U.S. patent number 3,819,934 [Application Number 05/337,596] was granted by the patent office on 1974-06-25 for fail-safe solid state highway crossing protection apparatus.
This patent grant is currently assigned to Westinghouse Air Brake Company. Invention is credited to John W. Kramer.
United States Patent |
3,819,934 |
Kramer |
June 25, 1974 |
FAIL-SAFE SOLID STATE HIGHWAY CROSSING PROTECTION APPARATUS
Abstract
Solid state static relays, with contact circuits including
insulated signal couplers formed by light emitting diodes and light
responsive transistors, are used as track circuit detectors and
directional stick devices in highway crossing protection systems.
Each relay control circuit requires modulated switching across
control input terminals to condition that relay to an energized
state which activates front contact couplers. Absence of the
modulated switching or a continuous circuit across the terminals
conditions the relay coil circuit to activate only back contact
couplers. A solid state directional logic network for highway
crossing protection is formed by a selected circuit arrangement of
insulated coupler elements which fulfills in a fail-safe manner the
Boolean functions representing the directional crossing protection
logic. The crossing protection device is controlled through an
output buffer circuit by other selected couplers representing the
control functions by which the device is activated only for
approaching trains. My invention pertains to fail-safe solid state
highway crossing protection apparatus. More particularly, this
invention relates to a highway crossing signal protection scheme in
which solid state light emitting and responsive devices are used to
provide logic control circuits for activating and deactivating the
crossing warning units at the proper times with respect to the
movement of trains across the highway. There is at present a desire
to improve the systems used for protecting highway traffic where
such highways intersect railroads in grade crossings. One feature
of any improvement is to reduce the cost of the installation and
its subsequent maintenance since any reduction in cost will make
possible more installations with the same financial outlay. This is
particularly important to railroad companies with limited capital
funds. An improved reliability of such systems is also important in
increasing confidence and respect of highway users in the operation
of such warning systems. Conversely, if the reliability can be
increased, there will be less ignoring of warning indications or
devices with a reduction in a number of crossing accidents. One
manner in which the cost may be reduced is to replace the relay
logic circuits of conventional design using large, expensive, vital
type relays with solid state logic circuitry with equal or improved
fail-safe characteristics. Such solid state circuits also require
less operating energy and, therefore, are cheaper to operate. Solid
state apparatus also, in general, requires less maintenance and is
easier to repair than the conventional relays and individually
wired circuits. Accordingly, it is an object of my invention to
provide an improved, fail-safe highway crossing protection system
using solid state elements in the control logic circuitry. Another
object of the invention is a highway crossing protection signaling
system in which fail-safe solid state static relay devices replace
the vital electromechanical relays in the control logic circuitry.
Still another object of the invention is a fail-safe solid state
control logic arrangement for highway grade crossing protection
systems. A further object of my invention is a fail-safe
arrangement using light emitting diodes and light responsive
transistors as logic elements to provide a protection system for
highway-railroad grade crossings. Yet another object of the
invention is a highway crossing protection system in which the
directional logic circuits are comprised of solid state static
relays which have fail-safe characteristics and which control a
vital crossing relay to activate the warning devices. A still
further object of the invention is to provide a highway crossing
protection system in which illumination emitting and illumination
responsive solid state devices provide fail-safe train detection
and direction logic circuitry for controlling a final vital
crossing relay which activates the warning signals or devices. It
is also an object of my invention to provide a highway crossing
protection system in which algebraic formulas designating control
logic functions for operation of the warning devices are performed
by solid state logic elements using light emitting diodes and light
responsive transistors. Other objects, features, and advantages of
the invention will become apparent from the following specification
and appended claims when taken in connection with the accompanying
drawings. SUMMARY In practicing the invention, solid state logic
elements, also defined as static relays, are incorporated into the
highway crossing protection system in both the train detection
function and the directional logic function. Only the final
crossing relay controlling the protection devices is retained as a
conventional electromechanical, vital type relay. Each static relay
or logic element has a first electronic solid state circuit which
is equivalent to the coil of an electromechanical relay. A second
type of solid state electronic circuit simulates or is equivalent
to the switching contacts of a conventional relay. Depending upon
the drive connections from the coil circuit, a second type circuit
is equivalent to a front or a back contact of the conventional
relay, and thus represents a yes or no logic function,
respectively. A single solid state coil circuit element may drive
any reasonable number of second type or contact circuits connected
in both front and back configuration. As specifically illustrated,
each second or switching type circuit is composed of an
