Iec 60068-2-6-2007.Pdf

IEC 60068 2 6 Edition 7 0 2007 12 INTERNATIONAL STANDARD NORME INTERNATIONALE Environmental testing – Part 2 6 Tests – Test Fc Vibration (sinusoidal) Essais d''''environnement – Partie 2 6 Essais – Essai[.]

Required characteristics

Basic motion

The fundamental motion is characterized as a sinusoidal function of time, ensuring that the specimen's fixing points move in unison and along straight parallel paths, while adhering to specific constraints.

Spurious motion

The maximum vibration amplitude at check points must not exceed 50% of the specified amplitude for frequencies up to 500 Hz, and 100% for frequencies above 500 Hz Measurements should focus solely on the specified frequency range In special cases, such as with small specimens, the permissible cross-axis motion may be restricted to 25% if dictated by the relevant specification.

For large or high mass specimens, achieving the specified figures may be challenging, particularly at certain frequencies In these instances, the relevant specification must clarify which requirements apply: a) any cross-axis motion exceeding the stated limits must be documented in the test report; or b) cross-axis motion that poses no risk to the specimen does not require monitoring.

LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.

For large or heavy specimens, spurious rotational motion of the vibration table can be significant Therefore, the relevant specifications should define an acceptable tolerance level, which must be documented in the test report (refer to A.2.4 for more details).

Signal tolerance

Acceleration signal tolerance measurements must be conducted as specified, focusing on the reference point and covering frequencies up to 5,000 Hz or five times the driving frequency, whichever is lower This maximum frequency may be increased to the upper test frequency for the sweep or beyond if indicated in the relevant specification Unless otherwise specified, the signal tolerance should not exceed 5%.

The acceleration amplitude of the control signal at the fundamental driving frequency must be restored to the specified value using a tracking filter, as outlined in the relevant specification.

For large or complex specimens that cannot meet specified signal tolerance values across certain frequency ranges, and where using a tracking filter is impractical, it is not necessary to restore the acceleration amplitude However, the signal tolerance must be clearly stated in the test report (refer to A.2.2).

If a tracking filter is not implemented and the signal tolerance exceeds 5%, the choice between a digital or analogue control system can significantly impact reproducibility.

The relevant specification may require that the signal tolerance, together with the frequency range affected, is stated in the test report whether or not a tracking filter has been used

Vibration amplitude tolerances

The motion amplitude along the specified axis at the check and reference points must match the designated value, adhering to defined tolerances that account for instrumentation errors Additionally, the relevant specifications may mandate the inclusion of the confidence level for measurement uncertainty in the test report.

Achieving the required tolerances can be challenging for large, high-mass specimens or at low frequencies In such instances, specifications may allow for wider tolerances or recommend alternative assessment methods, which will be detailed in the test report.

Tolerance on the control signal at the reference point shall be ±15 % (see A.2.3)

Tolerance on the control signal at each check point: ±25 % up to 500 Hz; ±50 % above 500 Hz

Frequency tolerances

The following frequency tolerances apply

4.1.5.1 Endurance by sweeping ±0,05 Hz up to 0,25 Hz; ±20 % from 0,25 Hz to 5 Hz; ±1 Hz from 5 Hz to 50 Hz; ±2 % above 50 Hz

4.1.5.2 Endurance at fixed frequency a) Fixed frequency: ±2 % b) Almost fixed frequency: ±0,05 Hz up to 0,25 Hz; ±20 % from 0,25 Hz to 5 Hz; ±1 Hz from 5 Hz to 50 Hz; ±2 % above 50 Hz

When comparing critical frequencies before and after endurance during vibration response investigations, the following tolerances should be observed: ±0.05 Hz for frequencies up to 0.5 Hz, ±10% for frequencies ranging from 0.5 Hz to 5 Hz, ±0.5 Hz for frequencies between 5 Hz and 100 Hz, and ±0.5% for frequencies exceeding 100 Hz.

