Automatic Threshold Detection for Tachometer Signals

• US 20170160302A1
• Filed: 02/20/2017
• Published: 06/08/2017
• Est. Priority Date: 06/17/2013
• Status: Active Grant

• Current Assignee: Computational Systems Incorporated (Emerson Electric Company)
• Original Assignee: Computational Systems Incorporated (Emerson Electric Company)
• Inventors: Bowers, III, Stewart V.
• Granted Patent: US 10,345,326 B2
• Time in Patent Office: Days
• CPC Class Codes: G01H 1/003 of rotating machines G01H1/10 takes precedence
• CPC Class Codes: G01P 3/481 of pulse signals

Abstract

A method is described for automatically determining a proper threshold for a tachometer signal in order to produce desired tachometer pulses necessary for analysis of machine vibration data. A tachometer signal is low-pass filtered to exclude high frequency noise and a running derivative of the filtered tachometer waveform is taken to create a derivative waveform. Another waveform is created that includes only positive values from the derivative waveform that correspond to positive values in the low-pass filtered tachometer waveform. In general, a tachometer signal has the greatest derivative value (slope) when a tachometer pulse is present. Based on this observation, a threshold value is determined using both the low-pass filtered tachometer waveform and the positive-value derivative waveform along with statistics from both waveforms.

Claims

1. A method for determining peak amplitude values in a tachometer signal in order to calculate a threshold value for the tachometer signal and for determining associated statistical outlier values, the method comprising:

(a) sensing the tachometer signal;

(b) determining a set of peak amplitude values in the tachometer signal over a period of time and defining P₀ as the number of peak amplitude values;

(c) calculating a mean amplitude value μ and

a standard deviation amplitude value σ

of the peak amplitude values in the set;

(d) if

2. The method of claim 1 wherein x=0.1.

3. A method for determining a plurality statistically significant amplitude values of a signal and excluding statistical outlier values prior to further processing of the signal, the method comprising:

(a) determining a set of peak amplitude values in the signal and defining P₀ as the number of peak amplitude values;

(b) calculating a mean amplitude value μ and

a standard deviation amplitude value σ

of the peak amplitude values in the set;

(c) if

4. The method of claim 3 wherein x=0.1.

5. The method of claim 3 wherein the first lower statistical boundary is μ

−

nσ and

the first upper statistical boundary is μ

+nσ

.

6. The method of claim 3 wherein the second lower statistical boundary is

7. The method of claim 3 wherein the third lower statistical boundary is (1−

x)×

μ and

the third upper statistical boundary is (1+x)×

μ

.

8. The method of claim 3 wherein the first, second, and third lower statistical boundaries are set to zero.

9. A method for determining a plurality statistically significant amplitude values of a signal and excluding statistical outlier values prior to further processing of the signal, the method comprising:

(a) determining a set of peak amplitude values in the signal and defining P₀ as the number of peak amplitude values;

(b) calculating a mean amplitude value μ and

a standard deviation amplitude value σ

of the peak amplitude values in the set;

(c) if

10. The method of claim 9 wherein the lower statistical boundary is set to zero.

11. The method of claim 9 wherein x=0.1.