An open-loop dc motor speed control system
is developed using National Instrument's Data
Acquisition (DAQ) Board (Model 6040E) and
LabVIEW software package. Pulse Width
Modulation (PWM) technique is employed to
control motor speed. A vi (virtual instrument) is
developed with LabVIEW that allows the DAQ
to read a user selected reference voltage
continuously. The vi also generates a suitable
triangular wave that with the help of the
reference signal produces the desired PWM
signal. PWM is an analog signal that switches
between two predefined limits. The switching
interval of the PWM controlled by the reference
signal determines the average power delivered
to the motor circuit. The PWM signal is sent
through the output port of the DAQ by the vi
which in tum controls the motor speed. User
fiom the fi-ont panel of the vi may input the
amplitude and the frequency of the triangular
wave, sampling rate of the reference signal, and
the desired amplitude of the PWM. As the
reference voltage increases, the width of the
PWM (duty cycle) increases which in turn