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Патент USA US2409074

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Oct. 8, 1946.
F. R_ slAs HAL
Filed March 7, 1945
2 Sheets-Sheet l
__._L. FULL sous
m’” '
‘Frederick R. Sias,
Donald B. Pearson,
Their" Attorney
Oct. 8, 1946. >
F_ R_ 5M5 ETAL
2,409,073 ‘
Filed March ‘7, 1945
2 Sheets-Sheet 2
Frederick R. Sias,
Donald. B. Pearson,
by Wé? M44
Their Attorney.
Patented Oct. 8, 1946
Frederick R. Sias, Lynn?eld Center, and Donald
. Pearson, Marblehead, Mam, assignors to
General Electric Company, a corporation of
New York
Application March "I, 1945, Serial No. 581,494
6 Claims.
Our invention relates to improvements in liquid
fuel measuring apparatus and is suitable for the
remote measuring of the quantity of gasoline in
the tanks of aircraft and indicating such quantity
in the pilot's compartment. Our invention relates
(Cl. 177-351)
outer tube may conveniently be grounded to the
metal tank i. The side wall of tube 4 is per
forated at least at the top and bottom as indi
cated at 5, so that if there is gasoline in the tank,
it will fill the tube 4 to the level of the gasoline in
the tank as represented. By restricting the ex
tent of such perforations, there is a desirable
damping action to the flow of gasoline in and out
of the tube, and hence, a more uniform level
to capacitor type measuring apparatus where the
liquid .being measured is made the dielectric of a
condenser and has a diil'erent dielectric constant
than that of air such that by the displacement
of the liquid fuel by air, the capacitance is 10 when the tank is tippedabout violently. It is
changed and measured in terms of liquid quan
also noted that the condenser is positioned in the
tity. The capacitor type liquid fuel measuring
of the tank so that, ordinarily, tipping of
apparatus idea is not new. Such apparatus is
the tank will have as small e?ect as possible upon
disclosed in British Patent No. 441,576 of 1936, for
example. Our invention pertains to improve 15 the length of tubing which is ?lled with gasoline.
It is evident that the dielectric between the
ments in such apparatus and inparticular to fea
plates constitutes air above the liquid
tures of the measuring circuit which make good '
level and gasoline below the liquid level. In the
accuracy and reliable apparatus of this type prac
case of gasoline it has approximately twice the
ticable for installation and use on aircraft.
The features of our invention which are be
lieved to be novel and patentable will be pointed
out in the claims appended hereto.
For a better
understanding of our invention, reference is made
in the following description to the accompanying
drawings in which Fig. 1 shows a preferred form
of capacitor gauge measuring circuit suitable for
use where a 110-volt source of direct current sup- '
ply is available. Fig. 2 shows modi?cations in the
dielectric constant of air so that as the gasoline
level rises from bottom to top of the tank during
filling, the capacitance of the condenser increases
by a factor of 2. Hence, we have here a variable
condenser, and the means for varying the con
denser is the change in level of the gasoline.
This change in capacitance may be measured in
terms of liquid level or gallons or, more accu
rately, as we will point out, in weight of the liquid
fuel in the tank. Thus there is provided a liquid
level measurement transmitter having no moving
parts, such as ?oat levers, gearing, electrical con
circuit as adapted for use where the direct cur
rent source of supply is of the order of 27 volts.
Figs 3 and 3a are diagrams representing flux rela
tacts, and the like. Also, while the condenser
tions in the instrument of Fig. 2. Fig. 4 illus
plates are exposed directly to the gasoline, there
trates certain advantages of employing the ca
is no danger of sparks such as would ignite the
pacitor type gasoline gauge transmitter where
will explain in connection with Fig.
odd-shaped tanks are encountered. Fig. 5 illus 85 4 that theWe
condenser may be adjustable inde
trates parallel condensers located outside of a ' pendently of changes in dielectric.
tank. which is subject to considerable tipping ac
The condenser structure may be secured se
tion. Figs. 6, 7, and 8 showiforms of condensers
in the tank and, in fact, the outer tube
having a varying capacitance over their length.
