CN114526810A - Frequency measurement method of vibrating wire type sensor - Google Patents

Abstract

The invention discloses a frequency measuring method of a vibrating wire type sensor, and belongs to the technical field of health monitoring. The method comprises the steps of firstly carrying out full-frequency scanning to obtain the response frequency of a sensor, carrying out frequency scanning in a second scanning process by taking the response frequency obtained in the first scanning process as a median value and reducing a frequency scanning range, wherein the obtained frequency is compared with the response frequency obtained in the first scanning process; if the difference value of the two acquired frequencies meets the requirement, determining the initial frequency of the sensor to be the average value of the sum of the first response frequency and the second response frequency; the method has the advantages of short measurement period and high precision, greatly reduces the labor input and labor intensity, improves the measurement efficiency and reduces the application difficulty of the vibrating wire sensor.

Description

A frequency measurement method of a vibrating wire sensor

technical field

The invention relates to a frequency measurement method of a vibrating wire sensor, belonging to the technical field of health monitoring.

Background technique

With the rapid development of economy and science and technology, more and more large-scale complex engineering structures have been built, such as long-span bridges, gymnasiums, high-rise buildings, water conservancy facilities, etc. These engineering structures are very important to protect people's lives and property safety. . Vibrating wire sensors are usually used to monitor the pressure, displacement, temperature, deformation, leakage and other physical quantities of the project, so as to determine the operation status of the project and predict some geological disasters or project loopholes. In order to ensure the safe use of large structures, it is necessary to establish a reliable structural health monitoring system.

The vibrating wire sensor mainly has two structures: single coil and double coil. Among them, the single coil refers to the structure in which the excitation coil and the pickup coil are the same coil. One end of the vibrating wire is fixed, and the other end is connected to the elastic pressure-sensitive membrane. a. The middle of the string is equipped with a piece of soft iron, which is placed in the magnetic field of the exciter formed by the magnet and the coil. The exciter doubles as a vibration pickup when the excitation is stopped. During operation, the vibrating wire vibrates under the excitation of the exciter, and its vibration frequency is related to the magnitude of the pressure on the diaphragm. When the excitation is stopped, the coil can also be used as a pickup coil to detect the electromotive force generated by the vibration of the vibrating wire. By measuring the frequency of the electromotive force, the frequency of the vibrating wire can be measured. The disadvantage of the single-coil structure is that it cannot be continuously measured, but the device is simple and stable. The double-coil structure means that the excitation coil and the pickup coil are separated, and the electromagnetic method is generally adopted. The electromagnetic method uses two magnets equipped with coils, which are used as the excitation coil and the pickup coil respectively. The induction signal of the pickup coil is amplified and sent to the excitation coil to supplement the vibration energy. In order to reduce the influence of the sensor nonlinearity on the measurement accuracy, it is necessary to select a moderate optimal working frequency band and set the prestress, or adopt a differential structure with a vibrating wire on each side of the pressure-sensitive membrane. The double-coil structure can be continuously measured, and the measurement accuracy is better, but the structure is more complicated and the stability is not good.

There is an approximate range for the natural frequency of vibration of a vibrating wire sensor, usually 400-4500 Hz. According to the resonance principle in physics, when the frequency of the excitation signal applied to the sensor is close to or equal to the natural frequency of the steel string of the sensor, the steel string will resonate. In the resonance state, the steel string oscillates with a larger amplitude. There are two excitation modes for vibrating wire sensors, one is high-voltage strumming excitation, and the other is low-voltage sweeping excitation.

SUMMARY OF THE INVENTION

Aiming at the shortcomings of the existing frequency measurement methods of the vibrating wire sensor, the present invention provides a frequency measurement method of the vibrating wire sensor, which greatly improves the measurement accuracy, measurement efficiency and measurement stability, and reduces the loss of the sensor.

A frequency measurement method of a vibrating wire sensor, comprising the following steps:

Step 1: During the first measurement, perform a full-band low-voltage sweep at a certain step frequency according to the frequency range distribution of the vibrating wire sensor, and perform step 2;

Step 2, determine whether there is a response frequency f ₁ , if there is, then perform step 3 after the frequency weighted calculation obtained by measurement is obtained f ₁ is stored in the memory; otherwise, the step frequency of the reduced scan returns to step 1;

Step 3, take the first frequency f ₁ as the median, reduce the frequency sweep range, reduce the step frequency to sweep the frequency, then store the measured frequency in the memory by taking the median f ₂ , and execute step 4;

Step 4, judge whether the difference between the frequency f ₁ and the frequency f ₂ meets the requirements, if so, go to step 5; otherwise, return to step 1 to execute;

Step 5, store _f3 in the memory as the initial value of the sensor frequency, and execute step 6;

Step 6, take the initial frequency _f3 as the median value, reduce the frequency sweep range, reduce the step frequency to sweep the frequency, obtain the sensor response frequency f, and perform step 7;

Step 7, determine whether the difference between the frequency f and the frequency f ₃ meets the requirements, if so, execute step 8; otherwise, return to step 1 to execute;

Step 8, output the frequency f of the sensor.

