CECS 74:95 Technical Specification for Site Micro-Vibration Measurement
Some standard content:
Technical Specification for Site Micro-Vibration Measurement
CECS74:95
Editor: Ministry of Construction Comprehensive Survey and Research Institute Approval Department: China Engineering Construction Standardization Association Approval Date: June 15, 1995
This specification is compiled by the Ministry of Construction Comprehensive Survey and Research Institute in conjunction with the China Academy of Building Research, the Institute of Engineering Mechanics of the State Seismological Bureau, and the Ministry of Metallurgical Industry Survey and Research Institute in accordance with the notification of the former Ministry of Urban and Rural Construction and Environmental Protection (88) Chengbiaozi No. 141. Site micro-vibration measurement is one of the important bases for engineering seismic evaluation, analysis and calculation of seismic sub-divisions, important buildings and precision facility sites. However, due to the lack of unified standards, the on-site measurement, data processing and instrumentation of various units are different, and the results are difficult to apply, resulting in potential losses.
Based on the above reasons, the compilation team collected data and solicited opinions. The draft for soliciting opinions was completed in March 1990, and the draft was sent to more than 60 relevant units and individuals across the country for comments. On the basis of the participants revising their respective chapters according to their opinions, the drafting group held a finalization meeting of the "Draft for Review" in Harbin in September 1991. After completing the text and clause explanations of the Draft for Review, peer experts were invited to review (by letter), and the drafting group revised it into a draft for approval based on the review opinions. The "Technical Regulations for Site Micro-Vibration Measurement" is now approved, numbered CECS74:95, and recommended to all parties concerned for use. If you have any questions or suggestions during use, please send them to the "Technical Regulations for Site Micro-Vibration Measurement" Compilation Group of the Institute of Comprehensive Surveying and Design of the Ministry of Construction, No. 177, Dongzhimen Nei Dajie, Beijing (Postal Code 100007). China Association for Engineering Construction Standardization
June 15, 1995
1 General Provisions
1.0.1 This regulation is formulated to unify the site micro-vibration testing technology in my country and provide a basis for site soil classification, earthquake damage prediction, and site selection and evaluation of building sites. 1.0.2 This code is applicable to the micro-vibration measurement of construction sites, and the micro-vibration measurement of other engineering sites can be implemented as a reference.
1.0.3 In addition to complying with the provisions of this code, the site micro-vibration measurement shall also comply with the provisions of the relevant national standards and specifications.
2 Terms and symbolsWww.bzxZ.net
2.1 Terms
2.1.1 Site micro-vibration
is a stable non-repetitive random fluctuation of the ground, which is mainly caused by factors such as artificial activities, meteorology, rivers, lakes, oceans, and underground tectonic activities. The inherent micro-vibration of a certain place on the earth's surface has an amplitude displacement of microns and an acceleration of 2.1.2 The dominant period of the site micro-vibration is the period that appears most frequently on the time history curve. 2.1.3 Sampling theorem
For a stable random signal X(t), sampling is performed at points with an interval of △T=h. The Nyquist frequency fN=h/2 determined by these points, and the sampling frequency can be fsampling ≥ 2fN. 2.2 Symbols
A—the sum vector of the three component amplitudes;
Ax—the root mean square amplitude of the east-west component; Ay—the root mean square amplitude of the north-south component; Az—the root mean square amplitude of the vertical component: T
period;
average period;
frequency;
Nyquist frequency;
irregularity index:
the number of points where the wave with a positive slope intersects the zero line; Nm—the number of maximum points (peak values) of the recorded curve. 3 Basic provisions
3.1 Characteristics of site micro-vibration
3.1.1 The physical characteristics of site micro-vibration should be characterized by amplitude and frequency. The main parameters of amplitude and frequency characteristics should be the representative value of vibration amplitude and the dominant period (or dominant frequency). 3.1.2 According to the site micro-vibration record and its periodic frequency curve, the site soil can be divided into four categories: 3.1.2.1 Hard site soil represented by bedrock or hard soil layer, the main periodic component is 0.1~0.2s; 3.1.2.2 Hard and thick site soil represented by alluvial layer, the main periodic component is 0.2~0.4s; 3.1.2.3 Soft and thick site soil represented by alluvial layer, the main periodic component is 0.4~0.6s. 3.1.2.4 Abnormally soft and thick site soil represented by artificial backfill soil and silty soil, the main periodic component is 0.6~0.8s. 3.1.3 The frequency band of site micro-vibration can be divided into a short period segment of 0.05~1.0s and a long period segment of 1.0~10.0s.
