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Oct. l, 1946.
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Patented Oct. 1, 1946
2,408,392
UNITED STATES PATENT OFFICE
2,408,392
VIBROIWETER
Donald E. Gillum, Hermosa Beach, and Charles
J. Gallant, Brentwood Heights, Calif., assign
ors to North
American Aviation, Inc., Ingle
wood, Calif., a corporation of Delaware
Application November 29, 1941, Serial No. 421,078
1
5 Claims.
(Cl. 177-311)
2
The .present invention relates generally to elec
trical vibrometers, the recordings of which are
so that the oscillator amplifier translates the var
iation in capacity into electrical impulses of suf
ficient magnitude to operate the galvanometer
lineal, the amplitude of recording being directly
proportional to the amplitude of vibration irre
or other responsive element of a recording in
spective of frequency, and has for its main pur
pose the provision of a displacement measuring CII strument, such as a recording oscillograph.
instrument of this type which is particularly
adapted and suited to the recording of vibra
tions in aircraft and parts thereof, although not
necessarily limited to such use.
In furtherance of the above general purpose,
it is an object of the invention to produce a small,
The pick-up instrument, constituting the pres
ent invention, as hereinafter set forth in greater
detail, may be better understood by reference
to the accompanying drawing, in which the best
10 mode thus far devised for carrying the same
lightweight displacement measuring unit, com
bining high sensitivity, wide frequency range,
into practical effect, is illustrated mechanically
and diagrammatically. In this drawing, which
forms a part of this speciñcation,
Fig. 1 is a vertical sectional View through the
and a highdegree of calibration stability.
pick-up instrument.
vIt may be said to be a further object to pro~
Fig. 2 is a horizontal sectional View there
vide an instrument of this type in the nature
through taken substantially on line 2-2 of Fig. 1.
of a variable capacity pick-up which may be made
Fig. 3 is an enlarged fragmentary view partly
light in weight whereby the Weight of the in
in elevation and partly in section, of one of the
strument itself will have a minimum effect upon 20 condensers, looking substantially along the line
its operation; which will eliminate friction as
3_3 of Fig. 2.
a factor of inefficiency, and which will have a
Fig. 4 is a detail vertical sectional view through
low natural period of oscillation so as to effec
the bearing of one of the rotors, looking sub
tively determine the characteristics of relatively
stantially along line 4-4 of Fig. 2.
low frequency vibrations.
25
Fig. 5 is a detail horizontal sectional view
In providing a vibrometer of variable capaci
through the supporting connection of one of the
tance pick-up type, it is a further object to uti
stators, looking substantially along the line 5-5
lize bodies of rotation in a manner which will
of Fig. 1.
cancel out the effect of torsional vibrations, leav~
Fig. 6 is a view illustrating in diagram the
ing the instrument sensitive to only the lineal 30 electrical
hook-up of the stators and rotors.
components of vibrations being measured.
Referring now to the pick-up as a mechanical
With these and other objects in mind, the in
instrument responsive to vibrations, and shown
vention proposes in a general Way the use of a
in detail in Figs. 1 to 5, a generally fiat mounting
pick-up in which statically balanced members
base is indicated at I 0. This base member is
are opposed to vibration responsive members in
used as a means of securing the instrument or
35
a manner to constitute a variable condenser.
unit to a test member or frame, indicated at II,
This condenser is connected across the terminals
and may, therefore, be made to coincide more or
of an inductance coil, forming a radio frequency
less with the test member or frame as may be
tuned or resonant circuit. It is contemplated in
necessary to properly mount the unit for vibra
practice that such a coil may be suitably con
40 tion with, and in accord with, vibrations of the
nected to a recording instrument such as a re
test frame to be measured.
cording oscillograph, as for example by induc
The base member I0 may be secured to the test
tively connecting the coil to a source of constant
frame Il by the same screws or other fastening
radio frequency, such as an oscillator amplifier,
members I2 utilized to hold, on the base member,
the inductance of the coil and the maximum 45 a shell or cover I3 whose purpose is to protect
capacity of the condenser being such that the
the working parts of the unit from dust and dam
resonant frequency of the pick-up is the same
age. This shell or cover, it will be noted, has a
as the frequency of the oscillator whereby maxi
top opening i4 receiving the upper open end of a
mum energy is transferred from the oscillator
socket I5 in which a plug I6 is disposed with a
to the pick-up when they are in resonance, and 50 bayonet or other secure holding connection, indi»
a minimum when they are detuned or out of
cated at Il, for plugging in such external elec
resonance. If the pick-up is vibrated, causing
trical connections as may be used, for example, to
a. relative movement between the members of
record the vibrations developed by the vibration
the condenser, the resultant change in capacity
responsive means.
