GB/T 11807-1989 Characteristics, design and operating procedures of acoustic monitoring systems for detecting loose parts
Some standard content:
UDC 621.039-79
National Standard of the People's Republic of China
GB 11807—89
Acoustic monitoring systems for loose parts detection--Characteristics, designand operational procedures
Published on November 21, 1989
Implemented on July 1, 1990
Published by the State Administration of Technical Supervision
Easy to process with Xiaoniu DaoKe—URL to PDF
National Standard of the People's Republic of China
Acoustic monitoring systems for loose parts detection-Characteristics, design and operational proceduresGB 11807-89
This standard adopts IEC45A (C: O) 114 "Characteristics, design and operating procedures of acoustic monitoring systems for detecting loose parts" (1988 edition) by reference.
1 Subject matter and scope of application
This standard specifies the characteristics, design requirements and operating procedures of acoustic monitoring systems. This standard applies to acoustic monitoring systems for light water reactors. The acoustic monitoring system is used to monitor the sound that is transmitted through the reactor structure and can be detected outside the reactor coolant cladding. Its purpose is to detect abnormal events, especially metal-to-metal impact events caused by loose parts, and if possible, to determine the location of these events. The monitored sound is limited to the audible frequency range of 30Hz to 20kHz. This standard is based on the assumption that piezoelectric accelerometers are used to detect structural sound, but it does not exclude the use of other alternative sensitive elements.
2 Terms
The following are the definitions of the terms used in this standard. 2.1 Monitoring areas monitoringareas
refer to areas within the reactor coolant pressure boundary where parts may become loose or where there is a high probability of loose parts being retained. 2.2 Loose parts looseparts
Loose parts include detached parts, loose parts and foreign objects. 2.2.1 Detached parts
refer to parts that have lost connection with parts in the reactor coolant and can be carried by the coolant. 2.2.2 Loose parts 1oosenedparts
Parts that have become loose but are still connected to the parts on which they were originally fixed. 2.3 Structural sound structure-hornsound refers to sound propagated in solids. In this standard, structural sound mainly refers to sound with a frequency of 30Hz to 20kHz. 2.4 Structural sound sensors structure-hornsound sensors are transducers that convert mechanical signals into electrical signals. They receive sound on the outer surface of the reactor coolant pressure boundary, which is detected by displacement, velocity or acceleration. Note: In the following text, structure-borne acoustic sensors are referred to as acoustic sensors. 2.5 Background noise background noise refers to the noise generated during the operation of the reactor. This noise will also exist when there are no loose parts. Background noise includes stationary background noise and single acoustic events related to operation.
2.5.1 Stationary background noise stationary background noise stationary background noise consists of random parts (such as coolant flow noise) and deterministic parts (such as noise dependent on water pump speed). 2.5.2 Single acoustic events singles sound event approved by the State Administration of Technical Supervision on November 21, 1989 and implemented on July 1, 1990
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single acoustic event is the structural sound caused by a single event (such as the impact of loose parts, the drive of control rods, the sudden reduction of stress, etc.), which is superimposed on the stationary background noise. 2.6 Burst
A burst is a signal component generated by an acoustic sensor that reflects an acoustic event and is superimposed on a constant background noise (see Figures 1 and 2).
2.7 Burst interval distribution of frequency refers to the frequency distribution of the time intervals between adjacent observed bursts. 2.8 Burst amplitude distribution of frequency refers to the frequency distribution of the maximum amplitude of the observed bursts. 2.9 Delay delay refers to the time difference between the bursts generated by a single acoustic event in different structural acoustic sensors. 2.10 System sensitivity systems c sensitivity The minimum energy of an acoustic event that can be distinguished by the system from the background noise. 2.11 Passband
This standard specifies the lower bound j and upper bound f of any passband, both of which are frequencies at 3 dB. 3 Loose Parts Monitoring Technology
As long as the detached or loose parts hit the inner surface of the reactor coolant pressure boundary or its internal structure, energy will be transferred to the pressure boundary wall, resulting in a single acoustic event. The background noise is generated by the coolant flow, water pumps and components fixed inside or on the reactor coolant pressure boundary, or caused during operation (such as valve movement or control rod movement). The background noise includes constant background noise and operation-related single acoustic events.
