Note: Descriptions are shown in the official language in which they were submitted.
(Case ~o. 6997) ~ ~ ~
VITAL OPTICAL COUP~ER CIRCUIT ARRA~GEME~T
FOR RAILROAD S IG~ Ç; SYSTEMS
BACKGRO~ND OF THE I~VENTIO~
My invention pertains to a vital optical coupler circuit
arrangement for railroad signaling systems. More specificallyO
the invention relates to a vital optical coupler circuit
arrangement usable as a track relay means in alternating
current trac~ circuits on electrified railroads.
As a matter of economy and efficiency, electrified rail-
xoads in the United States are planning to change to commercial
60 Hz propulsion power sources to replace the long used 25 Hz
propulsion power generated by special apparatus at privately
~wned generating stations. Any new electrification will also
be at the commercial power frequency. The signaling systems in
such electrified railroad~ have for many years used lOQ Hz
alternating current (A. C.) track circuits including centrifu-
gal ~ype track relays which effectively are two winding, dual
input, synchronous motor or detector devices designed ~o be
immune to the 25 Hz propulsion current flo~ing in the rails.
- 20 One winding of the relay is energiz~d direct from the track
circuit power source. The second winding recei~es energy
through the section rails from the same track circuit source
connected at the other and. The relay operates ~o indicat~ an
unoccupied track section only when both windings are energized
by track circuit frequency currents having a phase angle rela-
tio~ship within predetermined limits~ It is impractical, in
the process of changing propulsion frequency, to also change
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3L~33~ 9L
out the existiny 100 ~z track circuits. However, the present
centrifugal r~lays are not sufficiently immune to the 60 Hz
frequency to assure no response by the relay to propulsion
currents of the new frequency flowing in the rails. In addi-
tion, centrifugal relays inherently require considerable and
frequent preventative maintenance to assur~e proper and re~able ~ ~
operation. Therefore~ it is desirable, even required, to sub- ~1
stitute a passive network not responsive to 60 Hz currents
which will permit continued use of the 100 ~Iz track circuits
but with conventional, vital direct current (D.C.) track re-
lays which will not respond to, that is, which are immunized
from, propulsion currents whether of the 25 or 60 Hz frequency. ~;
OBJECTS A~D SUMMARY OF THE I~VENTION
Accordingly, an object of my invention is a passive
~ .
circuit network fcr controlling a vital relay which serves as
the track relay means for alternating current track circuits
in electrified railroads.
Also an object of my invention is a vital optical coupler
circuit arrangement responsive only to dual input signals of
the same preselected frequency and within a predatermined
phase relationship to provide a usable output signal.
Another object of the invention is an optical coupler
circuit arrangement to replace the frequency and phase re-
sponsive track relay in vital track circuits for electri-
fied railroads.
A still further object of the invention is an improvedfrequency sèlective track relay means for alternating current
track circuits in electrified railroads.
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It is also an object of my invention to provide a track
circuit arrangement for electrified railroads which includes
a tuned optical coupler circuit networX at the receiving end
of the track section to energize a vital track relay only in
response to received energy of the preselected track circuit
frequency.
StiIl another object of the invention is a half wave
synchronized rectifier circuit network, including an optical
coupler, usable in alternating current railroad track circuits
for detecting ~he presence of two signals having the same
frequency and within a predetermined phase relationship.
Still another object of the invention is a frequency -~
selective synchronous rectifier network including an optical
oupler to replace the centrifugal relay in alternating
current track circuits for electrified railroads.
A further object of my invention is an optical coupler
circuit network responsive only to two source related input
signals of the same frequency and having a predetermined~ -
phase relationship for producing a registerable output signal
indicating the presence or condition of one or both of the
input signals.
