U.S. patent number 3,850,390 [Application Number 05/348,944] was granted by the patent office on 1974-11-26 for railway signal system with speed determined movement detector.
This patent grant is currently assigned to Erico Rail Products Company. Invention is credited to Willard L. Geiger.
United States Patent |
3,850,390 |
Geiger |
November 26, 1974 |
RAILWAY SIGNAL SYSTEM WITH SPEED DETERMINED MOVEMENT DETECTOR
Abstract
A railway signal system for detecting a train approaching a
railway crossing or track section transmits in the track a
periodically interrupted carrier wave signal the amplitude of which
is attenuated by an approaching train effecting a variable shunt
across the track. A receiver converts the received signal to a DC
level with an impressed AC pulse for application through a DC
blocking differentiating capacitor to an amplifier, which produces
an AC output used to effect pick up of a signal relay unless an
approaching train is detected. The system is self-checking and
fail-safe using an astable multivibrator to control power supplied
to the relay driver, and the system provides for increased
sensitivity with increased train proximity. Additional circuits
including a broken rail detector power monitor, island amplifier,
loss of shunt detector, and disabling circuit for the latter
provide added capability for the system.
Inventors: |
Geiger; Willard L. (Chagrin
Falls, OH) |
Assignee: |
Erico Rail Products Company
(Cleveland, OH)
|
Family
ID: |
23370248 |
Appl.
No.: |
05/348,944 |
Filed: |
April 9, 1973 |
Current U.S.
Class: |
246/128;
246/34CT; 246/121 |
Current CPC
Class: |
B61L
1/187 (20130101) |
Current International
Class: |
B61L
1/00 (20060101); B61L 1/18 (20060101); B61l
023/04 () |
Field of
Search: |
;246/125,128,13R,34R,34CT,40,121 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wood, Jr.; M. Henson
Assistant Examiner: Libman; George H.
Attorney, Agent or Firm: Donnelly, Maky, Renner &
Otto
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track
comprising a transmitter and a receiver; said transmitter including
means for producing an AC signal, means coupling said means for
producing to said track for transmitting said AC signal in said
track, means for monitoring the power level of said AC signal; and
said receiver including receiver means coupled to said track for
receiving said AC signal, said receiver means including means for
detecting said AC signal to effect production of said output signal
in response to changes in said AC signal occurring upon the
approach of a train, said means for detecting including means for
responding to changes in said AC signal effected by an approaching
train located beyond the island defined between connections of said
means for transmitting and said receiver means to said track; and
said means for monitoring being also coupled to said receiver means
and including means for causing at least a portion of said receiver
means to produce said output signal when the power level of said AC
signal coupled to said track drops below a minimum level.
2. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 1, wherein said means for producing comprises
tone generator means for producing an interrupted carrier signal as
said AC signal.
3. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 2, wherein said means for producing further
comprises oscillator means coupled to said tone generator means for
effecting interruption of said carrier signal.
4. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 3, wherein said means for producing further
comprises switching diode means and capacitor means coupled to said
oscillator means for interrupting said carrier signal.
5. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 1, wherein said means for coupling comprises
impedance matching circuit means for matching the output impedance
of said means for producing to the input impedance of the track to
which the latter is coupled, said impedance matching circuit means
including a coupling transformer.
6. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 1, wherein said means for monitoring comprises
means for producing a voltage output signal in response to said AC
signal current produced in said track by said means for
producing.
7. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 1, wherein said receiver means comprises highly
selective filter means for passing a signal having the frequency of
said AC signal, and amplifier means coupled to said filter means
for amplifying the output thereof.
8. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 1, wherein said receiver means comprises
amplifier means having a variable effect gain over the major extent
of the operational range thereof, the magnitude of such effective
gain being determined by the characteristics of a received input
signal.
9. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 8, wherein said receiver means further comprises
wave shaping circuit means for producing from said received AC
signal an output signal having a DC signal component and a
proportional AC pulse component impressed thereon, and capacitor
means for normally blocking said DC signal component from said
amplifier means and for normally passing said AC pulse component to
said amplifier means, whereby upon receipt of said AC pulse
component said amplifier means produces an AC output signal and
upon decrease of said DC signal component at a rate greater than
the rate of increase of said AC pulse said amplifier means produces
a DC output signal.
10. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 9, further comprising negative slope detector
means coupled to said amplifier means for producing an AC output
signal when a portion of the amplifier means output signal has a
negatively sloped portion.
11. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track as
set forth in claim 1, further comprising means coupled to said
receiver means and responsive to the presence of a train in at
least a portion of said island for effecting production of said
output signal.
12. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track
comprising means for producing an AC signal; means coupling said
means for producing to said track for transmitting said AC signal
in said track; means for monitoring the power level of said AC
signal; receiver means coupled to said track for receiving said AC
signal, said receiver means including means for detecting said AC
signal to effect production of said output signal in response to
changes in said AC signal occurring upon the approach of a train;
and said means for monitoring comprising means for causing at least
a portion of said means for receiving to produce said output signal
when the power level of said AC signal coupled to said track drops
below a minimum level, including means for producing a voltage
output signal in response to the AC signal current produced in said
track by said means for producing an AC signal, said means for
producing a voltage output signal comprising amplifier means for
amplifying a signal proportional to the AC signal current produced
in said track, and trigger circuit means coupled to said amplifier
means for producing output pulses having a duration proportional to
the output from said amplifier means.
13. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train in a track as
set forth in claim 12, wherein said means for monitoring further
comprises rectifier means coupled to said trigger circuit means for
producing a DC output signal proportional to the duration of said
pulses.
14. A railway signal system for producing an output signal
indicative of the occurrence of an approaching train on a track
comprising means for producing an AC signal, means coupling said
means for producing to said track for transmitting said AC signal
in said track, means for monitoring the power level of said AC
signal, receiver means coupled to said track for receiving said AC
signal to effect production of said output signal in response to
changes in said AC signal occurring upon the approach of a train,
said means for monitoring including means for causing at least a
portion of said means for receiving to produce said output signal
when the power level of said AC signal coupled to said track drops
below a minimum level, and a utilization circuit including astable
multivibrator means having first and second input circuits
providing separate DC power signals therefor, one of said input
circuits being responsive to the power level of said AC signal
coupled to said track and the other one of said input circuits
being responsive to receipt of an AC output signal from said means
for receiving.
15. A railway signal apparatus for detecting a train approaching a
location on a railroad track comprising means for producing a
detectable signal along such track such that a train approaching
such location causes a change in the level of such detectable
signal, means for receiving said detectable signal for sensing
changes in the level of such detectable signal and producing a
first output when no changes occur and a second output when changes
occur in a given direction from a first level, said second output
being indicative of an approaching train, means for preventing said
means for receiving from changing to said first output when said
means for receiving is producing said second output and said
detectable signal temporarily changes toward said first level, and
means for disabling said means for preventing when said means for
receiving is producing said first output whereby upon occurrence of
a train leaving such location on such railroad track said means for
disabling is ineffective.
16. A railway signal apparatus for detecting an approaching train
as set forth in claim 15, wherein said means for producing
comprises tone generator means for producing an interrupted AC
carrier signal.
17. A railway signal apparatus for detecting an approaching train
as set forth in claim 16, wherein said means for producing further
comprises oscillator means for interrupting said carrier
signal.
18. Railway signal apparatus for detecting an approaching train as
set forth in claim 15, wherein said means for receiving comprises
means sensitive to the rate at which said detectable signal changes
in said given direction including wave shaping means for producing
in response to receipt of said detectable signal a DC signal with a
proportional AC pulse impressed thereon.
19. Railway signal apparatus for detecting an approaching train as
set forth in claim 18, further comprising an amplifier having an
input and an output and capacitor means for coupling said amplifier
input to said wave shaping means, whereby said capacitor means
normally blocks said DC signal from said amplifier input and
normally passes said AC pulse to said amplifier input.
20. Railway signal apparatus for detecting an approaching train as
set forth in claim 19, wherein said means for preventing comprises
further amplifier means having an input and an output, said output
of said further amplifier means being coupled to said amplifier
means for disabling same upon receipt of an input signal at said
input of said further amplifier means, and time delay circuit means
coupled for energization upon such temporary changes for providing
an input signal to said further amplifier means.
21. Railway signal apparatus for detecting an approaching train as
set forth in claim 15, wherein said means for preventing comprises
further amplifier means having an input and an output, said output
of said further amplifier means being coupled to said amplifier
means for disabling same upon receipt of an input signal at said
input of said further amplifier means, and time delay circuit means
coupled for energization upon such temporary changes for providing
an input signal to said further amplifier means.
22. Railway signal apparatus for detecting an approaching train as
set forth in claim 21, wherein said means for disabling comprises
means for disabling said output of said further amplifier means
upon receipt of said first output from said means for
receiving.
23. Railway signal apparatus for detecting an approaching train as
set forth in claim 15, further comprising monitoring means for
producing a power level signal indicative of the power level of
said detectable signal.
24. Railway signal apparatus for detecting an approaching train as
set forth in claim 23 further comprising utilization circuit means
coupled to said means for receiving and said monitoring means for
producing an AC output signal indicative of no approaching train
when said first output occurs from said means for receiving and
said power level signal is produced by said monitoring means, and a
DC output signal indicative of an approaching train upon receipt of
said second output or an insufficient power level signal
conditions, whereby the latter condition is indicative of a defect
in said track or said apparatus.
25. Railway signal apparatus for detecting an approaching train as
set forth in claim 24, wherein said utilization circuit means
comprises an astable multivibrator circuit, and said means for
receiving and said monitoring means are coupled to said astable
multivibrator circuit for providing respective first and second DC
power inputs thereto.