illumination emitting diode, such as a light emitting diode, and an
illumination responsive semiconductor, or specifically, a light
responsive transistor. Each pair of these units is physically
positioned to couple so that the light emitting diode output
actuates the light responsive transistor, resulting in an insulated
signal coupler device. Obviously, other arrangements providing such
an insulated signal coupler may be used. In order to provide
fail-safe characteristics to the logic element or static relay, the
coil circuit is designed to require a modulated control or
switching input in addition to an operating energy input to produce
an output which will actuate the front contact coupler circuits. If
the control input is absent, or is unmodulated, only the back
contact type switching circuits can be actuated by the coil
circuitry. Of course, if the operating energy is lost from the coil
circuit, none of the contact circuits are active and no relay
output can occur. In applying the logic elements to a crossing
protection system, the logic concept in Boolean algebra form is
developed from a conventional relay type crossing signal system. A
static relay coil circuit then replaces each conventional track
detector and directional stick relay winding. Contact circuits of
the static relays are then arranged circuitwise to fulfill the
algebraic formulas for a crossing warning logic operation. A
modulation or pulsing source for the system is provided to supply
the modulated or pulsed switching control inputs required by the
static relay coil circuits in order for them to activate the front
contacts when approprate. The train detector circuits are also
supplied with control input energy from overlay track circuit
receivers which are part of the approach warning section detector
track circuits for the crossing. The final output signals from the
logic circuitry are applied through an output buffer circuit with a
rectifier component to operate the crossing relay. The crossing
relay is normally energized to hold or lock out the warning device
except when a train approaches. The crossing relay, of course,
releases in response to the detection of train occupancy of an
approach section to actuate the warning signals and devices. In
addition, any failure in the solid state logic circuits, either the
coil or contact circuitry, or a loss of the modulation of the
control inputs, causes the crossing relay to release to actuate the
warning signals in a fail-safe manner.
Inventors: |
Kramer; John W. (Pittsburgh,
PA) |
Assignee: |
Westinghouse Air Brake Company
(Swissvale, PA)
|
Family
ID: |
23321184 |
Appl.
No.: |
05/337,596 |
Filed: |
March 2, 1973 |
Current U.S.
Class: |
246/130; 361/175;
361/182 |
Current CPC
Class: |
B61L
29/286 (20130101) |
Current International
Class: |
B61L
29/00 (20060101); B61L 29/28 (20060101); B61l
001/02 () |
Field of
Search: |
;246/125,13R,128
;317/148.5R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: King; Lloyd L.
Assistant Examiner: Libman; George H.
Attorney, Agent or Firm: Williamson; H. W. Williamson; A.
G.
Claims
Having thus described my invention, What I claim is:
1. A highway crossing protection system for a stretch of railroad
track intersected by a highway, having a protection device at said
crossing selectively activated to warn highway traffic of an
approaching train occupying an approach warning section along each
direction of movement, comprising in combination,
a. first and second train detection means, one for each approach
warning section, each responsive to the presence or absence of a
train within the corresponding section or detecting the occupancy
condition of that section,
b. a static train detector relay means associated with each train
detection means and coupled for registering the absence of a train
in the corresponding warning section only when also supplied with a
modulated control switching signal,
c. a first plurality of insulated signal couplers controlled by the
first static detector relay means to first and second states as a
train absence or presence in the corresponding section is
detected.
d. a second plurality of insulated signal couplers controlled by
the second static detector relay means to first and second states
as a train absence or presence in the corresponding section is
detected,
e. direction registry means controlled jointly by said first and
second plurality of signal couplers for registering the direction
of a train approaching the crossing in an approach section and for
retaining that direction registry while that train recedes from
said crossing in the opposite approach section,
f. another pair of static relay means associated with said
direction registry means and activated only when also supplied with
a modulated control switching signal,
g. a third plurality of insulated signal ouplers selectively
controlled by said direction registry static relay means to first
and second states selectively as one or the other train direction
is registered,
h. each static direction registry relay means coupled to said
first, second, and third pluralities of insulated signal couplers
in a manner for selectively activating one predetermined direction
relay means only to register the direction of an approaching train
and for retaining that relay means activated until that train
clears the opposite warning section during its receding movement
from said crossing,
i. a source of modulated switching signals coupled to each static
relay means for providing a modulated switching signal to activate
the relay when other required input conditions coexist, and
j. control means for said protection device controlled jointly by
said first, second, and third plurality of signal couplers for
activating said device when an approaching train occupies one
approach warning section and for deactivating said device when that
train occupies only the other approach section while receding from
said crossing.