Preferably, in step 1, the frequency distribution range of the vibrating wire sensor is 400Hz-6000Hz.

Preferably, in step 1 or 3 or 6, the step frequency is Δf that is increased by each frequency sweep.

Preferably, in step 2, the weighting calculation is `x=(x ₁ f ₁ +x ₂ f ₂ +x ₃ f ₃ +...+x _k f _k )/∑ ₁ ^k f _i , where x _k is For each adjacent frequency data, _fk is the weight of each difference, and the weight decreases from 10 to 1 as the distance time increases.

Preferably, 5. The method for measuring the frequency of a vibrating wire sensor according to claim 1, wherein in steps 3 and 6, the frequency sweep range corresponds to (f ₁ ±10) Hz and (f ₃ ±10) Hz.

Preferably, in step 4 or 7, the difference between f ₁ and frequency f ₂ is required to be less than 5 Hz in absolute value, and the difference between f and frequency f ₃ is required to be less than 5 Hz in absolute value.

Preferably, in step 5, f ₃ is (f ₁ +f ₂ )/2.

In the subsequent frequency sweep measurement, the initial frequency result of each measurement is the median value, and the approximate frequency range can be quickly determined, avoiding the disadvantages of slow positioning and slow measurement speed in the traditional sweep frequency measurement. The frequency band is affected by the recent measurement results. During the actual measurement, there are more and more historical data, and the frequency sweep range is getting smaller and smaller. Under the condition of a certain number of sampling times for each frequency sweep, the accuracy of each frequency sweep is higher than the previous one. If the scanned current frequency is too different from the initial value, the initial value will be re-calibrated. It has the characteristics of high precision and high efficiency. The invention has the advantages of short measurement period and high precision, greatly reduces labor input and labor intensity, improves measurement efficiency, and reduces the application difficulty of the vibrating wire sensor.

With the measurement method of the present invention, when there is no vibration frequency that meets the requirements within the frequency sweep range, the original reset method can be adopted to re-collect the initial value, which ensures the reliability of the measurement of the method.

Description of drawings

FIG. 1 is a schematic flowchart of the frequency measurement method of the vibrating wire sensor of the present invention.

Detailed ways

Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in Figure 1, the present invention is a frequency measurement method of a vibrating wire sensor, comprising the following steps:

Step 1: During the first measurement, perform a full-band low-voltage sweep at a certain step frequency according to the frequency range distribution of the vibrating wire sensor, and perform step 2;

Step 2, determine whether there is a response frequency f ₁ , if there is, then perform step 3 after the frequency weighted calculation obtained by measurement is obtained f ₁ is stored in the memory; otherwise, the step frequency of the reduced scan returns to step 1;

Step 3, take the first frequency f ₁ as the median, reduce the frequency sweep range, reduce the step frequency to sweep the frequency, then store the measured frequency in the memory by taking the median f ₂ , and execute step 4;

Step 4, judge whether the difference between the frequency f ₁ and the frequency f ₂ meets the requirements, if so, go to step 5; otherwise, return to step 1 to execute;

Step 5, store _f3 in the memory as the initial value of the sensor frequency, and execute step 6;

Step 6, take the initial frequency _f3 as the median value, reduce the frequency sweep range, reduce the step frequency to sweep the frequency, obtain the sensor response frequency f, and perform step 7;

Step 7, determine whether the difference between the frequency f and the frequency f ₃ meets the requirements, if so, execute step 8; otherwise, return to step 1 to execute;

Step 8, output the frequency f of the sensor.

The following is an example to illustrate. In the example, a vibrating wire stress gauge produced by Changsha Jinma Measurement and Control Technology Co., Ltd. is used.

First, install the sensor in the on-site acquisition system, apply a stress of 500με to the sensor, and the theoretical frequency at this time is 1860HZ. When the acquisition system is working, the first measurement starts, and the low-voltage sweep frequency is used to excite the coil, the sweep frequency range is 400HZ-6000HZ, and the step value is 50HZ, that is, the low-voltage signal of 450, 500, 550...6000HZ and other frequencies is used to sequentially stimulate sensor coil. The excitation coil of this single-coil sensor is the pickup coil. When the frequency sweep voltage is 1855HZ measured by the pickup coil, its resonance amplitude is the largest, and its resonance electromotive force strength is greater than the minimum strength, so the first measurement frequency result is 1860HZ, f ₁ = 1850Hz.