changes the tuning of its resonant frequency, 55
Secured to, and upstanding from the base
2,408,392
n,
à
»
4
of the ñns 22 and 23 are disposed Within the
U-shaped stators there will be no change in the
capacitance of the condenser and therefore no
member IS, in spaced apart, slightly offset rela
tion, are a pair of brackets I8 and to relatively
opposite sides of these brackets, and insulated
change in a recording instrument to which the
vibrometer is connected. With such construc
tion, no variation in capacitance of the con
therefrom, are rigidly secured the stationary ele
ments, or stators I9 and 28 of a pair of relatively
opposed variable condensers. The brackets I8
denser :and resultant change in 4a 'recording in
include parallel ‘upright ïposts 2l 'between which'
strument will‘be'h'ad except'in >response to vibra
are pivoted the smaller "ends of >segmental Yiins
22 and 23 constituting the movable elements or
rotors of the condensers.
tory movement in a direction normal to the base
¿~I"l and to the transverse axes of the ñns 22 and
23 kin a direction normal to the base Il. It is
obvious that as thus described, the vibrometer as
The offsetting of the brackets I8 relative to ,
each other alines the stator of one bracket with
the rotor of the other bracket, as plainly seen in
proposed thereinhas many advantages in practi
vvcal use in ’that'the pick-up requires but one, sin
gle conductor shielded, lead and is of small size
Fig. 2, and each ñn is normally 'held inhorizon
tal position with' its larger Íreeendineiîective
and light weight -adaptable for. practical use in
relation to its relatively opposite stator, ‘each ñn
~
many
instances Where in aircraft vibration meas
having at its smaller pivoted end -al depending
uring, a larger, heavier pick-up would be 'unus
angular extension 24 connected by a, _balance
able( In addition to its light weight and com
spring 25 to its respective bracket I8 in ¿order to
seismically support the ?ln whose form is prefer 20 pactness, the pick-up as set forth herein pro
vides a device by means of which the character
ably ksuchas to place Aits centeri'ofl gravity as
l
nearly as possible toitsfree‘end.
»
,
. v
3
listics of relatively low -frequency vibrations may
be readily and accurately determined by reason
of an output proportional to amplitude of vibra
tion independent of frequency. The fact ¿that
alternating current ampliñers'm'ay be used, lin
creases the overall frequency response.
While we have illustrated and described what
,
AIn vorder to eliminate friction, the ¿posts'2l :of
each bracket support >adjustable' pivot bearing
members v2â’ias seen best Vin Figf‘l, having inner
recesses ,cooperating with the conical -ends of a
balance stair >Z'I `to form needle pointbearings
for the ' fin pivots.f TheY stallc >2`I is pressed
we now regard as the kpreferred embodiment rof
through its respective ñn fand-through ydamping
fluid cups 28 at opposite sidesioi the iin. The 30 our invention, the construction is, of course,~subject to modifications Without departing' from the
cups 28present outer-concave faces spaced-from
spirit and scope of «our invention. We, .there
the adjacent innersurfaces of the ¿posts 2| yto
fore, do'not Wish to restrict ourselves tothe par
maintain therein, by surface .tension and capil
ticular form of construction‘illustrated and -de
-larity, a suitable damping fiuid,:indicated at 29,
around the needle point bearings-.7:L
_
Y
ì
.
K
scribed, but desire to ‘availourselves of rallrmodi--
«
ñcations that may `fall within the scope of the
» The manner :of , insulating; eachstator from,
appended'claims.
andlconneeting the same'_to,~“one ofthe posts 2i
Having thus described our invention, whatwe
claim and desire to Asecure by -Letters Patentis:
l. A víbrcmeter comprising a .base .adapted rto
1 The A`two variable 'îcond'ensers 'formed în'zthe 40
be 4placed adjacent a Vibrating ibo'dy, a pair of
manner just set forth, are connected in'fparallel,
variable 4condenser-s connectedin 'parallelmount
as >byjwires 3| `and .132,.respectively Which‘may
ed Ion said base and including 1azpair .of >stators
join thestators. and rotors, across the .terminals
and a pair of rotors, and means for‘seismically
of an inductance .coil .tofthus .fzformiaîradi'oïfre
voi'zits respective` bracket ,IS-_ is _plainly :seen 'in
Figs. 3 andâ,.aconnect'ingbolt appearingatßß;
quency. tuned orresonant- circuit.
.
» ïIt will-be understoodthat.frelativeamotion‘be
tween thezdamped, balanced rotor‘ii'ln's .22, .23 .and
the base, including the stators I9, 28 is.directly
proportional tothe @vibrations offthe member lll
to Which the base .is attached. Therefore, ras
each frespective rotor .andstator >constitutes a
variable îcond'en'ser, lthe vcapacity :of this -con-.
supporting the rotors with‘re’spectV tothe'stators
so that vibrations transmitted tothe ibase will
produce relative movement of therotors the sta
tors and rotors being so _.positionedth'at vibra
tionalforces in a direction perpendicular tothe
:50 plane of «the -base vcause the capacities to in.
denser .varies'in direct proportion :to theam'pli
‘oude-of vibration. :Were ‘a single .condenser yof
this character utilized in .connection lWith ilineal 55
crease or decrease simultaneously While-torsional
vibrations will increasethe capacity of one con
denser when decreasing `the capacity of theother.
