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Патент USA US2123964

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July 19', 1938.
F. x. REES
TRACK’CIRCUIT FOR
2,123,964
RAILROADS
Filed May 29, 1955
I
I
2 Sheets-Sheet 2
FIG.4.»
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2 Ohm‘ ballasf
4 Ohm baHasT
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10 Ohm
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ballas'l’.
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I
25 Ohm ballas‘r
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50 Ohm balms?‘
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| VENTOR
BY elm:
2,123,954
Patented July 19, 1938
UNETED STATES
FATEN'E' OFFE€E
2,123,964
_
TRACK CIRCUIT FOR RAILROADS
Frank X. Rees, Albany, N. Y., assignor to General
Railway Signal Company, Rochester, N. Y.
Application May 29, 1935, Serial No. 24,074
'7 Claims. (Cl. 246-41)
This invention relates to improvements in the
well-known track circuit for railroads commonly
employed in various types of railway signalling
and interlocking systems.
The primary object of this invention is to im
prove the safety and reliability of the track cir
cuit by providing a special organization by which
dependable shunting and operation of the track
relay are obtained by a higher and more uni
form shunting resistance under the varying con
ditions of rail surface and ballast resistance en
countered in practice.
The well-known track circuit is subject to un
ing voltage for the track relay and thus tend
ing to reduce the resistance of the wheel con
tact and establish a wheel shunt of suitable low
resistance; the ballast resistance across the track
rails, together with an additional shunt or bleeder
resistance as may be required, constituting a
conducting path into which the relay may dis
charge current during the time intervals be—
tween the impressed voltage pulses; and the
voltages and resistances being so proportioned 10
that the rate of decay of current through the
relay varies with the ballast resistance in such
a way as to compensate for the change in the
insulated joints between the track sections im
inner-rail impressed voltage with changes in bal
last resistance, thereby maintaining a substan 15
tially constant average operating current through
the track relay throughout a wide range of vari
ation in ballast resistance.
Other characteristic features, attributes, and
advantages of the invention will be in part ap 20
parent, and in part pointed out as the descrip
tion progresses.
In the accompanying drawings, Fig. 1 illus
trates diagrammatically and conventionally one
speci?c embodiment of the invention; Fig. 2 illus
trates a modi?ed arrangement; and Figs. 3 and
poses a limitation upon the voltage and resistance
of the relay that can be advantageously used,
otherwise the track circuit may not perform its
4 show curves of current, resistance and the like
for explanatory purposes.
Referring to Fig. 1 of the drawings, it is con
usual and peculiar operating conditions which
15. materially affect the margins or limitations for
its reliable operation. Among other things, there
is a relatively low insulating resistance between
the track rails, commonly known as ballast leak
age or resistance; and this ballast resistance also
varies widely with the kind of ballast, drainage,
type of ties, and the like. Moreover, this ballast
resistance varies greatly for the same track sec
tion in wet and dry weather.
Also, the leakage through the ballast or ground
' around breaks in the track rails and around the
30 important function of detecting broken rails.
Further, the weight of the equipment and con
dition of the rail surfaces materially modi?es the
effective resistance of the wheel shunt and im
pairs the dependable operation of the track re
; I lay.
In the case of branch lines, station tracks,
switches and cross overs, and the like, the track
rails may not be frequently used and may be
templated that the track rails I will be bonded 30
together in the usual way, with insulated joints
2 de?ning the ends of the track sections, one
of which is illustrated. This track section may
be a cut-section or block length of a system of
automatic block signalling, or automatic train
control or the like, or may be a relatively short
section at a switch or cross-over in an interlock
come rusty or dirty to an extent that there is a
ing plant.
high contact resistance between the wheels and
At one end of the track section, preferably at
the entering end, a direct current track relay R
of the usual type and construction is connected
the rails. Even where tracks are frequently
used, the track rails seem to accumulate on the
surface something in the nature of a coating or
?lm which is of relatively high resistance at the
low voltage commonly used.
