Garwood, D. C.

English

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D. C. GARWOOD 
IONIZATION VACUUM GAUGE 
Filed Feb. 19, 1962 
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- United States Patent Office Feb. 23, 11965 
B 
3,171,081 
IONIZATION VACUUM GAUGE 
Donald C. Garwood, Altadena, Calif., assignor, by mesne 
assignments, to the United States of America as repre- 
sented by the AdminMrator of the Na~onal Aero- 
nautics and Space Admiitration 
Filed Feb. 19,1962, Ser. No. 173,981 
3 C i h .  (Cl. 324-33) 
This invention relates to ionization vacuum gauges and, 
more particularly, to improvements therein. 
A presently favored type of ionization vacuum gauge 
is one which consists of two short concentric cylinders, 
the outer cylinder being connected to a high poteniial 
source and the inner cylinder being connected to a micro- 
ammeter and then to ground. These cylinders are usually 
enclosed in a glass envelope which is evacuated. Any 
electrons which arise, for example, from cosmic-ray ion- 
ization, gas-field emission, photo emission, or other causes 
are attracted to the outer cylinder. A magnetic field is 
provided which has a direction along the axes of the 
cylinders. This magnetic field causes the emitted elec- 
trons to orbit around the inner cylinder, instead of flow- 
ing to the outer cylinder. These electrons collide with 
residual gas, which results in the creation of positive ions. 
The positive ions flow to the inner cylinder, rather than 
orbit around it (because of their larger weight). The 
flow of ions to the inner cylinder is detected as a curent 
flowing to ground on a microammeter, and this indicates 
the degree of vacuum. 
Because many electrons are present between the cylin- 
ders which have a component of velocity along the axial 
direction of the cylinders, they will travel out to the ends 
of the cylinders. To prevent this, many gauges have end 
plates connected to the inner cylinder. These end plates 
are at ground potential and serve to reflect electrons back 
toward the space between the cylinders. 
When an electron happens to collide with the outer 
cylinder, soft X-rays are produced, which may hit the end 
plates. Electrons ejected from the end plates will go into 
orbit around the inner cylinder, and the Iost electrons will 
appear as a curent flowing through the microammeter to 
ground and thus give a false reading of the degree of 
vacuum. A gauge of the type described is mechanically 
weak and difficult to install. The presence of end plates 
requires that the outer cylinder have holes open to the 
vacuum to be measured. The high voltage of the outer 
cylinder results in a need for insulation. Furthermore, a 
typical gauge, of the type described, requires some time 
to begin functioning where a very high vacuum exists, 
since there is little gas to ionize the high vacuum to pro- 
duce ionizing electrons. 
An object of the present invention is to provide an 
improved ionization vacuum gauge which does not pro- 
vide false readings of the degree of vacuum. 
Another object of the present invention is to provide a 
vacuum ionization gauge in which the problem of high 
voltage insulation is considerably simplified. 
Yet another object of the present invention is the provi- 
sion of an ionization vacuum gauge that can be readily 
started even in a very high vacuum. 
Yet another object of the present invention is to pro- 
vide a structurally sound ionization vacuum gauge. 
Still another object of the present invention is the provi- 
sion of an ionization vacuum gauge that can be readily 
mounted to have access to a vacuum desired to be meas- 
ured. 
These and other objects of the invention may be 
achieved in an  arrangement wherein an outer cylinder 
surrounds a centrally disposed electrode or inner cylinder. 
The outer cylinder has its length at least equal to its inner 
diameter or longer. The central cylinder extends sub- 
stantially the length of the outer cylinder. One of the 
end plates usually found in an ionization vacuum gauge 
may be omitted. The omission of one end plate affords 
easier access of the cylinders to the vacuum to be measured 
5 than when two end plates are employed. The electrical 
connections of the cylinders and end plates are such that 
any curent flowing from the end plate as a result of a 
loss of electrons will not be indicated on the microam- 
meter which is employed with the gauge. Furthermore, 
10 the inner cylinder is connected to ground through a mi- 
croammeter instead of to a negative voltage, while the 
outer cylinder is connected to a positive voltage source. 
