Lab 1 - Motor Identification Lab


In this lab, you will be measuring the speed-dynamics of a DC motor. A schematic of the setup you will use is shown below. You will measure the speed of the motor using a second, identical motor connected to the first. The second motor acts as a generator, and is called a tachometer. The tachometer's output is measured with the oscilloscope. The signal to command the motor is produced by the function generator. Since the function generator is not capable of powering the motor by itself, it's signal is first passed through an amplifier to boost the power of the signal.

The lab will consist of three sections:

Identify Amplifier
Relate output voltage of the amplifier to the input voltage.
Motor Step Response
Look at the motor's step response and identify the time constant and DC gain parameters.
Motor Frequency Response
Obtain the motor's response to sinusoidal inputs of varying frequencies. Relate this to the step response.

Amplifier Model

The amplifier is assumed to output a voltage which is proportional to the input:
Vout = Ka * Vin Where Ka is the gain of the amplifier.

Motor-Tach Model

The motor and tach together is assumed to be a first order system with a transfer function from voltage into the motor to voltage out from the tach of the form:


t s + 1

where K is the DC (or steady-state) Gain of the motor, obtained from the Final Value Theorem, and t is the Time Constant of the motor, obtained from the exponential form of the step response.


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