3.2 Predominant period
3.2.1 The predominant period can be obtained by one of the following two methods: 3.2.1.1 When processing in the time domain, draw a period frequency (number) curve, and the period corresponding to the peak point of the curve is the predominant period;
3.2.1.2 When processing in the frequency domain, it can be determined by the peak period of the Fourier spectrum or autopower spectrum, the peak period of the single-point response spectrum, or the peak period of the transfer function (or amplification curve) of soil layer fluctuation analysis, or by the minimum group velocity on the surface wave dispersion curve. 3.2.2 The predominant period can be determined by the following method: 3.2.2.1 When the site is a single soil layer, the periods of the three-component recording curves coincide or are close to each other, and the site has only one predominant period;
3.2.2.2 When the site is a multi-layer soil with a large layer thickness and multiple spectrum peaks, the main peak (the highest spectrum peak) can be determined as the predominant period of the site. If necessary, a site can provide two or more predominant periods for the engineering design department to select; 3.2.2.3 When the predominant periods of the three components are different, the horizontal predominant period should be the main one. If necessary, the horizontal and vertical predominant periods can be proposed separately. 3.3 Amplitude value
3.3.1 The physical quantity recorded by the site micro-vibration can be displacement, velocity or acceleration according to the dynamic characteristics of the site soil and the sensitivity of the observation instrument. For bedrock or hard soil, velocity or acceleration should be used; for soft soil, displacement or velocity should be used. It can also be selected according to the requirements of the design department. 3.3.2 When taking the amplitude value, it should be strictly controlled and the environmental conditions during the observation period should be noted. 3.3.3 The amplitude characterization value should be determined according to formula 3.3.3: The amplitude should be measured using the peak-to-peak value. When the recording length is long enough, Ax, Ay, and Az can simply use the maximum amplitude value.
4 Field measurement
4.1 Ground measurement
4.1.1 The workload of the ground micro-vibration measurement of the site should be determined according to the needs of the engineering design, the size of the construction site, and the complexity of the geological structure. There should be no less than three measuring points on a site (each measuring point is arranged in the x, y, and z directions). 4.1.2 The vibration measurement direction of the measuring point should take into account factors such as the geological structure of the site, the geomorphic unit, and the axial direction of the proposed building.
4.1.3 During field measurement, the three direction vibration pickups of each measuring point are placed perpendicular to each other on the leveled ground or the bottom of a shallow pit, and the distance between each vibration pickup shall not be greater than 10m. 4.1.4 To facilitate the close contact between the vibration pickup and the ground, the vibration pickup support plate should be tightly fitted with the ground without gaps, and then the vibration pickup should be placed on the support plate, connected to the amplifier and leveled. 4.1.5 The measuring point should be far away from the artificial vibration disturbance point, and the distance from the building should be greater than 2/3 of the building's height.
4.1.6 The measurement time should be selected when the site environment is the quietest, preferably at night. 4.1.7 Before measurement, the vibration pickup should be leveled, connected to the amplifier and recorder, and the vibration pickup, amplifier, and recorder should be zeroed respectively. According to the measured physical quantity, adjust or trigger the relevant switches to measure and record.
