Mechanical listening pole

The listening pole is a primitive listening tool that transmits the sound of water leakage to human ears through simple physical sound transmission phenomena. The early listening poles were made of solid wood or copper metal, with a resonance chamber and a vibrating diaphragm added to the top. The front end of the rod contacted exposed points of the pipeline, such as valves, fire hydrants, and exposed pipeline parts. When using, carefully identify the relevant sounds through the opening of the vibration cavity of the ear patch. Its advantages are simple sound quality, no noise, easy to distinguish, obvious changes in sound intensity, and no additional electrical noise. Its disadvantages are high labor intensity and the need for extensive detection. Experience shows that there are certain technical difficulties in ground inspection of deeply buried pipelines. As an auxiliary tool, it has a good effect especially in conjunction with drilling listening method and other positioning method verification.

Currently, Japan's Fujifilm has launched a new generation of listening rods, which have made disruptive innovations in the internal structure of the vibrating cavity.

Leak detector

Leak detector is a product commonly promoted in the leak detection industry. Regardless of domestic or foreign manufacturers, its basic principles and main structures are roughly the same. It basically consists of three main parts: probe, host computer and earphone. Not used in older models, new leak detectors have developed from the original analog signal processing to the current digital signal processing. Leak detectors that use digital signal processing technology have significantly enhanced anti-environmental interference capabilities and can achieve digital frequency analysis, Digital filtering, the latest digital dynamic noise reduction leak detector has the function of effectively shielding dynamic background noise signals and effectively extracting abnormal water leakage signals (also called minimum sound pressure values), and can compare sounds at different pickup points in real time. The pressure value helps technicians determine the real leak point.

Features of the leak meter:

l? Adjust the filter combination and set the instrument to a suitable filter range;

l? Adjust the instrument gain and volume , to make the earphones comfortable to listen to;

l? Detect along the S-shaped path directly above the pipe, paying attention to carefully distinguish abnormal water leakage noise;

l? If abnormal areas are found, multiple times should be Repeat the measurement and compare the frequency and intensity changes of the sound until the abnormal location is confirmed.

l ?Affected by environmental noise, we usually work at night.

The latest digital dynamic noise reduction leak detector signal processing technology and functions:

l? Digital filtering technology.

l? Digital noise intensity recording.

l? Comparative records of the effective values ??(or minimum sound pressure values) of multiple tests before and after.

l? Dynamic noise reduction technology

When choosing a leak detector model, you should pay attention to the following basic performances: 1. Stability and durability; 2. Sensitivity and additional noise; 3. Real sense of sound quality; 4. Frequency selection and background noise immunity; 5. Convenience of portability and operation; 6. Battery working time; 7. Applicability and economy for use in this unit.

Sensitivity and additive noise:

The sensitivity needs to be quite high but not "higher is better". This is related to the user's requirements, and generally speaking, once the pickup design of the instrument is defective, the higher the sensitivity, the greater the electronic spoiler sound that comes with the instrument. Compared with a well-designed pickup, the higher its sensitivity, the more abnormal water leakage sounds and background noise it will pick up at the same time, so this is indeed a contradiction. For example, in the northeastern and southern regions of my country, instruments with high sensitivity should be used in the northeastern region, while in the southern region, moderate sensitivity is sufficient. Sensitivity is to solve the problem of detecting and not detecting (that is, hearing and not hearing) water leakage deep underground.

When selecting a model, attention should be paid to the main scope of use of the unit, and it is not advisable to seek both sides. You should try your best to choose an instrument that has high enough sensitivity, low electronic noise inside the instrument, and can effectively shield background noise.