Then, the embedded controller in the system will access the memory _of the system with the obtained f1;

When measuring the frequency for the second time, the controller reads the historical data in the memory, f ₁ =1855HZ. At this time, the sweep frequency median value of the second sweep frequency measurement is the result of the previous time, that is, the median value is equal to f ₁ , the sweep frequency range is f ₁ ±10, and the step value is 1HZ, that is, 1745, 1746, 1757… The low-voltage signal of 1965 and other frequencies excites the sensor coil in turn, and the maximum resonant frequency is 1860HZ. At the same time, it is confirmed that the resonant electromotive force intensity at this frequency is greater than the minimum intensity, so f ₂ =1860HZ, and f ₂ is stored in the memory.

Comparing the frequency difference between f ₁ and f ₂ is smaller than 5Hz, the frequency of f ₃ is (f ₁ +f ₂ )/2=1857.5HZ, which is stored in the memory as the initial frequency of the sensor.

Then, in the subsequent measurement, the controller takes the historical data in the memory, f ₃ =1857.5, at this time, the median value of the low-voltage sweep frequency is f ₃ sweep frequency result, that is, 1857.5HZ, and the sweep frequency band is f ₃ ±5, The step value is 1HZ, that is, the sensor coil is excited by low-voltage signals with frequencies of 1852, 1853, 1854, 1859...1830 in turn, and the maximum resonance frequency is 1860HZ, so f=1860HZ, and f is stored in the memory.

The above-mentioned embodiments only represent the preferred embodiments of the present invention, and the descriptions thereof are specific and detailed, but the present invention is not limited to these embodiments, and it should be pointed out that those skilled in the art are of ordinary skill in the art. Any improvements made without departing from the spirit of the present invention fall within the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (7)

1. A frequency measurement method of a vibrating wire sensor is characterized by comprising the following steps:

step 1, during first measurement, performing full-band low-voltage frequency sweeping at a certain stepping frequency according to the frequency range distribution range of the vibrating string type sensor, and executing step 2;

step 2, judging whether a response frequency f exists₁If yes, calculating the measured frequency weight to obtain f₁Step 3 is executed after the data is stored in the memory; otherwise, the step frequency of the reduced scanning returns to the step 1;

step 3, using the first frequency f₁For the median value, the sweep frequency range is narrowed, the step frequency is reduced for sweep frequency, and the measured frequency is subjected to median f₂Storing the data into a memory, and executing the step 4;

step 4, judging the frequency f₁And frequency f₂Whether the difference value meets the requirement or not, if so, executing the step 5; otherwise, returning to the step 1 for execution;

step 5, f is processed₃Storing the initial value of the sensor frequency in a memory, and executing the step 6;

step 6, using the first frequency f₃For the median value, reducing the sweep frequency range, reducing the step frequency to sweep frequency to obtain the response frequency f of the sensor, and executing the step 7;

step 7, judging whether the frequency f and the frequency f are the same₃Whether the difference value meets the requirement or not, if so, executing a step 8; otherwise, returning to the step 1 for execution;

and 8, outputting the frequency f of the sensor.

2. The method for measuring the frequency of the vibrating wire sensor according to claim 1, wherein in step 1, the frequency range of the vibrating wire sensor is distributed in a range of 400Hz to 6000 Hz.

3. The method of claim 1, wherein the step frequency is Δ f increased for each frequency sweep in step 1, 3 or 6.

4. The method as claimed in claim 1, wherein the weight calculation in step 2 is' x = (x) in the method₁f₁+x₂f₂+x₃f₃+…+x_kf_k）/∑₁ ^kf_i

Wherein x_kIs each time adjacent frequency data, f_kIs the weight of each difference, decreasing from 10 to 1 as the distance time increases.

5. The method according to claim 1, wherein the sweep frequency range in steps 3 and 6 corresponds to (f)₁10) Hz and (f)₃±10）Hz。

6. The method for measuring the frequency of a vibrating wire sensor according to claim 1, wherein in step 4 or 7, f₁And frequency f₂The difference between f and f is required to be less than 5Hz and f₃The difference between them is required to be less than 5Hz in absolute value.

7. The method of claim 1, wherein f is the step 5₃Is (f)₁+f₂）/2。

Images