4.1.8 Each measurement record should comply with the following regulations: 4.1.8.1 The recording time of the light recorder should be greater than 30s. When the amplitude accuracy requirement is high, the recording time should be appropriately extended;
4.1.8.2 The recording time of the tape recorder should be greater than 5min. 4.1.9 During measurement, the vibration pickup should be kept away from the recorder to prevent the recorder, measurement personnel, etc. from affecting the vibration pickup. During measurement, it is strictly forbidden for personnel and vehicles to move around the measuring point. 4.2 In-hole measurement
4.2.1 When the proposed building is a high building or a precision instrument factory, the site should be measured for ground and in-hole micro-vibration at the same time. 4.2.2 The depth of the in-hole measuring point depends on the engineering design requirements or the complexity of the geological structure. Generally, it is advisable to measure at 2 to 3 depths. The vibration pickup orientation of the in-hole vibration pickup should be consistent with that of the ground vibration pickup for comparison.
4.2.3 In order to facilitate comparative analysis with ground micro-vibration, the horizontal distance between the ground projection of the in-hole measuring point and the ground measuring point shall not be greater than 1.0m. Before micro-vibration measurement, in-hole inclination measurement should be carried out to ensure the measuring point and measurement accuracy.
4.2.4 The depth of the test hole should be slightly greater than the depth of the deepest test point, and the hole diameter should be such that the vibration pickup in the hole can be raised and lowered smoothly, and should not be too large. 4.2.5. Before drilling, the vibration pickup and cable in the hole must be checked for sealing and for short circuit and leakage. After checking that everything is normal, lower the vibration pickup to the predetermined depth and fix it to the hole wall before measuring.
4.3 Compilation of on-site data
4.3.1 The records of on-site micro-vibration measurement should be compiled according to Table 4.3.1. 4.3.2 After the on-site records and compilation are sorted, they must be checked by the technical person in charge or the indoor calculation and processing personnel for correctness before the on-site measurement work can be completed. If the measured data is found to be suspicious, supplementary or re-measurement should be carried out according to the opinions of the technical person in charge. Site micro-vibration observation record table Table 4.3.1
Project name: Year Month Day Time
Record number
Technical person in charge: Recording calculator: Operator: 5 Data processing of measurement signals
5.1 Time domain processing of measurement signals
5.1.1 Before processing the site micro-vibration measurement signal, the zero drift and recorded waveform should be checked to deal with the waveform distortion.
5.1.2 The outstanding period of site micro-vibration can be obtained by statistically processing the site micro-vibration curve using the zero crossing method.
5.1.3 The local maximum amplitude of the site micro-vibration curve can be obtained by using the 2 times of the zero crossing interval, that is, the frequency as the horizontal coordinate, and the maximum amplitude between these two points as the vertical coordinate. 5.1.4 When using the zero-crossing method to find the dominant period and local maximum amplitude of the site micro-vibration, if the missed period occurs due to the irregular recording curve, the irregularity index ε of the curve can be calculated using formula 5.1.4:
5.2 Frequency domain processing of measurement signals
5.2.1 When performing frequency domain processing on the site micro-vibration measurement signal, a reasonable sampling frequency should be selected first according to the requirements of the sampling theorem. In actual engineering applications, the sampling frequency can be selected as 3 to 5 times the upper limit of the required frequency.
5.2.2 When processing the site micro-vibration signal in the frequency domain, 1024 sampling points are appropriate. The averaging method can be arithmetic averaging or linear averaging. If conditions permit, entropy averaging can be selected. The number of averaging times is determined according to the accuracy required by the project and the capability of the equipment. 5.2.3 In order to improve the accuracy of finding the dominant period of the site micro-vibration signal and reduce leakage, the Hanning window or Hamming window should be selected when performing spectral analysis on the site micro-vibration signal. 5.2.4 When processing the site micro-vibration signal in the frequency domain, Fourier spectrum or auto-power spectrum analysis should be performed. On the Fourier spectrum or auto-power spectrum, the frequency corresponding to the spectrum line with the largest amplitude is the dominant frequency of the measured site micro-vibration signal. The dominant period can be calculated from this.
5.2.5 While performing auto-power spectrum and Fourier spectrum analysis on the site micro-vibration signal, correlation analysis and cross-spectrum analysis can also be performed to compare and analyze the calculation results of the site micro-vibration signal of different components at the same site and the same measuring point or at different measuring points in the same direction to obtain a reliable dominant period.