The key component that determines the sensitivity is the pickup. The sensitivity of the sensor is often expressed in units of V/G. The amplification of the instrument can adjust the overall sensitivity of the instrument, but at the same time the noise of the machine also changes accordingly and should be adjusted at When working with a sufficient signal-to-noise ratio, bigger is not always better, because if the amplification factor is too large, it will also amplify the impact and interference noise from the outside, causing oversaturation of the amplifier circuit, thus causing sound distortion. It should be used when using Adjust the amplification to the level where you can hear clearly through the headphones. The so-called "sufficient signal-to-noise ratio" intuitively means that there is a sufficient dynamic range signal on the display device, which can swing from zero display to maximum display.

Real sense of listening, frequency selection and anti-interference:

It is more convenient to combine these two issues. Everyone knows that sound is emitted by the vibration of objects. The vibrating object that emits sound is called a sound source. People live in the air, and the sounds that human ears are used to hearing are transmitted by the air. Sound can also be transmitted in liquids and solids. During the propagation process, the energy distribution surface also expands as the path moves away from the vibration source. At the same time, the propagation medium also absorbs, reflects, and scatters the vibration, which will further weaken the intensity of the vibration and the sound will gradually decrease.

In addition to the "sound intensity" that describes the size of sound, there is also "frequency" which refers to the number of vibrations per second. The unit is Hertz (Hz) (number of vibrations/second). The higher the vibration frequency, the "sharp" it feels to the human ear. But the highest frequency that the human ear can hear is about 16000Hz. The higher it is, the "ultrasound" is entered. The lower the vibration frequency, the "lower" the human ear feels. But the lowest frequency that the human ear can hear is about 16HZ. The lower it is, the "ultrasound" is entered. Infrasound".

The so-called "sound quality", as the name suggests, refers to the quality of the sound. It is a concept that is difficult to describe, but it can basically be said to be determined by the synthesis of vibrations at different frequencies. A single frequency sound is like a single strike of a piano. The sound of impact, and the various sound emitters in the surrounding environment, with different strengths and weaknesses, and different frequencies are superimposed to form environmental noise, which is a typical multi-frequency sound.

As for the "water leakage sound", the sound generation mechanism is different due to the vibration of the water spout, the vibration of the surrounding impacted layer, the disturbance of the water flow, the additional vibration of the pipe wall, etc., and it is complicated to the human ear. The path is different. It is transmitted to the ground and then through the sensors and amplifiers through the earphones. When it reaches the complexity of the human ear, it is also an extremely messy sound. However, no matter how messy it is, there are still quite some rules to be found. Listening at the same point has at least the following three characteristics:

1. Continuity: As long as the leakage does not stop suddenly, the sound will not be interrupted.

2. Stability: As long as the water supply process does not change suddenly, such as the water pressure rising or falling rapidly, the loudness of the sound will not change suddenly.

3.? The content is rich: it is not a single frequency sound, music sound, or white noise, but a comprehensive noise of some kind of impact, tumbling, and disturbance.

The first and second characteristics can be directly measured by instruments. The third characteristic is more complicated and cannot be fully displayed by general instruments. It often requires the help of analysis by the leak tester's listening. It is also the main aspect of leak detection technology and experience of leak detection personnel.

Drilling rod

In order to avoid damaging a large area of ??the road surface after detecting suspected water leakage, a hole drilling rod is used to drill holes in the suspected spots on the ground to check whether there is water flowing out. , or insert a mechanical listening rod to verify the situation.

Inspection of the stability and durability of the instrument should start from the following points:

(1) For a complete box of instruments, first look at the appearance. The appearance is rough and the structure is loose. , it can be seen that the manufacturer has not yet lacked scientific and serious management.

(2) Carefully observe whether the parts are made of high-quality materials. The quality of the product can only be seen from some details, such as whether the cable is highly elastic and thick, whether the earphones are Whether it is fully enclosed and soundproof, whether the headphone cable is strong enough and should not be broken, etc., these details can reflect the quality awareness of the manufacturer. The solidity of the structure and components often affects durability.

(3) According to the instructions, whether it can work normally immediately after installation, that is, what is the often said "unpacking qualification rate".

(4) Whether various plug-ins and knobs are loose, and whether the contact is reliable.