402
5 Laser Specklometer, Speckle-Optical Diagnostics and Laser …
5.5.1 Measurement of Amplitude and Diffuser Vibration
Frequency Using the Laser Specklometer. Comparative
Analysis of the Results of Laser Anemometry
and Speckle-Optical Diagnostics of Vibrational Activity
of Technical Products
The study of the developed device was conducted using a certified vibrator for estimation of certainty of determination of amplitude–frequency characteristics of a
vibrating surface by means of informative parameters of intensity fluctuation spectrum of the scattered radiation, which are registered and calculated with a laser
specklometer.
The calibration of the specklometer was conducted through comparison of its
results while measuring the amplitude of harmonic vibration of diffusing surface with
the results of the model sensor in the form of a certified laser Doppler vibrometer. The
electrodynamic vibrator RTF 11076 was used for the creation of harmonic vibration
with a vibration exciter covered with a coating providing diffuse reflection of the
laser radiation. The vibrometer was certified for the absence of transverse vibration
components.
The experimental scheme of measurement of the amplitude and the frequency
of the transverse component of diffuser harmonic vibration is shown in Fig. 5.17.
The operating principle of the laser Doppler vibrometer is based on isolation of the
Doppler shift of frequency of the laser radiation scattered by the vibrating object and
on measuring the number of vibration periods.
Isolation of shift of frequency was conducted with a double-beam interferometer
made according to a modified scheme of the Michelson interferometer.
The radiation scattered by object 5 was spatially superposed on the photoreceivers 7 and 8 with reference radiation reflected by the triple prisms 3. Detection
of the Doppler signal was conducted with a balanced detector, which consists of the
photoreceivers 7 and 8 and the differential amplifier 9 that gave the possibility to
increase the signal/noise ratio at the expense of lowering the noise level due to the
laser power fluctuations.
Alteration of vibroshift amplitude, which is determined with the method of
interference fringes counting during vibration period according to the formula
A =
1
8
λ
N
n
,
where λ is the wavelength of the laser radiation and N/n is the ratio of N periods of
the Doppler signal to a certain number of vibration periods n.
This ratio was determined in the following way. The Doppler signal came from
the output of the differential amplifier 9 to count the pulse former 10 build according
to the Schmitt flip-flop circuit. The count pulses were fed from the outlet of the
former 10 to one of the outlets of the frequency meter 13, which operates in the
measurement mode of the ratio of two frequencies. Signal came from the generator
5 Laser Specklometer, Speckle-Optical Diagnostics and Laser …
5.5.1 Measurement of Amplitude and Diffuser Vibration
Frequency Using the Laser Specklometer. Comparative
Analysis of the Results of Laser Anemometry
and Speckle-Optical Diagnostics of Vibrational Activity
of Technical Products
The study of the developed device was conducted using a certified vibrator for estimation of certainty of determination of amplitude–frequency characteristics of a
vibrating surface by means of informative parameters of intensity fluctuation spectrum of the scattered radiation, which are registered and calculated with a laser
specklometer.
The calibration of the specklometer was conducted through comparison of its
results while measuring the amplitude of harmonic vibration of diffusing surface with
the results of the model sensor in the form of a certified laser Doppler vibrometer. The
electrodynamic vibrator RTF 11076 was used for the creation of harmonic vibration
with a vibration exciter covered with a coating providing diffuse reflection of the
laser radiation. The vibrometer was certified for the absence of transverse vibration
components.
The experimental scheme of measurement of the amplitude and the frequency
of the transverse component of diffuser harmonic vibration is shown in Fig. 5.17.
The operating principle of the laser Doppler vibrometer is based on isolation of the
Doppler shift of frequency of the laser radiation scattered by the vibrating object and
on measuring the number of vibration periods.
Isolation of shift of frequency was conducted with a double-beam interferometer
made according to a modified scheme of the Michelson interferometer.
The radiation scattered by object 5 was spatially superposed on the photoreceivers 7 and 8 with reference radiation reflected by the triple prisms 3. Detection
of the Doppler signal was conducted with a balanced detector, which consists of the
photoreceivers 7 and 8 and the differential amplifier 9 that gave the possibility to
increase the signal/noise ratio at the expense of lowering the noise level due to the
laser power fluctuations.
Alteration of vibroshift amplitude, which is determined with the method of
interference fringes counting during vibration period according to the formula
A =
1
8
λ
N
n
,
where λ is the wavelength of the laser radiation and N/n is the ratio of N periods of
the Doppler signal to a certain number of vibration periods n.
This ratio was determined in the following way. The Doppler signal came from
the output of the differential amplifier 9 to count the pulse former 10 build according
to the Schmitt flip-flop circuit. The count pulses were fed from the outlet of the
former 10 to one of the outlets of the frequency meter 13, which operates in the
measurement mode of the ratio of two frequencies. Signal came from the generator