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Патент USA US2407141

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Sept. 3, 1946.
‘c. F. ‘coAKE
‘ 2,467341
ELECTRIC MICROGAUGE SYSTEM
Filed Feb. 15, 1945
3 Sheets-Sheet 1
98y
mJ
INVENTOR
(‘H/M255 ?fe/IKE
BY
'7
,
/
I
,
.
T'TORNEY
.
Sept. 3, 1946.
c. F. COAKE
I
v
, 2,407,141
-ELECTRIC MICROGAUGE SYSTEM
Filed Feb.‘ 15, 1945
'
3 Sheets-Sheet 2
ATTORNEY
Patented Sept. 3, 1946
UNITED
2,407,141
STATES I PATENT ' OFFICE
2,407,141
ELECTRIC MICROGAUGE SYSTEM
Charles F. Coake, Indianapolis‘, Ind., assignor to
Sean Corporation, New Augusta, 'Ind., a cor
poration of Indiana
Application February 15, 1945, Serial No. 578,074
10 Claims. (Cl; 177--351)
l
with the quantity to be measured, and more par
7 ticularly to a novel and improved system for 5
actuating an instrument in response to such
changes in impedance.
2
- i
This invention relates to electric microgauges
of the type including a variable impedance device
the impedance of which is varied in accordance
,
This application is a continuation in part of
my co-pending application Ser. No. 548,281, ?led
passing through the two recti?ers. If a more
sensitive response is desired the outputs of the
recti?ers may be fed to ampli?ers and the in
dicator may be connected to the output circuits of
the ampli?ers.
‘
I
Although the novel features which are believed
to be' characteristic of this invention are pointed
out more fully in the claims, the invention will
be better understood by referring to the follow
Aug. 5, 1945, for Micro-limit indicating system.
ing description, taken in connection with the ac
An object of the invention is to provide a sys
tem of the above type having 3‘ novel and im
companying drawings in which certain speci?c
embodiments thereof have been set forth for
purposes of illustration.
In the drawings,
Fig. 1 is a schematic diagram of a microgauge
proved operating characteristics.
. Another object is to provide a system of the
‘above type which is extremely sensitive to minor
changes in impedance of the variable ‘impedance
device.
Various other objects and advantages will be
circuit embodying the‘present invention;
, Fig. 2 is a schematic diagram of a similar cir
cuit illustrating an embodiment of the invention
apparent as the nature, of the invention is more
in which the ampli?er is omitted.
fully disclosed.
20 ‘Fig. 3 is a schematic diagram of a similar cir
In accordance with one embodiment of the
cuit illustrating a modi?ed form of bridge; and
invention a pair of variable impedance devices
Fig. ‘4 is a schematic diagram of a bridge hav
are connected to constitute two adjacent legs of
ing variable capacity legs.
a bridge circuit, the other two legs of which con
‘ Referring to Fig. 1, the bridge is shown as
stitute?xed impedances. An alternating volt
comprising a pair of variable impedance coils l0
age is applied across one diagonal of the bridge
and H and the primaries l2 and I3 of trans
and the voltage to be measured is taken from
formers l4 and‘ [5 respectively, connected in
across the other diagonal. The bridge circuit is
‘series toform the four legs of a bridge circuit
made resonant or nearly resonant at. the fre-‘ - with a zero set potentiometer 16 connected in
quency of the applied voltage. In the case of 30 series between the primaries l2 and I3; The coils
an inductance bridge a tuning condenser is con
l0 and I I are associated with an armature I‘! the
nected across the bridge or condensers are‘ con
position of which may be varied by a measuring
nected in the various legs of the bridge so as to
stylus (not shown) so as to vary the impedance
form series or parallel resonant circuits when the
of the coils I0 and II in an opposite sense.
variable impedances have a predetermined value. "
An alternating current of ?xed frequency is
Any alteration in the value of these variable im
‘supplied ‘to a point 18 intermediate the'coils l0
pedances will alter the tuning of the bridge and
and H and ‘to the adjustable tap [9 of the po
will cause a corresponding change in the current
tentiometer [6 by lines 20 and 2| which are con
distribution therein.
is
nected respectively to“ one side and to the ad
A resonant bridge of the above type' is ex
justable ‘tap 22 of a potentiometer 23. In the
tremely sensitive to changes in impedance be
case of coils using an iron core, a low frequency
cause with a ?xed input voltage, the output volt
age rises rapidly as resonance is‘approached and
falls rapidly as the values of the impedances are
within the limits of the characteristics of the
changed to depart from resonant conditions.