Fig. 7a represents a cross section of the structure 40 may serve also as a strengthening center brace
between the top and bottom of the tank and may
‘of Fig. '1. Fig. 9 illustrates how a tank side or
welded, bolted, or threaded thereto. The mag
.baiiie may conveniently be made one of the con
nitude of the capacitance depends upon the area
denser plates. Figs. 10, 11, and 12 are cross sec
tions of adjustable forms of condensers. Fig. 13
of the adjacent condenser plate surfaces, their
represents a tank with condenser arranged to 45 spacing and the dielectric. Hence, the inner plate
may be tubing or a rod, and the outer tube may
compensate for tipping errors.
any desired thickness and outer diameter.
Referring now to Fig. 1, I may represent a gas
Thus the condenser may be made to have what
oline tank ?lled to a level 2. The tank contains
ever mechanical strength and stiffness as are de
a condenser with its plates extending from top
sirable to enable it to withstand bending and
to bottom of the tank. This condenser may take 50 other forces to which it may be subjected with
a variety of forms as will hereinafter be explained.
out restricting the choice of condenser value.
In Fig. 1 the plates of the condenserare repre
The variable capacitance above described is
sented as a central rod or tube 3 extending
connected in the input of a. vacuum tube oscil
through a tube 4. These plates are insulated
lator having tuned grid and plate circuits induc
from each other and are made of metal. The M tively coupled together. The ungrounded plate
I of the measuring condenser is connected to the
grid 0! the vacuum tube 6, and the grounded
plate 4 is connected to the cathode of tube 8. In
parallel with the measuring condenser is a coil
1 cooperating with a coil 2 to provide inductive
coupling between the plate and grid circuits. This
coupling is preferably initially adjustable as indi
cated by movement of the coils relative to each
The indicator has three separate windings; one
winding l3 supplied from the oscillator is in the
same axis as a winding i1 connected across the
direct current supply through an adjustable cali
brating resistor it. The windings l3 and I‘! are
connected in bucking relation.
The reason for
this is that when the tank I is empty, the direct
current from the plate circuit of the tube is not
zero. By the use of the bucking winding ll, the
other. In the grid circuit is a grid leak compris
ing a resistance 0 in parallel with a condenser 10 empty tank condition current in winding II can
be bucked out and a longer indicator. scale ob
ll. In addition to its grid leak function. the re
tained. The third winding l9 also connected
sistance 2 is designed with just the proper tem
across the direct current supply through a call
perature coe?icient of resistance to compensate
brating resistor 20 has its flux axis 90 degrees
the circuit for temperature changes as will be
explained below. In the cathode circuit are a 15 from the axis of windings l3 and H and provides
the controlling torque of the instrument in much
variable resistance ii and an inductance l2. The
the same way as a control spring does for a
variable resistance Ii is adjustable for the pur
D’Arsonvai instrument. The instrument thus has
poses of full scale adjustment. Adjustment of
no control spring. The armature consists of a
this cathode resistor changes the grid bias of the
lightweight polarized magnet 2i. The armature
tube in proportion to the cathode current and
may be bar-shaped or may comprise a cylindrical
permits a full scale measurement current adjust
magnet polarized across a diameter. The pivoted
ment that does not appreciably affect the current
armature carries a pointer 22 cooperating with
in the measurement circuit at the zero point, as
a stationary scale 23. The circle 2| surrounding
the resistor has little eilect when the current
the armature represents a, damping conductor.
through the tube is low. The inductance i2 in
structurally this instrument is quite similar to
the cathode circuit serves as a stabilizer and
that shown and described in United States Patent
makes the relation between the measurement ca
No. 2,354,555, July 25, 1944.
pacitance value and plate circuit output more
By adjusting the resistor I! in series with the
nearly linear. It also assists in making the full
bucking winding H, the midpoint of the scale
scale adjustment independent of zero adjustment
may be made to correspond to an armature posi
The output or plate circuit of the tube contains
tion in line with the axis of winding l9. The
the coils ll of the direct current receiving instru
resistance 20 in series with the winding as may
ment, the inductance coil 0, and the 110-volt
then be adjusted to expand or contract the scale.
direct current supply. The plate circuit is tuned
by the use or condensers II and it connected 3 Increasing the torque produced by winding is
decreases the scale length. Thus the indicator
across the inductance coil 8 through the con
is provided with a center scale adjustment and
denser lt. The condenser I5 is adjustable and
a scale length adjustment. A scale length of
is used to change the natural frequency of oscil
approximately 110 degrees is feasible. The in
lation of the plate circuit for~ zero scale adjust
ment. Zero and full scale adjustments are desira so strument as thus designed and connected is
ble in case it becomes necessary to change the
tube at I. It is seen that both the input and
output circuits of the oscillator tube are tuned
and that these circuits are coupled together not
largely compensated for voltage changes.
