· A digital multimeter.
· Assorted wires.
You are to use both the oscilloscope and digital multimeter to examine various signals which are set up by the laboratory instructor. Take this opportunity to begin good laboratory practices by (1) keeping a log of what you did, when you did it, with whom, date, equipment used, and any other pertinent information, (2) observing safety in the laboratory, and (3) keeping your work area clean and orderly.
The experimental apparatus is to be connected as depicted in Figure 1. Turn on the equipment and allow it to warm up for a period of 3-4 minutes. During this time, begin studying the settings and functions of the oscilloscope and the multimeter. Establish basic settings for the oscilloscope and multimeter and then ask your instructor to establish a signal for you to measure.
An oscilloscope is perhaps the most useful general purpose instrument available to the experimenter. It provides one with a window into the signal's temporal domain and translates signal-time into a pictorial we can comprehend with our limited (in some ways) human senses.
In general, most signals can be categorized as having both AC (time varying) and DC (constant) components although one of these may be zero. This is shown in Figure 2.
1. Plot the following signals (Mathematica, Maple, Excel) over 0 ≤ t ≤ 10. For each signal, A=0.1 (volts), f=100(Hz), w=p*f/180 (rad/sec).
· y0=0.25 + 0.1 cos(wt)
· y1=0.25 + 0.1 [cos(wt) - cos(3wt)/3]
· y2=0.25 + 0.1 [cos(wt) - cos(3wt)/3 + cos(5wt)/5]
· yn=0.25 + 0.1 [cos(wt) - cos(3wt)/3 + cos(5wt)/5 - cos(7wt)/7 + cos(9wt)/9 - cos(11wt)/11 + cos(13wt)/13 - cos(15wt)/15 + cos(17wt)/17]
2. What is the DC Level for all of these signals?
3. What is the AC level (peak-to-peak)?
Measure the signals provided to you by the instructor. Use both the multimeter and the oscilloscope to determine what the signal is and then record your findings. A sketch or photo of the oscilloscope pattern may be useful to aid you in remembering the signal. Don't forget to record the instruments you used (make, model, serial number), settings, your setup, and then date and sign your datasheet(s).
You are to present your findings in your laboratory workbook. It is to contain the specific elements shown on the grading form below. Summarize your findings and suggest which instrument is most appropriate for which kind of signal and why you feel that way. Are there any limitations to the use of either instrument?
Please note that your Laboratory Assistant will be using the following grading form for your Lab Notebook.
Table 1. Laboratory Grading Form.
You will be responsible for helping the students to understand the settings on both the digital multimeter and the oscilloscope. These are not really difficult instruments to use and they are generally straightforward, once you know how they function and have spent some time using them. In other words it is like most things in life, once you understand something, it's easy to understand.
It is your responsibility to instruct them on the use of the oscilloscope. Keep your instructions basic to allow them to quickly determine the signal levels.
You will also be responsible for providing signals for the students. Use the function generator as your signal source and be certain to give them at least one of each of the following:
· A signal having no DC level, AC-only.
· A signal having no AC level, DC-only.
· A signal combining both AC and DC levels. The AC level should be large compared to the DC level.
· As above, but the AC level should be small compared to the DC level.
· A signal comprised of mostly noise.
Standardize the specific signal levels you give to your students, allowing them to work with each other and learn from each other.