2. A crossing protection system as defined in claim 1 in which,
a. said modulated switching signal source is coupled to said static
detector relay means through additional insulated signal couplers
controlled by said source, and
b. said modulated switching signal source is coupled to said static
direction registry relay means through said first and second
plurality of insulated signal couplers jointly with other
additional insulated signal couplers controlled by said source.
3. A crossing protection system as defined in claim 2 in which,
each insulated signal coupler comprises an illumination emitting
diode and an illumination responsive semiconductor.
4. A crossing protection system as defined in claim 2 in which,
each insulated signal coupler comprises a light emitting diode and
a light responsive transistor.
5. A crossing protection system as defined in claim 4 in which each
train detection means further includes,
a. an alternating current overlay track circuit having a
transmitter coupled to the rails at the remote end of the
corresponding approach warning track section and a receiver coupled
to the rails at said crossing on the opposite side of the highway
from the associated transmitter,
b. each transmitter supplying an alternating current of distinctive
frequency through the rails to the associated receiver which is
responsive only to an input of that frequency for providing an
output signal,
c. each receiver output being coupled by a separate insulated
signal coupler controlled by said modulation switching source to
the associated static detector relay means for supplying a
modulated activating signal when the corresponding section is
unoccupied by a train.
6. A highway crossing protection system for a stretch of track
intersected by a highway, with a protection device at said crossing
to warn highway traffic of the approach of trains within an
approach warning section for each direction of train movement,
comprising in combination,
a. a train detection means for each approach warning section
responsive to the presence of a train within that section and
including a static type detector relay normally activated when the
section is unoccupied by a train,
b. a train direction registry means including a pair of static type
direction relays activated at times for registering the direction
of movement of a train traversing the stretch, one relay for a
first direction and the other relay for a second direction,
c. each static relay including a solid state coil circuit network
and a plurality of contact circuits each comprising an insulated
signal coupler, preselected contacts being active when said coil
circuit is activated, the remaining contacts being active when said
coil circuit is nonactivated,
1. said coil circuit network being activated only when also
supplied with a modualted control switching signal,
d. a source of modulated switching signals coupled to each detector
relay coil circuit network for activating a particular relay when
the associated train detection means detects the corresponding
approach section nonoccupied,
e. a circuit network including contact couplers of said detector
relays and of both said direction relays and further controlled by
aid modulation signal source, connected for activating, when a
train is first detected, a single direction relay selected in
accordance with the approach section occupied and for retaining
that selected relay activated while the detected train traverses
said crossing and recedes through the opposite direction approach
section, and
f. a control circuit means including contact circuits of said
detector relays and of said direction relays and connected for
actuating said crossing protection device to warn highway traffic
when an approaching train occupies the approach section in its
direction of movement, for deactuating said device when that train
clears said crossing and occupies only the approach section for the
opposite direction of movement, and for retaining said device
deactuated when both sections are unoccupied.
7. A crossing protection system as defined in claim 6 in which,
a. each relay contact insulated signal coupler comprises an
illumination emitting diode and an illumination responsive
semiconductor so positioned that each semiconductor is responsive
only to illumination from the associated diode,
b. said modulated switching signal source is coupled to the diode
of each said contact signal oupler for modulating the conducting
period of each associated semiconductor to provide fail-safe
characteristics to the operation of said direction relays and said
protection device control circuit means.
8. A crossing protection system as defined in claim 6 in which,
a. each relay contact insulated signal coupler comprises a light
emitting diode and a light responsive transistor responsive only to
illumination from the associated diode,
b. said modulated switching signal source is coupled to the diode
of each said contact signal coupler for modulating the conducting
period of each associated transistor to provide fail-safe
characteristics to the operation of said direction relays and said
protection device control circuit means.
9. A crossing protection system as defined in claim 8 in which each
train detection means further includes,
a. an alternating current overlay track circuit comprising,
1. a transmitter coupled to the rails at the remote end of the
corresponding approach warning section and operable for supplying a
track current having a preselected distinctive frequency,
2. a receiver coupled to the rails at said crossing on the opposite
side of the highway from its associated transmitter and responsive
only to track current having the distinctive frequency of the
associated transmitter for providing an output signal when the
corresponding section is unoccupied,
b. each receiver being coupled by a separate insulated signal
coupler to the associated detector relay coil circuit network, the
coupling being also controlled by said switching signal source, for
supplying a modulated activating signal to that relay coil circuit
network when the corresponding approach section is unoccupied.
