Oscilloscope Lab Report

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Statement of Objectives

The objective of this lab was to gain understanding of the use and functions of oscilloscopes and the methods used to measure a system’s time constant. Several methods were used throughout the laboratory in order to gain familiarity with the equipment as well as investigate characteristics of an RC high pass filter. The ability to problem solve and critically think was necessary for completion of this laboratory and therefore an objective.

Apparatus

Table 1. List of Equipment Used During Session 1 and 2 of Laboratory

Device
Manufacturer
0.301μF Capacitor
Unknown
Variable Resistance Box
Omega Engineering
NI Soft Front Panel Oscilloscope
National Instruments
LabVIEW Software
National Instruments
DAQ Device
The apparatus was tested, using Measurement and Automation Explorer (MAX) software. The ability to use the oscilloscope was demonstrated to Professor Mountain using the test inputs provided in the lab handout. A resistor and capacitor pair was selected by each team member, for a total of three pairs.
Next, multiple methods of calculating time constants, τ, were conducted. The first method was calculating theoretical time constants using equation 1 and selected values of resistance and capacitance. τ=RC (1)
The second method used a high pass filter, which was set up using the wiring diagram shown in figure 1. A 300mV square wave was produced using the oscilloscope. Signal periods were calculated using equation 2 and the theoretical time constants previously calculated. Period ≅10*휏theoretical (2) Slight alterations were made to the signal produced by the oscilloscope as needed to allow complete charge or discharge cycles. For each resistor/capacitor pair, times required to achieve 63.2 percent of maximum voltage change and 86.5 percent of maximum voltage change were
Gain versus Frequency for 22kohms Resistance

Figure 7. Gain versus Frequency 33000ohms

Discussions and Conclusions

Report Question 1:
The percentages represented the amount of voltage that was gained or lost during the charge and discharge cycle for each iteration of , , .
Report Question 2:
This plot is called the Bode Plot.

Session 1: For session 1, the setup was found to be correct after the test signal was inputted and deemed correct by the instructor, Professor Mountain.
The first method for determining tau was a calculation. No equipment was used, other than a basic calculator, and no errors occurred. The values were then established as control for comparison in later parts.
Method two involved using the soft front panel software, specifically using the cursor feature. The potential error for this method was the placement of the cursors for determining change in voltage and time. The signal produced by the oscilloscope was associated with noise, which made the exact values of the maximum and minimum voltages difficult to determine. The cursors were placed in the center of the noise surrounding the sine wave as a best estimate of the actual value. This value was then assumed to be correct, due to the fact that it was very close to the value entered into the oscilloscope. The results from this method were all within .328ms of the theoretical values, which was assumed to be

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