With these and other considerations in mind,
and by way of explanation of the nature of the
invention and without attempting to de?ne its
scope, it is proposed to employ a track relay of
the usual direct current tractive type but hav
. ing a substantial value of resistance and/or in
ductive reactance in series with it, and to sup
ply the track circuit with time spaced unidi
rectional voltage pulses, in series with the usual
limiting resistances; such voltage pulses having
55 peaks materially in excess of the steady operat
across the track rails i in series with a suitable
current limiting device 3, preferably adjustable,
which may be an ohmic resistance, or a reactance
or choke coil having a relatively high inductance
as compared with its ohmic resistance, the choice
of the characteristics of this resistance or re
actance 3 being dependent upon the nature of
the ballast resistance and a number of other fac
50
tors, as will presently appear.
It is contemplated that the resistance of the
track relay R and its connections to the track
rails will be some two to six or more times greater
than ordinarily used, as for example, a 4 ohm
track relay in series with an external resistance 55.
2
2,123,964
or reactance 3 of about 25 ohms. ‘The purpose
of such relatively large resistance or reactance
of the track relay and its connections is to permit
rupter suitable for this purpose is one compris
ing a balance wheel or rotary pendulum, such as
disclosed for example in the patent to Bossart,
the use of a greater inter-rail potential for re
ducing the relative resistance of the wheel con
tact to that part of the track circuit in multiple
therewith to provide a wheel shunt of suitable
No. 1,858,876, May 17, 1932, an interrupter of
this type having the advantage that the rate of
relatively low resistance. Also, such external
applied voltage.
resistance or reactance 3, tends to make the track
relay quicker in releasing its armature when a
wheel shunt is applied, since the resistance of
the circuit through the relay and the wheel
shunt is higher, and the current and flux through
Considering now the operation of the track
circuit organization of this invention, and the 10
theory believed to underlie the results obtained,
the impressed voltage applied to the track rails
at the feed end comprises uni-directional time
the relay may fall at a faster rate, than if a
spaced pulses or half waves.
15 relay of the same resistance and operating cur
rent were directly connected across the track
rails.
In accordance with this invention, the track
circuit is supplied with time-spaced uni-direc
tional voltage pulses, the duration of the pulses
and space between them, as well as the peak
voltage, being chosen with due regard to the
other characteristics of the circuit, so as to ob
tain the desired operating characteristics of the
25 track circuit. In the embodiment of Fig. 1, a
source of alternating current of an ordinary fre
quency, such as 60 cycles, is employed. Such
source of current is shown conventionally as a
transformer 4, assumed to have its primary con
30 nected to a suitable power supply line, prefer
ably With a motor-generator driven from a bat
tery as a stand-by source. The secondary of
this transformer 4 is connected across the track
rails i in series with a half-wave recti?er 5, and
an adjustable resistance 6 performing the func
tion of the usual limiting resistance used with
track circuits. In certain applications of the
invention, for reasons hereinafter explained, it
is also desirable to employ a bleeder or regulat
40
may be employed; and another type of inter
ing shunt resistance ‘I, preferably adjustable,
which is connected across the track rails as
shown, preferably at the feed end.
In the arrangement of Fig. 1, the recti?er 5
interruption is not effected by change in the
These voltage
pulses supply current to the ballast resistance 15
and to the relay through the limiting resistance
6; and each half wave causes a corresponding in
crease and decrease of the impressed voltage for
the track relay R, such as indicated for ex
planatory purposes by the curves ER in Fig. 4. 20
As this impressed voltage at the relay end of
the track circuit increases, current through the
relay increases, with a time lag due to the in
ductive reactance of the relay, in the manner
indicated generally by the curves IR in Fig. 4; 25
and as this impressed voltage falls, the current
through the relay decreases. The usual type of
direct current track relay intended to be used
in this invention comprises the well known core
and winding constituting an electro-magnet for 30
attracting a movable armature, usually biased by
its weight to assume a retracted position; and
such an electro-magnetic structure has consider
able self-induction. As the relay current de
creases, the accompanying decay of ?ux induces 35
a voltage in its winding in a direction to sus
tain the current; and in accordance with estab
lished principles, the rate of decrease or decay
of the current is dependent upon resistance of
the circuit into which the relay may discharge 40
current. It is found that the rate at which the
relay current will fall during the half waves
where the impressed voltage is cut oil‘, depends
serves to impress across the track rails half
upon the ballast resistance and the shunt or
waves or half cycles of the alternating current
bleeder resistance 1. This is illustrated by the
curves in Fig. 4 for different ballast resistances,
voltage, thereby providing the time spaced volt
age pulses characteristic of this invention. Cer
tain types of recti?ers, such as the well-known
copper-oxide dry plate type, have the property
50 or characteristic that the resistance to the flow
of current in the direction in which the recti?er
is conducting, varies inversely with the current
conducted, such forward resistance of the recti
?er increasing as the conducted current de
55 creases.
