ASTM D1531-95
(Test Method)Standard Test Methods for Relative Permittivity (Dielectric Constant) and Dissipation Factor by Fluid Displacement Procedures
Standard Test Methods for Relative Permittivity (Dielectric Constant) and Dissipation Factor by Fluid Displacement Procedures
SCOPE
1.1 These test methods provide techniques for the determination of the relative (Note 1) permittivity and the dissipation factor of solid insulating materials by fluid (Note 1) displacement.
Note 1--In common usage, the word "relative" is frequently dropped.
Note 2--The word "fluid" is a commonly used synonym for "liquid'' and yet a gas is also a fluid. In these test methods the words fluid and liquid appear as synonyms, but the word fluid is also used to show that liquid is not all that is meant.
1.2 Test Method A is especially suited to the precise measurements on polyethylene sheeting at 23oC and at frequencies between 1 kHz and 1 MHz. It may also be used at other frequencies and temperatures to make measurements on other materials in sheet form.
1.3 Test Method B is limited to the frequency range of available guarded bridges. It is especially suited to measurements on very thin films since it does not require determination of the thickness of the specimen. The test method provides an estimate of the thickness of thin films which is more accurate and precise than thickness measurements obtained by other means.
1.4 Test Method B is also useful for measurements of polymer sheeting up to 2 mm thickness.
1.5 These test methods permit calculation of the dissipation factor of the specimens tested.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. 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. For a specific precautionary statement, see Note 3.
1.7 The values stated in SI units are to be regarded as the standard.
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Designation: D 1531 – 95 An American National Standard
Standard Test Methods for
Relative Permittivity (Dielectric Constant) and Dissipation
Factor by Fluid Displacement Procedures
This standard is issued under the fixed designation D 1531; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 2. Referenced Documents
1.1 These test methods provide techniques for the determi- 2.1 ASTM Standards:
nation of the relative (Note 1) permittivity and the dissipation D 150 Test Methods for AC Loss Characteristics and Per-
factor of solid insulating materials by fluid (Note 2) displace- mittivity (Dielectric Constant) of Solid Electrical Insulat-
ment. ing Materials
D 374 Test Methods for Thickness of Solid Electrical Insu-
NOTE 1—In common usage, the word “relative” is frequently dropped.
lation
NOTE 2—The word “fluid” is a commonly used synonym for “liquid’’
D 618 Practice for Conditioning Plastics and Electrical
and yet a gas is also a fluid. In these test methods the words fluid and
liquid appear as synonyms, but the word fluid is also used to show that Insulating Materials for Testing
liquid is not all that is meant.
D 831 Test Method for Gas Content of Cable and Capacitor
Oils
1.2 Test Method A is especially suited to the precise
D 924 Test Method for Dissipation Factor (or Power Factor)
measurements on polyethylene sheeting at 23°C and at fre-
and Relative Permittivity (Dielectric Constant) of Electri-
quencies between 1 kHz and 1 MHz. It may also be used at
cal Insulating Liquids
other frequencies and temperatures to make measurements on
D 1711 Terminology Relating to Electrical Insulation
other materials in sheet form.
E 1 Specification for ASTM Thermometers
1.3 Test Method B is limited to the frequency range of
available guarded bridges. It is especially suited to measure-
3. Terminology
ments on very thin films since it does not require determination
3.1 Definitions—Definitions are in accordance with Termi-
of the thickness of the specimen. The test method provides an
nology D 1711.
estimate of the thickness of thin films which is more accurate
3.2 Description of a Term Specific to This Standard:
and precise than thickness measurements obtained by other
3.2.1 compatibility, n—A fluid is considered compatible
means.
with a test specimen if, during the time required to complete a
1.4 Test Method B is also useful for measurements of
test of the specimen in the fluid at the specified temperature and
polymer sheeting up to 2 mm thickness.
frequency, the calculated permittivity of the specimen does not
1.5 These test methods permit calculation of the dissipation
change by more than 0.1 %, and the dissipation factor change
factor of the specimens tested.
is less than 0.0001.
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4. Summary of Test Methods
responsibility of the user of this standard to establish appro-
4.1 Test Method A— The single fluid technique:
priate safety and health practices and determine the applica-
4.1.1 Measurements are made with a fixed-plate, two-
bility of regulatory limitations prior to use. For a specific
terminal self-shielded test cell assembly. By two measure-
precautionary statement, see Note 3.
ments, one with the cell filled with the fluid (which in this case
1.7 The values stated in SI units are to be regarded as the
is a liquid) only and the second one with the solid specimen
standard.
immersed in the liquid, a change in capacitance is determined.
This capacitance difference is used with the approximate
thickness of the specimen, the plate spacing, and the precisely
These test methods are under the jurisdiction of ASTM Committee D-9 on
known permittivity of the liquid to calculate the permittivity of
Electrical and Electronic Insulating Materials and are the direct responsibility of
Subcommittee D09.12 on Electrical Tests.