chances in supply voltage.
value by selecting a resistor 9 in the grid leak of
What little voltage error remains is greatest
at full scale and may be further reduced by the
use of a pull-off magnet which opposes the voltage
only by the intercapacity eilects of the tube elec 45 error and has its greatest torque in the full scale
position. Thus at 23' we have shown a small
trodes but also by the inductance coils ‘I and 8.
permanent magnet suitably fixed to some sta
After calibration the natural frequency of oscilla
tionary part of the instrument and positioned to
tion of the plate circuit remains fixed and the
cooperate with the permanent magnet armature
natural frequency of oscillation of the grid circuit
varies with the capacitance oir the measurement so 2| to rotate the latter to a position where the
pointer 22 is of!’ scale in case the power supply to
condenser. Since both circuits are coupled, they
the instrument fails, thus preventing a false indi
oscillate at a resultant intermediate frequency
cation and giving warning of such failure. The
which varies with the amount of gasoline or other
pull-oi! magnet 01' course has some small torque
dielectric ?uid being measured. Assuming a con
stant voltage supply. the direct current fed to 55 effect on the armature when the instrument is
energized, and this torque effect has greatest con
instrument coils it changes with frequency, and
trol when the instrument voltage is low and when
hence, can be a measure of the fuel in tank I.
the pointer is near the up-scale end of its deflec
A high degree of stability and low distributed
capacity is desirable with respect to the grid and
tion range. Hence, the pull-off magnet in addi
plate circuit elements. Relatively adjustable 50 tion to its usual function is used to still further
reduce the voltage error of the instrument. The
parts should be so designed and constructed as
not to change their adjustment when subjected
instrument as thus constructed and used has a
voltage error of less than 1% for supply voltage
to vibration and temperature and humidity varia
tions. The condensers l0 and it are preferably
variations of 20%.
silver plated. mica condensers so as to have high 65 It was found that when reading mass of fuel
without temperature compensation and when
stability. Shielding of circuits should be used
using low temperature coefiicient resistors, the
where necessary.
system had a positive temperature error; that is,
As mentioned above. the resultant frequency
the receiver instrument reading was high at high
of oscillation changes with the fuel level. This
results in a change of grid current which is ac 70 temperatures and low at low temperatures. This
companied by a change in D.-C. plate current.
is an over-all temperature error and is probably
The plate current is used to operate a ratio type
the resultant of a plurality of temperature errors
direct current instrument. A ratio type instru
in various parts of the system. It was further
ment is desirable to minimize errors due to
found that this could be reduced to a negligible
the oscillator tube which had the proper tem-~
perature coe?icient of resistance, which was not
necessarily the same for different installations,
tubes, etc.
If the resistor at 0 is all copper, the system will
generally have a temperature error opposite to
that mentioned above. We have found that the
Fig. 2 shows the capacitor type gasoline gauge
circuit adapted for use on av 24-volt direct current
source of supply 20. Parts similar to those of Fig.
1 are designated by like reference characters. In
this case we ?nd it desirable to employ a double
triode 21 as the vacuum tube unit of the oscillator.
The two plates of the tube are connected in
parallel to one side of inductance coil 8. Temper
ature compensating grid leak resistors of the
temperature coeiilcient of resistance of the re
sistance at 9 should be reduced toward a zero
value, and that the desired results can be arrived 10 same type as used in Fig. 1 are provided in the
at by using a resistor partially of copper and
arid circuits, and the grid circuits are connected
partially of a material having a zero or negligible
in parallel beyond the grid leaks to the un
temperature coe?lcient connected in series, and
adjusting the relative values of each until com
grounded plate 3 of the variable measurement
condenser and to one side of inductance coil 1.
pensation for the average conditions encountered 15 Separate grid leak resistors of equal value pro
is obtained. In general, the temperature coei’?
duce better operation than does a single grid leak
cient to be used here was found to be nearer zero
for both grids. The resistances used in these
than that of copper but that it varied somewhat
grid leaks may vary over a considerable range.
with different systems.