26. A railway signal system comprising means for providing an
interrupted carrier wave, means for receiving said interrupted
carrier wave, and means responsive to an output from said means for
receiving for providing an indication of an approaching train, said
means for receiving including means for producing from said
received interrupted carrier wave a signal normally having DC and
AC parts, amplifier means for producing from an input signal a
corresponding output signal, and differentiating capacitor means
coupled to said amplifier means for normally blocking said DC part
and passing thereto said AC part of said signal, an AC output from
said amplifier means coupled to said means responsive being
indicative of no approaching train and a DC output from said
amplifier means occasioned by a drop in the level of said DC part
at a rate at least approximately equal to the rate at which said AC
part increases being indicative of detection of an approaching
train.
27. A railway signal system as set forth in claim 26, wherein said
means for providing an interrupted carrier wave comprises an
oscillator for producing said carrier wave and a pulser circuit for
periodically interrupting said carrier wave.
28. A railway signal system as set forth in claim 26, wherein said
means for producing comprises a resistance and capacitor wave
shaping circuit.
29. A railway signal system as set forth in claim 26, further
comprising a normally saturated negative slope detector means
coupled to the output of said amplifier means for producing an AC
output signal when a portion of said corresponding output signal is
negatively sloped.
30. A railway signal system as set forth in claim 29, wherein said
means responsive comprises an astable multivibrator.
31. A railway signal system as set forth in claim 29, further
comprising means for maintaining an indication of an approaching
train after such has been detected and such detection has been
temporarily lost, said last mentioned means including timing
circuit means for determining the duration of such maintained
indication.
32. A railway signal system comprising means for providing an
interrupted carrier wave; means for receiving said interrupted
carrier wave; negative slope detector; and astable multivibrator
means responsive to an output from said negative slope detector for
providing an indication of an approaching train; said means for
receiving including means for producing from said received
interrupted carrier wave a signal normally having DC and AC parts,
amplifier means for producing from an input signal a corresponding
output signal, and differentiating capacitor means coupled to said
amplifier means for normally blocking said DC part and passing
thereto said AC part of said signal; said negative slope detector
being normally driven at saturation and coupled to the output of
said amplifier means for producing an AC output signal when a
portion of said corresponding output signal is negatively sloped
driving said negative slope detector out of saturation; and said
astable multivibrator having a first input coupled to said negative
slope detector output and a second input responsive to the power
level of said interrupted carrier wave; whereby an AC output from
said amplifier means coupled to said astable multivibrator means is
indicative of no approaching train and a DC output from said
amplifier means occasioned by a drop in the level of said DC part
at a rate at least approximately equal to the rate at which said AC
part increases is indicative of detection of an approaching train
or of insufficient power of said interrupted carrier wave.
33. A railway signal system as set forth in claim 32, further
comprising means for sensing the power level of said interrupted
carrier wave.
34. A railway signal system comprising means for providing an
interrupted carrier wave; means for receiving said interrupted
carrier wave; negative slope detector; and means responsive to an
output from said negative slope detector for providing an
indication of an approaching train; said means for receiving
including means for producing from said received interrupted
carrier wave a signal normally having DC and AC parts, amplifier
means for producing from an input signal a corresponding output
signal, and differentiating capacitor means coupled to said
amplifier means for normally blocking said DC part and passing
thereto said AC part of said signal; said negative slope detector
being normally saturated and coupled to the output of said
amplifier means for producing an AC output signal when a portion of
said corresponding output signal is negatively sloped driving said
negative slope detector out of saturation; whereby an AC output
from said amplifier means coupled to said means responsive is
indicative of no approaching train and a DC output from said
amplifier means occasioned by a drop in the level of said DC part
at a rate at least approximately equal to the rate at which said AC
part increases is indicative of detection of an approaching train;
means for maintaining an indication of an approaching train after
such has been detected and such detection has been temporarily
lost, said last mentioned means including timing circuit means for
determining the duration of such maintained indication; and means
for disabling said means for maintaining upon occurrence of a
leaving train.
Description
BACKGROUND OF THE INVENTION
This invention relates to a fail-safe railway signal system for
detecting an approaching train and particularly to such a system
having increased sensitivity with increased train proximity.
Prior art railway signal systems for detecting approaching trains
have used various techniques to compensate for train approach and
speed to achieve minimum down time during which a signal device is
activated to provide an indication, for example, at a grade
crossing or at another track section, when a train is approaching,
existing in, or leaving a railway crossing area or a specific track
section. The signal device may be coupled to provide a signal to a
control system, for example, a computer, for automated train
control.
Several already existing signal systems for detecting trains
require long islands defined by the track connection points of the
transmitter and receiver in order to provide adequate time for
train detection. Other prior art devices are sensitive to train
approach speed, but do not vary their sensitivity as the approach
distance varies; and if a train were to slow gradually as it
approached an island, the train would be nearly in the island
before being detected.
Still further existing systems use signals of varying frequency
with each frequency matched to the distance and time requirements
to achieve a constant working time throughout the approach to the
island, and one disadvantage of such systems is that there often is
a speed below which detection will not occur.