This characteristic or property of the
recti?er 5 is a factor in connection with other
features to compensate for variations in ballast
resistance.
Fig. 2 illustrates a modi?ed arrangement, in
60 which the desired time spaced voltage pulses are
obtained from a battery “I, or other source of
direct current, by the operation of a suitable
chopper or interrupter.‘ In the particular ar
rangement shown, the battery I0 is connected
65 across the track rails through a back contact
from which it can be seen that the decay of re
lay IR during the time intervals between the
voltage pulses is at a slower rate with the lower
ballast resistances, the greater rate of decay at 50
the higher ballast resistances being also indi
cated by a reversal of the voltage curves ER.
The pick up and drop-away of the track relay
R depends upon what may be termed the aver
age current through it; and it can be seen that 55
the magnitude of this average current depends
upon the rate at which the relay current de—
creases or decays during the half cycles where
the impressed voltage is cut off, as well as upon
value of the pulsed voltage. In other words, the 60
higher the pulses of impressed voltage, the
greater the impressed or applied current; and
the slower the rate of decay of relay current,
the greater will be the average current through
the relay; and vice versa.
65
ll of a relay l2 which is energized from the bat
tery ID by a circuit readily traced on the draw
ings and including this back contact H, such
that this back contact H is intermittently
70 opened and closed to alternately connect and
disconnect the battery it) from the track rails.
A condenser l3 or equivalent means, is employed
in accordance with well-known practice to pro
the voltage drop through the limiting resistance
tect the contact H from injury by sparking.
75 Various other kinds of choppers or interrupters
then becomes smaller, and a greater voltage is
impressed across the track rails to increase the n
In the ordinary track circuit, when the bat
tery voltage and limiting resistance have been
selected or adjusted to provide su?icient current
for the track relay under wet ballast conditions
with low ballast resistance, if the ballast dries 70
out and its resistance increases, less current flows
to the ballast through the limiting resistance,
3
2,123,964?
current through the relay.
The general trend
in this respect is indicated by the curve A in
Fig. 3; and it can be seen that, once the ordi
nary track circuit has been adjusted to hold up
Ul the relay under wet ballast conditions, there will
be excessive current through the relay under
dry ballast conditions, which materially inter
feres with the proper shunting of the track relay.
For these reasons, it is desirable to provide some
thing which will act automatically to maintain
a uniform current through the track relay under
Varying ballast conditions, so that the energiza
tion of the relay is the same at all times, and
so that the relay can be shunted safely under
15 both wet and dry ballast conditions. An im
portant feature of this invention is the auto
matic compensation provided to maintain the
relay current substantially uniform for various
ballast resistances throughout a wide range at
20 the higher ballast resistances above what may
be termed the zone of wheel shunt resistance.
Explaining the theory apparently underlying
the operation accomplishing this result, it ap
pears that changes in the voltage applied to the
25 .relay with variation in ballast resistance are ac
companied by .a compensating change in the rate
of decay of the relay current between the
voltage pulses, in such a way that, with suit
able proportioning of parts, the average operat
30 ing current through the relay is maintained sub
stantially uniform throughout a wide range of
ballast resistances above the lower values, around
2 ohms per thousand feet of track. The cur
rent variations in this respect are indicated gen
erally by the curve B in Fig. 3.
The curves of Fig. 4, based upon oscillograms
taken with a typical track circuit organization,
may be referred to for explanatory purposes as
indicating the voltage and current variations in
volved in this compensating operation. From
the curves of Fig.4, it will be noted that as the
ballast resistance increases, the peak voltages ER
likewise increase, and are accompanied by higher
peaks or humps of relay current IR: but at the
same time the change of decay in relay current
IR. between the voltage pulses. varies, decreasing
more rapidly with the higher ballast resistances,
in a manner to: compensate for the higher peak
currents, and give a substantially uniform aver
50 age current, upon. which the operation of the
relay depends.