A resistance value of 4000 ohms is very satisfac
Without intending to con?ne our invention to 20 tory. The zero scale measurement current ad
any particular values of circuit constants em
justment is the same as in Fig. 1 by means of the
ployed, it'may be ‘stated that the following may
condenser II.
be employed together to give satisfactory results.
In Fig. 2 the cathodes are connected in series
Use a variable measurement condenser in the
across the source of supply 26 and it is not
tank I having a capacitance of 150 m. m. f. with 25 easily possible'with this type of tube to provide
tank empty and 300 m. m. f. with tank full.
full load adjustment by means of a cathode re
Condenser l0 _____ __> ___________ __m. m. f.-- 400
sistor, as this would change the cathode ?lament
voltage and temperature. Provision is made as
Condenser ll __________________ __msm. f.__ 250
by an adjustable resistance 29 in shunt to one
Condenser l5 _______________ __m. m. i’.-- 4 to 30
Condenser I6 _____________________ __m. i’.__ .01 30 ?lament for obtaining a proper balance between
Resistance 9 __________________ __ohms__ 14,500
the two cathode heating currents, and the heater
Coil ‘I ___________________________ __turns__ 200
Col] 8 ____________________________ __do____ 200
current of both may be adjusted by a variable
resistance 30 in series. The series reactance at
3| in conjunction with condenser 30 provides ?l
Coupling spacing between coils ‘I and 8 with
out iron core __________________ __inches__ 0.2 85 tering action, and at 32 we provide an iron ?la
Coil I2____I _______________ __microhenrys__ 200
Frequency range-—240 kilocycles tank full to
280' kilocycles tank empty.
In calibrating the apparatus, the zero adjust
ment with condenser l5 should be made ?rst.
Thus with the tank empty, adjust~condenser ii
ment ballast lamp in the cathode heater circuit
to compensate for variations in the voltage of
the supply source. This is important where the
voltage of the source 26 varies, since without it
40 the apparatus has an appreciable voltage error.
With the lamp at 32 the voltage source may vary
from 422.5 to 29.5, with a. practically constant
cathode ?lament voltage and operation within
Now with the tank full, adjust ll until the pointer
acceptable voltage error limits over the entire
22 reads at the full scale point of the scale. The 45 load range.
reason for this order of procedure is because the
Full scale measurement current adjustment is
full scale measurement current adjustment with
provided for by an adjustable resistor 33 in the
resistance ll does not affect the zero scale read
plate circuit of the electronic oscillator leading
ing, whereas this zero scale adjustment does in
to the measuring instrument. While in Fig. 1
?uence the full scale reading‘. These adjust GI the‘full scale current adjustment resistor ll
ments should be made in conjunction with the
might be placed at any point in the tube instru
scale distribution adjustments with resistances l8
circuit, in Fig. 2 it may not readily be placed
and 20.
between the cathode and source of supply, be
While the apparatus may be calibrated in gal
cause then it would in?uence the heating cur
lons or inches of fuel in the tank, there is some _- rent of the cathode ?laments. An inductance l2
advantage in calibration in terms of weight of
may be desirable to improve stability. Also, in
fuel because essentially that is what is measured
the plate circuit, Fig. 2, is a ?ltering connection
and the calibration will not change appreciably
comprising an inductance 34 and a condenser 35
with different grades of gasoline or fuel in the
which amists in screening the alternating cur
tank. It was found that the dielectric constant 60
rent of the oscillator from the instrument circuit.
of different grades of gasoline is substantially
The instrument used is the same as in Fig. 1,
proportional to the gasoline density. Hence, if
although a somewhat different arrangement for
calibrated in pounds or mass of fuel, changes in
adjusting the length of scale distribution is pro
the grade of gasoline used and changes in the
vided. In Fig. 2 the potentiometer 36 adjusts the
temperature of the gasoline with corresponding
relative values of bucking ?eld current in wind
changes in density will have little effect upon the
ing l1 and the cross ?eld current in winding I9,
calibration and, in general, such calibration will
while the potentiometer 31 is in series with both
be closer to the actual fuel value of the gasoline
of these ?elds.
used than if made on a volume basis.
