DC MOTOR RPM CONTROL
Interesting ...
Therefore, you can adjust the frequency of the frequency generator (FG) to 'set' the motor speed that you wish, am I correct?
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If my statement above is correct ...
Let's say the frequency of FG is 100Hz and the speed of the motor is 100 rev/second. Assume that there is only one pair of sensor/marker in your system, so the motor can be considered to rotate at 100Hz (100 revolution per second).
Let's say now we wish to set the motor speed to 50 rev/second. So, we adjust the frequency of the FG to 50Hz. After a short instant the frequency is set to 50Hz, the motor speed should still remain at 100 rev/second. As 100Hz is an integer multiple of 50Hz ('harmonic'), the controller will still receive a 'matched' signal every time it promts to update the sensor/marker signal. Consequently, the controller will not update the PWM duty cycle and therefore, the motor speed will remain at 100 rev/second.
How do you adjust the frequency? Manually (using knob)?
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However, it will not be so lucky to get both signals (frequency and sensor/marker) matched after the frequency is set to 50Hz. So, your system will still be working.
In my opinion, it's kind of conventional method used in OLD day to control the speed of the motor. In modern day, microcontroller is used to calculate the motor speed based on the sensor/marker signal (or opto-slotted disk). One of the advantages to use microcontroller is probably you can include kind of control algorithm (e.g. PI controller) to improve the response of the motor. However, if your application does not need fast response, then this advantage might not sound great to you.
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