5.2.6 When it is necessary to understand the relationship between the measuring points on the ground and the measuring points in the hole, transfer function or cross-power spectrum analysis can be performed.
5.2.7 When multiple peaks appear on the power spectrum or Fourier spectrum, and the amplitude of each peak is not much different, and the dominant period cannot be determined from the spectrum peak, correlation analysis and cross-spectrum analysis can be performed at the same time as the spectrum analysis to comprehensively evaluate the dominant period of the site micro-vibration signal. 6 Instruments and main equipment
6.1 Vibration pickup
6.1.1 The vibration pickup for site micro-vibration measurement should have high resolution and sensitivity and meet the following requirements:
6.1.1.1 When measuring on the ground, it is advisable to use a velocity type vibration pickup, the sensitivity should be greater than 6V·s/cm, and the self-vibration period should be greater than 1s;
6.1.1.2 Resolution
(when measuring displacement),
(when measuring acceleration);
6.1.1.3 Frequency band range: 0.5~20Hz. 6.1.2 The vibration pickup should have dustproof, moisture-proof and waterproof measures. The instrument must be locked when not in the measurement state to prevent damage.
6.1.3 When measuring in the hole, a hole pickup should be used. The hole pickup should be able to automatically level and determine the orientation.
6.2 Amplifier
6.2.1 The amplifier used for field micro-vibration measurement should have the following technical indicators: 6.2.1.1 If the output signal is a voltage, it shall not be less than 0.1V; if it is a current, it shall match the working current required by the selected vibrator; 6.2.1.2 The bandwidth should be: 0.2~100Hz; 6.2.1.3 The signal-to-noise ratio should be greater than 3.
6.2.2 The amplifier should have linear, differential and integral circuits to meet the requirements of measuring different vibration parameters.
6.2.3 The amplifier should have the properties of small size, light weight, dustproof, moisture-proof, and easy to carry. 6.2.4 The instrument should be able to work normally within the range of -10 to 40℃ to adapt to different regions and different seasons.
6.2.5 The amplifier should have multiple channels and good consistency, and can simultaneously measure micro-vibrations in different directions in the hole and on the ground. The amplifier should have a normalization network to improve the test accuracy. 6.3 Recorder
6.3.1 The field micro-vibration recording can use an optical oscilloscope or a tape recorder, which should have real-time processing functions to process the signal on site. 6.3.2 When using a tape recorder, it should be equipped with a monitoring oscilloscope to select the best record. 6.4 Instrument calibration and maintenance
6.4.1 In order to ensure the integrity and measurement accuracy of the instrument, the vibration pickup should be calibrated every six months or one year to check the changes in sensitivity and other performance. When the change exceeds 3% of the factory sensitivity, the component should be replaced and calibrated again, and the new sensitivity and other technical indicators should be used when using it.
6.4.2 When measuring at large-scale projects or particularly important engineering sites, the vibration pickup, amplifier, and recorder should be calibrated online, and the amplitude and frequency characteristic curves of each channel and each gear should be drawn. 6.4.3 When the entire set of instruments is not used for a long time, it should be powered on regularly to ensure that the components are intact. 6.4.4 When transporting the instrument, it should be placed in an instrument box with shockproof facilities, and be careful to load and handle with care. 6.5 Ancillary equipment and precautions
6.5.1 Shielded cables should be used for connecting the vibration pickup, amplifier, and recorder. 6.5.2 The cable under the hole of the vibration pickup in the hole should be waterproof and insulated, and the lifting line should have sufficient tensile strength and be soft in texture; if conditions permit, the cable can be lifted by combining the conductor and the wire rope. 6.5.3 The vibration pickup support plate used for ground observation should be a non-magnetic aluminum or copper plate with a thickness of 3 to 5 mm. Its area should be able to support the three bases of the vibration pickup. Its size should be 1 cm larger than the length and width of the vibration pickup on each side. It should not be too large or too heavy.
