JP2572249B2 - Laser doppler velocimeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial application field" The present invention irradiates a moving object with laser light, receives reflected light thereof, extracts a moving frequency component proportional to the speed of the moving object, and obtains the moving frequency. The present invention relates to a laser Doppler velocimeter for measuring the period of a component.

FIG. 6 shows a conventional laser Doppler velocimeter. The laser light from the laser light source 11 is applied to the moving object 12, and the reflected light is received by the photoelectric converter 13 and converted into an electric signal. Light incident on the moving object 12 undergoes a frequency shift proportional to the speed of the moving object 12. Only the transition frequency component 14 is extracted from the photoelectric converter 13. This transition frequency component 14
Is shaped into a square wave 16 by a waveform shaping circuit 15. The square wave 16 is supplied to a period measuring circuit 17, and the period is measured by counting reference pulses from a reference pulse generating circuit 18. The measured cycle is converted into a frequency by the reciprocal calculator 19.

According to this conventional laser Doppler velocimeter, an output is obtained for each cycle of the transition frequency component, and the output is excellent, but in the case of a fluid or the like in which the scattered light from the moving object 12 is weak,
Since each waveform is blurred by noise, errors increase.

According to the present invention, the period of the transition frequency component is measured by the period measurement counter, each wave of the transition frequency component is counted by the generation order counter, and the time lapse is measured by the clock counter. Is counted. Each time the period measurement counter measures, the measured value and the count value of the generation order counter and the clock counter are stored in the storage circuit. The storage circuit is read, and arithmetic processing is performed on reliable data by the arithmetic circuit.

When a wave having a cycle shorter than the shortest time that can be stored in the storage circuit comes due to noise or the like, the count value of the generation order counter read from the storage circuit is skipped, and data in the vicinity is unreliable. It is understood that there is.
When the count value of the clock counter is not proportional to the integrated value of the count value of the period measurement counter and becomes a large value, it can be understood that there is a non-signal section.

"Embodiment" FIG. 1 shows an embodiment of the present invention, and portions corresponding to FIG. 6 are denoted by the same reference numerals. In the present invention, the transition frequency component whose waveform has been shaped by the waveform shaping circuit 15 is supplied to the period measurement counter 21, and the period of the transition frequency component is measured by counting the reference pulse of the reference pulse generation circuit 18. Waveform shaped transition frequency component is generated order counter
It is supplied to 22 and its wave number is counted. The reference pulse of the reference pulse generation circuit 18 is counted by the clock counter 23. The pulse counted by the clock counter 23 may be obtained by dividing the reference pulse.

The count values of the period measurement counter 21, the generation order counter 22, and the clock counter 23 are stored in the storage circuit 24 at the same timing at each period of the transition frequency component. The storage circuit 24 is read, and the reliable data (the count value of the period measurement counter 21) is supplied to the arithmetic circuit 25, where the data is subjected to arithmetic processing.

For example, when a waveform-shaped transition frequency component as shown in FIG. 2 is input, measurement is performed by the period measurement counter 21 for each period, and the generation order counter 22 counts at the rise of each waveform. When noise is input as shown in the sections A and B, the count value cannot be stored in the storage circuit 24 because the cycle is short. However, since the generation order counter 22 also counts the short noise, the storage state of the storage circuit 24 is as shown in FIG. Looking at the stored state, the count value of the occurrence order counter 22 jumps from 5 to 9, 10 to 13, and it is understood that there is a narrow noise at this position. The count value of the period measurement counter 21 is not reliable, and therefore the data is not used for the arithmetic processing.

