Yes, the pulses occur at a rate of a hundred or a few hundred pulses per second. You can hear the buzz or whine if you stand near the brakes while someone steps on the brake pedal.
The controller puts out a string of pulses. All the pulses have the same height (say 12 volts). And they occur at a constant rate (say 100 pulses per second), or one pulse every 10 milliseconds. What changes is the width of each pulse.
If all the pulses have 50% duty cycle (5 msec ON followed by 5 msec OFF), then the average value is 6 volts. If the controller makes all the pulses narrower (say 2.5 msec ON followed by 7.5 msec OFF), then the average value is 3 volts. And if it makes the pulses wider, then the average value is higher.
A meter that measures average value will tell you that the voltage in the first case is 6 volts, and in the second case is 3 volts. But a peak-reading voltmeter - and that is most of them, especially the cheaper ones - will tell you that the voltage is always 10 volts, because it reads the maximum height of whatever it sees, without regard to pulse width.
Aren't you glad you asked?
Bill
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