GB/T 2423.12-1997 Environmental testing for electric and electronic products Part 2: Test method Test Fda: Broadband random vibration - High reproducibility
Some standard content:
GB/T2423.12-1997
This standard is equivalent to the International Electrotechnical Commission standard IEC68-2-35 "Environmental testing Part 2: Test method Test Fda: Wideband random vibration - High reproducibility" (1st edition in 1973) and Amendment No. 1 (August 1983). This standard replaces GB2423.12-82 "Basic environmental testing procedures for electrical and electronic products Test Fda: Wideband random vibration test method High reproducibility".
Chapters 1 and 2 of this standard are different from Chapters 1 and 2 of GB2423.12-82. GB2423.12-82 rewrites Chapters 1 and 2 of IEC68-2-35. This revision also adds the content of Amendment No. 1 of the International Electrotechnical Commission to IEC68-2-35 in August 1983.
This standard was first issued in 1982, revised for the first time in September 1997, and implemented on October 1, 1998. From the date of implementation of this standard, it will replace GB2423.12-82. This standard was proposed by the Ministry of Electronics Industry of the People's Republic of China. This standard is under the overall jurisdiction of the Standardization Institute of the Ministry of Electronics Industry. This standard is under the jurisdiction of the National Technical Committee for Environmental Standardization of Electrical and Electronic Products. The drafting units of this standard are: the Standardization Institute of the Ministry of Electronics Industry, the Fifth Institute of the Ministry of Electronics Industry, and the Shanghai Electronic Instrument Standard and Measurement Testing Institute. The main drafters of this standard are: Zhou Xincai, Wang Shurong, Lu Zhaoming, Xu Liyi, Wang Zenglan, etc. 148
GB/T2423.12—1997
IEC Foreword
1. A formal resolution or agreement on a technical issue formulated by a technical committee of the International Electrotechnical Commission with the participation of all national committees that are particularly concerned with the issue, which reflects and expresses the international consensus on the issue as much as possible. 2. These resolutions or agreements are accepted by the National Committees in the form of recommended standards for international use. 3. In order to promote international unification, the International Electrotechnical Commission hopes that all member countries will adopt the contents of the International Electrotechnical Commission recommended standards as their national standards when formulating national standards, as long as the specific national conditions permit. Any differences between the International Electrotechnical Commission recommended standards and national standards should be clearly indicated in the national standards as far as possible. This standard was prepared by the 50A Subcommittee (Shock, Vibration and Other Dynamic Tests) of the 50th Technical Committee (Environmental Testing) of the International Electrotechnical Commission.
The first draft was discussed at the Stockholm Conference in 1968, and the new draft was discussed at the Tehran Conference in 1969. As a result of this conference, the final draft 50A (Central Office) No. 133 was submitted to the National Committees for voting according to the "six-month method" in February 1971.
The following countries voted explicitly in favor of this standard: Australia
Austria
Belgium
Czechoslovakia
Hungary
Israel
Portugal
Turkey
National Standard of the People's Republic of China
Environmental testing for electric and electronic products
Part 2: Test methods
Test Fda : Random vibration wide band-Reproducibility high
GB/T 2423.12--1997
idt IEC68-2-35:1973
Replaces GB2423.12-82
The basic requirements for broadband random vibration testing are given in GB/T2423.11--1997 (IEC68-2-34) Test Fd: General requirements for broadband random vibration. In addition, three possible levels of reproducibility are specified, called high, medium and low reproducibility, and are represented by tests Fda, Fdb, and Fdc respectively. Each of these test methods, together with its recommended verification method, constitutes a separate complete standard. Therefore, all the information required by the specification writer is included in test Fd. The information required by the test engineer is included in test Fda, Fdb or Fdc respectively.
It is strongly recommended that users of this standard read this standard in conjunction with GB/T2423.11--1997 (IEC68-2-34). It must be noted that two particularly important terms in the field of random vibration testing are frequently mentioned throughout the text of the standard. In order to make the readers better understand the content of this standard, the following definitions are given: Acceleration spectral density acceleration spectral density (ASD) is the spectral density of the acceleration variation, expressed as the square of the acceleration unit per unit frequency. The frequency spectrum of the acceleration spectral density ASDspectrum is the way the acceleration spectral density changes within the frequency range. 2 Purpose
To determine the ability of components and equipment to withstand random vibrations of specified severity levels. This random vibration test is applicable to components and equipment that may be affected by random vibration conditions during use. The purpose of the test is to determine whether mechanical weaknesses and/or specified performance have been degraded, and to use this information in conjunction with relevant specifications to determine whether the test sample is acceptable. When applying the environmental stress (conditional test) specified in this test, the test sample shall be subjected to a random vibration test of a given level within a wide frequency band. Because the test sample and its fixture will produce complex responses, this test requires special attention to the preparation, conduct and verification of the specified requirements of the test.