6.5.4 If necessary, in order to prevent sudden attacks by wind, sand, dust and rain, the vibration pickup should be covered with transparent organic glass during ground micro-vibration measurement, and the wire at the output end of the vibration pickup should be fixed to the ground with a heavy object to prevent swinging.
6.5.5 The instrument operator must be familiar with the performance and technical indicators of the instrument and must be careful when operating it.3 In order to improve the accuracy of finding the dominant period of the site micro-vibration signal and reduce leakage, the Hanning window or the Hamming window should be selected when performing spectrum analysis on the site micro-vibration signal. 5.2.4 When processing the site micro-vibration signal in the frequency domain, the Fourier spectrum or the auto-power spectrum analysis should be performed. On the Fourier spectrum or the auto-power spectrum, the frequency corresponding to the spectrum line with the largest amplitude is the dominant frequency of the measured site micro-vibration signal. The dominant period is calculated from this.
5.2.5 While performing auto-power spectrum and Fourier spectrum analysis on the site micro-vibration signal, correlation analysis and cross-spectrum analysis can also be performed to compare and analyze the calculation results of the site micro-vibration signal of different components at the same site and the same measuring point or at different measuring points in the same direction to obtain a reliable dominant period.
5.2.6 When it is necessary to understand the relationship between the measuring points on the ground and the measuring points in the hole, transfer function or cross-power spectrum analysis can be performed.
5.2.7 When multiple peaks appear on the power spectrum or Fourier spectrum, and the amplitude of each peak is not much different, and the dominant period cannot be determined from the spectrum peak, correlation analysis and cross-spectrum analysis can be performed at the same time as the spectrum analysis to comprehensively evaluate the dominant period of the site micro-vibration signal. 6 Instruments and main equipment
6.1 Vibration pickup
6.1.1 The vibration pickup for site micro-vibration measurement should have high resolution and sensitivity and meet the following requirements:
6.1.1.1 When measuring on the ground, it is advisable to use a velocity type vibration pickup, the sensitivity should be greater than 6V·s/cm, and the self-vibration period should be greater than 1s;
6.1.1.2 Resolution
(when measuring displacement),
(when measuring acceleration);
6.1.1.3 Frequency band range: 0.5~20Hz. 6.1.2 The vibration pickup should have dustproof, moisture-proof and waterproof measures. The instrument must be locked when not in the measurement state to prevent damage.
6.1.3 When measuring in the hole, a hole pickup should be used. The hole pickup should be able to automatically level and determine the orientation.
6.2 Amplifier
6.2.1 The amplifier used for field micro-vibration measurement should have the following technical indicators: 6.2.1.1 If the output signal is a voltage, it shall not be less than 0.1V; if it is a current, it shall match the working current required by the selected vibrator; 6.2.1.2 The bandwidth should be: 0.2~100Hz; 6.2.1.3 The signal-to-noise ratio should be greater than 3.
6.2.2 The amplifier should have linear, differential and integral circuits to meet the requirements of measuring different vibration parameters.
6.2.3 The amplifier should have the properties of small size, light weight, dustproof, moisture-proof, and easy to carry. 6.2.4 The instrument should be able to work normally within the range of -10 to 40℃ to adapt to different regions and different seasons.
6.2.5 The amplifier should have multiple channels and good consistency, and can simultaneously measure micro-vibrations in different directions in the hole and on the ground. The amplifier should have a normalization network to improve the test accuracy. 6.3 Recorder
6.3.1 The field micro-vibration recording can use an optical oscilloscope or a tape recorder, which should have real-time processing functions to process the signal on site. 6.3.2 When using a tape recorder, it should be equipped with a monitoring oscilloscope to select the best record. 6.4 Instrument calibration and maintenance
6.4.1 In order to ensure the integrity and measurement accuracy of the instrument, the vibration pickup should be calibrated every six months or one year to check the changes in sensitivity and other performance. When the change exceeds 3% of the factory sensitivity, the component should be replaced and calibrated again, and the new sensitivity and other technical indicators should be used when using it.