10. Control logic circuitry for a highway crossing protection
system including an approach warning track section or each
direction of train movement, each provided with means for detecting
the presence of a train occupying that section, and a crossing
protection device selectively activated for warning highway traffic
of a train approach, comprising in combination,
a. static relay means associated with each track section detection
means and controlled thereby for registering the absence or
presence of a train occupying the section,
b. a pair of static relay means for selectively registering the
direction of travel of a train while approaching and receding from
said crossing, one relay of said pair activated for each direction
of travel,
c. each static relay means having a solid state coil circuit
portion and a plurality of contact circuits each comprising an
illumination emitting diode and an illumination responsive
semiconductor,
d. the contact circuits of each detection relay mean selectively
activated by the associated coil circuit, some to indicate the
corresponding section unoccupied and others to indicate the
presence of a train occupying the corresponding section,
e. the contact circuits of each direction registry relay means also
selectively activated by the associated coil circuit, some to
register a train movement in the corresponding direction and others
to indicate absence of any movement direction registry,
f. a control circuit network for activating each direction relay
means to register a train approaching in the corresponding
direction and for holding that relay activated until that train
clears the opposite direction approach section, including,
1. a contact circuit activated by the detection relay for the
opposite direction approach section when a train is detected
occupying that section,
2. a contact circuit of the other direction relay means activated
when no train direction is registered,
3. a contact circuit of the corresponding direction relay means
activated when a train direction is registered, and
4. a contact circuit of the detection relay means of the
corresponding approach section activated when a train is detected
occupying that section,
g. a modulation switching means coupled to each detection relay
coil circuit and to the control circuit network of each direction
relay means for providing the modulated switching input upon which
relay activation depends, and
h. a control circuit network for said crossing device, controlled
by first, second, and third circuit paths and connected for
normally holding said device inactivated and for activating said
device only when all said circuit paths are simultaneously
incomplete,
1. said first circuit path completed when both detection relay
means detect the corresponding approach sections unoccupied,
2. said second circuit path completed when one detection relay
means detects the corresponding one approach section unoccupied and
said direction relays register a train receding from said crossing
through the other approach section,
3. said third circuit path completed when the other detection relay
means detects said other approach section unoccupied and said
direction relays register a train receding from said crossing
through said one approach section.
11. Control logic circuitry for a highway crossing protection
system including an approach warning track section for each
direction of train movement, each section provided with track
circuit means for detecting the presence of a train occupying that
section, and a crossing protection device activated at times for
warning highway traffic of an approaching train, comprising in
combination,
a. a modulation switching means operable to provide a modulated
switching signal,
b. a detector means associated with each track circuit means and
operable to a first and a second condition or detecting the
presence or absence, respectively, of a train occupying the
corresponding section,
c. an AND circuit network for each detector means, controlled by
the associated track circuit means and by said switching means, and
connected for operating the corresponding detector means to its
second condition only when the corresponding approach section is
unoccupied by a train and a switching signal is present,
1. each detector means otherwise operating to its first
condition,
d. a train direction registry means associated with each detector
means for registering the direction of movement of trains which
approach said crossing through the track section with which the
other detector circuit means is associated,
1. each registry means normally in a first condition when no train
direction is registered and operable when actuated to a second
condition to register a train movement in the corresponding
direction,
e. a first AND circuit network for each direction registry means,
controlled by the opposite direction registry means and the other
detector means and coupled to said switching means, connected for
actuating the associated direction registry means when an
approaching train is detected in the other approach section and no
opposite direction train is registered, only if a switching signal
modulates the network,
f. a second AND circuit network for each direction registry means;
controlled by the corresponding direction registry means, the
opposite direction registry means, and the associated detector
means, and coupled to said switching means; connected for retaining
actuated the previously actuated corresponding direction registry
means when the train occupies the associated track section and no
opposite direction train is registered, only if a switching signal
modulates the network, and
g. an OR circuit network for said crossing protection device,
controlled jointly by both detector means and both direction
registry means, and coupled to said switching means, and connected
for holding said crossing device inactive only when both approach
sections are unoccupied, or when one approach section is unoccupied
and the other section is occupied by a train receding from said
crossing, or when said other approach section is unoccupied and
said one section is occupied by a train receding from said
crossing, only if a switching signal modulates the active portion
of said OR network.