A disadvantage to the prior art railway signal systems is that
without sensitivity changes with respect to distance, a train
consisting of only a single car and engine may suddenly accelerate
after approach time prediction to put the engine almost in the
crossing before gate actuation. A further disadvantage is the
relatively long ring-by time, during which the presence of the
train is indicated even when the train is actually leaving the
island.
Some train detection systems use DC amplifiers to produce output
signals indicative of train detection, and in such systems it is
necessary to maintain a constant check on the DC portion of the
amplifier, such as, for example, by the use of a checking pulse
introduced at regular periods, for example, every five or six
seconds. Such devices result in a loss of authenticity of the
amplifier for each five or six second period, and train detection
will not be credible until after a self-check pulse is initiated;
but the five or six second delay in assuring train detection
coupled together with inherent relay and other similar delays can
be critical when the train is approaching at high speed.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the invention to provide a
fail-safe railway signal system for indicating the presence of a
train while assuring minimum down time of the railway signal
relay.
Another object of the invention is to provide a railway signal
system in which sensitivity increases as the train approaches.
An additional object of the invention is to provide a fail-safe
railway signal system with maximum integrity, such system
recognizing its own signal, being self-checking, and having low
signal and low voltage monitoring capability.
A further object of the invention is to provide a railway signal
system having broken rail detection, island control, and motion
detection functions.
Still another object of the invention is to provide a railway
signal system with minimum ring-by.
Still an additional object of the invention is to provide in a
railway signal system loss of shunt protection which is disabled by
a leaving train.
Still a further object of the invention is to provide a constant
checking of track integrity and self-compensation for low ballast
conditions in a railway signal system that indicates a train
approaching or existing in an island.
Yet another object of the invention is to provide an amplifier with
variable sensitivity.
Yet an additional object of the invention is to provide a fail-safe
circuit for producing an AC output signal upon occurrence of plural
DC input signals.
Yet a further object of the invention is to detect a slow or fast
moving train approaching a railway crossing or a track section
without requiring an extended island.
Even another object of the invention is to provide a railway signal
system having continuous rapid self-checking capability to provide
a credible indication of an approaching train.
These and other objects and advantages are realized in the instant
invention which comprises a transmitter for transmitting an
interrupted carrier signal in a track, a broken rail detection
circuit for monitoring the track signal, a receiver for receiving
and amplifying the track signal, a movement detector for
determining changes in such signal indicative of an approaching
train, a negative slope detector for providing noise immunity,
signal regulation, and minimum ring-by, an island amplifier for
detecting a train in the island, a loss of shunt detector for
disabling the movement detector upon occurrence of a temporary loss
of shunt and a circuit for disabling the latter upon occurrence of
a leaving train, a multivibrator for providing an AC output in
response to respective DC inputs, and a relay driver for providing
a signal to energize or to pick up a relay when no trains are
approaching or present and the entire railway signal system is
properly operating and to drop or to release the relay when train
motion or presence is detected or when the system malfunctions.
To the accomplishment of the foregoing and related ends, the
invention, then, comprises the features hereinafter fully
described, the following description and the annexed drawings
setting forth in detail certain illustrative embodiments of the
invention, these being indicative, however, of but several of the
various ways in which the principals of the invention may be
employed.
BRIEF DESCRIPTION OF THE DRAWINGS
In the annexed drawings:
FIG. 1 is a schematic electric circuit diagram partially in block
form of a railway signal system in accordance with the
invention;
FIG. 2 is a schematic electric circuit diagram of the movement
detector and driver therefor, negative slope detector, and loss of
shunt detector of the railway signal system;
FIG. 3 is a graph of an interrupted carrier wave signal produced in
the transmitter of the railway signal system;
FIG. 4 is a graph of a DC signal with an impressed AC pulse applied
to the movement detector; and
FIG. 5 is a graph of an AC signal having a negatively sloped
portion applied to the negative slope detector.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The railway signal system has a transmitter and a receiver
connected to a section of railroad track, for example, at a
railroad grade crossing or on a specific track section in a block
signal arrangement, with an island being defined between such
connections. In the preferred embodiment a beginning of approach
shunt is connected across the railroad tracks at a distance in
either or both directions sufficient to provide adequate time for
indicating a rapidly approaching train. The system compensates
automatically for varying ballast conditions, which often change
with temperature, moisture, and normal track wear, is self-checking
at a rate of approximately five times per second, is insensitive to
noise, and is sufficiently sensitive to detect motion as slow as
several feet per second on a close approach.
Referring now more specifically to the drawings wherein like
reference numerals refer to like elements in the several figures,
the railway signal system generally indicated at 1 includes a
transmitter 2, a broken rail detector 3 and a receiver 4. The
transmitter 2 receives power at the input terminals 5, 6 and has a
plural resistor, capacitor, and zener diode voltage regulation
circuits 7, 8 and an isolating diode 9 connected between a buffer
amplifier 10 and a track driver amplifier 11 with the output from
the former being connected through a coupling capacitor 12 to the
input to the latter.
