Claims
- 1. A method of determining speed of rotation of a motor (1), the method comprisingconnecting a measuring sensor (2) to the motor (1); determining the synchronous speed of the motor (1); setting the length of a measurement period (T); setting a sampling frequency (fs); collecting samples (x[n]) with a measuring sensor (3) at the sampling frequency (fs), set on the basis of mechanical vibration of the motor (1), for the duration of the measurement period (T); storing the samples (x[n]) in the memory of a data carrier (4) as measurement data of a fixed format, determining the speed of rotation of the motor (1) from the measurement data by determining the cycle length of a periodic vibration signal in the time domain by applying a maximum likelihood estimate calculated by maximizing a maximum likelihood function (J) adjusted to the measurement data, the speed of rotation being obtained from a frequency point (13f) where the maximum likelihood function (J) obtains its maximum value (13max).
- 2. A method according to claim 1, wherein, before the speed of rotation is determined, the vibration signal is filtered in a bandpass filter to attenuate the interference that is in the signal.
- 3. A method according to claim 1, wherein the maximum likelihood function (J) takes the following form J=ABS(∑n=0N-1x[n]ⅇ-j2πυ n),in which formula ABS=the absolute value of a complex number J=a maximum likelihood function to be maximized N=the number of samples n=the order number of a sample x[n]=an individual sample υ=the digital frequency of a periodic vibration signal, and υ=f/fs, in which formula f=the frequency of the periodic vibration signal fs=sampling frequency.
- 4. A method according to claim 1, the wherein length of the measurement period (T) is at least 50 times the cycle length of the vibration signal.
- 5. A method according to claim 1, t wherein he sampling frequency (fs) is at least three times the synchronous speed (fn) of the motor (1).
- 6. A method according to claim 1 wherein, the speed of rotation is determined using a maximum likelihood estimate of the time domain.
- 7. A method according to claim 1, wherein the measuring sensor (3) is an acceleration sensor or a speed sensor.
- 8. A computer software product for determining speed of rotation of a motor, the product comprisinga program code portion for collecting samples with a measuring sensor at a sampling frequency, set on the basis of mechanical vibration of the motor, for a duration of a measurement period; a program code portion for storing the samples in a memory of a data carrier as measurement data of a fixed format; a program code portion for determining the speed of rotation of the motor from the measurement data by determining the cycle length of a periodic vibration signal in the time domain by applying a maximum likelihood estimate calculated by maximizing a maximum likelihood function adjusted to the measurement data, the speed of rotation being obtained from a frequency point where the maximum likelihood function obtains its maximum value.
Priority Claims (1)
Number |
Date |
Country |
Kind |
000646 |
Mar 2000 |
FI |
|
RELATED APPLICATION
This application is a continuation of PCT/FI01/00271 field Mar. 19, 2001 designating the United States.
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
5365787 |
Hernandez et al. |
Nov 1994 |
A |
5424636 |
Rollwage et al. |
Jun 1995 |
A |
6085121 |
Stern |
Jul 2000 |
A |
Foreign Referenced Citations (3)
Number |
Date |
Country |
196 00 640 |
Jul 1997 |
DE |
0 632 261 |
Jan 1995 |
EP |
9910715 |
Mar 1999 |
WO |
Non-Patent Literature Citations (1)
Entry |
English Language Abstract for 196 00 640 A1 (DE). |
Continuations (1)
|
Number |
Date |
Country |
Parent |
PCT/FI01/00271 |
Mar 2001 |
US |
Child |
10/233627 |
|
US |