12. Control logic circuitry as defined in claim 11 in which,
a. said AND circuit network for each detector means includes a
first insulated signal coupler controlled by said switching means
and a second insulated signal coupler connected for coupling the
modulated switching signal and a section unoccupied signal from the
corresponding track circuit means to that detector means,
b. each detector means controls a plurality of other insulated
signal couplers for activating some couplers when in its first
condition and the remaining couplers when in its second
condition,
c. each direction registry means controls still another plurality
of insulated signal couplers for activating some couplers when in
its first condition and the remaining couplers when in its second
condition,
d. each first and second AND circuit network is coupled to said
switching means by an insulated signal coupler for receiving a
network modulating signal and further includes signal couplers of
the controlling detector and registry means for performing AND
logic functions to determine the existence of the required
conditions for operating the associated direction registry means to
its second condition, and
e. said OR circuit network includes insulated signal couplers
controlled by each detector means and each direction registry means
for performing AND logic functions to determine the existence of at
least one set of the required conditions for holding said crossing
device inactive, and is coupled to said switching means by selected
ones of the included couplers for receiving a network modulating
signal.
13. Control logic circuitry as defined in claim 12 in which each
insulated signal coupler comprises a light emitting diode and an
associated light responsive transistor.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
I shall now describe in more specific detail and terms the highway
crossing protection arrangement embodying the features of my
invention, and will then point out the novelty in the appended
claims. During this specific description, reference will be made
from time to time to the accompanying drawings in which:
FIG. 1 is a partly a schematic but principally a circuit diagram of
a highway crossing protection system employing solid state logic
elements and embodying the features of my invention.
FIG. 2 is a diagrammatic illustration of a conventional prior art
overlap type highway crossing protection system employing
conventional relays on which the logic algebra employed in my
invention is based.
FIG. 3 is a circuit diagram of a logic element or static relay
device usable in the system of FIG. 1.
The circuit diagram shown in FIG. 4 is a suitable modulation or
pulse source for supplying modulation or switching pulses to the
static relays and other logic circuits in the arrangement of FIG.
1.
In all figures of the drawings, similar reference characters
designate the same or similar parts of the apparatus. In each of
the drawings, a source of direct current operating energy is
provided for the apparatus. This source is not specifically shown,
since any suitable known type may be used, and only its positive
and negative terminals are designated by the references B and N,
respectively. It will be understood that wherever either of these
reference characters appears in any of the circuit drawings, a
connection to the corresponding terminal of the direct current
operating energy source is designated.
DETAILED DESCRIPTION
Referring initially to the prior art arrangement shown in FIG. 2, I
shall first lay the groundwork and develop the Boolean algebra
expressions for the crossing logic on which the arrangement
embodying my invention is based. A stretch of railroad track, shown
across the top of FIG. 2 by a conventional two-line symbol, is
intersected by a highway H, shown by the dashed lines. A highway
signal device HS, operable to warn highway traffic of the approach
of a train, is shown in the vicinity of the crossing. The device HS
is representative of any of the several warning or protection means
presently in common use at highway crossings, including flashing
signal lights with or without gates or barriers and other newer
types of warning devices. The device HS is activated when the
crossing relay XR releases to close its back contact a. This
completes a circuit between terminals B and N of the source through
the operating mechanism of signal HS, as shown in a schematic
fashion which will be understood by those familiar with the
art.
The stretch of track is equipped for highway crossing protection by
two well-known overlay detector track circuits which are overlapped
at the crossing itself to provide a positive ring or protection
island track section. Each overlap track circuit includes a track
transmitter TTU having an assigned distinctive frequency and a
receiver unit TRU tuned to respond only to the frequency of the
associated transmitter. For example, the track circuit provided for
the approach warning section on the left includes transmitter 1TTU
rail connected at the remote end and receiver 1TRU connected across
the rails at the crossing but on the opposite side of the highway
from its associated transmitter. These transmitters and receivers
are well-known units, and any one of several types may be used to
provide a selected frequency track current and a tuned or selective
response thereto, respectively. Each receiver unit provides, when
it is receiving the proper track current from the rails, a direct
current output for controlling the associated detector track relay.
For example, track relay 1TR, associated with track receiver 1TRU
for the left track circuit, is energized and picked up when no
train is occupying any portion of the left approach warning track
section. Relay 1TR is deenergized and releases when this rack
section is occupied by any part of a train. Relay 3TR is associated
with the opposite approach track section and operates or responds
to the track section occupancy conditions in a similar manner.
The arrangement is also provided with a directional stick relay for
each direction of train movement, the directional relays 1XS and
3XS being associated with the correspondingly numbered track
relays. However, each of these XS relays is energized and picks up
when a train approaches in the opposite direction of travel and the
other track relay releases. For example, relay 3XS is energized,
when a train approaches from the left, by a circuit extending from
terminal B of the source over back contact a of relay 1TR, which
closes when the train passes transmitter 1TTU, front contact a of
relay 3TR, back contact b of relay 1XS, and the winding of relay
3XS to terminal N. Relay 3XS picks up and closes its own front
contact a to complete a first stick circuit also including back
contact a of relay 1TR and back contact b of relay 1XS. Eventually,
when the train crosses the highway to enter the other or
corresponding track section, relay 3TR releases and closes its back
contact a to complete the final stick circuit for relay 3XS which
otherwise includes back contact b of relay 1XS and front contact a
and the winding of relay 3XS. This relay then remains energized
until the train, having cleared the crossing, finally clears the
other approach warning section in the reverse direction, that is,
as it recedes from the highway.
