Speed-to-Frequency Conversion
Speed-to-frequency conversion is the translation of the pulse frequency coming from a sensor into revolutions per minute. The relation is: speed equals 60 times frequency divided by the number of pulses per revolution. For a correct result, the number of pulses per revolution must be known exactly.
The measurement is done by one of two methods:
- Pulse counting: the pulses arriving during a fixed period are counted. This is accurate at high speed; at low speed the resolution drops.
- Period measurement: the time between two pulses is measured. This is far more precise at low speed; at high speed it runs into the timer resolution.
In practice the sources of measurement uncertainty are these: teeth that are not evenly spaced, false pulses caused by noise, and too short a measurement window. To eliminate false pulses, a filter and a threshold are applied to the signal; the sensor cable is run separately from power cables and is shielded.
This conversion is the basis of systems that really control speed. The standard GS740 kit and the GS740-3P do not perform this measurement; both of them drive throttle position. For this reason these kits have no speed reading of any kind, and speed verification is done with a separate tachometer.
Context in which this term is used: Why is constant speed important on a generator?