A frequency or tone generator circuit generally indicated at 15
includes a conventional reed oscillator 16 having an energization
circuit including the transistor 17 and a feedback circuit
including the transistor 18 which is connected through an RC
network 19 to the base of the former transistor. Additional
resistors and capacitors are provided to effect resonant vibration
in the reed oscillator 16, thereby producing at the potentiometer
20 a carrier wave having a frequency depending on the oscillator
and an amplitude depending on the setting of such potentiometer. A
more detailed description of the tone generator circuit 15 may be
found in my co-pending patent application Ser. No. 105,509, filed
Jan. 11, 1971, and assigned to the same assignee as the instant
application.
A pulser 21, having a positive input connected through a light
emitting diode 22 and a negative input, provides a pulse signal on
the line 23 to a diode gating circuit generally indicated at 24
including a diode 25 and capacitors 26, 27. The pulser circuit 21
may include, for example, a well known unijunction transistor
oscillator circuit which produces a periodic pulse signal on the
line 23 to effect interruption of the carrier wave, and a flashing
of the diode 22 indicates proper pulser operation. The interrupted
carrier wave is shown graphically in FIG. 3 and is provided through
the capacitor 27 to the buffer amplifier 10, which may include one
or more stages for shaping such signal. The track driver amplifier
11 including a conventional potentiometer off-set circuit 29
provides the resulting interrupted carrier signal to the railroad
tracks 30, 31 through a coupling transformer 32, an impedance
matching network 33, and a surge protection apparatus 34, such as,
for example, a lightning arrester arrangement.
The broken rail detector 3 includes a broken rail detector
amplifier 40 having a power input taken across input terminals and
a resistor, capacitor, and zener diode voltage regulating network
41 with a conventional potentiometer off-set circuit 42. A coupling
transformer 43 provides to the broken rail detector amplifier 40 an
input signal proportional to the power level of the interrupted
carrier wave signal applied to the tracks 30, 31, and the output
from such amplifier is coupled through a transformer 44, full wave
rectifier 45, and filter network 46 to an output terminal 47a.
Thus, a DC signal representative of the power applied to the track
is produced at terminal 47a the purpose of which will be described
in detail below. The broken rail detector amplifier 40 may include,
for example, one or more buffer stages and a threshhold device,
such as a schmitt trigger circuit, whereby the output signal from
the broken rail detector amplifier is an AC signal having an
amplitude, phase, and frequency characteristic indicative of the
power applied to the track by the transmitter 2.
The receiver 4 is connected to the tracks 30, 31, defining an
island 50 between such connection and the connection of the
transmitter 2 to the tracks, and receives a signal therefrom
through the surge protection apparatus 51, impedance matching
network 52, coupling transformer 53, potentiometer 54, and highy
selective filter 55. The output from the filter 55 is applied to
the receiver amplifier 56, which receives a power input across
appropriate terminals and a zener diode and transistor voltage
regulation circuit 57. A first output from the receiver amplifier
56 is connected by line 60 to the movement detector driver 61,
which has power input terminals and a voltage regulation circuit 62
with a conventional potentiometer off-set circuit 63; and a second
output is connected by line 64 to the island amplifier and relay
driver 65, which has an off-set circuit 66 and power input across
an RC network 67.
The movement detector driver 61 is coupled through a transformer 70
and a full wave rectifier 71 to the input of the wave shaping
circuit 72, the normal output signal E.sub.d from which is a DC
level v with an AC pulse impressed thereon as shown in FIG. 4. The
wave shaping circuit 72 provides an input to the movement detector
73, which has a power connection at the terminals and a voltage
regulation circuit 74. A light emitting diode 75 connected in the
movement detector emits light pulses as the latter produces an AC
output indicating proper operation when no train is detected.
Another input to the movement detector is made by the line 76
coupled to the loss of shunt detector 77 to be described in more
detail below.
The movement detector 73 outputs, having a normal signal wave form
as shown in FIG. 5, is coupled to a negative slope detector 80,
which is responsive only to the negatively sloped portion of such
signal and provides for noise immunity in the railway signal system
1 while minimizing ring-by when a train leaves the island 50. The
negative slope detector 80 has an additional input from the island
amplifier and relay driver 65 by way of the loss of shunt detector
77, which is shown in more detail in FIG. 2; and the power
transistor 81 and pulse transformer 82 provide an output from the
negative slope detector.
The island amplifier circuit including an island amplifier and
relay driver 65 is coupled to a coupling transformer 83, full wave
rectifier 84, and filter 85 and to the loss of shunt detector 77,
which has another input taken on the line 86 from the full wave
rectifier 71. The island amplifier circuit and loss of shunt
detector provide a power input to the negative slope detector 80 on
the line 78, whereby, if no output is produced by the former, the
latter is incapable of producing an output. A resistor 87a and a
relay coil 87b of comparable impedance are shown for optional
connection across the island amplifier and relay driver output and
the loss of shunt detector input.