A still further o~ject of the invention is an alternating
current track circuit, for an electrified railroad track
section with impedance bonds for propulsion current return,
which includes a source of alternating current energy, having
a frequency different from the propulsion power frequency,
connected to the rails at one end of the section and a train
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detector means with a ~irst input coupled to the track circuit
source and a second input connected across the rails at the
other sec*ion end, second input signals ~eing rectified by a ;~
photo resistive element controlled by a light emitting diode
actuated by the first input signal through a tuned filter
com~ ) ~7~ Of ~c
element, the rectified~output signal of the photo resistive
element energizing the vital D. C. track relay to register an
unoccupied track circuit condition only if both input signals
are present and are within a predetermined p~ase relationship.
lG Other objects, features, and advantages of the invention
will become apparent from the following specification and
appended claims w~en taken in connection with the accompanying
drawings.
- According to the invention, a vital circuit arrangement
has a first input means, tuned to a preselected frequency, to
activate a light emitting diode (~ED) element when supplied
with an alternating current signal of that frequency. The
pulsed emission from the LED controls a photo re~istive cell,
periodically reducing its resistanca to produce an averaged `
direct current output from another A. Cn signal having the
same frequency and a related phase angle applied thr~ugh a
second input means of the circuit arrangement. The averaged
Do C. output signal produced by this optical coupler energizes
a direct current registry relay which picks up only when the
two input signals have the same fre~uency and are within a
predetermined phase relationship. The vital circuit arrange-
ment is substituted for a dual input, frequency responsive
_ D~ _
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track relay in an alternating current track circuit for an
electrified railroad and maintains the required inhibition
of response to the propulsion current, of a different but
closely spaced frequency, flowing in the rails to prevent
the improper registration of an unoccupied track section
when a train is present or a braken rail exists.
In the specific practice of the invention, the illustrated
vital circuit arrangement is a dual input detector means in-
tended for use as the receiver or registry element in an al-
ternating current track circuit for an alectrified railroadwhich uses alternating current propulsion powerO The input
means for the circuit arrangement are coupling transformers
with a first transformer co~nected to receive input signals
direct from the track circuit alternating current energy
source. This track circuit source has a frequency differ-
ent from but close to the frequency o~ the propulsion cur-
rent. The secondary output of this transformer is applied ~-
to the Light emitting diode element through a filter circuit
path tuned to the track circuit frequency. The LED is thus
turned on during each positive half cycle of the local input
signal. The ~ED is positioned to illuminate a photo resistiva
element, during each period when the LED is turned on, to thus
actuate periodic reductions in the resistance of this photo re--
sistive element. The second input transformer is a saturable
type connected across the rails to receive the track current
signal transmitted from the track energy source connected at
the other end of the corresponding track section. The
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. . ~,
~3~
secondary of this second transformer is connected in series
with the photo resi,stive element and a biased direct current
vital relay which serves as the track circuit registry relay.
~he periodic actuation of the photo resistive cell by the LED
produces a modified or pulsed wave output which has an averaged
D. C. component somewhat equivalent to that of a half wave
rectified alternating current. When both inputs are present
at normal levels~ are relatively in phase, and of course of
the same frequency, the level or magnitude of the D. C. com-
ponent in the output signal sufficiently energizes the registry
relay to pick up, indicating the presence of both signals with
proper characteristics and thus an unoccupied track section
with no broken rails. Fre~uency and phase characteristics of
the vital network are sharp enough to reject signals at other
requencies and/or out of phase, that is, beyond the accepted
phase relationship limits.
BRIEF DESGRIPTI:Ol!l OF THE DRAWI~GS
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I shall now describa in greater detail the specific
embodiment o~ my invention as illustrated and characterized
in the accompanying drawings, in which:
FIG. 1 is a circuit diagram of a vital circuit arrange-
ment including an optical coupler for reyistering the presence
or absence of two input signals by the position of a relay
element.
FIG. 2 is a chart illustrating the wave form of the
output signal from the circuit arrangement illustrated in
FIG. 1 which is used to energize the registry relay.
`~ ~.1.33~
FIG. 3 illustrates schematically the use of the optical
coupler circuit arrangement of FIG. l as a dual input track
relay means in an alternating current track circuit.
