JPH07151735A - Cavitation detector of fluid machine - Google Patents

Abstract

PURPOSE:To provide a cavitation detector of a fluid machine wherein cavitation can be detected by separating a signal caused by the cavitation from impact noise detected with an acoustic sensor. CONSTITUTION:An acoustic sensor 2, a wave height level detector 4 for comparing its acoustic signal with a wave height threshold value, an excess time comparator 5 for outputting a cavitation state signal when a time which exceeds the wave height threshold value exceeds a set excess time after the signal compares the time which exceeds the wave height threshold value with the set excess time, a minimum excess time producer 6 for outputting a preset excess time signal and a cavitation state output device 7 for performing measurement display and preservation from the cavitation state signal are included.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cavitation detecting device for a fluid machine for detecting cavitation generated in a fluid machine such as a pump.

[0002]

2. Description of the Related Art Pumps installed in various plants,
In a fluid machine such as a valve, an orifice, or a water turbine, there is a phenomenon that performance deteriorates due to erosion due to cavitation on an inner surface of a flow path where a fluid flows at high speed during long-term operation. This phenomenon is caused by the generation of bubbles due to cavitation, and immediately after this, the bubbles collapse instantaneously to generate impact noise in the ultrasonic band of several tens to several hundreds of kHz, and the impact causes the inner surface of the flow path, etc. It is believed that erosion will occur.

However, conventionally, the sound generated by cavitation cannot be separated from the sound in the ultrasonic band generated by other causes and transmitted through the fluid, piping, etc. The occurrence of cavitation was detected empirically.

[0004]

In order to prevent erosion from occurring on the inner surface of the flow path of a fluid machine, first, the occurrence of cavitation, which is the cause of erosion, is detected and the phenomenon is eliminated. Is essential.

However, with regard to the detection of cavitation, the conventional acoustic sensor detection methods are as follows:
It is difficult to easily detect the occurrence of cavitation because the sound caused by cavitation is transmitted through the fluid and the like together with the sound in the ultrasonic band generated by other causes.

It is an object of the present invention to provide a cavitation detecting device for a fluid machine which separates a signal due to cavitation from an impact sound detected by an acoustic sensor to detect the occurrence of cavitation.

[0007]

To achieve the above object, a cavitation detecting device for a fluid machine according to the present invention comprises:
An acoustic sensor attached to a fluid machine, an electroacoustic signal amplifying means from this acoustic sensor, and the output of this amplifying means are compared with a preset crest threshold to detect the time when the crest threshold is exceeded. Excess detection means is provided.

Further, the excess time signal of this output is compared with a preset excess time signal, and when the excess time exceeds the preset excess time, it is determined that cavitation has occurred and a cavitation state signal is output, and excess time comparison is performed. Means are provided.

Further, an excess time generation means for outputting a predetermined set excess time signal at the first timing when the peak value threshold detected by the excess time detection means is exceeded, and a cavitation state signal output from the excess time comparison means. It is characterized by comprising a cavitation state output means for inputting and displaying and storing.

[0010]

[Operation] The impact sound due to the collapse of the cavitation bubbles generated in the fluid machine and the impact sound in the ultrasonic band generated by other normal operation are input as electroacoustic signals from the acoustic sensor, and excess detection is performed through the amplifying means. By means, the time for which the preset crest threshold is exceeded for the signal is determined.

Next, the excess time comparing means compares the excess time output from the excess detecting means with a preset excess time set by the excess time generating means,
When the excess time is longer than the set excess time, it is determined that cavitation has occurred, a cavitation state signal is output to the cavitation state output means, and measurement display and storage are performed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. As shown in the block diagram of FIG. 1, an acoustic sensor 2 mounted on the outer wall of the fluid machine 1 and an amplifier which is an amplification means for amplifying an electric acoustic output signal S ₁ from the acoustic sensor 2 to an appropriate size. 3 and a crest level detector 4 which is an excess detection means for outputting the excess time signal S ₃ only while the crest threshold value set in advance for the envelope signal S ₂ of the output is exceeded.

