New low-noise tachogenerator

The paper describes a new device which uses optically generated pulses to produce a d.c. output directly proportional to the speed of rotation of a shaft. The importance of the device lies in the very low noise content of the generated voltage, which is therefore suitable for differentiation to give an accurate acceleration signal of wide bandwidth. The different sources of noise and the application of lowpass filters to its removal are discussed. The viability of the system is demonstrated by results obtained from a prototype.