3 Installation and Control
3.1 Installation
The test sample shall be installed on the test equipment in accordance with the requirements of GB/T2423.43-1995 (IEC68-2-47) "Installation requirements and guidelines for components, equipment and other products in dynamic tests such as impact (Ea), collision (Eb), vibration (Fc and Fd) and steady-state acceleration (Ga). 3.2 Reference points and control points
Approved by the State Administration of Technical Supervision on September 1, 1997 150
Implementation on October 1, 1998
GB/T2423.12-1997
The test requirements are verified by measurements made at the reference points and control points related to the test sample fixing points. If many small test samples are installed on a fixture, when the lowest resonant frequency of the load fixture exceeds the test upper limit frequency. When the reference point and/or control point are related to the fixture, it can be considered that the reference point and/or control point are related to the fixture, but not to the fixed point of the test sample (that is, the fixed points of the fixture and the vibration table are selected as the reference point and/or control point, rather than the fixed points of the test sample and the fixture). 3.2.1 Fixed point
The fixed point is defined as the part of the test sample that contacts the fixture or the vibration table. It is usually the point where the test sample is normally tightened during use. If a part of the actual mounting structure is used as a fixture, the fixed points of these mounting structures should be used as fixed points, rather than the fixed points of the test sample.
3.2.2 Control point
The control point is usually the fixed point. The control point should be as close to the fixed point as possible. In any case, its connection with the fixed point should be rigid.
If the test sample has four or fewer fixed points, then each fixed point is used as a control point. If there are more than four fixed points, the relevant specifications should specify four representative fixed points as control points. Note
1 For large and (or) complex test samples, it is an important issue to specify control points in the relevant specifications. 2 Control points refer only to points that have requirements or are representative of vibration. 3.2.3 Reference point
The reference point is a single point used to obtain a reference signal to verify the test requirements and represent the movement of the test sample. It can be a control point or an assumed point established by manual or automatic processing of the control point signals. If an assumed point is used, the spectrum of the reference signal is defined as the arithmetic mean of the acceleration spectral density values of all control signals at each frequency. In this case, the total root mean square value of the reference signal is equal to the root mean square of the root mean square value of the control point signal. The relevant specifications should state the reference point used, or explain how to select the reference point. For large and (or) complex test samples, it is recommended to use an assumed reference point.
4 Frequency response measurement and resonance check
In the following sinusoidal vibration test stage, the tolerance shall comply with the provisions of GB/T2423.10--1995 (idtIEC68-2-6) Test Fc, Sinusoidal Vibration Test.
4.1 Sine amplitude
Unless otherwise specified in the specification, the sine amplitude used for frequency response measurement and resonance inspection shall be determined by Table 1 according to the acceleration spectrum density level. This amplitude shall be applied to the reference point. If the random vibration condition test uses a hypothetical point, then this sine amplitude shall be applied to the control point. Table 1
Acceleration spectrum density level
(m/s*)\/Hz
4.8~19. 2
4.2 Frequency response measurement method
(0. 05~~0.2)
Sine amplitude (peak value)
In the verification method of acceleration spectrum density, it is often required to measure the frequency characteristics of the test sample in the predetermined direction of the sample reference point.
When measuring, a sine sweep in both positive and negative directions shall be performed within the entire test frequency range (f~f2), and the sweep rate shall not exceed one octave per minute. During the sweep, the sine amplitude at the reference point shall be kept constant as specified in 4.1, and the AC input voltage of the power amplifier shall be measured.
