ASTM A712-97

Standard Test Method for Electrical Resistivity of Soft Magnetic Alloys

SCOPE
1.1 This test method covers the measurement of electrical resistivity of strip or bar specimens of soft magnetic alloys.  
1.2 This standard does not purport to address all of the safety problems, 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. 1.3 The values are stated only in S1 units and are to be regarded as standard.

General Information

• Status: Historical
• Publication Date: 09-Oct-1997
• Technical Committee: A06 - Magnetic Properties
• Drafting Committee: A06.01 - Test Methods

Relations

• Replaced By: ASTM A712-97(2002) - Standard Test Method for Electrical Resistivity of Soft Magnetic Alloys
• Effective Date: 10-Oct-1997
• Referred By: ASTM A901-19 - Standard Specification for Amorphous Magnetic Core Alloys, Semi-Processed Types
• Effective Date: 10-Oct-1997
• Referred By: ASTM A345-19 - Standard Specification for Flat-Rolled Electrical Steels for Magnetic Applications
• Effective Date: 10-Oct-1997

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.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: A 712 – 97
Standard Test Method for
Electrical Resistivity of Soft Magnetic Alloys
This standard is issued under the fixed designation A 712; 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 of substantially uniform cross-sectional area.
6.2 It shall have a minimum length of 0.25 m. Strip
1.1 This test method covers the measurement of electrical
specimens preferably should have a uniform width of 0.03 m
resistivity of strip or bar specimens of soft magnetic alloys.
minimum, unless not available.
1.2 This standard does not purport to address all of the
6.2.1 If width of the strip material to be sampled prevents
safety concerns, if any, associated with its use. It is the
obtaining a sample of 0.03-m minimum width, the specimen
responsibility of the user of this standard to establish appro-
width to be used shall be the maximum obtainable and shall be
priate safety and health practices and determine the applica-
agreed upon between the manufacturer and the purchaser.
bility of regulatory limitations prior to use.
6.2.2 Bars and wires having circular, rectangular, or other
1.3 The values are stated only in SI units and are to be
sections shall be used in the sectional dimensions as produced,
regarded as standard.
unless they are so large as to require cutting a representative
2. Referenced Documents
sample of suitable dimensions.
6.3 It shall be free of obvious surface defects.
2.1 ASTM Standards:
6.4 The surface shall be cleaned by wiping with a cloth. Oil
A 34 Practice for Sampling and Procurement Testing of
and grease, if present on the surface, shall be removed with a
Magnetic Materials
suitable solvent. Normal surface oxide or core plating need not
3. Summary of Test Method
be removed except in areas in which it is necessary to make
satisfactory electrical contact.
3.1 The electrical resistance of a 0.25-m long (minimum)
test specimen is measured with a Kelvin-type resistance bridge
7. Procedure
or a digital multimeter or the potentiometer-ammeter method.
7.1 Measure the electrical resistance of the test specimen
The resistivity is then calculated from the resistance measure-
using a Kelvin-type resistance bridge or a digital multimeter or
ment and the dimensions of the specimen and is known as the
potentiometer-ammeter system having separate current and
electrical resistivity of the material. This value is equal to the
potential leads.
resistance between opposite faces of a cube of unit dimensions.
7.2 The distance between each potential lead contact and the
4. Apparatus
corresponding current lead contact shall be at least twice the
width of the test specimen with the two potential contacts lying
4.1 Kelvin-type resistance bridge or a digital multimeter or
between the current contacts. The distance between the poten-
a d-c potentiometer and d-c ammeter providing resistance
tial contacts shall be not less than 0.12 m.
measurements to an accuracy within 0.5 % of the accepted true
7.3 The dimension of each potential contact in the direction
value.
of the length of the specimen shall be not more than 0.5 % of
5. Sampling
the distance between potential contacts.
7.4 The contacts to the specimen shall be located centrally
5.1 Samples shall be representative of the material in the
with respect to the specimen’s width dimension, and the
physical condition as shipped or agreed upon by the manufac-
current contacts shall cover more than 80 % of the width. A
turer and the purchaser.
reliable contact shall be made with the specimen by both the
6. Test Specimen
current and potential leads.
7.5 Specimen temperature during test should be about 25°C.
6.1 The test specimen shall be a straight strip or bar or wire
7.6 To eliminate errors as a result of contact potential, take
1 two readings, one direct and one with the current reversed, in
This test method is under the jurisdiction of ASTM Committee A-6 on
close succession.
Magnetic Properties and is the direct responsibility of Subcommittee A06.01on Test
Methods.
7.7 The electrical current in the test specimen must be
Current edition approved Oct. 10, 1997. Published December 1998. Originally
limited to avoid overheating but must be adequate to provide
published as A 712 - 75. Last previous edition A 712 - 75.
sufficient sensitivity to show an out-of-balance condition when
Annual Book of ASTM Standards, Vol 03.04.
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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.
A 712
the resistance reading is changed 0.5 % of the value recorded.
where:
If the current is too low, sensitivity is low also, and a balance
r = electrical resistivity of the material, V ·m;
can be shown for a broad range of resistance. R = resistance of electrical path, V;
A = cross-sectional area of electrical path, m ; and
8. Calculation l = length of electrical path between potential contacts on
the test specimen, m.
8.1 Strip Specimens:
8.4 The resistivity units in ohm-metres shown in Eq 2 can
8.1.1 Determine the average cross-sectional area of the test
be converted to microhm-centimetres by multiplying the ohm-
specimen from the weight, length, and density as follows:
metre figure by 10 microhm-centimetres per ohm-metre. For
A 5 m/ld (1) −6
example, if the resistivity is 0.25 3 10 V ·m;
−6 8
0.25 3 10 3 10 μV · cm/V · m is equal to 25 μV · cm.
where:
A = cross-sectional area of test specimen, m ;
NOTE 1—The resistivities of commercial soft magnetic alloys are
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