Device compensates for temperature and acceleration effects on a fluid-floated mass in a sealed container of a high performance angular or acceleration sensing instrument. It is used in precision instruments for regulation of gases or liquids in a moving body

Hughes, L. F.

English

NASA Technical Reports Server

August 1969	 Brief 68-1059 
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. 
Acceleration Insensitive Fluid Expansion Compensator 
Sealed HoL 
Bellows
ensity of Fluid 
ows Attached 
-lousing 
s Attached To 
DWS =
2 
luid 
= Acceleration 4 
To achieve high performance devels in floated-
angular and acceleration-sensitive instruments, the 
floated member must be free to rotate about the out-
put axis with minimum friction. The floatation plus 
magnetic suspension provide a friction-free rotational 
axis for the floated member. Float motions parallel 
or perpendicular to the output axis will, due to extreme 
rotational sensitivity of the float, produce error rota-
tions about the output axis. 
A device has been reduced to prototype stage that 
compensates for temperature and acceleration effects 
on a fluid-floated mass in a sealed container. It com-
pensates for the action of these forces on the floated 
member of a high performance angular or acceleration 
sensing instrument. 
An essentially incompressible fluid with a cubical 
expansion greater than the sealed housing containing
it, will at some increased temperature create a pres-
sure sufficient to rupture the container. However, 
fluid pressure can be maintained below the rupture 
strength of the container by a volume compensation 
capsule. 
The volume compensation capsules, sealed bellows, 
used in present-day sensing instruments are required 
to have a volume compensation-to-pressure relation-
ship that is sufficient to maintain a specified pressure 
level over a known temperature range. The bellows 
are mounted in holes about the floated member of the 
instrument. As the fluid expands with increasing 
temperature, the bellows contract and the fluid pres-
sure remains essentially constant within predetermined 
limits. 
In a hole without a bellows, expanding fluid must 
flow to equalize the pressure. The floated member has 
Continued toe rind 
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.
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a small clearance with the walls of its container (a few 
thousands of an inch), and is a restriction to the fluid 
flow. Because of the fluid flow restriction, the pressure 
in the hole will rise and act on the surface of the float, 
resulting in motion of the floated member. Tempera-
ture changes cannot cause float motion if bellows are 
mounted in all the holes surrounding the periphery of 
the floated member since the fluid pressure forces are 
then held in equilibrium. 
However, bellows mounted about the periphery of 
the floated member, in particular two bellows mounted 
on opposite sides of the float, cannot compensate for 
acceleration-induced float motion. With this configura-
tion, a pressure gradient is created by the fluid head 
that accompanies a change in acceleration and will ex-
pand one bellows while contracting the other. The 
differential behavior of the bellows will result in a 
motion of the floated member. 
In summary, one or more bellows mounted along 
one side of.the fluid container will compensate, within 
certain limits, for float motions induced by accelera-
tion changes. Bellows mounted on opposite sides of the 
float will compensate for float motions induced by 
temperature changes. However, neither configuration 
will compensate for both sources.of float motion. 
The object of the device described here is to elimi-
nate float motion induced, by either temperature or 
acceleration changes. Having the dimensions of the 
float, the container, and the constants for the bellows, 
calculations can be performed to determine the added 
force placed on the bellows by a fluid head ehange
caused by a change in acceleration. Knowing the force 
added by the fluid head, a mass can be determined 
that will produce the same force on the bellows for any 
acceleration. This calculated mass can be fastened to 
one end of the bellows and the other end of the bellows 
fastened to the container. The bellows end fastened to 
the container is the one towards the center of the float. 
With a change in acceleration, the force acting on 
the bellows changes due to the fluid head in the usual 
manner, but the mass fastened to the end of the bel-
lows applies an equal and opposite force; therefore, 
there is no motion of the bellows. 
If every hole distributed about the float has a bel-
lows with an attached mass as above, the float will not 
move due to acceleration or temperature changes. 
Notes: 
I. This design could find use in precision instruments 
for the regulation of gases or liquids in moving 
bodies. 
2. No further documentation is available. Inquiries 
may be directed to: 
Technology Utilization Officer 
Electronics Research Center 
575 Technology Square 
Cambridge, Massachusetts 02139 
Reference: B68-10559 
Source: Leo F. Hughes of
Massachusetts Institute of Technology
under contract to
Electronics Research Center
(ERC-10 152)
. 
Brief 68-10559	 .	 Category 01


Acceleration insensitive fluid expansion compensator

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