Question

How is RPM calculated?

Answer 1

RPM (Revolutions Per Minute) is a measure of how many times an object, like a motor shaft or a wheel, completes a full rotation in one minute. The calculation of RPM depends on the context in which it is used.

Basic Formula for RPM  

If you know the time it takes for one full rotation:  
\[
\text{RPM} = \frac{60}{\text{Time per revolution (in seconds)}}
\]
For example, if a wheel takes 2 seconds for one full rotation:  
\[
\text{RPM} = \frac{60}{2} = 30 \text{ RPM}
\]

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RPM in Terms of Frequency (Hz)

If you know the frequency in Hertz (Hz), which is the number of cycles per second:  
\[
\text{RPM} = \text{Frequency (Hz)} \times 60
\]
For example, if a motor runs at 50 Hz:  
\[
\text{RPM} = 50 \times 60 = 3000 \text{ RPM}
\]

---

RPM in Terms of Linear Speed

If you know the linear speed and radius:  
\[
\text{RPM} = \frac{\text{Linear Speed (m/min)}}{2\pi \times \text{Radius (m)}}
\]
For example, if a belt moves at 10 m/min and the pulley radius is 0.5 m:  
\[
\text{RPM} = \frac{10}{2\pi \times 0.5} \approx 3.18 \text{ RPM}
\]

---

RPM in Electrical Motors (AC Motors)

For an AC motor, RPM depends on the supply frequency and the number of poles in the motor:  
\[
\text{RPM} = \frac{120 \times \text{Frequency (Hz)}}{\text{Number of Poles}}
\]
For example, a 4-pole motor running at 60 Hz:  
\[
\text{RPM} = \frac{120 \times 60}{4} = 1800 \text{ RPM}
\]

Let me know if you need a specific calculation!