FIG. 4 is a chart illustrating the relative D. C. output
level of the FIG. 1 circuit arrangement as a function o the
pha~ relationship between the input signals.
FIG. 5 is another chart showing the D C. output of the
FIG. l circuik arrangement as a function of the frequency of
the track input signals. ~-
In each of the drawing figures, similar reference charac-
ters designate the same or similar apparatus or functions. ~;
DESCRIPTION OF T~ ILLUSTRATED EMBODIME~T ~:
Referring to FIG. 1, a vital optical coupler circuit arrange-
ment lS shown with its two principal or controlLing elements,
the light emitting diode D2 and the photo resistive cell or
device PRC. ~he LED element D2 is shown by conventional symbol
and has the normal expected characteristic of being actuated to
emit light when current flows in the conventional positive direc-
tion through the u~it. The photo resistive cell PRC is also
shown by a conventional symbol and has the characteristic of
reducing its series resistance when illuminated by a light source,
the reduction being to a relatively low level to allow a greater
magnitude of current to flow through the corresponding circuit.
As to physical mounting, the LED D2 may be either a single
element, as shown in the drawings for simplicity, or a series
connected cluster of high intensity diode emitters. In either
arrangement, the LED'S are focused on device PRC so that the
,~t - 7
~ 3L33~
emitted light actuates the photo resistive cell to lower its ~ -
resistance. Although not specifically shown in the drawings,
the LED element is preferably a cluster of such uniks so that
the photo resistive cell is actually overdriven to assure com-
plete response. This over-driving compensates for aging of the
LED units, for output variations due to temperature changes, and
provides some voltage regulation of the input signals. All sub-
sequent references to a light emitting diode element, including
those in the claims, refer to either arrangement.
The entire circuit arrangement is designed to detect or
indicate the presence of both of two input signals or the
absence of at least a selected one of the two, each supplied
through an input means from a selected source. These input
~means are the transformers Tl and T2. Transformer Tl is a
step-down transformer while transformer T2, of the saturable
type as shown, is a step-up transformer so that the two
secondary outputs will be o the same general voltage range
under normal conditions. The corresponding instant polarity of
the various windings of these two input transformers is desig-
nated in the conventional manner by the dot symbols.
The primary winding of transformer Tl is connected to alocal source of A. C. signal energy to receive input signal VL
which has a preselected frequency, for example, 100 Hz. The
step-down characteristic of transformer Tl supplies a secondary
~5 voltage signal VL2 which i5 of a comparable level with that
supplied by the other transformer, to be discussed shortly.
The secondary of transformer Tl is connected, in series with
a noise rejecting band pass filter comprised of capacitor C
~31 33~0~ :
and inductor L and series tuned to the frequency of signal
VLl, to supply signal VL2 to LED D2. A resistor R in this
circuit, together with the impedance of inductor L, limits
the current flowing through diode D2. A conventional diode ~ -
Dl is connected in parallel with diode D2 but with opposite
polarity to protect the LED against excess reverse polarity
voltage in the circuit. When signal VL2 is present, which is
normally continuously, diode D2 is turned on to emit light
every positive half cycle, that is, when current flows through
diode D2 in its low resistance direction. This LED, either a
single element or a cluster, is positioned so that its output
is focused on the photo resistive c~ll PRC. Thus the resis-
tance of unit PRC decreases periodically to a relatively low -
leve-l during each positive half cycle of signal VL2.
The primary winding of transformer T2 is connected to a
second source of alternating current, having the same freque~cy ~ .
as and synchronized with the local source previously mentioned
to receive ~he second input signal VTl. In the specific
example herein, this primary winding LS connected to a trans-
mission channel, e. g., the track rails, which is supplied
with energy from the same central source as the local energy
supply connected to transformer Tl. As mentioned, transformer
T2 is a step-up transformer and has saturable charackeristics
to provide an amplitude limiting feature for the circuit
arrangement. In the principal use of this arrangement in
trac~ circuits, the saturable characteristic of transformer
T2 limits excessive voltage levels of signal VTl when an
3~
insulated joint failure allows the transmitted signal from
the adjoining track section to feed direct into this receiver
apparatus.