In Fig. 3 ‘let the vector In represent the mag
In order to minimize radio interference, it is 70 nitude and direction of the ?eld of winding ill
desirable to segregate the oscillator circuit by a
of such polarity as to tend to pull the N pole
suitable ?lter or ?lters which will substantially
of the polarized rotor 2| in a corresponding di
to cause pointer 22 to read zero on the scale.
prevent undesirable frequency pulsations from
passing in either direction therethrough. Such
a ?lter is represented at 25 in Fig. l.
rection. Then vector In correspondingly repre
sents the bucking ?eld of ‘winding l1 and I1: the
75 ?eld of measurement winding l3. The result
ant o! the opposed ?elds I11 and In is their dif
ference, or I17——Ils, and the resultant of all of
the fields acting on the armature is R. This gen
erally represents the conditions when the meas
urement current In is low and the pointer 22 is
near the zero or low end of the scale.
It will now be evident that under such condi
from the vertical in proportion to the increase in
tank area from point to point. At the smallest
cross-sectional area with the lateral dimension
II, which may be referred to as the unit’ area.
the tubular condenser may be vertical. Where
the area is doubled at the dimension 8|. the slope
of the condenser is then made such that it has
tions when In is greater than 11:. moving the
double the length in rising a corresponding dis
slider of potentiometer II to the right will de
tance. Through the lower section having the
crease In and increase 111. and Iva-In. and move
dimension 20 and 4/3 the unit area, the con
the pointer to a lower point oi’ the scale. Mov
denser is sloped to have a length of 4/3 of that
ing the slider of potentiometer ll upward will
through the unit area section.
increase both In and In, and also 111-113, since
Through the upper section which has a uni
In stays constant. While this will increase B.
tormly increasing area from top to bottom with
it will have a negligible e?ect on its vector direc 15 the top dimension II and the bottom dimension
tion and the position of the pointer 22. On the
II. the tubular condenser is curved and has an
other hand. when In is large with respect to
inclination varying from the vertical at the top
In corresponding to the conditions represented
to that corresponding to the double unit area
in Fig. so. when the pointer 22 is near the upper
at the bottom 0! this tank section, such that
end of the scale. moving slider 0! ii to the right 20 its length per unit of rise is in the same pro
decreases In-In and 11s. and ii the Proportions
portion to the cross-sectional area of the tank
are properly selected, will have a negligible e?ect
at all points. It is further noted that the con
on the direction of R, and the pointer position.
denser is positioned centrally oi the tank so
Moving slider of II upward will increase In and
that if the tank tips, the level of the liquid being
measured in the condenser will closely approxi
In and decrease Iii-‘I1’! for the conditions repre
mate that corresponding to a level tank condi
sented in Fig. 3a, which will ,move the pointer
22 to a lower point on the scale. Thus potenti
tion. The tubular condenser will of course have
ometer I! may be used for adjusting the zero
openings to the tank at least at top and bottom,
end of the scale with negligible effect upon the
and will be suitably braced in place and be
upper scale distribution. and potentiometer Il 80 tween its insulated plates to remain in accurate
working condition.
may be used for adjusting the full end of the
scale with negligible effect on the down-scale
In Fig. 13. we have represented a tank with
any desired shape of cross section, here repre
This type of zero and full scale adjustment
sented as circular, having a baille plate I!
7 may of course be used in Fig. 1 and is the meter 35 through its center which will be metallic and
able arrangement in this respect. The other
secured to the tank wall. Positioned closely
resistances in the circuits of windings I1 and
thereto but insulated from the tank and balls,
II of Fig. 2 are voltage dropping resistors and
is a metallic plate 43. Forty-two (l2) and 43
may or may not be needed. In case the current
form the plates of the tank condenser and corre
through any of the windings is too large in pro 40 spond to plates 4 and 3 of Fig. 1. This arrange
portion to the current through other windings of
ment will correctly measure the liquid in the
the instrument. the excessive current may of
tank for reasonable angles of tilt in any direction
from the position shown.
course be shunted by a suitable resistor.
In any case where it is di?icult or undesirable
Figs. 6, 7. and 8 show di?erent forms of tubu
lar condensers having a varying capacity over
for any reason to mount the measurement con
denser or condensers within the tank. it or they
their lengths. In each case the capacity per
may be mounted outside as represented in Fig. 5.
unit length increases from top to bottom; in Pig.