The secondary of the coupling transformer 82 is connected to a
capacitor 88, which is coupled as one DC input to a conventional
astable multivibrator 89; and the other DC input to the astable
multivibrator is taken across the capacitor 90 connected for
charging through the resistor and diode network 91 by a signal at
the terminal 47b, which is coupled to terminal 47a at the broken
rail detector output. The astable multivibrator 89 output is
supplied on the line 92 to the railroad signal relay driver 93
having a power input across the terminals and voltage regulation
circuit 94, and the output from the railroad signal relay driver is
connected to a transformer 95. A full wave rectifier 96 supplies an
energization signal from such transformer to the railroad signal
relay 97 to pick up the same. Of course, when no signal is supplied
to the relay 97 it is dropped or released indicating detection by
the railway signal system 1 of an approaching train, the presence
of a train in the island, or a malfunction in the railway signal
system.
In the preferred embodiment the receiver amplifier 56, movement
detector driver 61, island amplifier and relay driver 65, and
railway signal relay driver 93 are conventional amplifier circuits
having one or more stages of solid state design for accuracy,
efficiency, durability, and longevity. In order to achieve an
energization signal to pick up the relay 97 it is essential that
both halves of the astable multivibrator 89 be energized which is
achieved only when the signal transmitted in the tracks is of a
sufficient level and the movement detector 73 and negative slope
detector 80 produce respective AC outputs to provide a signal
through the pulse transformer 82 to charge capacitor 88.
In operation of the railway signal system 1 the transmitter 2
transmits the interrupted carrier wave in the tracks 30, 31, and
the broken rail detector 3 produces at the terminal 47a a DC
voltage representative of the power delivered to the tracks by
sensing the current flow. The receiver 4, amplifies the filtered
signal from the tracks and applies an AC signal on the line 60 to
the movement detector driver 61 for further amplification with the
output from the latter being transformed, rectified, filtered, and
provided to the wave shaping circuit 72 to produce the signal wave
form illustrated in FIG. 4.
Each time the pulsed signal applied to the movement detector 73
goes negative, simulated movement is detected, and as the pulse
again recovers in the positive direction movement detection ceases.
The light emitting diode 75 produces light flashes indicative of
proper functioning of the railway signal system when no train is
detected and the diode 22 indicates the pulser 21 is operating. As
long as railway signal system 1 is operative and the power of the
track signal is sufficient, the capacitors 88, 90 drive the astable
multivibrator 89 to produce an AC signal, which is amplified in the
railway signal relay drive 93 to pick up the relay 97.
If a broken rail condition or an unusual ballast condition occurs
on the tracks 30, 31 to cause the current applied to the tracks by
the transmitter 2 to drop below a prescribed minimum, the voltage
level at the terminal 47a in the broken rail detector 3 drops and
is inadequate to charge the capacitor 90, and the relay 97 is
dropped. The railway system 1 is fail-safe. If the pulser 21, tone
generator circuit 15, or any other part of the transmitter 2
malfunctions, then no AC signal will be coupled through the
receiver amplifier 56, movement detector driver 61, movement
detector 73, and negative slope detector 80 to the transformer 82;
and the capacitor 88 will not charge. Thus, the astable
multivibrator 89 will not run, and the relay 97 will drop
indicating a circuit malfunction.
When a train crosses one of the beginning of approach shunts in a
direction toward the island 50, the voltage level of the signal in
the tracks begins to decrease, although the current increases since
the train as a travelling shunt reduces the effective ballast seen
by the transmitter 2, and the E.sub.d signal level v as well as the
pulse impressed thereon decreases proportionately. A train in the
island 50 shunts the entire track signal, and the input to the
receiver 4 is effectively zero. In the latter case the island
amplifier and relay driver 65 produces a zero or DC output and no
signal is produced in the transformer 83 secondary, thus releasing
the relay coil 87b if used, which may be coupled to effect firm
lock out of the railway signal, and/or preventing conduction in the
negative slope detector 80.
Referring now to FIG. 2 the wave shaping circuit 72, movement
detector 73, loss of shunt detector 77, and negative slope detector
80 are shown in detail. The movement detector driver 61 is
connected through the transformer 70 and full wave rectifier 71 to
provide a signal to the wave shaping circuit 72 which includes an
RC network 100 for normally producing at the node or terminal 101 a
signal having a wave shape as indicated in FIG. 4. A DC blocking
differentiating capacitor 102 is coupled between the wave circuit
72 and a darlington pair amplifier 103 base bias circuit, which
includes resistors 104, 105 and a potentiometer 106 for determining
the sensitivity of the movement detector 73, such circuit being
coupled across the voltage regulation circuit 74. The effective
gain over the operational range of the amplifier 103 is variable,
determined by the amplitude of the DC part of the E.sub.d signal
normally blocked by the capacitor 102 and the proportional pulse
thereof. The collector output of the amplifier 103 is connected to
a resistor 107 and to the base of a transistor 110 through a
voltage dropping resistor 111, the emitter of the latter transistor
being connected to the negative line 112 and the collector thereof
coupled through a resistor 113 and the light emitting diode 75 to
the positive line 114 serving as the output of the movement
detector 73.