Hence, a minor change in the value of the im
pedances when the bridge is operating‘ at or near
core may be used. For commercial reasons the
coils may be designed for a frequency of 60
cycles. If air core coilsare used a high frequency
may be preferred' The potentiometer 23 is con
nected by lines 24 and 25 across a secondary 25
of a multiple secondary power transformer 21
the point of resonance produces a greatly in
creased change in the output voltage across the
having a primary 28 connected by lines 29 and
bridge. This voltage change is applied to a 50 30 to a source’ 3| of alternating current of pre
measuring circuit which actuates an indicating
determined frequency. A switch 32 is provided to
instrument.
.
control the operation of the system and a posi
The measuring circuit may include balanced
tive temperature co-e?icient resistor such as a
recti?ers with an indicator connected to be ac
lamp 33Lis‘connected in series with the line 30
tuated by the di?erential effect of the currents 55 to develop a voltage suitable for compensating
2,407,141
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4
for variations in line voltage. The voltage across
the resistor 33 is supplied by lines 34 and 35 to
the primary 36 of a compensating transformer
31 having a secondary 38 connected in series with
the secondary 26 of the power transformer 21
ditions the series resonant circuits are tuned to a
point near but not exactly at resonance so that
one circuit approaches resonance and the other
circuit recedes from resonance in response to op
posed variations in the impedance of the coils
l0 and I I.
When equal currents pass through both pri
pensate for voltage ?uctuations in the secondary
maries I2 and I3 the current supplied from the
26 due to variations in line voltage.
secondaries 45 and 46 to the two recti?er paths
A tuning condenser 40 is connected across one
diagonal of the bridge and is shown as connected 10 are also equal, and equal voltage drops are pro~
duced in resistors 56 and 51. These voltage drops
across the primaries I2 and I3 and across the,
are applied to the grids 61 and E8 of the double
coils II! and I I in parallel. This tuning condenser
ampli?er tube 69 and cause equal space currents
is chosen to form with the inductances I0‘, II‘, I2
to ?ow in the tWo anode circuits thereof. Hence
and I3 circuits which are resonant or nearly reso
the voltage drops across the output resistors 82
nant at the frequency of the current supplied to
and 8.3. will be. equal and the indicator 90 will in
the bridge from the transformer 21.
dicate. a zerov potential.
Due to the resonant conditions of the circuits,
When the impedances of the coils I0 and I I are
the condenser 49 also serves to correct the wave
varied in an opposite manner in response to
form inasmuch as the current in a resonant cir
cuit operating under conditions of resonance 20 movement of the stylus one of the series reso
nance circuits is caused to operate nearer the
tends to take a sine form regardless of the shape
point of resonance‘ than the other circuit. thereby
of the applied wave.
producing comparatively large changes in the cur
The output transformers I4 and I5 are pro
rent passing through the respective primaries I2
vided with secondaries 45 and 46 which are con
nected respectively to anodes 41 and 68 of a 25 and i3 and. causing currents of different values
to be sup-plied from the secondaries 45 and 46 to
double diode recti?er tube 49. The recti?er tube
in a sense to introduce a voltage suited to com
49 is provided with cathodes 50 and 5t heated by
?laments 52 which are supplied by- lines 53 and
54 from a second secondary 55 of. the power trans
the recti?er 49. The voltage drops through the
vresistors 56 and 5'! then become unequal and
former 21'. The cathodes 59 and 5| are shown as
space current circuits of the ampli?er tube 69.
Hence the voltage drops across the resistors 82
connected to the ?lament supply line 53. The
anode returns through the secondaries 45- and 46
are connected through resistors 56 and 5'! respec
cause unequal space currents to flow in the two
and 83 become unequal and an indication of the
di?erence is obtained on the indicator 9B. The
indicator 6!] may be graduated linearly so that
tively to the two sides of a potentiometer 56 hav
ing an adjustable tap 59 connected by a line 60 to 35 equal increments of the indicator scale represent
equal increments of movement of the stylus
the ?lament supply line 54, thereby introducing
which actuates the armature I'l.
