Motor RPM test

I was able to use my DS0138 oscilloscope to measure the RPM of the latest motor. I took a signal reading from one of the two coil pairs, and as it switched on and off, it formed a square wave. The scope measured the frequency of the wave at 76hz. Multiplying by 30, I got the result: 2,280 RPM. Not bad!

Why multiply by 30? In this configuration, each coil pair turns on and off twice per full revolution of the rotor (the wave changes every quarter turn of the rotor). That means there isĀ  only half of a revolution in each cycle, or period, of the wave. So when the scope showed a frequency of 76hz, I had to first divide that by 2 to get revolutions/second, then I could multiply by 60 to get revolutions/minute.

76 cycles/second (hz) * 0.5 revolutions/cycle * 60 seconds/minute = 76hz * 30 revolution-seconds/minute-cycle = 2,280 revolutions/minute (RPM)

I shot a video of this, but it didn’t turn out well. I’ll update the post if I get a better one.