6 substantially uniformly; in Fig. 8 abruptly in
Here a pair of tubular condensers are mounted at
opposite ends or a tank at the centers thereof
a step; and in Fig. 'l in a gradual step. The
and connected thereto by conduits at top and 60 capacitance increases as the dimension between
bottom so that any liquid in the adjacent end
condenser plates decreases. It is‘ apparent that
of the tank will flow into the condensers at the
with the form of condenser 01 Fig. 7 the outer
same level. I! the two condensers are connected
pipe plate can be ?attened as indicated in Fig. ‘la
in parallel in the input circuit of the oscillator,
to vary the capacitance as desired within limits
the parallel capacitance will correspond to the
after the condenser is installed.
amount of ?uid in the tank even though the
In Fig. 9 we have represented cross-sectional
tank tips as represented. or at right angles to
views of condenser plates Ill and N where II;
that illustrated.
is a piece of angle metal and ‘I one corner oi’
In Fig. 4 we have represented an odd-shaped
the tank or a baille in the tank. At II and ll
tank in cross section. To‘ simplify the illustra-—
plates are represented, one being a baille
tion. the tank is assumed to have a unilorm 60 and a wall of the tank.
dimension in the direction perpendicular to the
Figs. 10 and 11 represent forms or condensers
plane of the drawings and to have four equal
which may be varied as a whole or from end to
height sections of diilerent lateral dimensions
end by changes in the separation of the plates.
or shapes in the plane of the drawings. such rela
Fig. 12 represents a variable condenser compris
tive latter dimensions being marked thereon. A
ing two slit tubular portions one within the other.
tubular condenser l of uniform cross-sectional
The condenser as a whole can be accurately ad
dimensions may be mounted in the tank from top
justed by turning one tubular part on its axis.
to bottom, as represented, and give a capacitance
while the condenser may be varied irom end to
variation which is linearly proportional to the 70 end by an eccentricity adjustment. It is under
amount 0! ?uid in the tank in spite of the fact
stood that in Figs. 6 to 13, inclusive, the dielectric
that the dimensions and cross-sectional capacity
used is a combination oi’ liquid to be measured
of the tank diiler materially from top to bottom.
and air, as explained in connection with Fig. 1.
This is accomplished by simply changing the
It will be observed that with a measurement
scope or inclination oi the tubular condenser 75 condenser like that shown in Fig. 1 or 4, for
example, the outer tube of the condenser is in
put circuit so as to respond to variations in the
effect a miniature tank as well as a condenser
plate, so that ii’ such condenser were included
as a part of a pipe line at any convenient point,
measurement condenser with minimum disturb
ance caused by variations in the voltage oi said
source oi swim a grid leak for said vacuum tube
one could tell by observing the measuring instru—
ment whether the pipe line contained liquid or
containing a resistance having a temperature co
emcient of resistance selected to compensate tor
the over-all temperature errors of said measur
The apparatus can also be used as a pressure
ing system, inductance included in the cathode
indicator by the simple expedient oi’ iorcinga
connection of said tube for stabilizing the opera
dielectric liquid up in a tubular condenser struc 10 tion of said system, and ?ltering means for seg
ture in respect to pressure instead of liquid level
regating the oscillation and measuring instru
and calibrating the measuring instrument accord
ment circuits;
4. An oscillation type measuring system com
What we claim as new and desire to secure by
prising a vacuum tube having cathode, control
Letters Patent of the United States is:
grid and plate electrodes, a variable measurement
1. An oscillation circuit measuring system com
condenser connected in a tuned input circuit be
prising a vacuum tube having cathode, control
tween the cathode and grid, an output circuit
grid and plate electrodes, a tuned input circuit
containing a direct current source of supply con
connected between the cathode and grid contain
nected between the cathode and plate, means for
ing a variable measurement condenser, a tuned
inductively coupling said input and output cir
output circuit including a direct current source of
cuits, a ratio type measuring instrument having
supply connected between the cathode and plate,
bucking windings in one axis, one winding being
said tuned circuits including a coil connected
supplied from said source and the other from said
across the input circuit and a coil connected in
output circuit, a winding in an axis at right
the output circuit for coupling said circuits, a
angles to the bucking windings also supplied from
measuring instrument responsive to changes in
said source, said instrument responding to
current in the output circuit caused by variations
changes in the current in the output circuit
of the measurement condenser in the input cir
caused by changes in the capacitance of said
cuit, variable resistance means in the output cir
measurement condenser, means for tuning the
cuit for obtaining full scale instrument adjust 30 output circuit for zero scale adjustment of said
ment, variable capacitance connected across the
instrument, resistance in the output circuit for
coil in the output circuit for varying the tuning
full scale adjustment oi said instrument, and
of such circuit and obtaining zero scale instru
means for varying the current in both or the
ment adjustment, and a grid leak in the grid con- ,
measuring instrument windings which are sup
nection oi said vacuum tube including resistance
plied irom said source, relative to each other and
having a temperature coefficient of resistance se
relative to the current in the winding supplied
irom the output circuit.
