Vibration monitoring in the frequency domain with a capacitive accelerometer
First Claim
1. A vibration monitoring system for determining the amount of energy at a certain frequency within a vibration signal spectrum of a mass, comprising:
- capacitive accelerometer means, disposed to be mounted to or rigidly coupled to the mass, and having two or more electrically conducting surfaces separated by a dielectric material, for producing a time varying change in capacitance between said electrically conducting surfaces in response to vibration of the mass, for mixing said time varying change in capacitance and a variable frequency signal by applying said variable frequency signal which is an AC voltage across said conducting surfaces, and for providing a mixed signal indicative of the product of said mixing, such that the frequency spectrum of said mixed signal comprises a certain beat frequency whose energy is indicative of the amount of energy at the certain frequency within the vibration signal spectrum of the mass;
a bandpass filter, responsive to said mixed signal, having a passband centered about a certain center frequency, for filtering said mixed signal and for providing a filtered signal indicative thereof; and
frequency control means, for providing said variable frequency signal, for setting the frequency of said variable frequency signal such that the location of said certain beat frequency created by said mixing and associated with the certain frequency of the vibration signal spectrum is within said passband, and being responsive to said filtered signal for providing an energy signal whose energy is a measure of the vibration energy associated with the certain frequency.
5 Assignments
0 Petitions
Accused Products
Abstract
A vibration monitoring system employing a capacitive accelerometer determines the energy associated with one or more frequency components within the frequency spectrum of the vibration signal. The capacitive accelerometer operates as a mixer due to its time varying capacitance which provides a measure of the vibration. When the accelerometer is excited by an AC signal the output from the accelerometer comprises beat frequencies due to the mixing of the time varying capacitance and the AC signal. By changing the frequency of the AC signal the location of the beat frequencies in the frequency domain of the accelerometer output can be shifted. Subsequent bandpass filtering to attenuate frequencies except those associated with the frequency component and demodulation to bandshift the energy of the filtered signal energy to DC, creates a DC value which provides a measure of the energy present at the frequency component.
42 Citations
23 Claims
-
1. A vibration monitoring system for determining the amount of energy at a certain frequency within a vibration signal spectrum of a mass, comprising:
-
capacitive accelerometer means, disposed to be mounted to or rigidly coupled to the mass, and having two or more electrically conducting surfaces separated by a dielectric material, for producing a time varying change in capacitance between said electrically conducting surfaces in response to vibration of the mass, for mixing said time varying change in capacitance and a variable frequency signal by applying said variable frequency signal which is an AC voltage across said conducting surfaces, and for providing a mixed signal indicative of the product of said mixing, such that the frequency spectrum of said mixed signal comprises a certain beat frequency whose energy is indicative of the amount of energy at the certain frequency within the vibration signal spectrum of the mass; a bandpass filter, responsive to said mixed signal, having a passband centered about a certain center frequency, for filtering said mixed signal and for providing a filtered signal indicative thereof; and frequency control means, for providing said variable frequency signal, for setting the frequency of said variable frequency signal such that the location of said certain beat frequency created by said mixing and associated with the certain frequency of the vibration signal spectrum is within said passband, and being responsive to said filtered signal for providing an energy signal whose energy is a measure of the vibration energy associated with the certain frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
-
-
12. A vibration monitoring system for monitoring the frequency spectrum of a vibrating mass, comprising:
-
capacitive accelerometer means, mounted or rigidly coupled to the mass, for producing a time varying change of capacitance in response to the vibration of the mass, for providing a sensed signal indicative thereof, for mixing said sensed signal with a variable frequency signal by exciting said capacitive accelerometer means with said variable frequency signal which is an AC signal, and for providing a mixed signal indicative of the product of said mixing; frequency control means, for selecting a frequency component from within the frequency spectrum of the vibrating mass, for determining the frequency which said variable frequency signal shall operate at based upon the frequency of said frequency component, and for providing said variable frequency signal; and signal processing means, for processing said mixed signal to attenuate the energy of frequency components other than the energy associated with said frequency component, and for providing a filtered signal whose frequency spectrum contains a dominant bandshifted frequency component with energy indicative of the energy of said frequency component. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
-
Specification