More F Knit fabrics shall additionally be tested and adhere accordingly to bursting strength characteristics. Conversely, woven fabrics shall also be tested and adhere accordingly to breaking load, tear resistance, and seam slippage characteristics. This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.
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A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. Scope 1. From the measured data, near-? These limits are not exact, but are based on decreasing displacement current due to decreased capacitive coupling at lower frequencies and on overmoding excitation of modes other than the transverse electromagnetic mode TEM at higher frequencies for the size of specimen holder described in this test method.
Any number of discrete frequencies may be selected within this range. For electrically thin, isotropic materials with frequency-independent electrical properties of conductivity, permittivity and permeability, measurements may be needed at only a few frequencies as the far-?
If the material is not electrically thin or if any of the parameters vary with frequency, measurements should be made at many frequencies within the band of interest. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Referenced Documents 2. Terminology 3. This concept of regions is further blurred by reradiating due to scattering by re? The interior of metallic structures often contains a mixture of near-? Current edition approved April 10, Published June Originally published as D — Last previous edition D —89 e1. According to these equations, SE will have a negative value if less power is received with the material present than when it is absent. An uncertainty analysis is given in Appendix X1 to illustrate the uncertainty that may be achieved by an experienced operator using good equipment.
Deviations from the procedure in this test method will increase this uncertainty. A program may be generated from the source code in Appendix X2 that is suitable for use on a personal computer. Separate measurement of re? Apparatus 5. The specimen holder is an enlarged, coaxial transmission line with special taper sections and notched matching grooves to maintain a characteristic impedance of 50 V throughout the entire length of the holder.
This impedance is checked in accordance with 7. There are three important aspects to this design. First, a pair of? This allows capacitive coupling of energy into insulating materials through displacement current. Second, a reference specimen of the same thickness and electrical properties as the load specimen causes the same discontinuity in the transmission line as is caused by the load specimen.
Third, non-conductive nylon screws are used to connect the two sections of the holder together during tests. This prevents conduction currents from dominating the desired displacement currents necessary for the correct operation of this specimen holder. A V output impedance is needed to minimize re? Precision step attenuators are useful in increasing the effective dynamic range for SE measurements. A wide dynamic range is desirable in order to achieve a wide dynamic range of measured SE values.
Typically, either a spectrum analyzer or a? These should all have a V characteristic impedance. Double-shielded cables provide lower leakage than single-shielded cables. Type-N connectors provide more reliability and less leakage than BNC connectors. Precision mm connectors give lower mismatch errors and are more reliable under heavy usage than other connectors, but are more expensive and are not used on most generators or receivers. Their main purpose in this system is for impedance matching.
AdB, V attenuator should be used on each end of the specimen holder. The material under test usually causes a large re? This may also cause variations of the incident power by changing the generator impedance loading. Use of a bidirectional coupler allows monitoring and correcting any changes in incident power due to this loading.
Attenuators greater than 10 dB will excessively decrease the dynamic range of the measurement system. Test Specimens 6. Both are shown in Fig. Dimensions are shown in Fig. The load specimen can be larger than the outer diameter of the? For the best repeatability of SE measurements, reference specimen and load specimen must be identical in thickness. For this method, two FIG. Measured SE values of inhomogeneous materials are dependent on geometry and orientation, and results are less repeatable than for homogeneous materials.
Tests must be performed immediately upon removal from conditioning environment. Preparation of Apparatus 7. A time-domain system can give location of a mismatch in addition to its magnitude. The lower limit of the measurement system sensitivity is a function of the sensitivity and bandwidth 3 of the receiver. Narrowing the bandwidth of the receiver lowers the detectable level, but increases the measurement time.
Leakage due to connectors or cables may reduce the DR of the system by providing a parallel signal path that does not pass through the specimen. If a step attenuator placed in series with the specimen holder causes a change in the minimum signal detected that corresponds to a change in attenuator setting, and if the step attenuator itself does not cause a leakage path, leakage is negligible and the DR measured above is correct.
If the levels do not correspond, the attenuation should be increased until a one-to-one correspondence is achieved to determine the DR. Since leakage from a coaxial connector is determined not only by the quality of the connector, but also by the amount of torque used in tightening the connector, connections should be rechecked. A specimen that has 5 V per square resistance should give a measured SE of? Any other known specimen may be used to check setup-to-setup repeatability.
Procedure 8. D 8. The specimen mounting procedure described in 8. This procedure can be automated if a computer and ancillary equipment with IEEE Bus capability are available. Remove two nylon screws, turn the holder end for end, remove the other two nylon screws, and carefully lift off the upper half of the holder. An indented, soft foam pad is useful for holding this upper half of the specimen holder while continuing the installation or removal of specimens.
Place the two pieces of the reference specimen on the? Use small amounts of transparent tape as needed. Replace the half of the specimen holder that had been removed so that the holes for the nylon screws are aligned. Reinstall two nylon screws. Turn the holder end for end and then reinstall the other two nylon screws. Reconnect the coaxial cables. Record the measured received values as P2 or V2 values at each frequency. Record these measured values as P1 or V1 values at the same frequencies used in 8.
If this value is within 10 dB of the smallest detectable signal of the measurement system, either the receiver bandwidth must be decreased and the measurement repeated, or the SE value is beyond the dynamic range of the measurement system and hence the SE value is reported as exceeding the DR of the system. If the recorded units were volts, use the voltage ratio Eq 2 from 3.
Report 9. Precision and Bias For analysis and details, see Appendix X1. Keywords Corrections to these? Measurements, P. Box , Boulder, CO The sources of error considered are operator errors, specimen-caused errors, and measurementsystem errors. No bound can be placed on such errors, but the deviation from any norm may be large enough that an experienced observer will be able to determine that the results are indeed erroneous.
Isotropic, homogeneous specimens with smooth surfaces will give the most repeatable results. If the reference specimen and load specimen are of different thickness, a bias error will be introduced.
If both specimens are of the same thickness, but 8 have irregular thickness over each specimen, random errors will be introduced. Inhomogeneities or anisotropicities in specimens cause various effects depending on size, distribution, and geometric arrangement. Experience with measurements on many types of specimens indicates that repeatability of measured data may be expected except when the surface is rough. A round-robin of measurements made on different types of specimens bears this out.
The random error that relates to drift over a few minute time period is very relevant. If no attenuators were used, the mismatch error on the generator side would be excessive, since, in one case, with the reference specimen installed in the holder, the impedance seen by the signal generator is determined almost entirely by the receiver, and, in the other case, with the load specimen installed, the impedance seen by the signal generator is almost a short circuit for conductive specimens.
The actual change in impedance is greatly reduced by the attenuator between the signal generator and the specimen holder. The actual change of impedance level seen by the signal generator may also load the signal generator and cause the output power to vary from one condition to the other. These changes can be monitored by use of a bi-directional coupler, and corrections can be made to compensate for them.