5. An oscillation type measuring system com
prising a vacuum tube having double cathode,
lected to compensate said measuring system for
temperature errors.
2. An oscillation type measuring system com
prising a vacuum tube having cathode, control 40 control grid and plate electrodes, an input circuit
grid and plate electrodes, a tuned input circuit
having parallel connections to the cathodes and
connected between the cathode and grid and in
grids, said input circuit containing a variable
cluding a variable measurement condenser ior de
measurement condenser which controls the tun
termining the tuning of the input circuit, a tuned
ing oi’ such input circuit, an output circuit con
output circuit containing a source of direct cur 45 taining a direct current source of supply having
rent supply connected between the cathode and
parallel connections to the cathodes and plates
plate, said tuned circuits including a coil connected
said direct current source of supply being con
across the input circuit and a coil connected in the
nected in series between said cathodes, a ballast
output circuit for coupling said circuits, a ratio
lamp in said series connection, means for induc
type measuring instrument having a winding
energized from said source and a winding ener
gized from said output circuit and responding to
variations in the capacitance of the measure
ment condenser, variable resistance means in the
output circuit for obtaining full scale instrument
tively coupling said input and output circuits, a
ratio type direct current measuring instrument
having bucking windings in one axis and a third
winding in a quadrature axis serving the purpose
of a zero return spring, one of said bucking wind
ings being supplied from said output circuit and
adjustment, variable capacitance connected 55 the other two windings from said source of sup
across the coil in the output circuit for varying
ply, said instrument being responsive to the cur
the tuning of the output circuit and obtaining
rent in said output circuit in response to varia
zero scale instrument adjustment, ?ltering means
segregating the measuring instrument and oscil
tions in tuning of the input circuit, a variable
resistance in the output circuit for full scale
lator circuits and inductance in the cathode con
instrument adjustment, adjustable capacitance
nection of said tube for obtaining stable opera
for tuning the output circuit to obtain zero scale
tion of said measuring system.
instrument adjustment, a potentiometer connec
3. All oscillation type measuring system com
tion between the source of supply and the two in
prising a vacuum tube having cathode, control 65 strument windings supplied therefrom whereby
grid and plate electrodes, an input circuit be
the relative magnitudes of the currents in these
tween cathode and grid including a, variable
windings may be adjusted, and an adjustable
measurement condenser by means of which said
resistance in series with both of the last-men
circuit is tuned, an output circuit including a di
tioned windings whereby their currents may be
rect current source of supply connected between 70 varied relative to the current in the winding
the cathode and plate, an inductive coupling be
supplied from the output circuit.
tween the input and output circuits, means for
6. An oscillation circuit measuring system com
tuning the output circuit, a ratio type of meas
prising vacuum tube means having cathode, con
uring instrument having a winding supplied from
trol grid, and plate electrodes, a tuned input cir
said source and a winding supplied from said out 75 cuit connected between a cathode and a grid of
said vacuum tube means and containing a vari
scale instrument adjustment, variable capaci
able measurement condenser, a tuned output cir
cuit including a direct current source of supply
connected between a cathode and a plate of said
vacuum tube means. said tuned circuits includ
ing a coil connected across said input circuit and
a coil connected in said output circuit for coupling
said circuits, a measuring instrument responsive
tance connected across the coil in said output
circuit for varying the tuning of such circuit and
obtaining zero scale instrument adjustment, and
a grid leak in the grid electrode connection of
said input circuit including a resistance havin:
a temperature coemcient oi’ resistance selected to
minimize temperature errors in said measuring
to chances in ‘ current in said output circuit
caused by variations 0! the measurement con 10
denser in said input circuit. variable resistance
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