In practicing this invention, the parts; are se
lected and proportioned to» provide adequate op
erating current for the relay under the most un
55 favorable or wet ballast conditions to be en
countered; but as. the ballast dries out, less cur
rent is supplied to‘ the track circuit as a whole,
and the voltage drop through the limiting resist
nearly uniform slightly above the pick-up or nor
mal operating current.
In some applications of the invention, it is
found that there is what may be termed over
compensation, such that the current through the
relay decreases at the higher ballast resistances
to the point where it will fail to hold up its arma
ture. In other words, the curve B of Fig. 3
may in some instances droopy at. the higher values
of ballast resistance below the drop away line 10
DA. This appears to be due to a relatively
greater change in relay current between the
voltage pulses for higher ballast resistances, than
changes in impressed voltage, with the result
that the average current decreases at the higher
values of ballast resistances. In such cases, the
shunt or bleeder resistance 1 across the track
rails is employed to provide what may be con
sidered to- be an arti?cial ballast resistance or
leakage for the purpose of maintaining a suf 201
?ciently low resistance of the discharge circuit
for the track relay under very dry ballast condi
tions to avoid too quick a decay in the relay cur
rent between the voltage pulses and thereby
maintain the average current.
This shunt or 251'
bleeder resistance 1 is preferably adjustable;
and by proper selection or adjustment of this
resistance'l, together with the adjustment of the
usual limiting resistance 6, it appears that the
desired regulation of relay current may be ob 30
tained for track circuits for Various lengths and
ballast resistance throughout the full operating
range encountered in practice.
The maintenance of substantially constant
current through the relay for different resist
ances seems to be helped also by the current
resistance characteristics of the copper-oxide
recti?er 5 in the arrangement of Fig. 1, the effect
of the recti?er in this respect, however, being
apparently dependent upon ‘a number of related
factors and dil?cult to explain and evaluate. A
source of alternating current, with a half-wave
recti?er 5, is a convenient way of obtaining the
time spaced impulses of impressed voltage; and
with such an arrangement, the operating char
acteristics of the recti?er contribute to or modify
the current regulating characteristics of the
track circuit.
For example, assumirng a setting for wet ballast
conditions, when the ballast dries out and less
current is supplied to the track, the forward re
50 '
sistance of the recti?er, i. e. the resistance in
the ‘direction in which it is conducting, increases
and in eifect adds to the limiting resistance 6
to maintain a voltage drop with the smaller cur
rent to give nearly the same impressed voltage
across the track rails.
For this reason, and in
this way, the characteristics of the recti?er may
relay current between the pulses. of impressed
be helpful in obtaining the desired current regu
60
lation.
Another important feature of this invention is
that the peak voltages of the half cycles of alter
nating current or other time spaced voltage
voltage, so that the average current remains sub
pulses are much in excess of the steady direct
stantially constant, rather than increase steadily
current voltage that would be required to pro
duce the same general average operating current
through the relay. In. other words, the peak
voltages applied across the track rails in accord
ance with this. invention are much greater than
the steady voltage that would be used with the 70.
same resistance and type of track relay. Such
peak voltages very materially assist in reducing
or breaking down the resistance of the wheel
contacts and establish an effective low resistance
wheel shunt, more particularly with‘ dirty or.
ance decreases to raise the voltage impressed
upon the relay, such increase in ballast resist—
ance is accomplished by a more rapid decay of
with increased ballast resistance as in the ordi
nary track circuit. Consequently, the track re
lay'R is not over energized under dry ballast
conditions and may be shunted as surely under
,-,dry as under wet ballast conditions. The lines
PU and DA in Fig. 3 indicate the pick-up and
drop-away currents for the organization illus
trated by these curves; and it will be noted from
the curve B for this invention that the current
.through relay above the shunting zone remains
4
2,123,964
dusty track rails, or with light-weight equip
ment, such as gas-electric cars.
The resistance of the wheel contact is found
the range of variation in ballast resistance to be
to vary greatly with the conditions of the rail
surface and the weight of the equipment; and
it appears that voltages much higher than the
relatively small voltages of about two volts nor
mally employed for track circuits are necessary
to reduce the resistance of the wheel contact in
encountered.