GB/T2423.12--1997www.bzxz.net
The measured voltage is a function of frequency and is approximately inversely proportional to the frequency response. Taking into account the displacement limit of the shaker, the amplitude of the sinusoidal acceleration can be reduced at the low frequency end, but this should be taken into account when calculating the frequency response. The acceleration amplitude should be measured at all control points and the lateral measurement should be carried out as described in 5.3. When measuring the frequency response, an excitation equalizer (an instrument used to correct the general response of an unloaded shaker), a low-pass filter (greater than f, cutoff), a high-pass filter (less than f cutoff) and other broadband filters can be used. Narrow-band equalizers, such as bee-shaped filters, should not be inserted during the measurement. The peak-to-valley amplitude ratio A/A (see Figure 1) is the ratio of the maximum value to the minimum value on the frequency response curve. This measurement does not require a precision frequency meter.
Figure 1 Determination of the peak-to-valley amplitude ratio
The valley frequency ratio (Bm) (see Figures 1 and 2) is calculated according to the following equation: Bpn
Where: f-
a peak frequency;
a valley frequency.
This measurement requires only a precision frequency meter. ,-fal
In the verification method for the acceleration spectral density shown in Appendix A (Standard Appendix) and Appendix B (Standard Appendix), the most severe pair of peaks and valleys should be specified. If the valley frequency ratio is to be used, A,/A, and Bpm should be measured for several pairs of peaks and valleys (four pairs in Figure 2), and the analysis error and residual ripple of each pair should be estimated in order to find the most severe pair of peaks and valleys.
Figure 2 Determination of several pairs of peaks and valleys and frequency ratios
4.3 Method of resonance check
If the relevant specification requires a resonance check, it is sometimes possible to make an initial resonance check at the same time as the frequency response measurement. During the check, a forward and reverse sine sweep should be made over the entire frequency range. 152
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During the resonance check, the test sample should be checked to determine the frequencies of the following phenomena: a) malfunction and/or performance degradation of the test sample due to vibration; b) mechanical resonance of the test sample.
In order to study these effects more closely and find the exact frequency, the frequency sweep may be interrupted. During the initial resonance check, all frequencies and amplitudes that produce the above phenomena should be recorded in order to compare them with the frequencies and amplitudes obtained in the final resonance check. The relevant specification should specify the measures to be taken in the event of any change in the resonant frequency. During the resonance check, the test specimen shall be operated, if applicable. If the mechanical vibration characteristics of the test specimen cannot be determined because it is in operation, an additional resonance check shall be carried out with the test specimen in a non-operating state. Any arrangements made to detect internal effects of the test specimen shall not significantly change the overall dynamic characteristics of the test specimen. A recovery time shall be specified after the conditioning test to allow the test specimen to recover to the same conditions as at the beginning of the resonance check, such as temperature effects.
5 Vibration motion requirements
5.1 Basic motion
The basic motion of the fixed points of the test specimen shall be linear and its instantaneous acceleration values shall have the random nature of a normal (Gaussian) distribution. The points shall also have essentially the same motion. 5.2 Distribution
The distribution of the instantaneous acceleration values at the reference points shall normally be within the tolerance band shown in Figure 3. If assumed points are used, this distribution also applies to the control points.
Note: For most random vibration tests, this distribution falls within the tolerance band and therefore only needs to be verified in exceptional cases. However, if possible, it is recommended to measure the acceleration waveform (e.g. visually) to ensure that the peak value that appears is at least 2.5 times the RMS value of the signal. 5.3 Spectrum of the acceleration spectral density and the total RMS acceleration The relevant specifications should specify the acceleration spectral density level and frequency range. The spectrum of the acceleration spectral density should be as shown in Figure 4. With these values, the nominal value of the total RMS acceleration can be determined at the same time, which can also be obtained by looking up Tables 3a and 3b. The tolerances of the acceleration spectral density and the true value of the total RMS acceleration are shown in Table 2. It can be seen from this table that the tolerance of the true value of the total RMS acceleration is much narrower than the tolerance of the true value of the acceleration spectral density. Table 2
True value of acceleration spectral density
Predetermined direction
Reference point
Each control point
Control point
True value of total RMS acceleration (~J)
Predetermined direction
Reference point
For frequencies exceeding the upper frequency limit f2~~2f2, the frequency spectrum of the acceleration spectral density shall be lower than the slope of -6dB per octave as shown in Figure 4. In addition, the RMS acceleration in the frequency band f~10f. or to 10kHz (whichever is narrower) shall not exceed 25% (-12dB) of the required total RMS acceleration within the specified frequency range. In order to verify the motion requirements, acceleration measurements shall be made in the predetermined direction of all control points and reference points. Transverse acceleration measurements shall also be made in two mutually perpendicular lateral directions of the control point farthest from the center of the mounting plane. For large structures, it is recommended to measure the lateral acceleration at more than one control point.
