PWM Control
A PWM signal is a digital signal, a "square" wave where the percentage of the time the
signal is high specifies the percentage of the full speed of the motor at which it should run So, suppose you have a motor and PWM drive with maximum speed of 3000 rpm then
figure 4.12 would run the motor at 3000 x 0.2 = 600 RPM. Similarly the signal in figure
4.13 would run it at 1500 RPM.
Mach3 has to make a trade off in how many different widths of pulse it can produce again how high a frequency the square wave can be. If the frequency is 5 Hz the Mach3 running with a 25000 Hz kernel speed can output 5000 different speeds. Moving to 10Hz reduces this to 2500 different speeds but this still amounts to a resolution of one or two RPM.
A low frequency of square wave increases the time that it will take for the motor drive to notice that a speed change has been requested. Between 5 and 10 Hz gives a good compromise. The chosen frequency is entered in the PWMBase Freq box.
Many drives and motors have a minimum speed. Typically because the cooling fan is very inefficient at low speeds whereas high torque and current might still be demanded. The Minimum PWM % box allows you to set the percentage of maximum speed at which Mach will stop outputting the PWM signal.
You should be aware that the PWM drive electronics may also have a minimum speed setting and that Mach3 pulley configuration (see section x.x) allows you to set minimum speeds. Typically you should aim to set the pulley limit slightly higher than the Minimum PWM % or hardware limit as this will clip the speed and/or give a sensible error message rather than just stopping it.