The nature of the invention is such that vari
ous modi?cations, adaptations, and additions
many cases to a point where actual shunting of
the track relay is obtained.
The peak voltages
provided by this invention, which are many times
those commonly used in track circuits, appar
ently break down the resistance at the wheel
15 contact, perhaps due to an ionization eifect, and
enable effective shunting with dirty or rusty track
rails and light equipment in a manner not ob
tainable with the ordinary track circuit arrange
ment.
In this connection, it will be noted that the
20
peak voltages are periodically applied at fre
quent intervals, and are available to break down
the resistance of the wheel contact, as the car
or train moves along the track and its wheels
25 contact with the rails at different points.
Further, the use of a pulsating current, ob
tained from an alternating current half-wave
recti?er or from a battery by an interrupter, as
distinctive from a steady current for energiz
30 ing the track relay, acts to improve the pick-up
and drop-away characteristics of the relay. In
other words, a direct current tractive type relay
of the usual construction will pick up on less cur
rent and drop-away on a greater current when
35 energized with half cycles of recti?ed alternating
current or equivalent time spaced voltage pulses,
than if energized with a steady uni-directional
voltage from .a battery or the like. This is at
tributed to the ?uctuating nature of the ener
gizing current which tends to initiate armature
movement at critical average current values in
a manner that does not occur with steady ener
gization. Also, the movement of the armature of
the relay is accompanied by a flux change which
45 appears to be a contributing factor to the su
perior ratio of drop-away current to pick-up cur
rent obtained by the use of pulsating energization
of the track relay in accordance with this inven
tion.
50
wet ballast conditions, and to maintain such av
erage current substantially constant throughout
1
From the foregoing it will be appreciated that
this invention involves certain selection and pro
portioning of parts in the complete organization;
and the various voltages, resistances, and induc
tive reactances are so complexly inter-related
55 that a variation or change in the value of one
factor tends to modify one or more of the other
factors. The quantitative values or relationship
indicated by the explanatory curves of Figs. 3 and
4 are merely typical; and it should be understood
60 that the invention is not limited to any such
may be made in the particular embodiments
shown and described without departing from the
invention.
What I claim is:—
1O
1. A track circuit for railroads comprising, in
combination with a direct current track relay of
the usual tractive armature type connected
across the rails at one end of a track section, a
source of alternating current connected across 15
the track rails in series with a half-wave recti?er
and a limiting resistance at the other end of
said track section, and an ohmic shunt bleeder
resistance connected across the track rails at said
other end of said track section, said resistances 20
being proportioned with regard to the operating
current and inductive reactance of the relay to
cooperate with the ballast resistance and main
tain approximately constant current through the
relay for a wide range of variation in ballast re
sistance.
2. In a track circuit for railroads, the combi
nation with a direct current track relay of the
usual tractive armature type connected across the
track rails at one end of the track section, a lim 30
iting resistance, means for impressing across the
track. rails at the other end of said section
through said limiting resistance time spaced uni
directional voltage pulses having peak voltages
greater than the steady operating voltage for the 35
track relay, a shunt bleeder resistance connected
across the track rails at said other end of said
track section, said shunt resistance and ballast
resistance forming a conducting path into which
the track relay may inductively discharge cur
rent during the time periods of cessation of im
pressed voltage pulses, the resistance of said con
of the current flowing so that the rate of decay
of the relay current during the intervals between 45
said voltage pulses varies with the ballast re
sistance to compensate for change in impressed
voltage with change in ballast resistance.
3. A track circuit for railroads comprising, a
direct current track relay of the tractive arma 50
ture type connected across the track rails at one
end of the track section in series with an ex
ternal ohmic resistance, a limiting resistance,
means for impressing time spaced pulses of uni
directional voltage across the track rails at the 55
other end of said track section in series with said
limiting resistance, and an ohmic bleeder resist
ance connected across the track rails, said bleed
er resistance co-acting with the ballast resist
ance to provide a conducting path into which the 60
relay may inductively discharge current when
and advantages of the invention may be obtained
tially compensate for the change in impressed
voltage with the change in ballast resistance,
the resistance of said conducting path varying
with the ballast resistance but being independent
of the intensity of the current flowing.
the length of the track circuit, condition of the
ballast, range of variation in ballast resistance,
and the like; the external resistance or inductive
reactance 3 in series with the track relay R is
70 selected or adjusted to require peak voltages suit
able for reducing the resistance of the wheel con
tact, and also utilize as high a wheel shunt re
sistance as desired; and these various factors are
relatively proportioned to provide the necessary
75 average current through the track relay under
40
ducting path being independent of the intensity
particular quantitative relations.