Verification of the acceleration spectral density tolerance can be performed by any method that meets the given tolerance. When such verification has great technical difficulties, it is recommended to select a verification method from Appendix A (Standard Appendix) to Appendix C (Standard Appendix). Guidelines to help make such a selection are given in Chapter 6 below.
GB/T 2423. 12-1997
(X+3g)
d(X-3a)
Total root mean square acceleration
Figure 3 Tolerance band of instantaneous acceleration distribution
22222222
171777777777777777777777777774E
Specified frequency range
Upper tolerance limit, high reproducibility
H2-——Lower tolerance limit, high reproducibility;
N——Nominal value of specified acceleration spectral density f2
Figure 4 Frequency spectrum and tolerance range of acceleration spectral density 3g
-6dB/act
In the special case of specifying a shaped spectrum, the verification methods shown in Appendices A to C can still be used. 1
-frequency
(logarithmic scale
2 It must be noted that, in order to verify the acceleration spectral density level, it is not permitted to use the scanning technique without correcting for error sources such as analyzer bandwidth, sampling time, etc. 154
GB/T 2423. 12—1997
automatically processing the signals from the control points to establish a hypothetical point. 5.4 Total rms acceleration values within the specified frequency range The required total rms acceleration values are given in Tables 3a and 3b. To verify these values, a low-pass filter is used. The cut-off frequency (3 dB point) of this low-pass filter should be 2. If the 3 dB bandwidth differs by more than 2 % from the equivalent noise bandwidth obtained when the filter output is used with a white noise input signal, this bandwidth should be taken into account when using the rms values calculated in the table. NOTE: To verify the total rms acceleration, It is allowed to use scanning technology to automatically process the signals from each control point to establish a hypothetical point for carrying out. 5.5 Displacement limit
All vibration tables have displacement limits. In order to limit the peak displacement, a high-pass filter must be inserted before the power amplifier. Note: If the acceleration spectrum density value must be reduced in the low-frequency region due to the limitation of the vibration table displacement limit, the reduced value must be indicated and the agreement of the supplier and the buyer must be obtained.
6 Selection of verification method
In Appendix A to Appendix C, three verification methods for acceleration spectrum density spectra are specified as recommended methods. 6.1 Selection criteria
When selecting a verification method, the following factors must be considered: a) the frequency range specified for the test;
b) the special requirements of the relevant specifications;
c) the mechanical response characteristics of the test sample;
d) the thrust of the shaker:
e) the size, stiffness and mass of the shaker motion unit; f) the stiffness and mass of the fixture,
g) the type of instrument used;
h) the characteristics of the instrument used (for example: filter bandwidth, dynamic range, frequency range, applicable scanning rate, hum and noise). 6.2 Applicability of the recommended verification method
If the basic errors included in the recommended verification method do not invalidate the test, the verification methods recommended in Annexes A to C can be used.
The verification method of the scanning filter technology shown in Annex A is more time-consuming than other methods. When the acceleration time history is recorded with a tape recorder during the conditional test and then analyzed. If the frequency range is wide and the conditional test time is short, then the spectrum of the acceleration spectral density needs to be verified.
If the filter bandwidth is very narrow and the resonance of the test sample has little effect on the system, then the verification method of the fixed filter technique shown in Appendix B can be used. This verification method is not suitable for some test samples and filter bandwidths at lower frequencies. This verification method also requires the use of a tape recorder.
The verification method of the sine sweep technique in Appendix C can only be used when the test sample is basically the same as the previous verification of this type of product on the same fixture using direct verification methods (such as the methods of Appendix A and Appendix B). If simple equipment is used, the test sample is very rigid, or the test sample has a much smaller total moving mass than the rigidity, such as small electronic components installed in a rigid box fixture, then the verification method using the sine sweep technique shown in Appendix C has its advantages. The use of narrow-band equalizers is not allowed. This method does not require complex analysis equipment when each test is performed.
