Lab 6

4. In the Excel spreadsheet, make three new columns to convert your measured data into the
armature voltage (ea), the steady-state current (ia,ss) and motor speed (ωss) using the
conversion factors for the power amplifier (5 V/V), the current sensor (2 V/A) and the
tachometer (52.4 rad/sec/V).
5. Make a plot with ωss on the y-axis and ia,ss on the x-axis. Using eq. (7), the slope of this line is
equal to (km/b). Find the slope, label the axes of this plot and save it to hand in with your
report.
6. Create an additional column to compute (ea - Ra ia,ss). Make a second plot with ωss on the xaxis
and ea - Ra ia,ss on the y-axis. Using eq. (6), the slope of this line is equal to km. Find the
slope, label the axes of this plot and save it to hand in with your report.
7. Write-up
In your typed lab report, indicate the following information by including tables such as those
shown below.
A. Electrical Characteristics
Ra = ________Ω Measured
Power Amp
Output, ea
[V]
3
4
5
Armature
Current,
ia,ss [mA]
Average:
B. Determining System Time Constant
14
Ra
[Ω]
Step Input (V) τ
4
5
6
Average
τ
[ms]
La
[mH]
Compare the electrical time constant to that of the overall system. Is it a good assumption to
neglect the electrical time constant?