ELEC 242 Lab

Experiment 6.3

Electromechanical Transfer Function

Components

The setup for this experiment is the same as for Experiment 5.3, i.e. we will mechanically connect two motors, using one as a tachogenerator and driving the other with the motor amplifier. However, instead of applying a square wave and measuring the step response, we will apply a sequence of sine waves and measure the frequency response.

Part 1: Setting Up



Step 1:

 Get two 18 V motors and a strobe test disk from the cart. Press the shaft of each motor half way into the hole on either end of the disk. One of these will be the "motor" and the other will be the "generator".


Step 2:

 Plug a phone plug patch cord into J1-5 on the interface board and another into J1-6. Connect the other end of the patch cords to the two motors.

Step 3:

 Set the function generator to produce a 10 V p-p, 1 Hz square wave.

Step 4:

 Ground one side of each motor (pins 7 and 9 on the interface board socket strip). Connect the other terminals of the motors to the scope (pin 6 to CH1 and pin 8 to CH2).

Step 5:

 Connect the driving motor (Pin 6) to the motor amplifier output. Connect the function generator to the motor amplifier input.
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Step 6:

 Turn on the power. If all is well you should see the same step response you did at the end of Experiment 5.3.

Part 2: Measuring Motor-Generator Frequency Response

We won't try to measure the frequency response of this system manually. At the low frequencies involved, this would be really tedious. Instead we will use our automated frequency response measurer to (hopefully) make short work of this segment of the lab.


Step 1:

 Disconnect the function generator from the input to the motor amplifier. Leave the scope connected.

Step 2:

 Connect D/A output 1 (pin 52 on the interface board socket strip) to $v_{in}$ . Also connect A/D input 4 (pin 46) to $v_{in}$ .

Step 3:

 Connect A/D input 5 (pin 47 on the interface board socket strip) to $v_g$ .

Step 4:

 Reload the "Frequency Response" program. Set the parameters as follows:
  • Flo=0.2 Hz
  • Fhi=100 Hz
  • Nsteps=20
  • Amplitude=10 V
  • Magnitude Scale: dB
  • Frequency Scale: Log


Step 5:

 Run the program. This will take a bit longer than the other two circuits (it takes 10 seconds to generate a single cycle of a 0.1 Hz sine wave).

Question 4:

 As in Question 2, estimate $\omega_0$ from the frequency response. Compute $\tau$ and compare it with what you measured in Experiment 5.3. Which do you think is more accurate?