6.3 Hybrid verification method
This verification method is intended to give the same reproducibility. However, in some cases, the analysis error or residual ripple (defined in Annex A and Annex B) may become too large in certain parts of the frequency range, which is not allowed. In other cases, the analysis time may be too long. These problems often force the use of different verification methods in different parts of the frequency range. It is worth noting that even if a mixed verification method is used, the conditional test should be carried out simultaneously over the entire frequency range. Even for spectra with more than one specified acceleration spectrum density level, such tests should not be separated. 155
GB/T2423.12—1997
Note: For the verification of the acceleration spectrum density spectrum, existing methods with higher accuracy can also be used. 7 Initial inspection
The test sample should be subjected to electrical and mechanical inspection in accordance with the requirements of the relevant specifications. If the relevant specifications require a resonance check before and after the conditional test, the entire test procedure including the resonance check should be completed in one axis and repeated in the other axis. The resonance check method is specified in 4.3. 8 Excitation before conditioning
When using sinusoidal vibration for frequency response measurements or resonance checks, the time should be minimized and the amplitude applied is as specified in 4.1. The entire test procedure, including the frequency response measurement, any resonance check and conditioning test, should be completed on one axis (without removing the test sample from the vibration table) and then repeated on each of the other axes in sequence. Before the formal (i.e. full-level) random vibration test, the test sample must be subjected to a lower level of random excitation for pre-adjustment (i.e. equalization and pre-analysis). The important issue is that the vibration level applied at this time should be kept to a minimum and the time should be kept to a minimum. Before the formal random vibration test, the allowable pre-adjustment excitation time (i.e., build-up time) is: a) less than 25% of the specified level, no time limit; b) between 25% and 50% of the specified level, the time should not exceed 1.5 times the specified test time; c) between 50% and 100% of the specified level, the time should not exceed 10% of the specified test time. It must be noted that these pre-adjustment excitation times mentioned above should not be deducted from the specified test time. 9 Conditioning test
Unless otherwise specified in the relevant specification, the test sample shall be vibrated in three mutually perpendicular axes in sequence. The axes shall be selected so as to expose the fault of the sample most easily. The severity level is specified in the relevant specification. Unless otherwise specified in the relevant specification, if conditions permit, the sample shall be operated during the conditioning test in order to determine the electrical function and mechanical effects.
For components, the relevant specification shall specify whether electrical checks are to be carried out during the conditioning test and at which stage of the conditioning test these checks are to be carried out. During the entire conditioning test, the total root mean square acceleration within the specified frequency range shall be measured and controlled. The applicable values are shown in Tables 3a and 3b, and the tolerances are specified in accordance with 5.3.
At the beginning and end of the conditioning test, the root mean square acceleration value greater than f shall be measured. The root mean square acceleration value within the frequency band f210f2 or to 10kHz (whichever is narrower) shall not exceed 25% (-12 dB) of the total root mean square acceleration value required within the specified frequency range. When using verification methods (such as those shown in Appendix A and Appendix B), in order to verify the spectrum of the acceleration spectral density, samples with instantaneous acceleration time history should be taken during the conditioning test. The minimum duration of each sample is twice the maximum averaging time of the analysis equipment used. For tests lasting no more than 10 minutes, one sample is sufficient. For longer durations, samples should be taken at the beginning and end of the conditioning test. If the vibration system device is changed during the endurance conditioning test, additional samples should be taken immediately after the change. For very long conditioning test durations, it is recommended to take additional samples during the conditioning test. Whether during or after the conditioning test, the acceleration spectral density should be verified according to the verification method used. 10 Final test
The test sample should be subjected to electrical and mechanical tests in accordance with the requirements of the relevant specifications. If a resonance check is required, the final resonance check shall be carried out in accordance with the method described in 4.3. 156
Specified
Acceleration
Spectral density
(m/s*)/Hz
Specified
Acceleration
Spectral density
GB/T 2423.12—1997
Table 3a Total RMS acceleration values
Total RMS acceleration for each acceleration spectral density per frequency range (rectangular spectrum, unit: m/s2) Specified frequency range (f～f2)
5~1505~20d10~15010~20020~15020~20020~50020~2 000|20~~5 00050~500,50~2 000150~5 000Total RMS acceleration
Total RMS acceleration value
Total RMS acceleration for each frequency range for each acceleration spectral density (rectangular spectrum, unit: g) Specified frequency range (～F)
5~1505~20010~15010~20020~15020~20020~50020~2 00020~5 00050~50050~2 00050~5000Total RMS acceleration
A1 Note
GB/T2423.12—1997
Appendix A
(Appendix of the standard)
Verification method using scanning filter technology In order to verify whether the requirements of the random vibration test have been met, this verification requires the use of a scanning analyzer. The accuracy of the obtained spectrum depends on the characteristics of the analyzer and the spectrum to be analyzed. The curve given represents the resulting decomposition error, hereinafter referred to as the analysis error. The calculation of the analysis error curve is based on the typical response of the test sample and the fixture to the vibration table system. For this verification method, the analysis time may be long because a large number of spectra need to be analyzed. Due to the long analysis time, verification after conditional testing is almost always necessary.