2. A vibrometer'comprising a base adapted to
be vplaced adjacent a vibratingfbocly, a pair vof
variable condensers connected in'parallel mount
vibrations occurring 'in va Ysingle v'plane at -:right
ed-on saidbase and including a pair ofstators
angles’to `the length :of ‘.:the >stator;iin,zit would be
and a-pair of rotors, the rotors Abeing >pivoted at
suñicient, `butsince zsuch‘vibrati'ons are seldom
one of their ends and `each one `of the pair :of
in ,practiceiandsince'the'ñn;is a body fof .rota
stators
being in substantial alignment Withxthe
tion ,andis sensitive to :torsional vibration, :the 60
pivot of one :of the rotors, and-means for seismi
two identical condensers iare .usedlín V.the Aopposed
cally supporting the rotors with' respect tothe
manner èp-reviouslyset :forth so as to :cancel the
stators
so that vibrations transmitted .to the base
effect'of torsional vibrations andleave the Vunit
Will produce relative movement of the rotors the
sensitive to onlythe lineal components of 'vibra
65 stators -androtorsbeing so positioned that vibra
tional .iorces-ina ‘direction’ perpendicular to the
. As :clearly illustratedin'Figures 1,12, '.3 and -5,
plane ofthe base 'cause thecapacities toincrease
the-stators -I9 and 28 .are U-shaped and receive
or decrease .simultaneously While torsional vibra
the .larger ends fof -the fins 22 ‘and 23 .between
tions -Will increase the tcapacity :of Aoneacondenser
their free rends,` such- largerendsof th'e flns'ex
tendingsubstantially -completely withinith‘e depth 70 when vdecreasing >the `capacity Vof :the other.
3.~.A vibromete'r comprising a base adapted te
of,A the ‘ U . VWith such .'construc‘tion,v anyvibratory
'be placed adjacent a vibrating body, -a pair of
movement of the base lII `in.ai‘di1‘ection other
variable condensers connectedv in parallel mount
thanzin a plane normal to the .baselvvill be trans
ed .on said base and including i’a pair of lstators
lated intc a sidewise movement .of >theiîn‘s >22
and î23. f-However, inasmuch' as 4theeiïectiveends 75 and 'a'pair of plate-likerotors pivotally mounted
tions.
-
,
2,408,392
5
6
at one of their ends, and means for seismically
While torsional vibrations Will increase the ca
pacity of one condenser when decreasing the ca
pacity of the other.
5. A vibrometer comprising a base adapted to
be placed adjacent a vibrating body, a pair of
variable condensers connected in parallel carried
supporting the rotors with respect to the stators
so that vibrations transmitted to the base Will
produce relative movement of the rotors, the sta
tors and rotors being so positioned that Vibration
al forces in a direction perpendicular to the plane
of the base cause the capacities to increase or
decrease simultaneously While torsional vibra
tions will increase the capacity of one condenser
when decreasing the capacity of the other.
4, A vibrometer comprising a base adapted to
be placed adjacent a vibrating body, a pair of
variable condensers connected in parallel carried
by said base and including a pair of U-shaped
stators mounted on the base with the U extend
by said base and including a pair of U-shaped
stators mounted on the base with the U extend
ing normal to the plane of the base, a pair of
plate-like rotors, each pivotally mounted adja
cent one of its ends and having its opposite free
end extending Within the U of one of the
U-shaped stators and each one of the pair of sta
tors being in substantial alignment with the pivot
of one of the rotors, and means for seismically
supporting the free ends of the rotors in eiîective
relation with respect to the stators so that vib-ra
cent one Aof its ends and having its opposite free
tions transmitted to the base will produce move
end extending Within the U of one of the
ment of the free ends of the rotors relative to the
U-shaped stators, and means for seismically sup 20 stators and resultant change in capacitance of
porting the free ends of the rotors in effective
the condenser, the stators and rotors being so
relation with respect to the stators so that vibra
positioned that vibrational forces in a direction
perpendicular to the plane of the base cause the
tions transmitted to the base Will produce move
capacities to increase or decrease simultaneously
ment of the free ends of the rotors relative to
the stators and resultant change in capacitance 25 While torsional vibrations will increase the ca
pacity of one condenser when decreasing the ca
of the condenser, the stators and rotors being so
pacity of the other.
positioned that vibrational forces in a direction
perpendicular to the plane of the base cause the
DONALD E. GILLUM.
capacities to increase or decrease simultaneously
CHARLES J. GAILANT.
ing ndrmal to the plane of the base, a, pair of
plate-like rotors, each pivotally mounted adja
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