_
the potential developed by the secondary 55 as a
The potentiometer I6 provides adjusting means
biasing potential in the recti?er circuit. Resist
for setting the bridge for equal currents in pri
ances 56 and 5'! are by-passed by suitable by-pass
condensers 6t and 62 to eliminate the alternating 40 maries I2 and I3 when the armature I‘! is in mid
position. This adjusting means compensates for
current component from the voltage drop devel
the variations in the parts and may be set to give
oped across the resistors by the recti?ed current.
a zero indication on the meter 90. The poten
The anode sides of the resistors 56 and 51 are
tiometer 23 provides means for adjusting the po
shown as connected by lines 65 and 66 to control
tential applied to the bridge and constitutes a
grids 6'! and 68 respectively of a double triode
sensitivity control, the sensitivity being greater
ampli?er tube 59. The tube 69 is shown as pro
when a greater potential is applied and vice
vided with cathodes ‘I0 and ‘II and with ?laments
versa. The potentiometer 58 provides means for
‘I2 which are connected by lines ‘I3 and ‘I4 across
adjusting the circuit to compensate for varia
the secondary 55 of the power transformer 21.
tions in the ampli?er tubes and other elements
The cathodes 19 and ‘II are connected to the line
so as to provide a zero indication on the indicator
‘!3 and thence by line 60 to the tap 59 of poten
90 in response to equal potential drops across the
tiometer 5B.
resistors 56 and 51.
The tube 69 is also provided with anodes ‘I8 and
The positive temperature co-e?icient resistor
. ‘F9 which are connected to third and fourth sec
33 is designed to maintain a substantially con
ondaries 60 and BI respectively of the power
stant voltage across the primary 28 of the trans
transformer 21. The anode returns are connected
former 2'! regardless of minor variations in the
through the secondaries 89 and 8| and resistors 82
supply voltage. The voltage supplied to the
and 83 respectively to the cathodes ‘I9 and ‘II.
bridge, however, is further corrected by the trans
Resistors 82 and 83 are shown as by-passed'by
suitable by-pass condensers 86 and 85. The anode 60 former 31 which introduces in series with the
voltage delivered by the secondary 26 of the trans~
sides of the resistors 82 and 83 are connected by
.former 21 a balancing potential which is propor
lines 86 and 81 to an indicator 90 shown as a cen
tional to variations in the voltage drop across
ter indicating millivoltmeter.
the resistor 33. By a suitable selection of these
Operation
elements it is possible to produce a substantially
constant voltage input to the bridge. It is of
It will be noted that the bridge comprises two
course obvious that other types of voltage reg
series resonant circuits. One circuit includes the '
ulating transformers may be used for this pur
coil I9, condenser 40, primary I3, line 2!, poten
pose.
tiometer 23 and line 20 to the coil Ill. The other
In the embodiment shown, ampli?cation is in
circuit includes coil ll, condenser 40, primary I2
troduced by the ampli?er tube 69. It is under
and thence through line 2|, potentiometer 23 and
stood, however, that in certain instances am
line 29 back to the coil I I. When the impedances
pli?cation may not be required, in which event
of the coils IE] and II are equal the two circuits
lines 65 and 66 may be connected directly to the
will have identical characteristics and equal cur
indicating instrument 96 as indicated‘in Fig. 2.
rents will flow therethrough. Under these con
2,407,141
v5
6
In the embodiment shown in‘Fig. 1, the rec
ti?er tube 49 is biased by the voltage introduced
tration, it ‘is ,to be understood that various
changes and modi?cations may be made therein
by the secondary 55. If this bias is not required
as will be readily apparent to a person skilled in
the cathodes 50 and 5| of the recti?er tube may
the art. The invention is only to be restricted
in accordance‘ with the scope of the following
claims.
What is claimed is:
be connected directly to the variable tap 59 of
the potentiometer 58 by a lead 9| as indicated.
in Fig. 2. The connections‘ in the embodiment of
Fig. 2 are otherwise similar to those of Fig. 1 and
1. An electric measuring system comprising in- .
the parts have been given corresponding refer
ductive and capacity elements connected to form
ence characters. It is to be understood that the 10 a bridge circuit, means supplying an alternating
leads 65, 66 of Fig. 2 may be connected to the in»
voltage of predetermined frequency across one
dicating instrument 90 as shown or may lead to
diagonal of said bridge, said inductive and ca
an ampli?er as in Fig. 1 if desired.
‘
pacity elements being related to form a pair of
In the embodiment shown in Fig. 3. the bridge
circuits resonant at said frequency, a pair" of
comprises variable impedance coils H0 and III 15 output circuits connected respectively across‘ a
and condensers H2 and H3 which are connected
pair of 111m elements of said bridge to carry equal
to form an inductance-capacity bridge. A zero
currents when said bridge is in balance near the
set potentiometer II 4, connected between the coils
point of resonance, means oppositely varying the
I I I} and III, is provided with an adjustable tap
reactance of a pair of like elements of said bridge
H5 which is connected by a line H6 to one side 20 in accordance with the quantity being measured
or a resistor assembly including ?xed resistors
to change the tuning of said‘resonant circuits and
H8 and a potentiometer H1. The other‘side of
to produce a corresponding unbalance in the cur
the resistor assembly is connected by a line IIS
rents in said circuits, and means responsive to
to the common point of the condensers H2 and
the unbalance between said currents.
