Instrument for measuring magnetic permeability of materials undergoing heat treatment as method for monitoring stress relief and tempering is described. Procedure is based on magnetic potentiometer principle with yoke compensating coils to cancel effects of reluctance of yoke and joint gaps. Instrument is heated with specimen being heat treated

Barranger, J. P.

English

NASA Technical Reports Server

August 1972	 B72-10443 
NASA TECH BRIEF 
Lewis Research Center
	
_4V 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code Kr, Washington, D.C. 20546. 
High Temperature Permeameter 
for Measuring Magnetic Properties 
The problem: 
To measure the magnetic properties of materials at 
temperatures up to 1000°C. In heat treating materials 
for stress relief and tempering, measurements of residual 
strain and hardness can be derived from the measurement 
of magnetic permeability. A permeameter placed in the 
heat treating furnace with the material being processed 
could provide continuous monitoring of these material 
properties, however, conventional permeameters are not 
suited for such use. Design and materials of construction 
limit their use to moderate and unvarying temperature 
conditions. 
Yoke
Compensating
Coil
Central Coils: 
H Coil Outside 
B Coil Inside 
Magnetic 
Potentiometer
End Auxiliary 
Magnetizing Coil
Specimen
The solution: 
A new permeameter which measures the magnetizing 
force and the corresponding magnetic induction of a 
specimen at temperatures up to 1000°C in a vacuum or 
an inert atmosphere. 
How it's done: 
The new permeameter is shown in the figure. The 
specimen may be a rod of solid material or a bundle of 
sheet material. Two symmetrical yokes close the magnetic 
path around the specimen. A coil (H) surrounding the 
specimen supplies the magnetizing force. A separate coil 
(B) is used to measure the magnetic induction. The end 
auxiliary coils are electrically and magnetically in series 
with the H coil and provide additional magnetizing force 
resulting in a uniform longitudinal flux distribution in 
the specimen. The magnetizing force is calculated from 
the coil current, while a fluxmeter is used to measure the 
induction. The permeameter uses the magnetic potentio-
meter principle with yoke compensating coils to cancel 
the effects of the reluctance of the yoke and the joint 
gaps. 
Each of the two symmetrical yokes consist of a com-
pensating coil wound on a magnetic core. The cores are 
made of a specially processed alloy of 9-percent iron and 
91-percent cobalt, a high temperature soft magnetic 
material. The central and end coils are wound on alumina 
bobbins that surround the specimen. All coils have rec-
tangular cross sections and are made by slipping short 
sections of alumina tubing over nickel wire. The weight 
of the upper yoke is supported primarily by the alumina 
bobbin of the central coil to minimize the introduction 
of undesirable stresses into the specimen. The magnetic 
potentiometer is a coil wound on a core of the same alloy 
as is used in the yokes. The ends of the magnetic strips 
are extended to the specimen surface through cutouts in 
the alumina bobbin.
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000442 2020-03-17T03:39:50+00:00Z
Electrically, a compensating coil current. reversing 
switch is ganged to the magnetizing current reversing 
switch so that the two currents are switched simul-
taneously. The compensating coil current is adjusted to 
obtain zero magnetic potentiometer output at each value 
of magnetizing current. 
In use, the permeameter and the specimen are heated 
together in the furnace. Electrical leads connect to the 
read-out instruments outside the furnace. 
Notes: 
1. Although the permeameter described is of the static 
type, a dynamic or ac version can be similary con-
structed. 
2. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95)
Reference: NASA TN-D-6659 (N72-17422), 
Permeameter for High-Temperature Magnetic 
Measurements 
3. Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B72-10443 
Patent status: 
No patent action is contemplated by NASA. 
Source: John P. Barranger
Lewis Research Center
(LEW-1 1609) 
B72-10443	 Category 03


High temperature permeameter for measuring magnetic properties

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