In order to acquire the precise control of equipments which
is driven by a DC motor, such as a constant-torque control orconstant-speed control or position control, some types of sensor
like the speed and/or the current sensors will be integrated into
the system controller for dynamically conducting a close-loop
control purpose. In addition, in the motor characteristic testing
fields (includes performance tests and product mass-production
tests), DC motor is necessary to be tested regarding its speed
related performances under different loads’ condition. How to
quickly and precisely measure the speed data of DC motor is
one of the critical problems because it is a very important
performance evaluating index during the DC motor
characteristic test and production mass-production test. In the
regular performance test of DC motor, the speed measurement
is often carried out through coupling a real speed sensor with
the axis of DC motor. The measured speed data of DC motor
will be read, calculated, and displayed by the system controller.
This is generally called as a direct speed measuring method. If
the speed sensor is incorporated into the hardware circuits and
software algorithms well, the testing precision by using this
speed measurement method is very high. But there are some
disadvantages will be occurred and described as follows