During this period that the train is receding, front contact c of
relay 3XS bypasses the open front contact b of relay 3TR in the
energizing circuit for relay XR. Relay 3TR, of course, is released
since the train is occupying the right-hand approach warning
section as it recedes from the crossing, and thus has interrupted
or shunted the flow of current in the corresponding track circuit.
More specifically, relay XR is normally held energized by a circuit
including in series front contacts b of relays 3TR and 1TR. Thus,
relay XR releases when this train, approaching from the left,
occupies the left approach section and causes the release of relay
1TR to open its front contact b. When the train clears the highway
and relay 1TR is again energized and picks up to close its front
contact b, an energizing circuit for relay XR then exists including
the front contact and front contact c of relay 3XS. When the train
eventually clears the stretch of track, relay 3TR will again pick
up to close its front contact b and restore the normal energizing
circuit for relay XR. When this occurs, the opening of back contact
a of relay 3TR will interrupt the remaining stick circuit for relay
3XS which then releases or resets to its normal deenergized
condition. A similar sequence of events in the reverse order will
occur when a train moving from right to left traverses the stretch
of track shown and crosses the highway. It is obvious that during
the period that relay XR is released, its closed back contact a
will retain the highway warning device HS activated.
With a reveiw of the preceding discussion and considering the
circuits shown in FIG. 2, the Boolean algebra logic equations for a
typical single track highway crossing with overlap can then be
written. The equation for energization of relay XR becomes:
XR = (1TR + 1XS) .sup.. (3TR + 3XS) (1)
considering together both pickup and stick circuits for the
directional relays 1XS and 3XS, the logic equations from an
inspection of FIG. 2 are:
1XS = 3XS[(1TR.sup.. 3TR) + 1XS(1TR + 3TR)] (2) 3XS =
1XS[(1TR.sup.. 3TR) + 3XS(1TR + 3TR)] (3)
the relays 1XS and 3XS are actually used as set, reset type flip
flop logic elements for which, as specifically shown,
1XS = 3XS .sup.. 3TR .sup.. 1TR (4) 3XS = 1XS .sup.. 1TR (5) p..
3TR
the reset equations for these relays as flip flops then may be
stated:
1XS = 3XS + (1TR .sup.. 3TR) (6) 3XS = 1XS + (1TR (7) p.. 3TR)
since the set and reset equations for relays 1XS and 3XS constrain
only one to be on or picked up at any one time, the equation (1)
for relay XR may be then rewritten, for logic element
implementation, in the following expanded form:
XR = (1TR .sup.. 3TR) + (1TR .sup.. 3XS) + (3TR .sup.. 1XS) (8)
it is to be noted that, in the prior art circuitry of FIG. 2, an
unnecessary front contact of the associated track relay is included
in the energizing circuit for each XS relay. Since the
corresponding dependent back contact completes the final stick
circuit for the associated directional relay while the train
recedes from the crossing, this redundant use of the front contact
saves an independent contact structure on the track relay, an
economy measure. However, such dependent front and back contacts
(yes and no logic functions) are not possible when using insulated
signal couplers. Therefore, the equations (2) and (3) for relays
1XS and 3XS may be simplified for implementation by logic elements
by eliminating the front contact function of the associated track
relay and rewriting as follows:
1XS = 3XS .sup.. [3TR + (1XS .sup.. 1TR)] (9) 3XS = 1XS .sup.. [1TR
+ (3XS (10) .. 3TR)]
these final functional equations (8), (9), and (10) are then the
basis for the logic arrangement embodying the features of my
invention and implementation in a fail-safe static relay logic
element form is shown in FIG. 1.