The secondary of transformer T2 supplies a signal VT2,
whic~ is of the same order of magnitude normally as signal
VL2~ ~o the circuit network consisting of device PRC and a
biased direct current vital relay TR. This relay as shown is
c~nnected between the output terminals ~+ and R-, for the
circuit arrangement, with the polarity such that conventional
current ~lowæ in the proper direction through the relay winding
as designated by the small arrow therein. A current arrow I
is shown ass~ciated with this circuit network in order to
provide a reference for correlation with the charts in the
other figures. When signals VLl an~d VTl are in phase, and
of course are of the same freguency, the current I flowing
through the network from the secondary of transformer T2 is
shown by the solid line in FIG. 2. This is a modified alter-
nating current of the frequency of signal VT2 and its wave
form is determined by the periodic change in the resistance
through photo resistive cell PRC. This current has a direct -~
current component shown by the dash line designated as the
AVERAGE DC LEVEL, which energizes relay TR. Thus this optical
coupler network acts as a synchronous rectifier to provide
the D. C. component in current I which is o~ the propex
polarity to enexgize relay TR when the input conditions or
signals have the proper characteristics.
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~L~33~LO~L
A principal use for the optical coupler circuit arrange-
ment of FIG. 1 is in a railroad trac~ circuit as illustrated
in FIG. 3. In this drawing, a track section T of a stretch
of electrified railroad is shown with its rails 1 and 2 illus-
trated by conventional single line s~mbols. The rails ofsection T are electrically insulated from the rails of the
adjoining sections by the insulated joints 3, also illustrated
by conventional symbols. In order to provide a return circuit
for the propulsion current, lmpedance bond windings 4 are con- :
nected across rails 1 and 2 at eac~ end of section T and the : ;
associated ends of the adjoining sections. Center taps of
each associated pair of bond windings 4 are connected by a
lead 5 to provide a conventional circuit path through section
T for propulsion current. It.is here assumed that the fre-
quency of the A. C. propulsion power is the ommonly used 25 ~.
or 60 Hz.
A signaling system for this stretch of railroad is based
on continuous train detection using an A. c. track circuit for
each track section such as section T. Signaling energy for
the track circuits lS provided from a central source S, shown
conventionally at the lower left and having a preselected
frequency, for example, 100 Hz, and is distributed along the
stretch of railroad by the line wires 6 and 7. Energy is
supplied across the rails of section T at the left or trans-
mitting end through a track trans~ormer TT from line circuit6, 7. The supply connections include an adjustable resistor
Z which limits the current flow when a train shunts the rails
~33~
at the transmitting end. Track transformer TT may be incorpor-
ated as part of the impedance bond but is preferably a separate
transformer~ as shown. At the other or receiving end of sec-
tion T, the optical coupler circuit arrangement of FIG. 1 is
connected across the rails and to the line circuit. This
circuit is illustrated by a dashed block with input and output
terminals designated by-~he same references as in FIG. 1. For
example, the terminals VLl are connected across line wires 6 and
7 to receive energy direct from source S at this local location.
Terminals VTl are connected across rails 1 and 2 at the same
point as bond winding 4 at ~his end of the tracX section. ~he
txa~k relay TR, which is of the same biased vital type as in
FIG. 1, is connected across terminals R~ and R- with proper
polarity for energizing the relay when output is pxesent.