The negative slope detector 80 has a control input connected
through a coupling capacitor 115 to the movement detector output. A
transistor 116 forming the active element in the negative slope
detector 80 is connected at its base to the coupling capacitor 115
and through a resistor 117 to the positive line 114, normally
maintaining the transistor 116 in saturation, and a capacitor 118
is connected between the positive line 114 and the negative line
112. The emitter of transistor 116 is connected to the negative
line 112, and the collector is connected through a resistor 119 to
the positive line. The output from the negative slope detector is
connected through a resistor 120 to the base of the transistor 81
which controls current flowing to the primary winding of the pulse
transformer 82, and a bias resistor 121 and clamping diode 122
connect the base of the transistor 81 to the negative line 112.
Power is supplied to the collector of the transistor 81 through the
resistor 123 and the line 124 connected to the island amplifier
circuit, whereby when no train is in the island the latter produces
a signal at the output of the filter 85 (FIG. 1) to provide such
power.
The loss of shunt detector 77 receives an input signal on the line
86 through an RC network 130 coupled to control a transistor 131,
which is connected between the positive line 114 and the timing
circuit 132. The output 133 from the timing circuit 132 is
connected by the line 76 to the base of a darlington pair amplifier
134, which is connected between the resistor 135 and the emitter of
the amplifier 103. A resistor 136 connects the emitters of the
amplifiers 103, 134 to the negative line 112. Thus, a control
signal to the base of the amplifier 134 causes the emitters of both
amplifiers to go positive to assure cut-off of the amplifier
103.
The timing circuit 132 includes a first capacitor 140 and diode 141
combination and a second capacitor 142 and diode 143 combination
with an isolating diode 144 connected between switch combinations.
A large resistor 145 is connected between the negative line and the
cathodes of the diodes 141, 143, and a resistor 146 connects such
cathodes to the output 133 of the timing circuit to the island
amplifier circuit, whereby when the latter is off, for example,
when a train is in the island, any potential accumulated in the
timing circuit 132 is discharged through the diode 147, resistor
148 and the island amplifier circuit.
A disabling circuit for the timing circuit 132 in the loss of shunt
detector 77 includes a transistor 150, coupled at its base by a
resistor 151 to the negative line and by resistor 152 to the
secondary winding of the transformer 82. Thus, whenever a signal is
induced in the secondary winding of the transformer 82, the
transistor 150 will conduct to discharge any potential accumulated
in the timing circuit 132 of the loss of shunt detector 77 and
disabling the same from any effect on the amplifier 134 or the
amplifier 103. 0
Operation of the wave shaping circuit 72, movement detector 73,
loss of shunt detector 77, and negative slope detector 80 is
described in detail below. When the railway signal system 1 has
been connected to the track and adjusted, the track signal
transmitted by the transmitter 2 is amplified in the receiver
amplifier 56 and coupled by the line 60 to the movement detector
driver 61, which effects the production of an unfiltered rectified
signal at the output of the full wave rectifier 71, such signal
being coupled to the wave shaping circuit 72 and by the line 86 to
the loss of shunt detector 77. The wave shaping circuit 72 operates
on the unfiltered rectified signal and produces at the node 101 the
E.sub.d signal shown in FIG. 4, the transistor 131 in the loss of
shunt detector being maintained non-conducting at this time. In one
embodiment when no train is within the beginning of approach
shunts, the E.sub.d signal has a 40 volt DC level v and a
proportional 2.5 volt peak to peak pulse. When a train is at a
certain location between one of the beginning of approach shunts
and the island 50 effecting a shunt across the tracks and reducing
the total track ballast seen by the transmitter 2 and receiver
circuit 4, the E.sub.d signal is reduced, for example, to a 20 volt
DC level and a 1.25 volt pulse.
The differentiating capacitor 102 normally blocks the DC part of
the E.sub.d signal and provides through the pulses impressed on
such DC part a constant self-checking of the railway signal system,
for example at the rate of approximately five times per second. The
differentiating capacitor 102 should be considered in a zero state
or charged state, i.e. it charges back to zero state condition at a
constant charging rate. Each time an E.sub.d pulse goes negative,
simulated motion is detected by the movement detector 77 and the
amplifier 103 is cut off; and as the pulse recovers in the positive
direction, the differentiating capacitor 102 is recharged and the
amplifier conducts. When a continued slow drop of the DC part of
the E.sub.d signal occurs, for example, due to a slowly approaching
train far from the island 50, the differentiating capacitor 102
maintains itself only a slight amount away from the zero state,
drawing very little current from its recharging circuit, the base
biasing network 104, 105, 106 of the amplifier 103. Thus, the
E.sub.d pulses will effect an AC output from the amplifier 103.