Structure-borne sound is received by sensors installed outside the reactor coolant pressure boundary. Loose parts can be detected by monitoring the amplitude of the signal measured by the structure-borne sound sensor within a certain frequency range. Operators can listen to the noise signal regularly or at any time. In order to set the alarm level of the signal amplitude, a reference record is required. If the alarm level is exceeded, the alarm is triggered. If a triggering alarm event cannot be clearly explained, the current signal and the recorded burst wave can be compared with the reference signal and reference record.
The criterion for distinguishing between a falling part and a loose part is the time difference of the associated single acoustic events, which is determined by the different positions of the acoustic sensor. In the case of a loose part, a constant time difference is observed, while in the case of a falling part, the time difference varies. The shape of a typical signal is shown in Figures 1, 2 and 3. 0.1V
Figure 1 Signal shape of burst wave caused by control rod drive mechanism of a PWR
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Figure 2 -@
Sensor
Sensor②
Note: a-
Impact point
Sensor?
Loose parts and foreign objects) Shape of burst wave caused by sensor Distance from impact point
5×10-s
Figure 3 Example of structural acoustic signal generated by test impact on BWR pressure vessel Schematic diagram of impact at the height of the measuring surface of 0.5m
;
Signal shape of test impact burst wave shown in a. In b, each signal has the same amplification factor, and in c, the signal of the farther sensor is amplified again to enable evaluation of burst wave analysis. Figure 4 shows a typical system. In this system, the signal from the structure-borne acoustic sensor (1) is passed through a broadband preamplifier (2) to an output stage (4) for further processing. The output stage is provided for connection to external devices (see 4.3.3). After further internal signal processing, interfering signal components (such as pump noise, electrical signal pickup, etc.) are reduced by means of a bandpass filter (3) and the signal itself is amplified by an amplifier (5). Signal monitoring is achieved by an alarm level monitor (9), a logic element (10) and an internal alarm unit (11). The signal is displayed by means of an indicator (6), a multi-channel recorder or memory (7) and an audio unit (8). The signal channel can be tested or calibrated by means of a calibration unit (12). The system can also be tested by means of test shocks. The system components should be arranged in accessible places as required to the extent technically possible or feasible. 3
4 System requirements
Function test unit
Calibration unit
Signal acquisition
Detection point
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External signal processing
Signal processing
Signal display
Return to the sun
Figure 4 Schematic diagram of loose parts detection system
Set alarm circuit
Operation information
Signal monitoring||t t||1-Structural acoustic sensor; 2-Preamplifier/converter; 3-Bandpass filter; 4-Signal output separation; 5-Amplifier; 6-Indicator; 7-Recorder or memory; 8-Monitoring unit, 9-Alarm level monitor; 10-Logic element; 11-Internal alarm unit; 12-Calibration unit; 13-Functional test unit 4.1 Basic structure and design criteria
The design and installation of the system must comply with the relevant provisions of the system instrumentation and control means formulated for the specific reactor. It is recommended that the system can detect loose parts with the following parameters: mass 0.1~15kg, impacting the inner surface of the reactor coolant pressure boundary with 0.7J kinetic energy, and the impact point is less than 1m away from the sensor. The system must have the following functions (see Figure 4) to enable continuous monitoring: a. Signal acquisition;
Signal processing;
Signal display;
Signal monitoring;
Calibration.
The design of the system is influenced by factors such as sensor sensitivity, amplifier gain and the specific installation of the sensor. It is difficult to predict the installation performance of the sensor. In general, the design of the sensor and amplifier should be such that the signal should match the maximum output of the linear amplifier at the minimum gain setting when the vibration acceleration at the sensor is 309 (g is the acceleration of gravity). The installation of the sensor should not cause resonance, thereby reducing false alarms.