Further, the excess time comparator 5 which is an excess time comparing means for comparing the excess time signal S ₃ with a preset set excess time signal S _4, and there is no cavitation in advance at the first timing of the excess detection. In this case, the minimum excess time generator 6 which is the excess time generation means for generating the set excess time signal S ₄ set based on the attenuation characteristic of the envelope signal S _{2 in} the above case is provided.

Furthermore, configured to provide a cavitation state output unit 7 is a cavitation state output means for measuring display by entering the cavitation detection signal S ₅ from the comparator 5 the excess time, each of the units is generally a computer Has been converted.

Next, the operation of the above configuration will be described. The characteristic curve diagram of FIG. 2 shows the state of the signal in each part of the detection device, FIG. 2 (a) shows the state without cavitation, and FIG. 2 (b) shows the state with cavitation.

First, in a state where cavitation is not generated, as shown in FIG. 2A, the acoustic sensor 2 attached to the outer wall of the fluid machine 1 detects the sound in the fluid machine 1 and outputs it as an acoustic output signal S _1. Output. The sound detected at this time is mainly generated in the fluid machine 1, and further, the sound in the related equipment and the fluid communicating with the fluid machine 1 through a pipe (not shown) is transmitted through the fluid or the pipe. To join.

The acoustic output signal S ₁ is amplified by the amplifier 3 and input to the crest level detector 4 as the envelope signal S ₂ . The peak level detector 4 outputs the excess time signal S ₃ to the excess time comparator 5 and the minimum excess time generator 6 only while the input envelope signal S ₂ exceeds the peak value threshold 8.

In the minimum excess time generator 6, when the excess time signal S ₃ is input, the set excess time signal S is immediately input.
₄ is output to the excess time comparator 5. Further, the excess time comparator 5 compares the input excess time signal S ₃ with the set excess time signal S ₄ from the minimum excess time generator 6.

However, the excess time signal S at this time is
_{Since 3} is shorter than the set excess time signal S ₄ because the sound caused by cavitation is not included, the excess time comparator 5 determines that cavitation does not occur and does not output the cavitation detection signal S _5. .

Next, in the cavitation generation state shown in FIG. 2B, the acoustic output signal S _1a detected by the acoustic sensor 2 from the outer wall of the fluid machine 1 is the acoustic output signal S ₁ in the normal state, Since an impact sound due to cavitation is added, the acoustic output signal S _{1 has a} larger amplitude and less attenuation.

The envelope signal S _2a output from the amplifier 3 is input to the crest level detector 4, and in the crest level detector 4, the excess time is exceeded only while the envelope signal S _2a exceeds the crest threshold value 8. The signal S _3a is output to the excess time comparator 5.

In the excess time comparator 5, the excess time signal S _3a is compared with the set excess time signal S ₄ input from the minimum excess time generator 6, but the excess time signal S is due to the sound caused by cavitation. _{Since 3a} becomes longer, which is longer than the setting overtime signal S ₄ , it is determined that cavitation has occurred.

As a result, the cavitation detection signal S ₅ is output from the excess time comparator 5 to the cavitation state output device 7, and the cavitation state output device 7 displays the count rate and saves the count data.

As shown in FIG. 2, when comparing the acoustic output signal S ₁ and the acoustic output signal S _1a detected by the acoustic sensor 2 or the envelope signal S ₂ and the envelope signal S _2a from the amplifier 3, respectively, the damping is obtained. The difference in characteristics is obvious.

In other words, the envelope signal S _2a having a large amplitude and a small damping oscillation with a small damping also has a long time for which the peak value 8 is exceeded, and thus the excess time signal S _3a.
Is an excess time signal S based on a preset normal time.
_{Since the} pulse is longer than _3, it can be seen that impact noise is generated due to cavitation.

FIG. 3 shows a flow chart of the cavitation detection process. In the present invention, the acoustic output signal from the acoustic sensor 2 is taken into the amplifier 3 after the start of monitoring, and after the envelope conversion, the peak level detector 4 compares it with the peak value. Here, the output of the wave height level detector 4 is turned on when the wave height is above the wave height threshold, and is turned off when the wave height is below the wave height threshold.