Generally speaking, the underlying principles
when the limiting resistance 6 and the shunt or
65 bleeder 1', if used, are selected to conform with
25
the impressed voltage pulse is cut off so as to par
4. A track circuit for railroads comprising,- a
direct current track relay of the usual tractive
armature type connected across the track rails
at one end of the track section in series with an
external ohmic resistance, a source of alternat
ing current, an adjustable limiting resistance, a
half-wave recti?er, and means connecting said
source of alternating current across the track 75
2,123,964
rails at the other end of said track section in se
ries with said limiting resistance and said half
wave recti?er, an ohmic bleeder resistance con
nected across the track rails at said other end of
the track section, the self-induction of said track
relay tending to maintain current in its wind
ing to keep its armature attracted between the
half cycles of impressed voltage by discharging
its current of self-induction into the ballast re
10 sistance in multiple with said bleeder resistance,
and the peak voltages of the half cycles of im
pressed voltage suitable for providing an average
current through said track relay comparable with
its steady operating current being materially
15 greater than the voltage for such steady operat
ing current, whereby peak voltages across the
track rails suitable for breaking down any ‘con
tact resistance of the wheel shunt are available
without a correspondingly greater average ener
20 gization of the track relay which would inter
fere with its shunting.
5. A track circuit for railroads comprising, a
direct current track relay of the usual tractive
armature type having its winding connected
25 across the track rails at one end of a track sec
tion, a limiting resistance, and means for sup
plying time spaced uni-directional voltage pulses
through said limiting resistance across the track
rails at the other end of said section, an ohmic
30 bleeder resistance many times greater than the
ballast resistance connected across the track rails,
the self-induction of said relay maintaining cur
rent through its winding between such voltage
pulses by discharging into the ballast resistance
35 in multiple with said bleeder resistance, the rate
of decay of said current of self-induction be
tween the voltage pulses varying with changes
in ballast resistance to compensate for the varia
tions in current supplied to said track relay by
the voltage pulses for di?erent ballast resistances,
whereby approximately the same average current
through the track relay is maintained for a wide
variation in ballast resistance.
6. A track circuit for railroads comprising, a
45 source of time spaced uni-directional voltage
5
pulses, an adjustable limiting resistance, an
ohmic shunt bleeder resistance many times
greater than the ballast resistance, means for
connecting said source of voltage across the
track rails at one end of the track section in
series with said limiting resistance and in multi
ple with said bleeder resistance, and a direct
current track relay of the usual tractive arma
ture type connected across the track rails at the
other end of said track section in series with an 10
external ohmic resistance, whereby peak voltages
materially greater than the steady operating
voltage for the track relay are applied across
the track rails to supply suf?cient energizing cur
rent for the track relay and are available for
breaking down the contact resistance of a wheel
shunt and also approximately the same average
current in the track relay is maintained for a
wide variation in ballast resistance.
'7. A track circuit for railroads comprising, a
direct current track relay of the usual tractive
armature type having its winding connected
across the track rails at one end of the track
section, an external ohmic resistance in series
with said track relay, an adjustable limiting re
sistance, means including a source of alternating
current and a half-wave recti?er for applying
half waves of impressed voltage across the track
rails at the other end of said track section in
series with said limiting resistance, and an ohmic 3O
bleeder resistance many times the ballast resist
ance connected across the track rails at the other
end of said track section, the self-induction of
said track relay tending to maintain current in
its winding between the half waves of impressed
voltage but discharging current into a conduct
ing path including the ballast resistance in mul
tiple with said bleeder resistance, the resistance
of said conducting path being independent of
the intensity of the current flowing so that the 40
rate of decay of such current of self-induction
in the relay winding varies with variations in
the ballast resistance.
FRANK X. REES.
45
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