Sweep

The sweeping shall be continuous and the frequency shall change exponentially with time

(see A.4.3) The sweep rate shall be one octave per minute with a tolerance of ±10 % This may be varied for a vibration response investigation (see 8.2)

NOTE With a digital control system, it is not strictly correct to refer to the sweeping being “continuous”, but the difference is of no practical significance.

Control strategy

Single/multipoint control

When multipoint control is specified or necessary, the control strategy has to be specified

The specification must indicate whether single point or multipoint control is to be utilized In cases where multipoint control is specified, it should clarify whether the average amplitude of signals at the checkpoints or the amplitude of the signal at a designated point will be measured.

(for example, that with the largest amplitude) shall be controlled to the specified level, see also

In situations where single point control cannot be achieved as per specifications, multipoint control should be implemented by managing the average or extreme values of signals at designated checkpoints In both cases of multipoint control, a fictitious reference point is utilized, and the method employed must be clearly outlined in the test report.

The implementation of multipoint control does not guarantee that the tolerances at each checkpoint are achieved However, it generally minimizes deviations from nominal values when compared to single-point control at a hypothetical reference point.

The following strategies are available

This method involves calculating the control amplitude from signals at each checkpoint A composite control amplitude is created by averaging the signal amplitudes from these checkpoints This averaged control amplitude is subsequently compared to the specified amplitude.

The control amplitude aC is formed by averaging the signal amplitude from the check points a1 to an according to their weighting w1 to w n : a C = (w 1 x a 1 + w 2 x a 2 +….+ w n x a n ) / (w 1 + w 2 +…+ w n )

This control strategy offers the possibility that different check point signals contribute a different portion to the control

In this method, a composite control amplitude is computed from the maximum (MAX) or the minimum (MIN) extreme amplitudes of the signal amplitude measured at each check point

This strategy generates a control amplitude that reflects either the maximum envelope of signal amplitudes from each checkpoint (MAX) or the minimum threshold of signal amplitudes from each checkpoint (MIN).

Multi-reference control

Multiple reference spectra can be established for various checkpoints, measuring points, or types of controlled variables, as outlined in the relevant specifications, such as in force-limited vibration testing.

When multi-reference control is specified, the control strategy shall be prescribed as follows:

Limiting: All control signals shall be beneath their appropriate reference;

Superseding: All control signals shall be above their appropriate reference.

Mounting

Specimens must be mounted on the test apparatus according to IEC 60068-2-47, unless specified otherwise For specimens typically mounted on vibration isolators, refer to the notes in sections 8.3.2, A.3.1, and A.3.2 for additional guidance.

A vibration severity is defined by the combination of the three parameters: frequency range, vibration amplitude and duration of endurance (in sweep cycles or time)

Each parameter must be defined according to the applicable specification, which may include options such as selecting values from sections 5.1 to 5.3, utilizing examples from Annex A or Annex C, or deriving them from the known environment or other relevant data sources, such as the IEC 60721-3 series.

To permit some flexibility in situations where the real environment is known, it may be appropriate to specify a shaped acceleration versus frequency curve and, in these cases, the

This document is licensed to MECON Limited for internal use in Ranchi and Bangalore, as supplied by the Book Supply Bureau The relevant specifications will define the shape based on frequency, with various levels and their associated frequency ranges, known as break points, being chosen from the values provided in this standard whenever feasible.

Examples of severities for components are given in Annex B, and for equipment in Annex C

Frequency range

Lower frequency f 1 Hz

Upper frequency f 2 Hz

Examples of ranges for particular applications are given in Tables B.1, C.1 and C.2.

Vibration amplitude

The amplitude of displacement, velocity or acceleration or combinations of those, shall be stated in the relevant specification

Below the cross-over frequency, amplitudes are defined as constant displacement, while above this frequency, they are characterized as constant velocity or constant acceleration Figures 1 and 2 illustrate example values for the two distinct cross-over frequencies.

