RU2690510C1 - Method for monitoring reliability of readings of embedded string sensors - Google Patents

Abstract

FIELD: measurement.SUBSTANCE: invention relates to testing and calibration of measuring devices, namely embedded string sensors of monitoring systems of massive reinforced concrete structures, in particular, hydro-electric stations and nuclear power stations. Method includes periodic measurement of the logarithmic decrement of the output signal and calculation of change in the string weight. Initial value of the logarithmic attenuation decrement of the output signal is removed from an additional model string relative sensor having a resonator identical to the resonators of the controlled sensors. At that, change of string mass is determined by difference of measured values of attenuation decrement of input signal and reference sensor.EFFECT: technical result is wider field of use and high accuracy of monitoring reliability of readings of embedded string sensors.1 cl, 1 tbl

Description

Technical field

The invention relates to the field of testing and calibration of measuring devices, namely mortgage string sensors for monitoring systems for massive reinforced concrete structures, in particular hydroelectric and nuclear power plants.

The level of technology

There is a method of monitoring the accuracy of the measurement results of embedded strings of reinforcing strings of force type PSAS-TM-40 described in the method of measurement [MI 2661-2001. The method of measurement of power transducers type PSAS-TM-40. Certificate №001-103-00 on certification of MVI. SE "VNIIFTRI"].

The evaluation of the measurement error for each sensor is performed as follows:

- The reinforcing bar, in which the sensor is welded, is exposed from concrete in a 40 cm long section;

- Along the exposed bare part of the reinforcing rod on the base of 150 mm, sensors of linear strain of the type PLDS-150 are installed with the limits of permissible basic measurement error of ± 2%;

- Carry out measurement periods PLDS-150 sensor output signals and determine their calibration curves, respectively acting force in the armature F (kN) and initial linear relative deformation ε (mn ^-1);

- A disk diamond cutter with a thickness of 3.0 mm cuts the working reinforcement in the area between the anchors of the PLDS-150 sensor;

и относительную деформацию

, которые соответствуют «нулевому» усилию в арматурном стержне;- Conduct measurements of the periods of the output signals of the PLDS-150 and determine their force according to their calibration characteristics

and relative deformation

that correspond to the "zero" force in the reinforcing bar;

;- Calculate the difference:

;

- The converter is considered metrologically intact (that is, providing reliable measurement results) if the ratio is:

0.94ΔF≤S⋅⋅⋅Δε≤1.06ΔF,

where: S is the cross-sectional area of the working reinforcement (according to the certificate of reinforcement), m ²

Е - modulus of elasticity of steel of working reinforcement (according to the certificate of reinforcement),

Mpa.

The disadvantages of this method are associated with the impossibility of its use for all embedded sensors, since access to more than 90% of the sensors is impossible. It should be noted unacceptably high accuracy control accuracy, very high complexity and cost of implementation of the method.

Closest to the proposed invention is a method of monitoring the reliability of the testimony of string sensors installed in the building for its monitoring, based on the detection of changes in the mass of the string [SU1775695]. The change in mass is a consequence of the ingress of moisture into the internal cavity of the sensor due to the loss of tightness of its body. The development of the process of corrosion of the metal of the string leads to an increase in its total mass. A change in the mass of the string is a sign of a disturbance in the normal functioning of the sensor, since it leads to a change in the informative parameter of the sensor (the frequency of the string oscillations) when the input physical quantity remains constant, that is, the measurement error increases up to its values outside the allowable limits. The logarithmic damping decrement of the vibrations of a string is also functionally related to the mass of the string and its tension force.

The change in the mass of the string and the parameters of the output signal can be calculated by the formula:

where: Δƒ is the change in the value of the sensor frequency during its operation;

- начальное значение частоты датчика;

- the initial value of the sensor frequency;

Δθ - changes in the value of the logarithmic damping factor during operation of the sensor;

- начальное значение логарифмического декремента затухания;

- the initial value of the logarithmic decrement decrement;

m and Δm is the mass of the string and its change;

Periodically, during operation of the sensor, simultaneously measure the frequency and logarithmic decrement of attenuation of the output signal. The change in the mass of the string is judged by the calculated value of the sum of the relative frequency increments and the damping factor compared to their initial values.

