Frequency characterizes any periodic or cyclical process, and specifies a number of cycles that occur in a given period of time, whether in one second or in one hour. The International System of Units (SI) defines “hertz,” abbreviated “Hz,” as a unit of frequency that refers to the number of periodic events per one second. However, rotation speeds or machinery vibrations are often measured using a different unit: cyclesperminute, which is abbreviated as "CPM."

Obtain the CPM value from the device or machine characteristics or elsewhere. If the rotation speed is given as revolutionsperminute, or RPM, it would be numerically equal to CPM. For example, 4,800 RPM is the same as 4,800 CPM.

Consider the following mathematical proportion, given that one minute equals 60 seconds: CPM is the number of cycles per 60 seconds (one minute); Hz is the number of cycles per one second. Solve this proportion to obtain:
number of cycles in Hz = CPM / 60. 
Apply the formula from Step 2 to convert CPM to Hertz. Using the CPM value
from Step 1 you get: number of cycles in Hz = 4,800 / 60 = 80.
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References
 “Handbook of Condition Monitoring  Techniques and Methodology;” A. Davies; 1997
 "Introduction to vibration technology;"Dennis H. Shreve; Nov. 1994
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