Each value of displacement amplitude is associated with a corresponding value of acceleration amplitude so that the amplitude of vibration is the same at the cross-over frequency (see

In cases where the cross-over frequencies outlined in this subclause are not technically suitable, the applicable specification may link displacement and acceleration amplitudes, resulting in an alternative cross-over frequency Additionally, there may be instances where multiple cross-over frequencies are specified.

NOTE Nomograms relating vibration amplitude to frequency are given in Figures 1, 2 and 3, but before their use in the low-frequency region, consideration should be given to the guidance in A.4.1

Up to an upper frequency of 10 Hz, it is normally appropriate to specify a displacement amplitude over the whole frequency range Therefore, in Figure 3 only displacement amplitudes are specified

Figure 1 – Nomogram relating vibration amplitude to frequency with lower cross-over frequency (8 Hz to 10 Hz)

This nomogram should not be considered a precise graphical representation of the severities It is licensed to MECON Limited for internal use at the Ranchi/Bangalore location and is supplied by the Book Supply Bureau.

Figure 2 – Nomogram relating vibration amplitude to frequency with higher cross-over frequency (58 Hz to 62 Hz)

This nomogram is not intended to serve as an exact graphical representation of the severities It is licensed to MECON Limited for internal use at the Ranchi/Bangalore location and has been supplied by the Book Supply Bureau.

NOTE This nomogram should not be taken as being a precise graphical representation of the severities

Figure 3 – Nomogram relating vibration displacement amplitude to frequency

(only applicable for frequency ranges with an upper frequency of 10 Hz)

Duration of endurance

Endurance by sweeping

The duration of the endurance in each axis shall be given as a number of sweep cycles

(see 3.4) in the relevant specification or may be chosen from the following values:

When a higher number of sweep cycles is required, the same series should be applied

Endurance at fixed frequencies

The endurance duration for each relevant axis at specified frequencies, as determined in the vibration response investigation (refer to section 8.2), will be outlined in the corresponding specification or can be selected from the provided values, allowing for a tolerance of +50% (see Clauses A.1 and A.6.2).

For almost fixed frequencies, see Clause A.1

The specified duration must consider the total time the specimen will experience vibration throughout its operational life Additionally, an upper limit of \(10^7\) stress cycles is applicable for each combination of frequency and axis.

The relevant specification may call for preconditioning and shall then prescribe the conditions

The specimen shall be submitted to the visual, dimensional and functional checks prescribed by the relevant specification (see Clause A.9)

General

The specification must specify the number of axes for specimen vibration and their positions If not specified, the specimen should be vibrated in three mutually perpendicular axes sequentially, selected to effectively reveal potential faults.

The control signal at the reference point shall be derived from the signals at the check points and shall be used for single point or multipoint control (see A.4.5)

The test procedure will be selected based on the relevant specification from the stages outlined below, with additional guidance provided in Annex A Typically, the test stages should be conducted sequentially along the same axis and subsequently repeated for the other axes, as detailed in Clause A.3.

Special measures must be taken when testing a specimen typically designed for use with vibration isolators without them, as outlined in Clause A.5 Additionally, when a product usually transported in packaging is tested without its packaging, special actions are also required, in accordance with IEC 60068-2-47.

To ensure compliance with the relevant specifications, the control of vibration amplitude must be accompanied by a maximum limit on the driving force applied to the vibrating system The specific method for force limitation should be detailed in the relevant specification (refer to Clause A.7).

Vibration response investigation

The vibration response of a specimen within a specified frequency range must be examined to understand its behavior under vibration, as outlined in the relevant specifications Typically, this investigation is conducted over a sweep cycle similar to endurance testing, although vibration amplitude and sweep rate may be reduced to achieve more accurate response characteristics It is crucial to avoid excessive dwell time and overstressing of the specimen In cases where packaged products cannot be instrumented, measuring the force excitation of the specimen can help identify the resonant frequencies within the packaging However, this approach requires careful consideration to balance the benefits of such measurements against the lack of knowledge regarding the resonance frequencies of the packaged specimens.