A train on the track inside a beginning of approach shunt
travelling in a direction toward the island is a travelling shunt
that reduces the track signal and, of course, the E.sub.d signal at
the node 101, such signal reductions being non-linear with respect
to distance from the island due to the non-linearity in the
approach of the accumulated track ballast resistance. It t to
distance from the island due to the non-linearity in the approach
of the accumulated track ballast resistance. It has been found that
signals having frequencies of from 20 to 65 Hz exhibit some
semblance of linearity of attenuation over a given length of rail,
whereas higher frequencies of from 300 to 3,000 Hz are
substantially non-linear throughout the entire approach.
The approaching train causes the E.sub.d signal to drop, and in one
embodiment when the DC part of the E.sub.d signal is at 40 volts
with a 2.5 volt pulse, a drop of E.sub.d signal in excess of
approximately 0.4 volt per second will bias the amplifier 103 in a
negative direction preventing it from passing the pulses through
the succeeding stages allowing the relay 97 (FIG. 1) to drop.
Similarly, when the E.sub.d signal is at 20 volts with a 1.25 volt
pulse, a 0.2 volt per second drop in the DC part will maintain the
amplifier 103 cut-off. Once cut-off by an appropriate E.sub.d
signal drop rate, the amplifier 103 is maintained cut-off due to
such E.sub.d drop since the differentiating capacitor 102 cannot
recharge instantaneously and the base of the amplifier 103 is held
negative due to the travelling shunt effect of the approaching
train.
The railway signal system 1 becomes increasingly more sensitive to
E.sub.d drop as the train approaches the island because the reduced
E.sub.d pulses require less of an E.sub.d signal drop to bias the
amplifier 103 toward cut-off. Since the track ballast resistance is
non-linear, a train 3,000 feet from the island must effect
reduction of the E.sub.d signal at a rate of approximately 0.4 volt
per second, whereas a train several hundred feet from the island
need only effect reduction of the E.sub.d signal at a rate of, for
example, 0.011 of a volt per second.
The AC output produced by the amplifier 103 when no train is
detected is coupled through the transistor 110 to provide an input
signal to the negative slope detector 80, such input signal being
illustrated in FIG. 5. Each time the transistor 110 conducts the
light emitting diode emits light to indicate that the movement
detector 73 is operating properly.
The transistor 116 in the negative slope detector 80 is maintained
in saturation by the potential applied to the base through the
resistor 117. The transistor 116 is cut-off, however, each time the
signal illustrated in FIG. 5 reaches its negatively sloped portion.
Therefore, the output from the negative slope detector 80 is a
square wave applied to the input of the transistor 81, which
effects production of an AC signal in the transformer 82 coupled at
the terminal 160 to the multivibrator 89 (FIG. 1) and to the base
of the disabling transistor 150 in the loss of shunt detector
77.
Since the negative slope detector 80 is operated alternately at
saturation and at cut-off, it is relatively immune to noise and
provides circuit isolation and uniform regulation of signals
applied to the multivibrator 89. Also, the negative slope detector
80 reduces ring-by time as the train leaves the island because it
is operated in saturation and cut-off, the AC output therefrom
being a strong broad square wave signal which assures energization
of the transformer 82.
The transistor 131 in the loss of shunt detector 77 is normally
maintained cut-off due to the blocking effect of the capacitors in
the RC network 130. However, when an approaching train has caused
the E.sub.d signal to drop to a point where motion has been
detected and the transistor 150 in the disabling circuit is
maintained cut-off, a rapid increase in E.sub.d voltage, due, for
example, to the train running over a rusty rail, causes the
transistor 131 to conduct charging the capacitors 140, 142 in the
timing circuit 132. The capacitor 140 rapidly discharges through
the diode 141 and resistor 146 to effect conduction in the
amplifier 134, which raises the potential at the output of the
amplifier 103 maintaining the latter cut-off. When the E.sub.d
signal has dropped again as the approaching train passes the rusty
rail, the transistor 131 is cut-off, and the capacitor 142
discharges through the resistor 146 to maintain conduction in the
amplifier 144 until the charge on the capacitor 142 has been
dissipated. When the approaching train has entered the island, any
charge retained on the capacitor 142 will be discharged by the
diode 147 and the resistor 148 through the island amplifier
circuit.
A train leaving the island causes a relatively slow increase in
E.sub.d voltage although the pulses thereof are quickly recognized
by the amplifier 103. The transistor 116 in the negative slope
detector 80, which was formerly operating only in saturation, then
begins to be periodically cut-off, effecting production of an AC
signal at the terminal 160 to power the multivibrator 89 and to
effect conduction in the transistor 150 in the disabling circuit of
the loss of shunt detector 77. Conduction of the transistor 150
causes a rapid discharge of the capacitors 140, 142 and assures
that any conduction by the transistor 131 will not effect operation
of the amplifier 134.
It will now be appreciated that the railway signal system operates
in a fail-safe mode to provide indications of a train approaching
or existing in an island or of a defect in the system itself. The
system also has variable sensitivity, is constantly self-checking,
and continuously monitors track conditions.
* * * * *