If the end plate is then connected to a point at a poten- 
tial between the potentials of the inner and outer cylinders, 
15 and yet not in the current path of the meter, then spiwious 
currents resulting from electrons leaving the end plates 
are not measured by the meter, and, furthermore, the 
inner cylinder will receive substantially all of the ion cur- 
rent. In addition, an external switch and potential source 
20 is provided for heating the inner cylinder, whereby it will 
emit electrons and start the gauge working very quickly. 
The novel features that are considered characteristic of 
this invention are set forth with particularity in the ap- 
pended claims. The invention itself, both as to its organ- 
25 ization and method of operation, as well as additional 
objects and advantages thereof, will best be understood 
from the following description when read in connection 
with the accompanying drawings, in which: 
FIGURE 1 is a partial sectional side-elevation view of 
30 the ionization vacuum gauge which is an embodiment of 
FIGURE 2 is a bottom elevation view of the ionization 
In accordance with this invention, an ionization vac- 
35 uum gage is provided which, considering FIGURES 1 
and 2, has a long outer cylinder 1@ which surrounds a 
central electrode 12. The central electrode 12 is cylin- 
drical in form and preferably constitutes a thin high- 
resistance wire. A magnet 14 provides a magnetic field 
*O within the outer cylinder 10 which is oriented along the 
axis of the cylinder. The central electrode 12, or inner 
cylinder, has one end connected to a microammeter 16. 
The other side of the microammeter 16 is connected 
to a high potential source, respectively 18, 20, which is *’ negative with respect to ground. The outer cylinder 10 
is electrically connected to ground. The open end 1OA 
of the outer cylinder is connected to the vacuum to be 
measured. An end plate 22 closes the other end l@B 
5O of the cylinder and serves to prevent loss of vacuum 
through the cylinder. Thus, no auxiliary envelope is re- 
quired, connection of this vacuum gauge to a vacuum 
to be measured being made simply by exposing the open 
end 1OA of the outer cylinder thereto, and by sealing 
55 the outer cylinder to whatever walls contain the vacuum. 
By connecting the inner cylinder to the high negative 
potential, instead of the connection being made between 
the outer cylinder and a source of high positive potential, 
the problem of insulation is considerably simplified, since 
6~ all that need be insulated with this embodiment of the 
invention is the thin inner cylinder or iilament wire, 
whereas heretofore it was necessary to insulatingly sup- 
port the large outer cylinder 10, which presents a much 
more difficult insulation problem. 
It has been indicated that the cylinder 18 and the inner 
cylinder 12 are long. As was pointed out previously, 
the commonly employed ionization vacuum gauges will 
have an outer cylinder having a diameter of about three 
times its length. It has been found that if the length 
70 of the outer cylinder chamber is increased to either equal 
its inner diameter or be larger than its inner diameter, 
electrons with any axial component of velocity will re- 
this invention; and 
vacuum gauge shown in FIGURE 1. 