To investigate the vibration response of an 'undefined type' specimen or package, it is essential to measure various signals, including driving force and vibration velocity Additionally, if required by the relevant specifications, the mechanical impedance spectra of the specimen can be calculated both before and after testing.

The specimen must operate during the vibration response investigation as specified If the mechanical vibration characteristics cannot be evaluated while the specimen is functioning, a separate investigation must be conducted with the specimen not in operation.

The vibration response investigation involves analyzing the specimen and its vibration response data to identify critical frequencies The test report will detail these frequencies, the applied amplitudes, and the specimen's behavior, as outlined in Clause A.1 Additionally, the relevant specification will specify the necessary actions to be taken.

When utilizing digital control, it is essential to exercise caution in identifying critical frequencies from the response curve plot This is due to potential limitations arising from the selected number of data points per sweep and the display screen's discrimination capability of the control system.

In specific situations, the relevant specification may mandate an additional vibration response investigation after completing an endurance procedure to compare critical frequencies before and after The specification will outline the necessary actions if any frequency changes occur It is crucial that both vibration response investigations are conducted consistently and at the same vibration amplitudes.

Endurance procedures

Endurance by sweeping

This endurance procedure is preferred

The frequency will be swept across the specified range at a designated sweep rate, amplitude, and duration If needed, the frequency range can be divided, ensuring that the stresses on the specimen remain unaffected.

Endurance at fixed frequencies

Vibration shall be applied either at: a) those frequencies derived from the vibration response investigation given in 8.2, using one of the following methods:

The applied frequency shall always be maintained at the actual critical frequency

When the actual critical frequency is unclear due to factors like chatter or simultaneous testing of multiple specimens, it is advisable to sweep a limited frequency range between 0.8 and 1.2 times the critical frequency to ensure full excitation of the effect This approach is also relevant for non-linear resonance situations, as outlined in Clause A.1, and should align with the predetermined frequencies specified in the relevant documentation.

The test shall be applied at the amplitude and for the duration stated in the relevant specification (see A.3.2)

When a product is mounted on vibration isolators or within packaging, the relevant specifications dictate whether the resonant frequencies of the product should be selected for the endurance test Refer to Clause A.5 for further details.

When prescribed by the relevant specification, the specimen shall be functioning and its performance checked during the test for the specified proportion of the total time (see A.3.2 and Clause A.8)

When specified, a recovery period after testing is essential to ensure that the specimen reaches the same conditions, such as temperature, as during the initial measurements The relevant specification will detail the exact recovery conditions required.

The specimen shall be submitted to the visual, dimensional and functional checks prescribed by the relevant specification

The relevant specification shall provide the criteria upon which the acceptance or rejection of the specimen is to be based (see Clause A.9)

12 Information to be given in the relevant specification

When incorporating this test into a relevant specification, it is essential to provide specific details, especially for the items marked with an asterisk (*), as this information is always mandatory.

Clause and/or subclause a) Choice of check points 3.2.3 b) Choice of control points* 3.3.2 c) Cross axis motion 4.1.2.1 d) Rotational motion 4.1.2.2 e) Signal tolerance 4.1.3

The document outlines essential parameters for vibration testing, including vibration amplitude tolerance, confidence level, and control methods It specifies mounting requirements, real environment severities, and frequency ranges, along with necessary measurements and preconditioning steps Key aspects such as the axes of vibration, force limitations, and the sequence of test stages are highlighted Additionally, it addresses functional checks, actions post-investigation, and criteria for acceptance or rejection, ensuring comprehensive evaluation and recovery processes are in place.