Current edition approved July 15, 1995. Published September 1995. Originally
e1 3
published as D 1531 – 58 T. Last previous edition D 1531 – 90 . Annual Book of ASTM Standards, Vol. 10.01.
2 4
Coutlee, K. G., “Liquid Displacement Test Cell for Dielectric Constant and Annual Book of ASTM Standards, Vol. 08.01.
Dissipation Factor up to 100 Mc,” 1959 Annual Report, Conference on Electrical Annual Book of ASTM Standards, Vol. 10.03.
Insulation, National Research Council, Publication 756, Washington, DC. Annual Book of ASTM Standards, Vol. 14.03.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 1531
the specimen. The dissipation factor of the test specimen is 5.2 Dissipation Factor—Normally, polyethylene has a very
calculated from measurements of the cell with the liquid alone low dissipation factor, and a test specimen exhibiting an
and with the specimen immersed in it. Precision and accuracy abnormally high dissipation factor would be suspected of
are made high by limiting the proportion of fluid to solid, containing impurities or being contaminated. The reproducibil-
limiting the difference in permittivity between the fluid and the ity of dissipation factor by this test method is somewhat better
solid, and designing the cell so that both the stray capacitance than that obtainable with the more conventional methods, but is
and the sensitivity limit of the measuring instrument are very limited by the sensitivity of commercially available measuring
small relative to that part of the capacitance due to the apparatus.
specimen. Also, due to its bulk, the measuring system is
6. Apparatus
insensitive to mechanical and thermal disturbances. Since it is
6.1 Measuring Circuits—Any low-voltage bridge or
not necessary to know the thickness of the specimen accurately
resonant-circuit method conforming to the requirements of Test
and it is not necessary to apply electrodes, there is an overall
Methods D 150 is suitable when the parallel substitution
saving in testing time.
method is employed. A capacitance sensitivity and readability
4.2 Test Method B—This is a two fluid technique that uses
of about 0.01 pF and a dissipation factor sensitivity and
a rigidly constructed, fully shielded, temperature controlled
readability of at least 0.00001 is needed. One means for
cell.
obtaining this sensitivity at 100 kHz and above is by using
4.2.1 The fluids are:
commercially available resonant circuit apparatus and high Q
4.2.1.1 Two liquids, or
coils (500 minimum).
4.2.1.2 One liquid and a gas such as air or nitrogen.
6.2 Leads and Connectors—Low-loss coaxial connectors
4.2.2 Observations of capacitance and dissipation factor
and leads are recommended for connecting the cell to bridges
from the four following conditions are used to compute relative
equipped with guard circuits for frequencies from 1000 Hz to
permittivity, dissipation factor, and the thickness of the speci-
1 MHz. Terminate the guard as close as possible to the cell.
men:
6.3 A rigid lead construction is necessary for connecting the
4.2.2.1 Without a solid specimen but with a single fluid in
cell to unguarded circuits including resonant circuits. Such
the cell,
construction stabilizes stray capacitance. Bare #10 AWG (2.5
4.2.2.2 Without a solid specimen but with a fluid different
mm dia) copper is suitable if rigidly mounted and maintained
from that in 4.2.1.1,
in the same position throughout the tests. At frequencies of 1
4.2.2.3 With a solid specimen and with the single fluid of
MHz and higher, lead resistance and contact resistance become
4.2.1.1, and
important because they affect dissipation factor measurements
4.2.2.4 With a solid specimen and with the different fluid of
of 0.0001 or less. Contact resistance can be minimized by use
4.2.1.2.
of bright solid copper clips for connections. Such clips should
TEST METHOD A—LIQUID DISPLACEMENT
be small in size to minimize the effect that placement of the
METHOD USING A SINGLE FLUID clip has on the measured capacitance. Take care to keep the
variations in capacitance between leads and surrounding ob-
5. Significance and Use
jects to less than 0.01 pF during measurements.