In the case of too high resonance amplitude, the sensitivity of the measurement circuit must be adjusted accordingly. If the resonance frequency of the installed acoustic sensor falls within the frequency range to be monitored, it is recommended to use a measurement unit designed to measure full-scale signals. The system must be designed to handle at least the frequency range of fa=1kHz to fb=20kHz. The difference between the amplitude-frequency response function of a measurement component and any other measurement component should not be greater than 1dB when the acoustic sensor is not connected. This requirement is also valid for each module of the measurement component, but does not include modules or correction elements that can be used to compensate for the acoustic sensor. The linear error of the amplitude should be less than 1dB within the frequency range used for monitoring and in the dynamic area. The deviation of the frequency response function of all measurement components should be within the 3dB frequency band. 4.2 Signal acquisition
4.2.1 Selection and installation of acoustic sensors
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Piezoelectric sensors should be preferred. It should be noted that the selected sensors can withstand the main environmental conditions around the installation point (such as simultaneous exposure to high temperature and radiation, water spray, etc.). Since the early warning and diagnostic system does not need to work under abnormal environmental conditions, no formal requirements for withstanding such abnormal environmental conditions are specified. The acoustic sensor must be installed on the outer surface of the reactor coolant pressure boundary. All installation methods (such as screw connection, magnetic connection, clamp connection, etc.) that meet the requirements of this standard and do not damage the integrity of the pressure vessel are allowed. All acoustic sensors used in the same specific system should have consistent response characteristics. The following items must be considered when selecting the installation location of the sensor: The reactor coolant cladding should be evaluated for the purpose of determining the location of the sound source; a.
b. The acoustic sensor must be located in the monitoring area (such as the lower head of the reactor pressure vessel and the water chamber at the inlet of the steam generator, etc.): c. The installation position of the acoustic sensor should have favorable conditions for the propagation of sound from the internal structure to the pressure boundary (such as the pipe seat area of the pressurized water reactor, the lifting ear of the pressure vessel head, the shroud support area of the boiling water reactor, and the steam dryer support ring area). The sensors at these locations can detect unexpected abnormal conditions. d. The acoustic sensor should be easy to replace;
The arrangement of the acoustic sensor should not affect the non-destructive inspection; e.
The dose rate at the selected location should be as low as possible. f.
For each monitoring area, the number of acoustic sensors is directly related to its function; if it is only to find out the detached or loose parts, then one sensor is enough (such as the inlet area of the steam generator). In order to distinguish whether it is a detached part or a loose part, it may be more appropriate to use two sensors. When it is necessary to locate the detached and loose parts in a large volume (such as in the reactor pressure vessel), at least three sensors must be used. In order to diagnose a single acoustic event, it may be necessary to add an acoustic sensor to the relevant equipment. The signal of this sensor is processed and sent directly to the logic element (10) (see Figure 4). The purpose is to prevent false alarms caused by normal operating vibrations (operation information channel). When installing sensors on equipment, the function and integrity of the equipment must not be affected. For the installation of acoustic sensors, the installation location must be prepared according to the nature of the connection to be used. It must be ensured that the installation location has a half surface whose size is at least equal to the installation surface of the sensor. The surface roughness must be adapted to the intended type of installation. In addition, screw connections and clamp connections must have anti-loosening devices, and magnetic connections must prevent slipping. Magnetic connection methods can only be used for temporary installations. There must also be means to clamp the sensor cable. The installation state should not be seriously affected by atmospheric thermal cycle corrosion and thermal aging. 4.2.2 Preamplifier
The signal received from the acoustic sensor should be converted in the preamplifier (or impedance converter) so that the signal is as undisturbed as possible when it is transmitted to the signal processing unit. The design of the preamplifier should take into account the prevailing environmental conditions at the installation location. The cable type, direction and length must be correctly selected to minimize electrical interference, while also taking into account the convenience of installation and maintenance. The cable must be designed according to environmental conditions. If the gain of the signal processing unit cannot be continuously adjustable, the preamplifier should be continuously adjustable so that the channels match each other. The upper cut-off frequency must be selected so that the resonant frequency of the installed sensor can pass. If the preamplifier is installed in the containment, special attention should be paid to its reliability and maintenance requirements. 4.3 Signal Processing
4.3.1 Overview
The functions of the signal processing unit are:
a. Improve the ratio of signal strength to constant background noise by means of bandpass filtering; b. Provide unfiltered or filtered signals for external processing; c. Process the signal to make it easy to display and monitor. All units must have sufficient dynamic range and frequency response corresponding to the overall requirements. If digital technology is used, the requirements for the signal processing system must also be met. These requirements can be achieved in different ways. The signal processing unit generally includes the following modules.