13 Information to be given in the test report

As a minimum the test report shall show the following information:

2 Test laboratory (name and address)

3 Test report identification (date of issue, unique number)

6 Purpose of the test (development test, qualifilcation, etc.)

7 Test standard, edition (relevant test procedure)

8 Test specimen description (unique identification, drawing, photo, quantity, etc.)

9 Mounting of test specimen (fixture identification, drawing, photo, etc.)

10 Description of test apparatus (cross-motion, etc.)

11 Control and measuring system, sensor location (description, drawing, photo, etc.)

12 Filters used for all signal(s) (types and bandwidth)

13 Uncertainties of measuring system (calibration data, last and next date)

14 Control strategy (multi-point control, multi-reference or MIN or MAX strategy)

15 Initial, intermediate or final measurements

16 Required severities (from test specification)

17 Test severities with documentation (measuring points, test spectra)

18 Test results (comment on status of test specimen)

19 Observations during testing and actions taken

21 Test manager (name of signature)

22 Distribution (list of those receiving report

NOTE 1 A test log should be written for the testing, where the test is documented as, for example, a chronological list of test runs with test parameters, observations during testing and actions taken and data sheets on measurements made The test log can be attached to the test report

NOTE 2 See also the requirements listed in 5.10 of ISO/IEC 17025

The test offers a way to replicate effects similar to those expected in real-world practice within a laboratory setting Its primary goal is not to perfectly mimic the actual environment.

Standardized parameters and appropriate tolerances are essential for achieving consistent results across various locations and operators, whether using analogue or digital control methods This standardization allows for the categorization of components based on their capacity to endure specific vibration severities outlined in the standard.

In vibration testing, traditional methods have focused on identifying resonances and conducting endurance tests at these frequencies for a set duration However, distinguishing between resonances that may lead to failure and those that are unlikely to cause issues remains challenging, even with prolonged vibration of the specimen.

Testing procedures for modern specimens often lack realism, making direct observation of vibration characteristics in enclosed items or miniaturized assemblies nearly impossible The application of vibration transducer techniques frequently alters the mass-stiffness distribution of the assembly When transducers can be utilized, the success of the measurements relies heavily on the test engineer's skill and experience in choosing the right measurement points within the assembly.

The preferred procedure of endurance by sweeping effectively minimizes challenges and eliminates the need to identify significant or harmful resonances This method is recommended due to the necessity for clearly defined test methods that align with the current standards of environmental testing, while also reducing reliance on the test engineer's expertise Endurance by sweeping is quantified by the number of sweep cycles, which are based on corresponding stress cycle counts.

The procedure may result in lengthy durations when aiming for a fatigue life that matches the required service time or achieves unlimited fatigue life under service-like vibration conditions Alternative methods, such as endurance testing at fixed frequencies, have been proposed This approach is suitable if the vibration response investigation reveals a limited number of frequencies—typically no more than four—per axis If the number of frequencies exceeds four, a sweeping endurance method may be more effective.

For nearly constant frequencies, the endurance duration should align with the critical frequency values Additionally, a portion of that time must be included, which is determined by the range of critical frequencies of the specimens.

It may be appropriate to carry out endurance testing both by sweeping and at fixed frequencies

It needs to be remembered that endurance at fixed frequencies still requires a certain amount of engineering judgement in application

In addition, for any predetermined frequency, the endurance time needs to be given in the relevant specification

Fixed frequency endurance refers to the duration at critical frequencies, typically determined by an expected number of stress cycles Due to the diverse range of materials, it is clear that a single, realistic figure for the number of stress cycles cannot be established.

Nevertheless, it is considered that 10 7 is a sufficiently practicable upper figure to be quoted for general vibration testing and need not be exceeded (see 5.3.2.1 and 5.3.2.2)

In situations with significant background vibration that is random or complex, sinusoidal testing may prove insufficient Consequently, it is the responsibility of the user to assess whether sinusoidal testing is appropriate for their specific application.

Tiêu đề	Test Fc: Vibration (sinusoidal)
Chuyên ngành	Environmental Testing
Thể loại	International Standard
Năm xuất bản	2007
Thành phố	Geneva

Định dạng
Số trang	86
Dung lượng	1,75 MB