6.4.2 When measuring at large-scale projects or particularly important engineering sites, the vibration pickup, amplifier, and recorder should be calibrated online, and the amplitude and frequency characteristic curves of each channel and each gear should be drawn. 6.4.3 When the entire set of instruments is not used for a long time, it should be powered on regularly to ensure that the components are intact. 6.4.4 When transporting the instrument, it should be placed in an instrument box with shockproof facilities, and be careful to load and handle with care. 6.5 Ancillary equipment and precautions
6.5.1 Shielded cables should be used for connecting the vibration pickup, amplifier, and recorder. 6.5.2 The cable under the hole of the vibration pickup in the hole should be waterproof and insulated, and the lifting line should have sufficient tensile strength and be soft in texture; if conditions permit, the cable can be lifted by combining the conductor and the wire rope. 6.5.3 The vibration pickup support plate used for ground observation should be a non-magnetic aluminum or copper plate with a thickness of 3 to 5 mm. Its area should be able to support the three bases of the vibration pickup. Its size should be 1 cm larger than the length and width of the vibration pickup on each side. It should not be too large or too heavy.
6.5.4 If necessary, in order to prevent sudden attacks by wind, sand, dust and rain, the vibration pickup should be covered with transparent organic glass during ground micro-vibration measurement, and the wire at the output end of the vibration pickup should be fixed to the ground with a heavy object to prevent swinging.
6.5.5 The instrument operator must be familiar with the performance and technical indicators of the instrument and must be careful when operating it.3 In order to improve the accuracy of finding the dominant period of the site micro-vibration signal and reduce leakage, the Hanning window or the Hamming window should be selected when performing spectrum analysis on the site micro-vibration signal. 5.2.4 When processing the site micro-vibration signal in the frequency domain, the Fourier spectrum or the auto-power spectrum analysis should be performed. On the Fourier spectrum or the auto-power spectrum, the frequency corresponding to the spectrum line with the largest amplitude is the dominant frequency of the measured site micro-vibration signal. The dominant period is calculated from this.
5.2.5 While performing auto-power spectrum and Fourier spectrum analysis on the site micro-vibration signal, correlation analysis and cross-spectrum analysis can also be performed to compare and analyze the calculation results of the site micro-vibration signal of different components at the same site and the same measuring point or at different measuring points in the same direction to obtain a reliable dominant period.
5.2.6 When it is necessary to understand the relationship between the measuring points on the ground and the measuring points in the hole, transfer function or cross-power spectrum analysis can be performed.
5.2.7 When multiple peaks appear on the power spectrum or Fourier spectrum, and the amplitude of each peak is not much different, and the dominant period cannot be determined from the spectrum peak, correlation analysis and cross-spectrum analysis can be performed at the same time as the spectrum analysis to comprehensively evaluate the dominant period of the site micro-vibration signal. 6 Instruments and main equipment
6.1 Vibration pickup
6.1.1 The vibration pickup for site micro-vibration measurement should have high resolution and sensitivity and meet the following requirements:
6.1.1.1 When measuring on the ground, it is advisable to use a velocity type vibration pickup, the sensitivity should be greater than 6V·s/cm, and the self-vibration period should be greater than 1s;
6.1.1.2 Resolution
(when measuring displacement),
(when measuring acceleration);
6.1.1.3 Frequency band range: 0.5~20Hz. 6.1.2 The vibration pickup should have dustproof, moisture-proof and waterproof measures. The instrument must be locked when not in the measurement state to prevent damage.
6.1.3 When measuring in the hole, a hole pickup should be used. The hole pickup should be able to automatically level and determine the orientation.
6.2 Amplifier
6.2.1 The amplifier used for field micro-vibration measurement should have the following technical indicators: 6.2.1.1 If the output signal is a voltage, it shall not be less than 0.1V; if it is a current, it shall match the working current required by the selected vibrator; 6.2.1.2 The bandwidth should be: 0.2~100Hz; 6.2.1.3 The signal-to-noise ratio should be greater than 3.