The disadvantages of this method are related to the fact that it can be used to diagnose the state of string sensors only after the initial measurement of their frequency and logarithmic decrement. At the same time, the measurement of the damping decrement of the output signal of the string is not provided for by regulations of field observations of the state of hydraulic structures during their construction and operation. In our country for all the time about 60,000 string sensors were manufactured and installed in the CTA and nuclear power plants. About 60% of them are still working and their measurement information is used to monitor the condition of the facilities. It is quite obvious that a significant part of these sensors can produce false information. This is due to the fact that during the operation of these sensors, their strings are subject to corrosion, it is possible for the string to creep out of the supporting parts and also to have a process of degradation of the string material. All this leads to a change in the measurement error in the flesh before it goes beyond the limits of permissible values, that is, to the onset of metrological failure.

The known method involves calculating the change in the mass of the string according to the results of measurements of the sum of the relative frequency increments and the damping factor relative to their initial values, which are missing for the above reason. It should be noted that the uncertainty of the measurement time of the initial values of the frequency and damping factor of the output signal of the sensor, relative to the time it was installed in the structure, significantly reduces the accuracy of monitoring the accuracy of sensor readings.

DISCLOSURE OF INVENTION

The present invention is aimed at expanding the scope and improving the accuracy of monitoring the reliability of the readings of embedded string sensors.

To achieve this result, an exemplary string sensor of relative deformations is made. The peculiarity of the sensor is that it contains a string resonator, similar to the string resonators used in all domestic-made string sensors installed in the HPP and NPP structures. All these sensors have a unified string resonator complying with the requirements of OST 3472.965-96 “Measuring string transducers for power engineering facilities. General technical requirements.

The longitudinal mechanical stiffness of monitored string sensors and the reference sensor should be the same. To compensate for the variation in the longitudinal stiffness of various embedded sensors of the string sensors, resulting from the tolerance of the geometric dimensions of the string resonators, the exemplary sensor is equipped with an additional transducer element allowing the sensor to adjust the longitudinal mechanical rigidity of the sensor in the range of 5-10%. Thus, an exemplary string sensor allows, by adjusting the longitudinal stiffness of the resonator, to ensure that the resonator stiffness matches the resonator of any embedded string sensor, and thus the full coincidence of the calibration characteristics of the reference sensor with any mortgage.

при заданном значении Т_макс.по формуле:The proposed method is implemented as follows. Measure the value of the output informative signal from the embedded string sensor. The calibration characteristic of this sensor determines the value of the output signal T at the maximum input value. Calculate the specified string deformation

for a given value of T _max. according to the formula:

Where:

- деформация струны;

- string deformation;

ρ is the density of the string material;

- длина струны;

- string length;

E is the elastic modulus of the string material;

T _max - the maximum output value of the informative signal.

по формуле 1 и измеряют выходной сигнал - Т_д. В том случае, если значение Т_д отличается от значения Т_макс в закладном датчике, то с помощью устройства регулирования жесткости образцового датчика устанавливают значение Т_д, равное Т_макс. Таким образом обеспечивают совпадение градуировочных характеристик испытываемого закладного струнного датчика и образцового струнного датчика деформации.Then set on an exemplary strain gauge the value of the output signal is equal to the zero value of the input physical quantity of the embedded sensor - T ₀ . Deliver the calculated value to the input of the reference sensor.

according to the formula 1 and measure the output signal - T _d . In that case, if the value of T _d differs from the value of T _max in the mortgage sensor, then using the rigidity control device of the reference sensor, set the value of T _d equal to T _max . Thus, the calibration characteristics of the embedded string sensor and the exemplary string deformation sensor are matched.

The logarithmic damping decrement of string oscillations is associated with a change in its mass by the relation:

Where:

θ is the logarithmic decrement of damping of string vibrations;

F - string tension force;

m is the mass of the string;

- длина струны;

- string length;

c is the constant damping.

The logarithmic damping decrement of the reference sensor and the embedded sensor is measured. From the difference of the measured values of the logarithmic damping decrements, the change in the string mass is calculated using formula 2.