4.3.2 Bandpass filter
The minimum requirements that the bandpass filter should meet are: filter steepness: 24dB/oct;
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b. Linearity of the top of the filter characteristic curve: ±1dB; c. Passband and cutoff frequency: selected within the passband range determined in Article 4.1. The amplitude range that can be passed must match the amplitude range of the preamplifier. 4.3.3 Signal output
The signal output unit should provide decoupled and isolated output signals and be able to withstand the test of short circuit. The design of the signal output stage must allow the entire amplitude and frequency range of the preamplifier to pass. The signal output must be compatible with data processing equipment. 4.3.4 Display amplifier
If a display amplifier is provided, the amplification factor of the display amplifier should be variable, with at least four steps, each step of about 10dB. If the signal monitoring unit is connected in series with the amplifier, the absolute alarm level of the signal monitoring is not allowed to change with the change of the amplifier's gain. Therefore, it is recommended that the signal monitoring unit be directly connected to the bandpass filter. 4.4 Signal display
The functions of the signal display are:
a. Indicate the background noise level and the signal level used for functional testing; b.Record the signal to obtain the parameters required to interpret the event. The burst waveform of the signal is particularly important for accurately determining the difference in rising edge and lag time, as explained in Appendix A (reference); c. Enable people to make subjective evaluations with the help of hearing. In analog technology, the signal display unit should normally include the modules described below. If digital technology is used, the same requirements should be met.
4.4.1 Root mean square (RMS) monitor
A means for monitoring the RMS value of the signal can be provided. The RMS indicator is used to make an objective evaluation of the background noise and functional test signals. The unit must be designed to be able to display the RMS value of all signals (such as an RMS voltmeter with a selector switch). The RMS monitor should meet the following requirements:
Frequency range: 0.7fa~1.5fb (the determination of fa and fb is shown in Section 4.1); a.
b.Crest factor: greater than 5;
Accuracy: better than 10% of full scale
d. Integration time: 1~5s.
4.4.2 Peak monitoring
A means of monitoring the peak value of the sensor signal can be provided. In order to assess potential impacts, a peak monitor can be used. The design performance of the peak monitor should be such that it can monitor the peak value of any signal within the system passband (f. to fb). 4.4.3 Recording and storage unit
No matter what recording method is used, compatibility with digital equipment and subsequent data processing equipment must be considered. It must be possible to record the signal between f and b of any measurement component. The recording unit can be designed so that all measurement components can be recorded at the same time. Or another method can be used, that is, a part of the measurement components can be selectively recorded at the same time. If the latter method is used, it must be possible to select representative measurement components from each monitoring area to record simultaneously. When the signal exceeds the alarm level, the recording unit must be automatically started and can automatically record within the pre-set time. The frequency range recording means should be able to cover most of the passband fa to fb in 4.1. The recording device should have good time history resolution over the entire frequency range.
4.4.4 Monitoring unit
The use of hearing to distinguish the signal of the acoustic sensor is a proven method for subjective evaluation of the signal. It must be possible to connect any measuring component or any recorded signal to a loudspeaker or headphones for monitoring by hearing. The minimum requirements that the monitoring unit should meet are: a. Frequency range: fa~fb passband;
b. Volume: adjustable.
4.5 Signal monitoring
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4.5.1 Alarm level monitor
Signal monitoring is achieved by such a unit, which provides a logical output signal when the monitored signal exceeds the set alarm level.