5.1 Permittivity: 6.4 The measuring cell in which the test specimens are
5.1.1 Polyethylene and Materials of Permittivity within 0.1 immersed in the liquid is shown in Fig. 1. It is a two-terminal,
of that of Polyethylene—Since the permittivity of benzene or 1 self-shielded type cell consisting of a rectangular 6.35 mm ( ⁄4
cSt silicone fluid is very close to that of polyethylene, these in.) thick gold-plated brass center electrode having parallel and
2 2
fluids are recommended for highly accurate and precise testing flat faces, each 58.06 cm (9.00 in. ) in area. This electrode is
of polyethylene or other materials with permittivity close to supported by 5 polytetrafluoroethylene post insulators, and is
that of polyethylene. These properties of the test method make located midway between two gold-plated brass electrodes
it a suitable tool to determine batch to batch uniformity of a which form an integral part of the walls of the cell. The
polyethylene compound in order to meet precise requirements standard spacing between the plates is 1.52 6 0.05 mm (0.060
of high capacitance-uniformity and capacitance-stability in 6 0.002 in.); however, other spacings may be used to accom-
electronic apparatus. It also serves as a means to detect modate test specimens of thicknesses other than 1.27 mm
1 1
impurities, as well as changes resulting from prolonged expo- (0.050 in.), such as 1.6 and 3.2-mm ( ⁄16 and ⁄8-in.) test
sure to high humidity, water immersion, weathering, aging,
specimens. The center electrode slides in grooves and can be
processing treatments, and exposure to radiation. removed readily to permit easy cleaning. The cell is equipped
5.1.2 Other Materials—The test method may provide ad-
with an overflow pipe in order to maintain a constant level of
vantages for routine testing of materials with a poorer match in the liquid with the test specimens either in or out. The cooling
permittivity between these liquids and the specimen than that effect resulting from the evaporation of the liquid is small at the
required above, because of the ease of testing, and the dilution specified test temperature due to the large mass of metal and
of errors due to inaccurate thickness. Correction factors can be the small area of liquid exposed to the air, so that under normal
calculated to account for the bias introduced by the permittivity testing conditions the required stability of capacitance and
mismatch. Also, other compatible liquids of appropriate and temperature can be obtained without the use of a cpover.
known dielectric properties different from the two mentioned 6.5 Thermometer—An ASTM Engler Viscosity Thermom-
above are available. eter having a range from 18 to 28°C and conforming to the
D 1531
Plate assembly shall be a sliding fit in the cell subassembly; if necessary the polytetrafluoroethylene post insulators may be modified very slightly to accomplish this.
The tolerances on the component parts have been apportioned so as to provide a spacing of 1.52 6 0.05 mm (0.060 6 0.002 in.).
FIG. 1 Measuring Cell For Test Method A
requirements for Thermometer 23°C in Specification E 1 can found generally satisfactory. However, in case of a dispute, dry
be used. the benzene as above, or measure the permittivity of the
benzene, or both. The dissipation factor of the benzene shall
7. Standard Liquid Dielectrics
not exceed 0.00001 during test. From 100 kHz to 1 MHz, the
−6 2
7.1 Silicone Liquid—Use a 1.0 cSt (1 3 10 m /s) silicone dissipation factor of ACS reagent-grade benzene is consistently
less than 0.000005. The benzene can be used a number of times
fluid. The permittivity of the liquid changes with temperature
and has to be measured to determine the exact value for each or until an increase in dissipation factor is observed.
lot of material. Use the three-terminal measuring cells and
NOTE 3—Precaution: Observe proper precautions due to the toxicity
procedures of Test Method D 924 for this purpose. The values
and flammability of benzene. Minimize benzene fumes from test speci-
of silicone liquid are quite similar to those of dry ACS grade
mens by dropping the specimens in a beaker and covering it at once. A
benzene as shown in Table 1. The dissipation factor of 1.0 cSt portable hood placed near the cell will also remove benzene fumes.
silicone liquid is less than 0.000005 from 100 kHz to 1 MHz
7.3 Other liquids may be used. Those selected should have
and therefore can be considered zero over this frequency range.
a permittivity which is approximately the same as that of the
The liquid can be used a number of times or until an increase
specimen, and is known precisely; that is to the fourth decimal
in dissipation factor is observed.
place at the test frequency.
7.2 Benzene—Use certified ACS reagent-grade (thiophene-
7.4 Avoid liquids that dissolve any constituents of the
free) benzene having a permittivity as specified in Table 1 as
specimen, result in swelling of the specimen, or are absorbed
the referee liquid. As the permittivity of a liquid is a function
within the body of the specimen.
of temperature, measure the temperature of the cell to an
7.5 Avoid liquids that exhibit peaks in dissipation factor in
accuracy of 60.1°C both with the test specimens in and out.
excess of 0.00005 in the frequency range 650 % of the test
The permittivity values shown in Table 1 are for benzene that
frequency.
has been dried over powdered calcium hydride for 3 months.
U.S. commercial certified ACS reagent-grade benzene has been
8. Sampling
8.1 Take samples according to the applicable material speci-
TABLE 1 Permittivity Values for Dry Benzene
fication, and observe the following precautions in handling.
Temperature,° C Permittivity Temperature,° C Permittivity
8.1.1 Handle specimens with tweezers so that no finger-
21.8 2.2802 23.2 2.2775
prints or other contamination is introduced onto the specimen.
22.0 2.2798 23.4 2.2771
This precaution is very important for polyethylene, and is
22.2 2.2794 23.6 2.2768
22.4 2.2790 23.8 2.2764 expected to be very important for other materials also.
22.6 2.2787 24.0 2.2760
8.1.2 Note the handling precautions of Test Method B which
22.8 2.2783 24.2 2.2756
relate to removing surface contamination and maintaining a
23.0 2.2779 24.4 2.2752
clean surface between sampling and test, not only to improve
...
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