'
H3. The resistors H8 prevent‘ over control by 25
2. An electric measuring system comprising in
the potentiometer I 11.
ductive and capacity elements connected to form
The other sides of the condensers H2 and H3
a bridge'circuit, means supplying an alternating
are shown as connected by lines I20 and. IZI re
voltage of predetermined frequency across one‘
spectively to grids I22 and I23 of a double triode
diagonal of said bridge, said inductive and‘ ‘ca
ampli?er tube I24 similar to the ampli?er tube 30 pacity elements being related to form a pair of
59 of Fig. 1. ‘
circuits resonant at said frequency, a pair of
The tube I24 is provided with cathodes 125
output circuits connected respectively across a
‘which are connected by a line I26 to the tap I2‘I
pair of like elements of said bridge to carry equal
of the potentiometer H1. The tube I24 is also
currents when said bridge is. in balance near
provided with anodes I28 and I29 which are con 35 the point of resonance, means oppositely varying
nected to the secondaries 8!) and 8| of the trans
' the reactance of a pair of like elements of said
former'2'l as in Fig. l. The remaining parts of
bridge in accordance with the quantity being
the circuit are similar to those‘in Fig. 1 and have
measured to change the tuning of said resonant
been given corresponding reference characters.
circuits and to produce a corresponding unbal
In this embodiment the condensers I I2 and I I3
ance ‘in the currents in said circuits, means pro
are of a value to form series resonance circuits
ducing voltage drops proportional to the respec
with the coils Ill! ‘and Ill respectively so ‘that
tive currents and means connected to respond
when the impedances of the coils H0 and II!
to the difference between said voltage drops.
are equal equal currents flow through the con
3.‘ An electric measuring system comprising in
densers H2 and H3 and equal potentials are ap
ductive and capacity elements connected to form
plied to the grids I22 and I23. Any change in
a bridge circuit, means supplying an alternating
the impedances of the coils H0 and Hi. how
voltage of predetermined frequency across one
ever, changes the resonant condition of the cir~ diagonal of said bridge, said inductive and ca
cuit's as in Fig. l and produces corresponding
pacity elements being related to form a pair of
voltage changes across the condensers‘ H2 and
circuits resonant ‘at said frequency, a pair of
H3 which are ampli?ed in the tube I 24 to pro
output circuits connected respectively across a
duce different voltage drops across the resistors
pair of like elements of said bridge to carry equal
82 and 83 which are indicated on the indicat—
ing device 90.
‘
currents when said bridge is in balance near
I
the point of resonance, means oppositely varying
In the embodiment of Fig. 4 the condensers‘ ‘Hill 55 the reactance of a pair of like elements of said
and IN of the bridge are made variable and the
bridge in accordance with the quantity being
coils H0 and II! of ?xed impedance. Otherwise
the bridge circuit is similar to those above de
measured to change the tuning of said resonant
scribed and operates in the same manner.
ance in the currents‘in said circuits, means recti
The
circuits and to produce ‘a corresponding unbal
condensers are arranged to be variable in opposite 60 fying‘the respective currents to produce corre
sense in response to movement‘of the stylus.
sponding direct potentials, and means connected
Obviously both the coils and the condensers may
torespond to the di?erence between said poten
be made variable if desired.
.
In the embodiments of Figs. 1 and 3 the plates
tials.
‘
4. An electric measuring system comprising in
are shown as supplied by A. C. However, a D. C. 65 ductive and capacity elements connected to form
plate supply may be used if desired since the
voltage di?erential is utilized for the indication.
The resonance bridge as described above has
the advantage of increased sensitivity due to the
a bridge circuit, means supplying an alternating
voltage of predetermined frequency across one
diagonal of said bridge, said inductive and ca
pacity elements being related to form a pair of
large increase of current ?owing therethrough at 70 circuits resonant at said frequency, a pair of
resonance. It is also less sensitive to changes
output circuits connected respectively across a
in wave form of the applied current than are
pair of like elements of said bridge to carry equal
non-resonance circuits.
currents when said bridge is in balance near the
Although certain speci?c embodiments of the
invention have been shown for purposes of illus
‘point of resonance, means oppositely varying the
reactance of a pair of like elements of said bridge
2,407,141
7
8
in accordance with the quantity being measured
to change the tuning of said resonant circuits
said transformers to produce direct potentials
said potentials and means connected to said am
impedances connected in series with said coils to
form a bridge circuit, means supplying an alter
corresponding to said currents, and means con
nected to respond to the difference between said
and to produce a corresponding unbalance in the
potentials.