If the waveform-shaped transition frequency component is as shown in FIG. 4, the period measurement counter 21, the generation order counter 22,
Each count value of the clock counter 23 is as shown in the figure,
The storage of these data in the storage circuit 24 is as shown in FIG. In this example, the clock counter 23 counts a clock having a cycle twice as long as the clock counted by the cycle measurement counter 21. Therefore, the clock counter 23
Is twice the corresponding count of the period measurement counter 21, or ± 1 from the double. When the count value of the generation order counter 22 is 2, 3, the count value 27, 30 of the count value of the cycle measurement counter 21 is obtained.
And the differences (increases) 14, 15 between the count value of the clock counter 23 and the count value immediately before it are approximately proportional to each other.
That is, the count value 29 of the period measurement counter 21 and the increment 72 of the count value of the clock counter 23 are not proportional to the count value 4 of the generation order counter 22. It is no longer a relationship and has grown significantly. From this, it is understood that there is a long non-signal time in which the period measurement counter 21 has overflowed, and it is understood that the data immediately before that is unreliable. Although the concept of the processing according to the present invention has been described above, this may be actually performed by, for example, the processing procedure shown in FIG.

First, i is initialized to 1 (S ₁ ), and it is determined whether the value obtained by adding 1 to the count value Ci of the _i- th generation order counter 22 is equal to the count value C _{i + 1 of the} (i + 1) -th generation order counter 22. It examined (S _2), if they are equal, the i-th period measurement counter 21 data K _i of correct data candidates, i-th and the front and rear of the i-1 as otherwise there noise short period
Th and (i + 1) -th each data K _i, discards the _{K i-1, K i +} 1 (S 3). If it is the correct data candidates in step S _2, 2 from the count value A _{i + 1} of the i + 1 th clock counter 23 of the i-th value obtained by subtracting the count value A _i clock counter 23
The double is equal to or equal to the data K _{i of} the i-th period measurement counter 21 (in this embodiment, the pulse of the reference pulse generation circuit 18 is used by the clock counter 23 to calculate the pulse of the period measurement counter 21).
(Since counting is performed twice, an error of only one occurs.) (S ₄ ), and if this condition is satisfied,
Elected K _i as the correct data (S _5), otherwise discard the K _i (S _3). Step S ₃ or S ₅ of the completion after i is incremented by returning to the step S ₂ (S _6).

The processing performed by the arithmetic circuit 25 includes filtering processing, averaging processing, correlation processing, reciprocal operation processing, and the like.

[Effects of the Invention] As described above, according to the present invention, the state in which noise having a cycle shorter than the shortest time that can be stored in the storage circuit 24 can be known from the storage content of the storage circuit 24, The no-signal section can also be known from the storage content of the storage circuit 24,
These unreliable data can be filtered out, and thus reliable measurements can be made at high speed.

Note that it is conceivable that the output waveform of the photoelectric converter 13 is sampled and digitized, the digital waveform is stored, and then an operation such as Fourier transform is performed to perform frequency analysis.In this case, a large-capacity memory is required. Required, and the load on the arithmetic circuit is large. However, this invention reduces both,
Moreover, high-speed frequency analysis is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a laser Doppler velocimeter according to the present invention, FIG. 2 is a diagram showing the relationship between a transition frequency component and each count value of a period measurement counter and a generation order counter, and FIG. FIG. 4 is a diagram showing a storage example of the storage circuit 24 with respect to the example of FIG. 2, FIG. 4 is a diagram showing a relationship between a modulation frequency component and each count value of a period measurement counter, a generation order counter and a clock counter, and FIG. FIG. 6 is a diagram showing an example of storage in a storage circuit for the example shown in FIG. 6, FIG. 6 is a block diagram showing an example of a conventional laser Doppler velocimeter, and FIG.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-90772 (JP, A) JP-A-52-151073 (JP, A) JP-A-50-31868 (JP, A)

Claims (1)

(57) [Claims] A laser Doppler for irradiating a moving object with laser light from a laser light source, receiving reflected light thereof, extracting a transition frequency component proportional to the speed of the moving object, and measuring a period of the transition frequency component. In the speedometer, a period measurement counter that measures the period of the transition frequency component, a generation order counter that counts each wave of the transition frequency component, a clock counter that counts the passage of time, A storage circuit for storing the measured values, the count values of the generation order counter and the clock counter, and reading out the storage of the storage circuit, from the normality of the change in the count value of the wave number, and corresponding to each of the measurement periods. The reliable data is selected from the comparison with the increase value of the count value of the adjacent clock counter, and the arithmetic processing is performed on the selected data. Laser Doppler velocimeter, characterized by comprising a Cormorant arithmetic circuit.