Emf comparing device nondestructively inspects metals and alloys for conformance to a chemical specification. It uses the Seebeck effect to measure the difference in emf produced by the junction of a hot probe and the junction of a cold contact on the surface of an unknown metal

Stone, C. C.

Walker, D. E.

English

NASA Technical Reports Server

February 1967	 Brief 67-10035 
E WIWX GO) AEC-NASA TECH BRIEF 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Thermoelectric Metal Comparator Determines Composition

of Alloys and Metals 
SIMPLIFIED CIRCUIT OF COMPARATOR 
The problem: 
To nondestructively inspect unknown metals and 
alloys for conformance to a chemical specification. A 
device is required to provide more precise and rapid 
determination than the spark testing technique, and 
which produces real numerical, values that can be 
reproduced or recorded for future reference. 
The solution: 
A device which measures the difference in emf 
produced by the junction of a hot probe and the 
junction of a cold contact on the surface of an un-
known metal. This instrument utilizes the "Seebeck" 
(thermal electromotive force) effect, where a hot junc-
tion between two dissimilar metals produces a charac-
teristic emf, the magnitude of which is dependent on 
the temperature of the junction and the composition 
of the metals. 
How it's done: 
The emf comparing device consists of a voltage
source, a null detector, and hot and cold probes. A 
temperature controller is used to adjust the proper. 
temperature at the hot probe. 
The hot junction is made with a heated iron probe 
held to the surface of the unknown metal, providing 
what may be considered an infinite heat source in 
contact with an infinite heat sink. The required tem-
perature of the hot probe is maintained at 350 0
 ±5°F 
by the temperature controller, with the controlling 
thermocouple imbedded in an enlarged section of the 
hot probe itself. The hot junction lead, which is made 
from the same material as the hot probe, is imbedded 
in an Armco iron ring or washer which is in tight con-
tact with the hot probe. The cold junction contact 
consists of a wire made of the same material as the hot 
probe and the hot junction lead. It is held in contact 
with the unknown metal sample by a magnet. 
An initial null setting is obtained by placing the hot 
probe in contact with the cold contact. The tempera- 
ture of the hot probe is then standardized by 'taking 
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
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sample readings on a known metal, such as SAE 1040 
steel, and adjusting the temperature of the probe until 
a standard emf is obtained. The hot probe and cold 
contact are then placed on the metal sample to be 
tested. The hot probe sample junction and the cold 
contact sample junction each display the "Seebeck" 
effect. The total emf produces an unbalance in the 
circuit which is indicated on the null detector. This 
unbalance is eliminated by adjusting the variable emf 
voltage source until a null is reestablished. The dif-
ference between the initial null emf and the sample 
null emf is read directly from the voltage source po.
-tentiometer. Emf values are read to 1/100 of a milli-
volt in the range of 0.01 to 10.0 millivolts, with an 
accuracy of ± I / 100 of a millivolt. 
Notes: 
1. Most commercial ferrous and nonferrous alloys do 
not have overlapping emf ranges and are easily de-
termined. However, if an alloy to be tested has an 
overlapping emf range with any other alloy or 
unalloyed metal being considered, it may be neces-
sary to supplement this device with some other 
means of determining whether the alloy has a given 
composition.
2. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B67-10035 
Source: C. C. Stone and D. E. Walker 
Metallurgy Division

(ARG-235) 
Patent status: 
Inquiries about obtaining rights for commercial use 
of this innovation may be made to: 
Mr. George A. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 67-10035	 Category 01


Thermoelectric metal comparator determines composition of alloys and metals

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