6.2.2 The amplifier should have linear, differential and integral circuits to meet the requirements of measuring different vibration parameters.
6.2.3 The amplifier should have the properties of small size, light weight, dustproof, moisture-proof, and easy to carry. 6.2.4 The instrument should be able to work normally within the range of -10 to 40℃ to adapt to different regions and different seasons.
6.2.5 The amplifier should have multiple channels and good consistency, and can simultaneously measure micro-vibrations in different directions in the hole and on the ground. The amplifier should have a normalization network to improve the test accuracy. 6.3 Recorder
6.3.1 The field micro-vibration recording can use an optical oscilloscope or a tape recorder, which should have real-time processing functions to process the signal on site. 6.3.2 When using a tape recorder, it should be equipped with a monitoring oscilloscope to select the best record. 6.4 Instrument calibration and maintenance
6.4.1 In order to ensure the integrity and measurement accuracy of the instrument, the vibration pickup should be calibrated every six months or one year to check the changes in sensitivity and other performance. When the change exceeds 3% of the factory sensitivity, the component should be replaced and calibrated again, and the new sensitivity and other technical indicators should be used when using it.
6.4.2 When measuring at large-scale projects or particularly important engineering sites, the vibration pickup, amplifier, and recorder should be calibrated online, and the amplitude and frequency characteristic curves of each channel and each gear should be drawn. 6.4.3 When the entire set of instruments is not used for a long time, it should be powered on regularly to ensure that the components are intact. 6.4.4 When transporting the instrument, it should be placed in an instrument box with shockproof facilities, and be careful to load and handle with care. 6.5 Ancillary equipment and precautions
6.5.1 Shielded cables should be used for connecting the vibration pickup, amplifier, and recorder. 6.5.2 The cable under the hole of the vibration pickup in the hole should be waterproof and insulated, and the lifting line should have sufficient tensile strength and be soft in texture; if conditions permit, the cable can be lifted by combining the conductor and the wire rope. 6.5.3 The vibration pickup support plate used for ground observation should be a non-magnetic aluminum or copper plate with a thickness of 3 to 5 mm. Its area should be able to support the three bases of the vibration pickup. Its size should be 1 cm larger than the length and width of the vibration pickup on each side. It should not be too large or too heavy.
6.5.4 If necessary, in order to prevent sudden attacks by wind, sand, dust and rain, the vibration pickup should be covered with transparent organic glass during ground micro-vibration measurement, and the wire at the output end of the vibration pickup should be fixed to the ground with a heavy object to prevent swinging.
6.5.5 The instrument operator must be familiar with the performance and technical indicators of the instrument and must be careful when operating it.3 The vibration pickup support plate used for ground observation should be a non-magnetic aluminum or copper plate with a thickness of 3 to 5 mm. Its area should be able to support the three bases of the vibration pickup. Its size should be 1 cm larger than the length and width of the vibration pickup on each side. It should not be too large or too heavy.
6.5.4 When necessary, in order to prevent sudden attacks by wind, sand, dust, and rain, the vibration pickup should be covered with transparent organic glass during ground micro-vibration measurement, and the wire at the output end of the vibration pickup should be fixed to the ground with a heavy object to prevent swinging.
6.5.5 The instrument operator must be familiar with the performance and technical indicators of the instrument and must be careful when operating it.3 The vibration pickup support plate used for ground observation should be a non-magnetic aluminum or copper plate with a thickness of 3 to 5 mm. Its area should be able to support the three bases of the vibration pickup. Its size should be 1 cm larger than the length and width of the vibration pickup on each side. It should not be too large or too heavy.
6.5.4 When necessary, in order to prevent sudden attacks by wind, sand, dust, and rain, the vibration pickup should be covered with transparent organic glass during ground micro-vibration measurement, and the wire at the output end of the vibration pickup should be fixed to the ground with a heavy object to prevent swinging.
6.5.5 The instrument operator must be familiar with the performance and technical indicators of the instrument and must be careful when operating it.
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.