Pulse Frequency ↔ RPM Calculator
Convert between encoder pulse frequency and motor RPM. Useful for HSC inputs and tachometer calibration.
pulse
frequency
RPM
encoder
HSC
PLC
tachometer
speed
Input values
⚙
Enter values and click Calculate to see results here.
Formula
RPM = (f × 60) / PPR
f = (RPM × PPR) / 60
Worked Example
Given: An encoder with 600 PPR is connected to a motor. The PLC HSC reads 4500 pulses per second.
Step 1: RPM = (4500 × 60) / 600 = 450 RPM
Verify: f = (450 × 600) / 60 = 4500 Hz ✓
If using x4 encoding, the effective PPR is 2400, giving RPM = 112.5. Check your encoder configuration.
Engineering Notes
- PPR vs CPR: PPR = Pulses Per Revolution (output pulses). CPR = Counts Per Revolution (quadrature decoding). A 600 PPR encoder gives 2400 counts/rev with x4 decoding.
- Quadrature encoding: x1 = 1 count/pulse, x2 = 2 counts/pulse, x4 = 4 counts/pulse. Most PLCs use x4 for direction detection.
- HSC hardware: Check your PLC maximum input frequency. Typical values: 20 kHz (standard), 100 kHz (high-speed), 1 MHz (specialty modules).
- Sampling time: For accurate RPM, measure pulses over a fixed time window (e.g., 100 ms) rather than instantaneous frequency.
References
- IEC 61131-3 — Counters and高速 counters
- Allen-Bradley SLC 500 HSC configuration