ASTM D3215-93

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 3215 – 93 An American National Standard
Standard Test Method for
Measurement of the Specific Electrical Impedance of
Electrical-Grade Magnesium Oxide for Use in Sheathed-Type
Heating Elements
This standard is issued under the fixed designation D 3215; 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.
1. Scope current density, and equal to the product of the measured
impedance Z and a geometrical shape factor F. (The impedance
1.1 This test method covers the determination of specific
is essentially resistive and phase effects are ignored).
electrical impedance of electrical-grade magnesium oxide by
externally heating a test cell to elevated temperatures using
4. Summary of Test Method
typical materials.
4.1 The specimen of magnesium oxide is poured into a
1.2 The values stated in SI units are to be regarded as the
length of tubing around a centrally located rod, and the
standard. The values given in parentheses are for information
assembly is compacted to form a test cell simulating a sheathed
only.
heating element. The test cell is placed in a heated furnace.
1.3 This standard does not purport to address all of the
Voltage is applied across the magnesium oxide in the test cell
safety problems, if any, associated with its use. It is the
in series with a known resistance. The leakage current is
responsibility of the user of this standard to establish appro-
measured in milliamperes. The leakage current and the geo-
priate safety and health practices and determine the applica-
metric factor are used to calculate the specific impedance.
bility of regulatory limitations prior to use.
5. Significance and Use
2. Referenced Documents
5.1 The specific electrical impedance can be used to indicate
2.1 ASTM Standards:
whether or not the magnesium oxide provides sufficient im-
B 344 Specification for Drawn or Rolled Nickel-Chromium
pedance to perform satisfactorily in high-temperature heating
and Nickel-Chromium-Iron Alloys for Electrical Heating
elements.
Elements
D 2755 Test Method of Sampling and Reduction to Test
6. Apparatus
Weight of Electrical Grade Magnesium Oxide
6.1 Tube Furnace, horizontal, having a uniformly hot zone
at least 178 mm (7 in.) long. A maximum temperature spread
3. Terminology
of 65.5°C (610°F) between three thermocouples is accept-
3.1 Definitions of Terms Specific to This Standard:
able.
3.1.1 measured impedance, Z, n—the ratio of the root mean
6.2 Tube Loading Devices (see Fig. 1 for suggested design).
square of the voltage applied between two electrodes that are in
6.3 Swaging Machine.
contact with the specimen to the root mean square of the
6.4 Swaging Dies, 12.06 mm (0.475 in.), 11.43 mm (0.450
current distributed throughout the volume of the specimen
in.), and 11.18 mm (0.440 in.).
(neglecting phase effects).
6.5 Metal Trimming Device.
3.1.2 shape factor, F, n—the ratio of the test cell length to
6.6 Vibrator.
the logarithm of the ratio of the test-cell diameters, relating the
6.7 Spot Welding Machine.
current flow per unit length to the logarithmic mean potential
6.8 Thermocouples, three, Type R, No. 24B&S gage,
gradient across the insulation.
3.1.3 specific electrical impedance, Z , n—the ratio of the
s
root mean square of an alternating potential gradient parallel to
the current in the material to the root mean square of the A Lindberg Single Zone Tube Furnace, Type 59545, 12 in., 500 to 1500°C,
available from Lindberg Co., 304 Hart St., Watertown, WI 53094, with Temperature
Control using Type R Thermocouple and suitable Ceramic Tube and Plugs, or
equivalent, has been found suitable for this purpose.
This test method is under the jurisdiction of ASTM Committee D-9 on
Size 4 swaging machines available from either the Torrington Co., 59 Field St.,
Electrical and Electronic Insulating Materials and is the direct responsibility of
Subcommittee D09.14 on Electric Heating Unit Insulation. Torrington, CN 06790, or the Fenn Mfg. Co., 200 Fenn Rd., Newington, CN 06111,
Current edition approved March 15, 1993. Published May 1993. Originally or their equivalent, are satisfactory for this test method.
published as D 3215 – 73. Last previous edition D 3215 – 83. The L & A vibrator, Model F-769, Type B, Size 3, available from the Pressed
Annual Book of ASTM Standards, Vol 03.04. Steel Co., 705 N. Pennsylvania Ave., Wilkes-Barre, PA 18703, or its equivalent, is
Annual Book of ASTM Standards, Vol 10.02. satisfactory.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 3215
0.510-mm (0.020 in.) diameter with appropriate potentiom-
eter.
6.9 Test Circuit, (see Fig. 2), capable of measuring tempera-
ture from 500 to 1500°C and leakage current from 0 to 19.99
mA, comprised of the following:
6.9.1 Essentially Sinusoidal Power Source, with a minimum
power rating of 100 VA at a frequency of 50 to 60 Hz.
6.9.2 Isolation Transformer, T , with a minimum power
rating of 100 VA and an output voltage of 500 V ac.
6.9.3 Multirange Electronic Voltmeter, M, capable of mea-
suring up to 500 V ac with an ac input impedance of not less
than 0.8 MV and an accuracy of 61 % or better,
6.9.4 Fixed Resistor, R , with a nominal resistance of 500 V
and a minimum rating of 5 W.
6.9.5 Ammeter, M , capable of measuring 19.99 mA with
FIG. 1 Test Cell Loading Devices
a sensitivity of 0.01 mA,
6.9.6 Capacitor, C , 0.01 MFD, 1000 VDC, and
6.9.7 Variable Transformer, T , capable of 0 to 120 V ac.
6.10 Tubing, 177.8 6 8 mm (7.0 6 0.03 in.) long by 12.70
6 0.08 mm (0.500 6 0.003 in.) in outside diameter by 0.89 6
0.08 mm (0.035 6 0.003 in.) in wall thickness.
6.11 80 Nickel-20 Chromium Alloy Rod, 203.2 6 0.8 mm
(8.0 6 0.06 in.) long by 4.11 mm (0.162 in.) in diameter (AWG
6), in accordance with Specification B 344.
6.12 Rubber Plugs, 12.70 mm (0.500 in.) lo
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