The monitored signal is the broadband signal of the acoustic sensor after being filtered by a bandpass filter (see Figure 4). Each channel must be equipped with a specific alarm level monitor. It must be possible to change the alarm level and read the alarm position (see 5.4). In addition, the alarm level monitor must be able to distinguish short-term amplitude increases (such as those caused by electrical interference in adjacent circuits) from bursts. If the alarm level monitor has a characteristic suitable for detecting bursts in the output signal of the bandpass filter, the relationship between the parameter characterizing the characteristic and the peak RMS must be known so that the conditions described in 5.4 are met. 4.5.2 Logic element
The logic element is used to suppress false alarms caused by known acoustic sources and it must be designed so that no alarm will be caused if the signal on a channel exceeds the alarm level at the same time as a single operationally relevant acoustic event (such as control rod movement, valve operation, etc.). The logic signal output by the alarm level monitor and can pass through the logic element to stimulate the internal and external alarm unit and cause recording and storage. 4.5.3 Internal alarm unit
It must be possible to enable the logic output signal of the alarm level monitor through the logic unit to cause an individual alarm for each channel. The alarm shall continue until the alarm is acknowledged.
4.6: Calibration
4.6.1 Overview
It is not possible to calibrate the entire system because the acoustic sensor itself is not normally included in the calibration test. However, it must be possible to inject the calibration signal from the input of the preamplifier and pass it into the subsequent signal processing channel (see Figure 4). The entire system can be tested with the help of test impulses (see 6.4.4). 4.6.2 Calibration unit
The calibration unit can be a sine wave voltage generator, which the signal channel can use to calibrate at any time. The unit must meet the following requirements:
It must be possible to match the frequency of the calibration signal to the set passband of the bandpass filter; a.
b. It must be possible to adjust the amplitude of the calibration signal, and its amplitude adjustment accuracy should reach 5% within the full range; c. It must be possible to check the set value of the alarm level; d. When testing one channel, the monitoring function of the remaining channels must be maintained. 4.7 System effectiveness
The design of the system should take into account the effects of aging and irradiation. All necessary analyses and tests shall be performed to ensure performance. 5 Initial Start-up
5.1 General
The initial start-up of the loose parts monitoring system is carried out after installation is complete, in accordance with the steps described below. 5.2 Testing of the system before initial start-up of the coolant circulation pumps The function of all channels of the system must be verified. The amplification factor must be adjusted for the sensitivity of each acoustic sensor so that each channel has nominally the same sensitivity.
When the reactor coolant system is full of coolant, a mechanical pulse (test shock) is applied to the pressure boundary. This allows the propagation of sound, the suitability of the acoustic sensors and the matching of the acoustic sensors to the preamplifier to be verified. The purpose of this test shock is to prove that each channel can perform its intended function. The details of the method of generating the mechanical pulse are not important, but the energy of the pulse must be such that the peak value of the burst reaches at least 50% of the selected volume range for the acoustic sensors close to the shock location. The amplification factor selected for the first shock test should refer to the amplification factor used for monitoring during operation of similar reactors. The signals of those acoustic sensors that generate bursts during the shock test must be recorded simultaneously. GB11807-89
The following data must be documented in an appropriate form: Results of visual inspection of installation;
Results of electrical functional tests;
Setting of preamplifier;
Method of mechanical pulse generation;
Characteristics of impact;
Location of acoustic sensor;
Location of impact point;
h, acoustic signal during impact.
