Mutual-inductance probe accurately measures liquid levels in a variety of liquid metals at elevated temperatures. It can be used in pyrochemical processes for the recovery of spent reactor fuel

Johnson, T. R.

Pierce, R. D.

Teats, F. G.

English

NASA Technical Reports Server

Millivolt 
Recorder 
July 1969
	 Brief 69-10256 
S	 ICY C AEC-NASA TECH BRIEF 
US
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. 
Induction Probe Determines Levels of Liquid Metals 
Hewlett-Packard	 6V6	 StancerA33O4 
Oscillator	 l3
4 
Model 200 CD
0	
5 K 
fl
Meg.	 2	 7 j
 Primary Coil 
.5  
470	
T015 1i 2W	 pF	
Liquid-Level Probe 
. FSV 
117V	 1A	 260 
AC
Stancor P8404
6	 2 
:I II_.	 30K 4 5W 
5Y3 
Fig. 1. Circuit diagram of the electronic equipment 
The problem: 
To develop a liquid-level probe for use in pyrochem-
ical processes for the recovery of spent reactor fuel. 
In these processes, liquid metals and molten salts serve 
as the solvents for the fuel materials. 
The solution: 
An intruthent, employing a mutual-inductance coil, 
that accurately and reliably measures liquid levels in 
a variety of liquid metals at elevated temperatures.
This mutual-inductance probe locates the interfaces 
between gas and liquid metal and liquid salt and liquid 
metal. 
The probe is a bifilar coil of nichrome wire on an 
alumina form contained in a well of type-304 stainless 
steel or ceramic. A high-frequency voltage supplied 
to one winding induces a voltage in the second winding 
that is inversely relaxed to the depth of liquid sur-
rounding the coil. Probes, about 5 and 14 inches long, 
(cunhintied overleal) 
This document was prepared under the sponsorship of the Atomic	 liability resulting from the use of the information contained in this 
Energy Commission and/or the National Aeronautics and Space document, or warrants that the use of any information, apparatus, 
Administration. Neither the United States Government nor any per-	 method, or process disclosed in this document may not infringe pri-
son acting on behalf of the United States Government assumes any vately owned rights.
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were calibrated in liquid cadmium, bismuth, and 
sodium at temperatures between 200' and 700C. 
The output signal was affected only slightly by the 
metal's resistivity, but it was influenced by the 
temperature. 
The device has several advantages over other means 
of measuring liquid levels of corrosive fluids at high 
temperatures. It is compact, rugged, reliable, and 
reasonably accurate. For a calibrated probe, the aver-
age deviation in measured liquid level is about 3% of 
the length of the windings. The instrument is well 
adapted to operations in remotely operated facilities 
because it has no moving parts and can be easily 
replaced. 
How it's done: 
The probe consists of two coils of 20-gage nichrome 
wire wound in the grooves of an alumina form that is 
contained in a protective well. The grooves hold the 
wires stationary and are deep enough to allow for 
thermal expansion of the wire without the wire con-
tacting the containment well. The lead wires terminat-
ing at the bottom of the probe are drawn through two 
holes in the center of the alumina form and are pro-
tected from contact with the bottom of the well by a 
protrusion from the form. The four wires leading from 
the top of the form are protected by a four-hole alum-
ina tube extending to the top of the well. 
The fluctuating magnetic field, created by the alter-
nating current in the primary coil of the probe, induces 
eddy currents in any nearby conductor, including the 
secondary coil, the well, and the liquid surrounding 
the well. The presence of electrically conducting ma-
terial near the coils decreases the mutual inductance 
between the coils, and thus decreases the voltage in-
duced in the secondary coil. 
The high-frequency signal is generated by an audio 
oscillator with output frequencies ranging from 5 to 
600,000 Hz and a maximum signal output of 10 v 
root-mean-square (Fig. I). The oscillator output is 
amplified by a class-A power amplifier and fed to the 
primary winding of the coil. The signal induced in the
secondary winding is rectified and then measured by a 
millivolt recorder. 
Changes in the mutual conductance of the coil, 
caused by variations of the eddy-current strength in 
the surroundings of the coil, are detected as change in 
the voltage induced in the secondary winding. The 
output signal is sensitive to the voltage supplied to the 
primary winding, and to changes in the electrical 
resistance of the coil and lead wires. The instrument 
is zeroed at a standard liquid level and temperature, 
and liquid depths are then determined by changes in 
the output signal from this standard. Because of the 
stability of the circuitry the zero needed setting only 
once with a single probe during an experiment lasting 
1,000 hours. 
Reference: 
For more detail see T. R. Johnson, F. G. Teats, and 
R. D. Pierce, in AA'L-7153 (Argonne National Labora-
tory, May 1967) (available from CFSTI, Springfield, 
Va. 22151, at $3.00—microfiche, $0.65): Nuclear Ap-
p/ic. 4, 47 (Jan. 1968). 
Notes: 
I. This information may interest persons and organi-
zations concerned with processing of liquid metals. 
2. Inquiries may be directed to: 
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Source: T. R. Johnson, F. G. Teats, R. D. Pierce
Chemical Engineering Division 
(ARG-10348) 
Patent status: 
Inquiries concerning rights for commercial use of 
this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 69-10256	 Category 03


Induction probe determines levels of liquid metals

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