Then by the formula

Where:

T is the period of string oscillations (output informative signal);

F - string tension force;

m is the mass of the string;

- длина струны;

- string length;

calculate the change of the oscillation period of the string from the change in the mass of the string. According to the obtained result, the measurement error of the embedded string sensor is estimated.

In the proposed method, a model sensor is used to obtain the values of the logarithmic decrement of damping of string vibrations corresponding to the values of the monitored sensor at the beginning of its operation.

The main reasons for the change in the mass of the string are: its corrosion due to the loss of tightness of the sensor body; corrosion of the string from the presence of water in the air, filling the internal cavity of the sensor; string creep out of the seals during operation of the sensor. Using the reference sensor to measure the logarithmic damping factor allows you to accurately determine the time of the output of the measurement error of the monitored sensor beyond acceptable limits.

To determine the reliability of the readings of the embedded string sensor, a number of its readings are checked at different times and, by the above-mentioned actions, the change in the string mass is calculated.

Consider the change in the mass of the string from exposure to water in the air located in the internal cavity of the sensor.

The water content in air at normal pressure is 30 g per 1.0 m ³ at an air temperature of + 30 ° C. During operation of the sensors, precipitation of water on the string is possible when the air temperature passes through the dew point. The average capacity of the inner core of string sensors is 50 cm ³ , from where it is easy to calculate that there can be 0.0015 g of water inside the sensor. The mass of the string with a diameter of 0.2 mm and a length of 60 mm is 0.0148 g, that is, the amount of water is about 10% by weight of the string. Thus, even if 20% of water precipitates on the string, its mass can increase by 2%; subsequent corrosion will only increase this mass by another 30 ÷ 40%. Substituting the value of the string mass equal to 0.015, increased by 2% into formula 1, we obtain that the value of the damping decrement θ changes by 3.0%. This change can be fixed instrumentally by measuring the damping factor with an error of no more than 2%.

. Подставляя полученное значение Δm в формулу 2, получим изменение θ на 1,25%. Это значение тоже можно инструментально измерить, фиксируя значение декремента затухания у закладного и образцового датчиков.Consider the change in the mass of the string from creeping out of its entrances. Assume that the string crawled out of the fits of 30 microns, which is about 15% of the working strain of the string. In this case, the string mass m will increase by

. Substituting the obtained Δm value into formula 2, we obtain the change in θ by 1.25%. This value can also be instrumentally measured, fixing the value of the damping factor for the mortgage and reference sensors.

The implementation of the invention

Testing of the proposed method was carried out in the analysis of the database of indications of embedded string sensors installed at the Zagorskaya PSP.

The readings of the embedded string sensors measuring the tension force of the PSAS armature installed in the PSPP building were subject to analysis. These sensors were installed in 1983. PSAS-28 sensors with serial numbers 1110, 1122, 1142 were selected from the database. The above technique was applied to them. A prototype of an exemplary strain gauge and a calibration tool for it were manufactured.

Table 1 shows the values of the logarithmic damping decrements of these sensors θд measured in 2018, as well as the decrements of these sensors measured in the exemplary sensor θod. In essence, the decrements measured at the present time on an exemplary sensor are initial, corresponding to the state of the string resonators of the sensors 1110, 1122, 1142 in the year of their release (1983). From the obtained results of the measured decrements it can be seen that all of them have changed in comparison with those measured in the model sensor, but quantitatively differently.

Using the obtained changes in the damping decrement using formulas (2) and (3), we obtain the change in the output signal T.

So for sensor No. 1110, a change in T value over 35 years was obtained by 7%, with a permissible value of 2%.

The obtained measurement results of logarithmic damping decrements for embedded and exemplary sensors prove the possibility of using the proposed measurement method to control the reliability of the measurement results of string sensors.

Claims (1)

The method of monitoring the reliability of readings of embedded string sensors, including periodic measurement of the logarithmic decrement of the output signal attenuation and calculation of the change in the string mass, characterized in that the initial value of the logarithmic decrement of the output signal attenuation is removed from the additionally manufactured exemplary string sensor of relative deformations having a resonator identical to the resonators of monitored sensors , and the change in the mass of the string is judged by the difference in the measured values of the decrement attenuation of the output signal of the mortgage and model sensors.