Measurement of A2 scanning analyzer characteristics
The 3dB, 12dB, 30dB and 50dB bandwidths (respectively called Bs, B12, B3 and Bso) should be measured, assuming that the shape of the filter is independent of the center frequency.
Bandwidth factor C: defined as a function of the filter shape factor B12/B: Cg = 0.1 + 2.4° B
The conditions are as follows:
B12 < 2.2 B
B3o≤ 3.8B
B5o≤6
·（A1）
If these conditions are not met, the error curve in this verification method cannot be used. In this case, the scanning analyzer is not suitable for this verification method.
The relative bandwidth B of the filter,Defined as the ratio of the 3 dB bandwidth of the analyser to the centre frequency to which it is tuned at a given moment in the analysis. Note: This measurement should only be made when necessary. A3 Estimation of analysis error
The frequency response measurement should be carried out according to 4.2.
The analysis error depends on the equivalent relative bandwidth B. B. is defined as: B. - CCBB.
=, where Bm is the frequency ratio corresponding to the amplitude ratio, see Figures A1 and A2 If it is not intended to use a very precise frequency meter to carry out the frequency response measurement to determine Bpm, then Ci = 1. After obtaining the value of A,/A., select the appropriate curve in Figures A1 and A2 and read the analysis error at the value of B. calculated above. Linear interpolation between the curves is allowed. In order to find the pair of peaks and valleys with the maximum error, several pairs of peaks and valleys must usually be studied. Note: When this test method is combined with the method shown in Appendix B, and the estimated residual ripple is lower than A,/A. obtained from the frequency response measurement, the lower value can be used as A/An for the relevant part of the frequency range in Figures A1 and A2, and the same as Cr obtained by the method of Appendix B. Example: Using a 4% swept analyzer, the waveform and waveform factor of the filter in the measured analyzer are: Bz = 1.55; B
B3o 2. 4+Bs
Bso = 4. 0;
C = 0.1 + 1. 55 × 2. 4
= 0. 75; B, = 4%
will be = 7dB, and the corresponding peak-to-valley frequency ratio Bm = 3. 9%. Using Bm=3.9%, then: The peak-to-valley amplitude obtained by frequency response measurement will be
GB/T2423.12-1997
× 0.75 × 4% = 1%
This leads to an estimated analysis error of 1.9dB in the trough area and 0.95dB in the peak area. If the frequency response measurement that has been carried out is not measured with a very precise frequency meter, then Cf1, and B. =1×0.75×4%=3%
Therefore, it can be seen that the analysis error is large, that is, 3.6dB in the trough area and 2.3dB in the peak area. After studying other pairs of peaks and valleys, it is found that the above errors are the largest. Figure A1Analysis error in the trough area
0.2 0.30. 5
Figure A2Analysis error in the peak area
A4Verification of the spectrum of the acceleration spectral density
425dB2.7%
3.5d31.3%
Ap/AnB'un
Equivalent relative bandwidth
Ap/AnB'm
3.5dB1.3%
7dB 1. 3%
14dB 1. 7%
18dB 2.0%
25dB 2. 7%
If the duration of the conditional test allows, it is recommended to verify the spectrum of the acceleration spectral density while the conditional test is in progress. Otherwise, the verification should be carried out after the conditional test. In the latter case, a preliminary verification should be made during the pre-adjustment excitation phase. The verification of the acceleration spectral density should be measured at all control points in the predetermined direction and at a number of specified control points in the transverse direction. During the verification, the analyzer should be swept from f to 2f:, and the scanning rate should be selected so that the error remains within the error range allowed when using a lower scanning rate. If the S value complies with the following formula, the error is always small in any case. 159
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