Sensor consisting of superconductive film mounted on a dipstick measures the level of liquid helium in a Dewar flask. The sensor is made by depositing a thin film of niobium metal to a thickness of 2000 angstroms on a quartz substrate, which is then mounted on a graduated dipstick

Becker, H. H.

English

NASA Technical Reports Server

September 1968
	 Brief 68-10341 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Superconductive Thin Film Makes Convenient Liquid Helium Level Sensor 
A convenient sensor for measuring the level of 
liquid helium in a Dewar flask consists of a supercon-
ductive film mounted on a dipstick. The sensor is 
made by depositing a thin film of niobium metal to a 
thickness of approximately 2000 angstroms on a 
quartz substrate, which is then mounted on a gradu-
ated dipstick. The film deposition is carried out, on 
the substrate at 600°F, in a vacuum of approximately 
10-6
 torr (with an electron beam evaporation source) 
at an evaporation rate of approximately 1500 ang-
stroms per minute. These conditions are required to 
obtain large crystallites in the niobium thin film for 
onset of superconductivity slightly above 4.2 0 K (tem-
perature of boiling liquid helium). For a sensor on a 
quartz substrate measuring 1/16x3/8x I inch, the 
electrical resistance of the device is 200 ohms at room 
temperature. 
To use the sensor as a gage for measuring the level 
of liquid helium, the niobium film is connected in 
series with a 1.5 volt battery, a No. 49 indicating 
lamp, and a normally open pushbutton switch. With 
the pushbutton closed, the top of the dipstick is held 
with thermally insulated gloves and the sensor is 
slowly and cautiously lowered into the Dewar until 
the indicator lamp lights. At this point, contact of the 
sensor with the liquid helium surface reduces the 
temperature of the sensor to that of the liquid helium 
and the resistance of the sensor suddenly falls to zero, 
permitting sufficient current from the battery to light
the lamp. The reading on the dipstick then corre-
sponds to the liquid level. Once turned on, the lamp 
will remain lit (with the switch closed) as long as the 
sensor is immersed in the liquid or is surrounded by 
helium vapor immediately above the liquid surface. To 
obtain a second level reading, the sensor is lifted a 
few inches above the liquid surface so that the lamp 
will automatically extinguish. The dipstick is again 
lowered into the Dewar flask until the lamp again 
turns on, indicating contact of the sensor with the 
liquid surface. A second level reading is taken on the 
dipstick, as in the first measurement, and the two 
readings are averaged. By this method, the level or 
depth of the liquid helium may be measured to an 
accuracy of ±0.25 inch. 
Note: 
Details may be obtained from: 
Technology Utilization Officer 
Langley Research Center 
Langley Station 
Hampton, Virginia 23365 
Reference: B68-10341 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546.
Source: H. H. Becker 
(LA R- 10289) 
-	 Category 01 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person 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 such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000341 2020-03-12T06:17:22+00:00Z


Superconductive thin film makes convenient liquid helium level sensor

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