Considering now the operation of the track circuit, it is ;;
to be re~embered that the ~ital optical coupler circuit network
~onnected within t~e track circuit of FIG. 3 acts as a two ele- `~
ment A. C. txack relay means to register the absence or presence
of a train within section T. This device will also detect the
presence of a broken rail within the section which interrupts
the normal flow of track current~ The track circuit is adjusted
with minimum ballast conditions Iwet weather, low resistance)
so that the track and local signals ~VTl and VLl~ at the
receiver end are in phase. Under these conditions, track
current is approximately at the minimum level which will s~ill
pick up relay TRo In other words, the averaged D. C. output
is at the relative 1.0 level of the charts shown in FIGS. 4
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and 5. Under dry weather conditions, with high ballast resis-
tance, the track current is at a maximum level. ~e phase of
the rack signal VTl, under these maximum current conditions, .
leads the p~a~e of the local signal VLl. In FIG. 4, the chart
illustrates that the output D. C. of the optical coupler
network is attenuated fxom its maximum value 1.0 under phase
shift conditions. However, with maximum track current, t~e
larger VTl input signal compensates for the reduced multiplier
function, from the phase shift curve, so that sufficient output
remains to energize track relay TR. In other words, the
out-of-phase attenuation is counterbalanced by the higher
level of the track current. Of course, the biased relay TR ~:~
. will not respond to a reverse polarity output, i. e., phase
shifts beyond ~ or -.90. Thus any extreme phase shift, or
a moderate shift without increased rail current, due to a
fault condition, results in the release of relay TR.
When a train occupies section T and shunts the rails, the
reception o~ rail current at the receiver end is inhibit~d.
With no input signal VTl and thus signal VT2 absent, no energy
is available to supply the current through the device PRC f
relay TR network, even though LED D2 is periodically activated
by the continuously supplied local signal VLl. Track relay ~-
TR i~ thus deenergized and releases to register the tracX
occupied indication. In other words, the circuit detects and
5 registers the absence of the one selected signal, i. e., VT
q~ afc
which may also be caused by~ broken rail condition.
~L~33~
This optical coupler circuit arrangement has extremely
sharp rejection of signals at o~her than the track circuit
frequency~ This is illustrated in the chart o~ FIG. 5 for
the spec fic assumed example of a track circuit frequency of
100 Hz. It is to be noted that the circuit arrangement rejects
large undesired propulsion current signals of either 25 or 60
Hz frequency, and the common second and third haxmonics
thereof, without any additional filtering. Even on the
amplified ~ertical scale used in FIG. 5, the averaged D. C.
output at these unwanted ~requencies is not measurable. This
results from the natural or inherent synchronous filter charac-
teristics of the disclosed circuit arrangement. In other
words, the synchronous rectifier action of LED D2 and photo
resistive cell PRC results in a registerable output from the
arrangement only when both input sic~nals are at the track
circuit frequency.
This circuit arrangement is al~o vital, that is, fail-
safe, since any failure in the LED drive circuit connected to
the secondary of transformer Tl, either an open or a short
circuit, results in a decreased light pulse level. If the
photo resistive cell opens, the xelay current ceases. Further,
should this photo cell short out, the relay will receive an
alternating current and will not respond since it is a biased
D. C. relay. A short or open circuit failure in transformer
TR2 will also result in a fail-safe condition, that is, the
track relay releasing to indicate an occupied section. Thus
any failure or circuit element fault within the arrangement
_ 14 -
~31~ ;
re~ults in the release of track relay TR to indicate an
occup~ed track section, which is a safe condition.
The optical coupler circuit arrangement of my invention
thus provides for an improved track circuit for electrified
railroads. The two element circuit network uses passive
circuit elemenks except for the final registry track relay
which is a conventional and readily availa~le type of high
reliability and low maintenance requirements. Preventative
maintenance for thP entire track circuit is ~hus reduced and
the reliability increased. The excellent phase angle and
frequency response of prior art apparatus is retained so that
broken rails can be detected and high level propulsion current
signals rejected. This results in an efficient and economical
track circuit apparatus.
Although I have herein shown and described but a single
optical coupler track circuit arrangement ambodying the inven~
tion, it is to be understood that various changes and modifi-
catlons therein may be made wi~hin the scope of the appended
claims without departing from the spirit and scope of my
inv~ntion.
