Electronic circuit, based on the principle of increased thermistor resistance corresponding to decreases in temperature provides an automatic level control for liquid nitrogen cold traps. The electronically controlled apparatus is practically service-free, requiring only occasional reliability checks

Turvy, R. R.

English

NASA Technical Reports Server

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March 1968
	 Brief 68-10061 
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. 
Electronic Circuit Provides Automatic Level Control for Liquid Nitrogen Traps 
The problem: 
To provide an automatic level control for liquid 
nitrogen cold traps. These traps are used with mass 
spectrometers, leak detectors, and other high-vacuum 
devices requiring traps to promote greater efficiency 
in diffusion pump operation. In the past, the liquid 
nitrogen levels have been mechanically controlled by 
a glass tube partially filled with mercury and methane.
Although such systems operate satisfactorily at first,
they require frequent cleaning and refilling. 
The solution: 
An electronic control of the liquid nitrogen levels, 
based on the principle of increased thermistor resistance 
corresponding to decreases in temperature. The elec- 
tronically controlled apparatus is practically service- 
free, requiring only occasional reliability checks. It 
-
	 ti ll
	 -	 -	
- ( continued overleafl 
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=19680000061 2020-03-12T05:44:04+00:00Z
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also eliminates the time-consuming and hazardous 
handling of glassware and liquid mercury. 
How it's done: 
The trap is filled by pressurizing the Dewar using 
ambient heating. The solenoid valve is in its normally 
closed position, so that the pressure forces the liquid 
nitrogen through the delivery tube. As the trap fills, 
the thermistor (THi), which is located at the desired 
trap level, is chilled by the liquid nitrogen. The 
thermistor resistance increases rapidly as it cools, 
causing the base of NPN transistor Qi to become 
more positive. When the base of Qi reaches a prede-
termined potential, the transistor conducts a current 
which energizes relay Ki, closing sw'itch S2. The 
resulting current through relay K2 activates the 
solenoid valve which opens the Dewar ventline, stop-
ping the pumping action at the desired trap level.
Notes: 
1. This device should be useful in the chemical 
process industries where constant liquid levels must 
be maintained aI low temperatures such as in 
nitration mixtures, standard low-temperature 
baths, and refrigerants. 
2. This invention may be of interest to manufactur-
ers of cryogenic equipment. 
3. Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
John F. Kennedy Space Center 
Kennedy Space Center, Florida 32899 
Reference: B68-10061 
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: Roscoe R. Turvy 
(KSC-10127) 
CONTROL CIRCUIT
Category 01 
Brief 68-10061


Electronic circuit provides automatic level control for liquid nitrogen traps

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