As the basis for subsequent functional tests during operation, further test impacts must be carried out at more points (which are accessible to personnel during reactor shutdown) (see 6.4.4). 5.3 Preliminary monitoring without alarm levels It must be ensured that the reactor coolant system is monitored for loose parts from the initial start-up of the coolant circulation pump. During the cold functional test of the power plant (pressure below 107Pa), especially during the start-up of each circulating pump, the monitoring task is carried out by the operating personnel using the monitoring unit to listen to each individual signal. The noise floor must be recorded for selected reactor operating conditions and different pressures so that it can be compared with empirical values from other reactors. These operating conditions and the recorded noise floor should be documented in an appropriate manner. 5.4 Adapting the system to the specific requirements of the reactor When the reactor operating state for which monitoring is intended is reached, the system should be put into continuous monitoring and the alarm level monitor should be set. The best signal-to-noise ratio can be obtained by using a bandpass filter to reduce the operational related noise. The amplification factor of the system and the setting of the filter depend on the installation and coupling of the sensor and the method used to detect the impulse. The gain of the amplifier should be set so that the constant background noise accounts for a share of the full amplitude of the dynamic range (such as 48dB). This share can be selected according to the following schemes a or b:
a:, based on the RMS value of the constant background noise, between 3% and 15%; b. Based on the peak value of the constant background noise, between 2% and 5%. This share ensures that the alarm level can be set within a large boundary area above the constant background noise and that there is a sufficient dynamic range to accommodate and record bursts greater than the alarm level. The alarm monitor should be able to be set individually so that the noise burst triggers the alarm. The setting method may be based on a or b as follows: a. The alarm setting value is at least 6 times the standard deviation of the constant noise floor (relative to the long-term average RMS value). b. It can be set according to a multiple of the peak value of the constant noise floor, taking into account the mathematical method of frequency sensitivity, so as to provide a peak signal alarm of at least 1C times the peak value of the constant noise floor. In order to better suppress false alarms, the setting value can be adjusted to be more sensitive or less sensitive according to the situation. For this purpose, the gain setting of the bandpass filter and the amplifier can be used. It must be possible to adjust the alarm setting value so that the test impulse triggers the alarm. If the constant noise floor changes during operation (such as power plant startup), it should be possible to change the alarm level setting value. The following data must be documented in an appropriate form: bandpass filter setting value;
alarm level monitor setting value;
constant noise floor after bandpass filter and amplifier gain setting. e.
In addition, a reference record must be made for any single audible event related to operation that has a certain characteristic and can be repeated. 6 Supervision Outline
6.1 Overview
6.1.1 Acoustic monitoring of the reactor coolant pressure boundary is ready when the following items have been carried out. a. The supervision system is able to perform its functions;
b. The alarm level has been set;
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c. The steps to be described in this chapter have been carried out. 6.1.2 Monitoring begins after initial startup (see Chapter 5). Monitoring includes continuous monitoring, intermittent functional tests and the making of reference records.
The prerequisites for starting monitoring are as follows:
a. Initial startup has been completed;
b. Reference records have been prepared, including reference records of operation-related single acoustic events, reference records of test shocks and reference records of constant background noise;
c. No unacceptable changes have occurred in system performance. 6.1.3 Automatic monitoring is implemented by means of regular acoustic monitoring of individual signals. In this way, the actual signal of the acoustic sensor or its parameters can be compared objectively or subjectively with the signal or parameters stored as a reference, so as to make an evaluation. In addition, some manual measures must be taken, some of which are generally effective, as described in 6.3, while others are only related to specific radio.
6.1.4 The procedures of the supervision program are used to ensure that a conclusion can be drawn within a reasonable period of time as to whether the alarm is caused by a loose part and the consequences of the loose part on the system. Since subjective judgment is involved, a training program should be established to train the personnel using the system.
6.2 Reference records
Reference records are necessary for evaluating the actual acoustic signals and for interpreting any changes. There are two types of reference records, namely reference records during reactor shutdown (test shock see 6.4.4) and reference records during reactor operation (operating noise). The reference record during reactor operation is the basis for interpreting the observed changes in the acoustic signal. To prepare a good reference record, the following requirements are imposed:
The RMS value of the peak value of all monitored channels must be read and recorded; a.
b. A tape record should be made for all channels, with a dynamic range of at least 50 dB and a maximum allowable amplitude error of ±5%; c. A record should be made for each case, using a dedicated system recorder. For longer reactor shutdown periods (i.e. during refueling), the reference record must be verified after the reactor is restarted. 6.3 Measurements during alarm-free operation and after an alarm The operator must listen to all monitored channels and must make signal records at the time intervals specified for the specific power plant. If it is determined that there is a significant change in the noise waveform, the subjective findings must be recorded and a signal record must be made at the same time, and this record must be evaluated relative to all channels. Finally, a decision must be made as to whether the reference record should be displayed. After an alarm, the following procedures should be carried out:
Make a record of those channels where the internal alarm unit has been triggered; a.
