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Browse Prior Art Database

Electronic Tachometer

IP.com Disclosure Number: IPCOM000082799D
Original Publication Date: 1975-Feb-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Pezdirtz, KF: AUTHOR [+2]

Abstract

The tachometer system illustrated is capable of providing a wide range of speed measurement, at relatively low speeds, and with relatively high accelerations.

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Electronic Tachometer

The tachometer system illustrated is capable of providing a wide range of speed measurement, at relatively low speeds, and with relatively high accelerations.

A rotary transducer 5 is mechanically attached to a shaft such as the shaft of a motor 7, the characteristics of which are to be measured. The output of the rotary transducer 5 is preferably a pure sine wave whose frequency is proportional to motor RPM. Any DC component of the transducer output must be eliminated. For the harmonic distortion and noise to be reduced, the transducer signal should be band-limited. In addition, because the peak-to-peak transducer output voltage will be low, this signal will have to be amplified. These requirements can be satisfied by amplifier and filter 9. The output of 9 will be a band-limited signal in which, it will be assumed, each frequency within the band is amplified equally with gain A.

The output of 9 is multiplied by a constant sine-wave carrier frequency supplied from carrier oscillator 11, which has been processed through a band- pass filter 13 to help eliminate any DC or harmonic distortion. The multiplication is carried out by an analog multiplier 15. The results of the analog multiplication are the same as an AM modulated signal with suppressed carrier. No additional phase information is added for the carrier, because it can be assumed with any given set of sine waves that one of them has zero phase with respect to the others.

Both the upper and lower sidebands of the analog multiplier signal contain information regarding the motor RPM. The upper sideband signal will yield a band-limited signal with the carrier frequency as a lower bound. If the carrier frequency is high enough, using only the upper sideband will assure that no unwanted frequencies will be in th...