65 
‘I . .  3,171,081 
3 4 
main within the chamber long enough to obtain suffi- dicating means, one end of said current-indicating means 
cient ion current for convenient operation of the gauge being connected to said central electrode, a source of op- 
with only one end plate, or with none at all. The elimi- erating potential, one end of said source of operating 
nation of one end plate allows one end of the outer cyl- potential being connected to the other end of said current- 
inder to be opened to the vacuum to be measured. Ac- 5 indicating means, the other end of said source of operat- 
cordingly, in accordance with this invention, the length ing potential being connected to said cylinder, and means 
of the outer cylinder is at least equal to its inner di- for applying potential from said source of operating po- 
ameter. The concentric inner cylinder, of course, will tential to said end plate having a value intermediate the 
substantially extend along with the outer cylinder. value of potential existing between said electrode and said 
bodment of the invention. I t  is insulatingly supported 2. An improved ionization vacuum gauge comprising 
from the outer cylinder I0 and helps to insulatingly sup- a conductive hollow cylinder, a conductive end plate 
port the inner cylinder 12. The end plate 22 is connected for said hollow cylinder, means supporting said con- 
between the potential sources 18 and 20 to bypass the ductive end plate insulatingly from said hollow cylinder, 
microammeter, so that any current flowing from the end 15 a central electrode means for insulatingly supporting said 
plate as a result of loss of electrons emitted therefrom central electrode coaxially within said hollow cylinder, 
will not register on the microammeter. If it were de- a first source of potential, a switch, means connecting 
sirable to reverse the polarity of the connection so that said switch and first source of potential in series, means 
the outer cylinder was connected to a high positive volt- connecting said serially connected switch and fist  source 
age source and the inner cylinder connected to ground 20 of potential across opposite ends of said central elec- 
through a microammeter instead of to a negative volt- trode for the purpose of heating said central electrode to 
age, then spurious currents could be eliminated by con- emit electrons for initiating operation of said vacuum 
necting the end plate directly to ground, bypassing the gauge, a second and third source of potential, means con- 
microammeter. The arrangement shown in FIGURE 1, necting one end of said second source of potential to one 
however, is preferable. The potential point to which the 26 end of said third source of potential, means connecting 
end plate is connected is preferably between the poten- said end plate to the junction of said second and third 
tials of the inner cylinder and the outer cylinder. In sources of potential, means connecting the other end 
an embodiment of this invention which was constructed, of said third source of potential to said cylinder, a cur- 
the end plates were connected to a point of the potential rent-measuring device, and means connecting said current- 
source which was one kilovolt above the potential of the 30 measuring device between said central electrode and the 
inner cylinder and over 90% of the ion current flowed to other end of said second source of potential. 
the inner cylinder. 3. In an ionization vacuum gauge of the type having 
In order to enable extremely rapid starting with this a cylindrical chamber within which a central electrode is 
invention, the inner cylinder 12 is preferably made of positioned, one end of said cylindrical chamber being 
a high-resistance wire. This is connected to a source 35 closed off by an insulatingly supported conductive end 
of potential 24 through a switch 26. Accordingly, if a plate, said central electrode being connected to one side 
very high vacuum is to be measured, the switch 26 is of a current measuring device and a potential source 
closed and the high-resistance wire heats up and emits being connected between the other side of said current 
some electrons to start the gauge working quickly. AS measuring device and the wall of said cylindrical cham- 
soon as the gauge begins to operate, the switch 26 is 40 ber, the improvement comprising means connecting said 
opened. The gauge will then continue operating in view end plate to said potential source for establishing said 
of the electrons which have already been produced. end plate at a potential between that of said chamber 
Accordingly, there has been described and shown herein and said current measuring device, whereby spurious 
a novel, useful, and improved vacuum ionization gauge currents flowing from said end plate do not pass 
which is simpler and stronger, and which operates with 45 through said current measuring device. 
substantially no spurious current. 
I claim: 
1. An ionization vacuum gauge comprising a hollow, 
conductive cylinder having a length at least equal to its 
end of said cylinder, means for supporting said end plate 
One end plate 22 need be employed with this em- 10 cylinder. 
References Cited by the Examiner 
UNITED STATES PATENTS 
2,884,550 4/59 Lafferty _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  313-7 inner diameter, a conductive end plate for closing one 50 2,817,030 12/57 Beck -------------- 313-161 x 
insulatingly from said cylinder, a central electrode, means 
for insulatingly supporting said central electrode along 
the axis of said cylinder from said end plate, current-in- 
GEORGE N. WESTBY, 
ARTHUR GAUSS, DAVID J. GALVIN, Examiners. 
Examiner. 


Ionization vacuum gauge Patent

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