I shall refer now to FIG. 3 for the circuitry of a solid state
logic element or static relay usable in the conventional blocks
incorporated in the arrangement shown in FIG. 1 and illustrated
separately for convenience and simplicity in order to avoid excess
circuit details in that figure. Actually, the circuit for the
static relay, as shown in FIG. 3, is initially disclosed and is
claimed in Letters Patent of the U.S. Pat. No. 3,746,942, issued
July 17, 1973, to C. R. Brown et al., for a Static Circuit
Arrangement. Although fully disclosed in this patent, I shall
briefly describe the relay circuit and operation for convenience
herein. The static relay circuit consists of two parts which may be
considered as analogous to the coil of an electromechanical relay
and to the switching contacts of such a relay. The portion
equivalent to the coil or relay winding is that in FIG. 3 shown
above the pair of terminals X and Y, while the second portion shown
below these two terminals is equivalent to the switching contacts
of an electromechanical relay. Direct current operating energy for
the coil circuit and for the relay in general is supplied from
terminals B and N of the local source which are connected to the
upper and lower plates of a four-terminal capacitor C2, shown in
the upper left of FIG. 3. One of the remaining two terminals of
capacitor C2 supplies positive potential to the electronic coil
circuit, while the other remaining terminal is connected to a
common ground terminal. Capacitor C2 isolates the direct current
supply voltage from any high frequency signals and thereby prevents
interaction between the various circuits connected to the same
direct current source.
An input circuit is formed by a pair of complementary transistors
Q1 and Q2 and a biasing resistor R1. The transistors Q1 and Q2 are
connected in an emitter-follower configuration which, in turn, is
connected between the positive potential bus and ground terminal.
The common connection of the two emitter electrodes is connected to
feed a diode pump rectifier circuit comprising resistor R2,
capacitor C7, diodes D3 and D4, and another capacitor C10. The
upper plate of capacitor C10 is connected to a potential divider
network formed by resistors R3 and R4, the common junction of which
is connected in multiple to the base electrodes of another pair of
complementary transistors Q3 and Q4. These two transistors are also
connected in emitter-follower configuration to form an output
circuit. The common junction point of the two emitter electrodes of
transistors Q3 and Q4 forms a first intermediate signal terminal
which is designated by the reference character Y. A second
intermediate signal terminal, designated by the reference X, is
connected to the lower plate of capacitor C10. A Zener diode D5,
connected between the collector electrode of transistor Q3 and
ground, limits the amount of negative voltage which may be
developed on capacitor C10. A current limiting resistor R5 is
connected between capacitor C2 and Zener diode D5. The coil circuit
portion of the static relay is further provided with a pair of
control input terminals, designated by the references D and E.
Terminal E is connected to the common junction between the base
electrodes of transistors Q1 and Q2, while terminal D is connected
to terminal X, the lower plate of capacitor C10, the cathode of
diode D4, and in common with all these points to the ground
terminal.
The electronic contact circuit portion of the static relay consists
of a plurality of insulated signal couplers, each connected in one
of two alternative circuit patterns across the coil signal
terminals X and Y. Only two such contact circuits are shown, one of
each type, designated by the reference characters IC8 and IC9. It
will be appreciated that any reasonable number of such solid state
contact circuits may be controlled by the electronic coil circuit
of the static relay. Each insulated coupler comprises an
illumination or light emitting diode and an illumination responsive
semiconductor, specifically a light responsive transistor. For
example, the insulated coupler IC8 includes the light emitting
diode D8 and the light responsive transmitter Q8. A current
limiting resistor is connected in series with each such light
emitting diode, for example, resistor R8 in series with diode D8.
The insulated signal coupler elements are so constructed that the
base of the light responsive transistor, such as Q8, is only
subject to illumination to which it is responsive when a
predetermined polarity of an intermediate signal, i.e., the voltage
across terminals X and Y, is applied to the associated diode, here
diode D8, to render the diode conducting in the forward direction.
For extreme safety or fail-safeness, it is preferable to so select
these light emitting diodes that they will not break down in the
reverse direction at any voltage which is less than the supply
voltage of the coil circuit, that is, the voltage of the local
source illustrated by the terminals B and N. As will be described
shortly, the contact circuit IC8 is equivalent to a back contact of
an electromechanical relay which is closed, i.e., active, when the
relay winding is deenergized and the relay released. Conversely,
the contact circuit arrangement IC9 is equivalent to a front
contact of an electromechanical relay which is closed (active) when
the relay winding is energized.