Further, if it is equal to or higher than the wave height threshold value, the set excess time signal from the minimum excess time generator 6 is turned on, but if it is already on, this process is bypassed. The minimum excess signal generator 6 sets a timer when it is turned on once, and automatically resets after a lapse of a certain time.

Next, the output of the crest level detector 4 is turned on,
Further, if the condition of turning off the output of the minimum excess time generator 6 is satisfied, that is, if an excess time signal having a length of a certain time or more is detected, a cavitation detection signal of a predetermined length is output using another timer circuit. To do.

At this time, even if the output condition of the cavitation detection signal is satisfied, if the cavitation detection signals are already being output, that is, if the cavitation detection signals overlap, the circuit configuration is ignored. Further, the above arithmetic processing is performed continuously and at high speed.

According to the present invention, the impulsive sound generated when the bubbles collapse due to the occurrence of cavitation is separated from the impulsive sound (electrical or mechanical noise) in the ultrasonic band generated by other causes. The occurrence of cavitation can be detected accurately.

Another embodiment is shown in the block diagram of FIG. The configuration is almost the same as that of the above-described embodiment, but a circuit for holding the maximum value S ₆ of the envelope signal S _2a (not shown) in the crest level detector 9 and the maximum value S ₆ in the cavitation state output device 10 are provided. A circuit to record ₆ is added.

According to this structure, the impact sound when the bubbles collapse due to cavitation is detected, and the frequency distribution for the acoustic signal exceeding the wave height level is calculated. From this, it is possible to obtain an accurate sound output for the impact sound when the cavitation bubbles collapse.

Further, as shown in the erosion characteristic diagram of FIG. 5, from the relationship between the cavitation erosion amount experimentally obtained in advance and the cavitation output (count number or frequency distribution) obtained in the present invention, 1
Accurate evaluation of damage and deterioration of performance can contribute to improvement of plant reliability.

[0034]

As described above, according to the present invention, it is easy to constantly monitor the occurrence of cavitation in a fluid machine with a simple detection device, and the degree of damage to the fluid machine or the degree of performance deterioration can be grasped at an early stage. Not only the reliability of the fluid machine is improved, but also the operation rate and maintainability of the plant are improved.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a cavitation detection device according to an embodiment of the present invention.

FIG. 2 is a characteristic curve diagram in each part of one embodiment according to the present invention.

FIG. 3 is a flowchart of a cavitation detection process according to an embodiment of the present invention.

FIG. 4 is a characteristic diagram showing the relationship between cavitation erosion amount and cavitation output.

FIG. 5 is a block configuration diagram of a cavitation detection device according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Fluid machinery, 2 ... Acoustic sensor, 3 ... Amplifier, 4, 9 ...
Crest level detector, 5 ... excess time comparator, 6 ... minimum excess time generator, 7, 10 ... cavitation state output device, 8
... Wave height threshold, S ₁ , S _1a ... Acoustic output signal, S ₂ , S
_2a ... envelope signal, S _3, S _3a ... overtime signal, S
₄ ... setting over time signal, S ₅ ... cavitation detection signal, S ₆ ... maximum value.

Continuation of the front page (72) Inventor Jun Hanawa 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company Toshiba Yokohama office

Claims (1)

[Claims] 1. A wave height threshold value is obtained by comparing an acoustic sensor mounted on a fluid machine, an electroacoustic signal amplifying means from the acoustic sensor, an output of the amplifying means and a preset wave height threshold value. Excess detection means for detecting excess time,
The excess time signal of this output is compared with the set excess time signal, and when the excess time exceeds the set excess time, excess time comparison means for outputting a cavitation state signal as cavitation occurrence is detected by the excess detection means. Cavitation for inputting and inputting the cavitation state signal output from the excess time comparison means for outputting a preset excess time signal at the first timing when the wave height threshold is exceeded, and for cavitation. A cavitation detection device for a fluid machine, comprising: a state output means.