Optical Encoder Speed
n = (count / PPR) × 60 / t
Quick answer
This calculator solves n_RPM = (count / PPR) × (60 / t) for Speed (RPM). With Pulse Count 1.1, Pulses Per Rev 2.35, Measurement Time 1 s, the result is 28.09.
Calculator
Formula
Description
An optical (or magnetic) encoder generates a fixed number of pulses per revolution (PPR). By counting pulses over a known time period, the rotational speed can be calculated. The count divided by PPR gives the number of revolutions in the measurement period, and multiplying by 60/t converts to RPM. This frequency-measurement method works best at moderate to high speeds. At very low speeds, the period-measurement method (measuring time between individual pulses) provides better resolution.
Variables
- n — Rotational speed (RPM)
- count — Number of encoder pulses counted in the measurement period
- PPR — Encoder pulses per revolution
- t — Measurement time window (s)
Practical Notes
Common encoder resolutions: 100-1000 PPR for general industrial, 2000-10000 PPR for precision servo. Quadrature encoders (A/B channels) multiply the effective resolution by 4× when counting all edges. At low speeds, quantization error is significant: for a 1000 PPR encoder at 1 RPM measured over 100 ms, only about 1.67 pulses are counted. Use longer measurement windows or the period-measurement method for low-speed applications.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| n | Speed (RPM) | — | — |
| count | Pulse Count | — | — |
| PPR | Pulses Per Rev | — | — |
| t | Measurement Time | s | ps, ns, µs, ms, s, min, h |
Step by step
- 1. What you know: Pulse Count 1.1, Pulses Per Rev 2.35, Measurement Time 1 s
- 2. The relation: n_RPM = (count / PPR) × (60 / t)
- 3. Substitute: count = 1.1, PPR = 2.35, t = 1 s
- 4. Result: Speed (RPM) = 28.09
Worked examples
Minimum range
Given: Pulse Count 0.055, Pulses Per Rev 0.118, Measurement Time 100 µs
Result: Speed (RPM) = 279700
Low range
Given: Pulse Count 0.55, Pulses Per Rev 1.18, Measurement Time 1 ms
Result: Speed (RPM) = 27970
Typical
Given: Pulse Count 1.1, Pulses Per Rev 2.35, Measurement Time 1 s
Result: Speed (RPM) = 28.09
High range
Given: Pulse Count 1.76, Pulses Per Rev 3.76, Measurement Time 1 min
Result: Speed (RPM) = 0.4681
Maximum range
Given: Pulse Count 17.6, Pulses Per Rev 37.6, Measurement Time 10 min
Result: Speed (RPM) = 0.04681
How Speed (RPM) changes with Pulse Count
| Pulse Count (input) | Speed (RPM) (result) |
|---|---|
| 0.242 | 1.277 |
| 0.605 | 3.191 |
| 1.21 | 6.383 |
| 1.815 | 9.574 |
| 2.42 | 12.77 |
| 3.63 | 19.15 |
| 4.84 | 25.53 |
| 9.68 | 51.06 |
| 16.94 | 89.36 |
| 24.2 | 127.7 |
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<p><a href="https://vbatpower.com/formulas/optical-encoder-speed/">Optical Encoder Speed</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Optical Encoder Speed?
Use n_RPM = (count / PPR) × (60 / t). With Pulse Count 1.1, Pulses Per Rev 2.35, Measurement Time 1 s, Speed (RPM) works out to 28.09.
How do you calculate encoder ppr to speed?
Rearrange for Speed (RPM): with Pulse Count 0.55, Pulses Per Rev 1.18, Measurement Time 1 ms, Speed (RPM) is 27970.
What is the formula for Optical Encoder Speed?
The formula is n_RPM = (count / PPR) × (60 / t). An optical (or magnetic) encoder generates a fixed number of pulses per revolution (PPR).
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