2.5.1 Theory
A basic feedback control system is shown in the figure below. In this system the controller will read a velocity signal from a feedback controller and compare it to a desired speed voltage. In this system the desired speed is specified using an input voltage. The deired voltage (Vd) is compared to the feedback voltage (Vt) from the tachometer. The result is the error (Ve = Vd - Vt). This is then passed through a simple proportional controller that amplifies the error by a gain (P) to produce a control output (Vu = P Ve). This output is then used to drive the amplifier produced in last weeks laboratory.
Figure 1.1 The complete feedback loop
In the previous lab the Amplifier, motor and tachometer were expolored. This week we will add a proportional feedback controller. A simple circuit based on an op-amp using the inverting op-amp configuration is shown below. This circuit can be manipulated to replace the subtraction and multiplication operations.
Figure X - A differential Amplifier
2.5.2 Procedure
1. Draw a circuit diagram for the complete control circuit. Select component values. If necessary check with the instructor.
2. Build the class AB amplifier from the previous laboratory and verify the operation.
3. Connect the oscilloscope CH1 (or A) to the function generator on the Cadet Trainer. Verify that the oscilloscope can display the signal.
4. Connect CH2 (or B) to the tachometer and verify that the displayed signal is correct.
5. Connect the input of the amplifier to the signal generator on the Cadet Trainer. Use a sine wave set to a low frequency and observe the results on the oscilloscope. Over a range of frequencies determine the phase shift of the signals.
6. Build the differntial amplifier and verify that it is working properly. Note: For the differential amplifier select components that have very similar values; verify the values with a multimeter.
7. Integrate the amplifier and differential amplifier into the complete control system and verify the operation. Repeat step 5.