Confirm the alarm;
Determine whether a new alarm has been activated and where the new alarm is; d.
Make a graphic or tape record;
Observe the correct operating rules of the system and recorder; e.
Listen to the alarm channel;
Evaluate the record and make a new record for all measurement components or special measurement components. In particular, if there is a significant change in the noise waveform during listening, this item (see Appendix A) should be implemented more emphasized; h. Evaluate the record and verify the results.
Further measurement measures such as the use of frequency recorder analyzers should be determined according to the specific power plant. 6.4 Periodic testing of the system
6.4.1 Overview
Tests must be conducted regularly. There are three types of tests: a. Functional test;
b. Electrical system test;
c. Test shock.
6.4.2 Functional test
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Functional test is carried out by qualitative evaluation of each channel signal during operation. The test is carried out within the scope of the monitoring procedure described in Article 6.3. www.bzxz.net
6.4.3 Electrical system test
Independent electrical system tests should be carried out for both reactor shutdown and reactor operation. The electrical part of the system must be tested during reactor shutdown to prove that the system input level and subsequent levels still have the required function-related performance.
Tests must also be carried out regularly during reactor operation (e.g. once every three months) to check the components of the electronic measuring assemblies, for example as follows:
The setting of the alarm level monitor is checked with a special calibration unit that sends a test signal with an adjustable signal crest factora.
The gain of the signal processing unit is checked with a special calibration unit included in the system;b.
The actual value must be recorded;
d. The nominal value must be recorded for each channel according to the setting of the monitoring gain and compared with the actual value of the indicator and the storage or recording unit;
e. For each channel, the amplitude of the calibration signal must be increased step by step until the alarm level monitor is triggered. The current alarm level must be compared with the alarm level recorded at the last setting of the alarm level and with the background noise. If variable alarm levels are used, their time characteristics must be checked;f. If the difference between the nominal value and the actual value is greater than ±10%, the difference should be eliminated as immediately as possible. If the cause of the problem lies in the sensor or preamplifier, it should be replaced during the next shutdown, especially when there is only one sensor in the supervision area. The use of a spectrogram can help identify the faulty component. 6.4.4 Mechanical test shock
The mechanical test shock is used to verify that the entire system, including the acoustic sensor and the signal line to the preamplifier, has the required technical characteristics. In addition, the mechanical test shock can also provide a comparison standard for evaluating any single acoustic event occurring during operation (see Section 6.2). The test shock must be performed before the initial startup of the reactor coolant circulation pump (see 5:2) or before the reactor is restarted after refueling, and in any case at least once every three years. If a permanent device for applying shocks is provided, it should be used once every three months. It can also be used for calibration in case of alarm. The test shocks must be applied to predetermined shock points. The number of shock points must be sufficient so that each sensor can be excited by the shock from at least one shock point. The shock points and the energy of the test shocks should be selected so that the alarm level monitor of the corresponding channel can be driven. When the test shocks are applied, the acoustic signals received by each sensor must be stored synchronously. In order to facilitate repetition and comparison, it is recommended to use a device that can apply mechanical pulses with known energy. It is recommended to use an impactor with a mass of 100g and a kinetic energy of 1J. Note: If the device for applying shocks is not permanently installed, the variables that affect the shock of the device must be determined. The following data must be documented:
a. The way of generating mechanical shocks;
b. Impact characteristics (characteristics in terms of absolute energy, or characteristics of the impactor for repeatable impacts); c. Location of the impact point;
d. Recording of acoustic signals and impact characteristics during the impact (sufficient time and amplitude resolution is required to determine the waveform and lag time difference of the burst wave).
Test impact data, especially impact energy and impact point, must be saved at a later time. 10
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