Single-sensor control system maintains liquid hydrogen at a preselected desired level within a tank, regardless of boiloff. It calibrates output in percentage. Thus, when the fuel is at the desired level, the system output will indicate 100 percent regardless of what percent of tank capacity the fuel has reached

Bergeson, R. L.

Schuck, J. W.

English

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February 1966	 0	 Brief 66-10039 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Control System Maintains Selected Liquid Level 
bJ^
- 
___.... r ----------- Discontinuous Gearing 
R4 I 
Phase
I	 [iotoj, 
• ------Digital 
Sensitive I Encod er 
Amplifier 
And Relay 
A7	 Phase	
Control 
Signal No 1 Counter I 
-
Sensitive 
Amplifier  
And Relay
Display
Ag
Amplifier 
Integrator 
Control 
Signal No. 2 
The problem: To provide a single-sensor control How it's done: A signal obtained from empty adjust-
system, in which liquid hydrogen is controlled to fill a 	 ment potentiometer R  is applied through the tank 
tank to a desired level, regardless of boiloff of the	 unit (liquid level sensor) to an amplifier—motor com-
hydrogen. Conventional techniques employ separate 	 bination. Mechanical linkage from the motor extends 
sensors for each monitored level.	 to R2, R3, R4, counter display, analog-to-digital 
The solution: A single-sensor control system in	 encoder, and discontinuous gearing units. Potentiom-
which the output is calibrated in percentage. Thus,	 eter R5 is adjusted to select the desired tank fill level, 
when the fuel is at a preselected desired level, the	 which may range from 60 to 100 percent of the tank 
system output will indicate 100 percent regardless of	 capacity. A correction signal applied through R2 from 
what percent of tank capacity the fuel has reached.	 R5 combines with the signal from the tank unit, and is 
The output will be the control signal for desired level	 applied as an input to the amplifier—motor combina- 
maintenance.	 tion. The motor will operate until the signal output 
(continued overleaf) 
ImW
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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. 
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from R2 is equal (true level) to the tank unit signal; 
this indicates that the fuel level in the tank has reached 
100 percent of the setting of R5. The counter display 
unit gives a visual percentage output indicative of the 
wiper position of R2. The analog-to-digital encoder, an 
optional circuit item, takes the analog signal provided 
by the gearing and provides a digital output for com-
puter use. Potentiometers R3 and R4, in conjunction 
with R6 and R7, respectively, may be set to desired 
levels to generate control signals from phase sensitive 
amplifier and relay circuits. 
The discontinuous gearing unit operates when the 
R2 wiper is at positions representing above 95 percent 
of its true level. Until R2 reaches 95 percent of its true 
level, the discontinuous gearing is inoperative, keep-
ing the wipers of R8 and R9 at one end of the potenti-
ometer; no control is applied through the summing 
circuit and the electrical-to-pressure converter (E/P 
converter) which allows the valve feeding liquid hydro-
gen to the tank unit to remain open. When R2 reaches 
95 percent of its true value, the discontinuous gearing, 
acting through summing circuits and the E/P con-
verter, starts the closing of the liquid hydrogen valve. 
Potentiometer R9 is the main control over the closing
of the liquid hydrogen valve until R2 has reached ap-
proximately 99.9 percent of its true value (represent-
ing 99.9 percent of a predetermined fill level in the 
tank unit). At 99.9 percent, vernier potentiometer R8 
becomes the controlling component until R2 reaches 
100 percent of its true value. Potentiometer R8 can 
be adjusted for a slight overfill to allow for the natural 
boiling-off process of the liquid hydrogen. 
Note: This gaging system would have value in con-
trolling liquid levels in tanks, such as in the filling of 
commercial tank cars where the fluids frequently boil 
or leak away, or for use in industrial processes where 
the level of fluids must be constant. 
Patent status: Title to this invention has been waived 
under the provisions of the National Aeronautics and 
Space Act (42 U.S.C. 2457 (f)), to Honeywell, In-
corporated, 2600 Ridgway Road, Minneapolis, Minne-
sota, 55413.
Source: Raymond L. Bergeson and

Jack W. Schuck of

Honeywell, Incorporated
under contract to

Marshall Space Flight Center

(M -FS-470) 
Brief 66-10039	 Category 01


Control system maintains selected liquid level

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