How do we measure speed?

Monitoring speed is an important aspect of operating a scroll compressor or vacuum pump, as operation over the specified maximum speed can result in premature or catastrophic failure.

For scroll compressors and vacuum pumps that have a brushless DC motor, speed can be measured by connecting a digital tachometer between a hall sensor and ground. The tachometer must be programmed to the correct number of pulses per revolution, which can be determined by dividing the numbers of motor poles by 2. For example, an 8-pole motor will have 4 pulses per revolution.

Alternatively, an oscilloscope can also be used to measure the frequency of the hall sensors. Divide the measured frequency by the number of pulses per revolution and multiply by 60 to determine the RPM.

For scroll compressors and vacuum pumps that have an AC motor, speed can be measured by multiplying the frequency of the variable frequency drive (VFD) by 60 to determine the RPM.

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