,
currents in said circuits, means rectifying the
8. An electrical measuring system comprising a
respective currents to produce corresponding di Cl
pair of variable impedance coils, a pair of ?xed
rect potentials, an ampli?er connected to amplify
pli?er to respond to the di?erence between said
nating current of predetermined frequency across
5. An electric measuring system comprising in 10 one diagonal of said bridge, means including said
?xed impedances tuning said bridge to resonance
ductive and capacity elements connected to form
at said frequency, means oppositely varying the
a bridge circuit, means supplying an alternating
impedance of said coils in accordance with the
voltage of predetermined frequency across one
‘quantity being measured to produce a correspond
diagonal of said bridge, said inductive and ca~
pacity elements being related to form a pair of 15 ing change in the currents in said ?xed imped
ances, and output circuits connected to said ?xed
circuits resonant at said frequency, a pair of
impedances having means responsive to the dif
output circuits connected respectively across a
ference between the currents therein.
pair of like elements of said bridge to carry equal
9. An electric measuring system comprising a
currents when said bridge is in balance near
the, point of resonance, means oppositely vary 20 pair of inductive elements and a pair of capacity
ampli?ed potentials.
ing the reactance of a pair of like elements of
elements connected in series to form a bridge cir
cuit with the pairs of like elements in adjacent
legs of said bridge, means supplying an alternat
measured to change the tuning of said reso
ing voltage of predetermined frequency to points
nant circuits and to produce a corresponding
unbalance in the currents in said circuits, means 25 of said bridge between the elements of each pair,
a pair of output circuits connected respectively
rectifying the respective currents to produce cor
across a pair of like elements of said bridge to
responding direct potentials, space discharge am
carry equal currents when said bridge is in bal
pli?ers having control grids connected to re
ance, means oppositely varying the reactance of
ceive said potentials and having plate circuits in
cluding resistors carrying the respective plate cur-, 30 a pair of like elements of said bridge in accord
ance with the quantity being measured to pro
ents, and means connected to respond to the
duce an unbalance in the currents in said output
voltage difference across said resistors.
circuits, each output circuit including a recti?er
6. An electric measuring system comprising a
and a resistor connected to develop a unidirec
pair of variable impedance coils, a pair of trans
said bridge in accordance with the quantity being
formers having primaries connected in series with 35 tional voltage drop proportional to the current
in said circuit, ampli?er means having input cir
said coils to form a bridge circuit, means supply
cuits connected to said resistors and having out
ing an alternating voltage of predetermined fre
put circuits including series resistors, and indi
quency to the mid-points between said coils and
cating means connected to respond to the differ
across said coils and said primaries in parallel 40 ence in voltage drops in said last resistors.
10. An electric measuring system comprising a
and adapted to form therewith a pair of circuits
pair of inductive elements and a pair of capacity
resonant at said frequency, means oppositely
elements connected in series to form a bridge cir
varying the impedance of said coils in accordance
cuit with the pairs of like elements in adjacent
with the quantity being measured to change the
between said primaries, a condenser connected
tuning of said resonant circuits and to produce A ' legs of said bridge, means supplying an alternat
a corresponding unbalance between the currents
in said primaries and means connected to said
transformers to respond to the difference between
said last currents.
7. An electric measuring system comprising a
pair of variable impedance coils, a pair of trans
formers having primaries connected in series with
said coils to form a bridge circuit, means supply
ing an alternating voltage of predetermined fre
quency to the mid-points between said coils and -
between said primaries, a condenser connected
across said coils and said primaries in parallel
and adapted to form therewith a pair of circuits
ing voltage of predetermined frequency to points
of said bridge between the elements of each pair,
a pair of output circuits connected respectively
across a pair of like elements of said bridge to
carry equal currents when said bridge is in bal
ance, means oppositely varying the reactance of
a pair of like elements of said bridge in accord
ance with the quantity being measured to pro
duce an unbalance in the currents in said output
circuits, each output circuit including a recti?er
and a resistor connected to develop a unidirec
tional voltage drop proportional to the current
in said circuit, a potentiometer connected between
said resistors and having an adjustable tap, a
resonant at‘ said frequency, means oppositely
varying the impedance of said coils in accordance 60 common return lead connected to said tap where
by adjustment thereof may be effected for bal
with the quantity being measured to change the
tuning of said resonant circuits and to produce
a corresponding unbalance between the currents
in said primaries, a pair of recti?ers connected to
ancing said bridge, and means responsive to the
difference in potentials across said resistors.
CHARLES F. COAKE.
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