In describing the operation of the static relay of FIG. 3, it is
first assumed that terminals B and N of the source are connected to
capacitor C2 but that no circuit connection exists across control
input terminals D and E, that is, these terminals are
open-circuited. Under this condition, the potential at the upper
plate of capacitor C10 has a positive value because the input
circuit formed by transistors Q1 and Q2 is quiescent since no
modulation input appears on terminals D and E. The amount of
voltage across capacitor C10 is equal to the sum of the voltage
drops across diodes D3 and D4. The voltage potential at terminal Y
under these conditions is somewhat more positive than the voltage
at the upper plate of capacitor C10 and is in fact equal to the
voltage at the junction point of resistors R3 and R4, if the
voltage drop across the base-emitter junction of transistor Q3 is
neglected or ignored. Thus, terminal Y is more positive than
terminal X when the control input switching circuit across
terminals D and E is open. If the circuit across the input
terminals 8d and 8e for coupler IC8 is closed, even intermittently,
diode D8 is forward biased and current flows so that diode D8 emits
light or at least pulses of light. Transistor Q8 responds to this
light and becomes conductive, that is, completes a circuit between
output terminals 8a and 8b through the collector to emitter path of
the transistor. Under these conditions, even if a circuit is
completed across the input terminals 9d and 9e of coupler IC9,
diode D9, with opposite polarity connections, in reverse biased by
the potential across terminals Y and X and no current flows. Thus,
no light is emitted from diode D9 to enable transistor Q9 to
complete a circuit between its collector and emitter electrodes.
This condition is analogous to an electromechanical relay with its
winding deenergized and armature released to lose back contacts,
the circuit element IC8 being equivalent of a back contact.
Conversely, front contacts of the deenergized relay are open, for
example, the contact circuitry or coupler IC9. It is to be noted
that a similar contact condition or operation will exist, i.e.,
back contacts active, if a continuous circuit connection is closed
across the control input terminals D and E of the winding
portion.
However, if a contact, or preferably a static switch, connected
across control input terminals D and E is closed intermittently at
a frequency which is sufficient to operate the diode pump circuit
arrangement formed by diodes D3 and D4, resistor R2, and capacitor
C7, this operation produces a negative potential on the upper plate
of capacitor C10, and thus also at the junction point between
resistors R3 and R4. Accordingly, the emitter-follower transistor
configuration Q3 and Q4 produces a corresponding negative potential
at terminal Y. In other words, under this condition, the potential
at terminal X is positive with relation to terminal Y. Diode D9
will now be forward biased when a circuit is closed across the
corresponding input terminals 9d and 9e. Current thus flows through
diode D9 which then emits light to which transistor Q9 responds and
becomes conducting. This completes a circuit between output
terminals 9a and 9b of coupler IC9. At the same time, diode D8 is
reverse biased if a circuit is completed across terminals 8d and 8e
so that no current flows and transistor Q8 remains open-circuited.
The condition now assumed is analogous to an electromechanical
relay with an energized winding so that its front contacts, here
represented by coupler IC9, are closed or active, while back
contacts equivalent to coupler IC8 are open or inactive.
Reviewing briefly, it is obvious that, in the absence of
intermittent switching across control input terminals D and E of
the coil portion of the static relay, the potential on terminal Y
will be positive with relation to the potential on terminal X and
the relay coil or winding is considered to be deenergized, i.e., in
an inactive state. The opposite condition, i.e., when intermittent
switching or modulation is applied across terminals D and E, will
activate the coil circuit so that terminal X is positive with
relation to terminal Y and the coil is considered to be energized.
In this latter condition, front contact couplers, such as IC9, are
active, i.e., provide a closed circuit between output terminals,
and back contact couplers, such as IC8, are inactive. In the
converse condition, with the coil circuit deenergized, contact
couplers IC8 are active and couplers such as IC9 are inactive.
Similar conditions will apply to any other insulated circuit
couplers which are included in the same relay circuit and, as
previously indicated, a reasonable number of such signal couplers,
as required for the logic functions to be performed by the static
relaying circuit, may be controlled by one coil circuit.
From the above description, it will be appreciated that, in order
to function, the relay circuit must be supplied signals from a
suitable pulse switching circuit or source connected across its
control input terminals D and E. This is in addition, of course, to
the operating energy from terminals B and N of the local source
connected across two of the terminals of capacitor C2. The pulse
source is used to generate the static switching signals which are
applied to terminals D and E and may also be applied to input
terminals of the circuit couplers such as terminals 8d, 8e and 9d,
9e, respectively. A typical such pulse source is illustrated in
FIG. 4. This pulse source is similar to that shown in FIG. 2 of the
previously mentioned Brown et al. U.S. Pat. No. 3,746,942. However,
a brief description is included herein for convenience.
Referring to FIG. 4, a direct current supply voltage from terminals
B and N is connected through a four-terminal decoupling capacitor
C30 to a relaxation type oscillator in the form of a free-running
or astable multivibrator. This multivibrator includes a pair of
transistors Q5 and Q6, coupling capacitors C33 and C34, and
resistors R35, R36, R37, and R38. The multivibrator may be tuned to
a typical operating frequency on the order of, for example, 10 KHz.
The emitter electrode of transistor Q6 is connected through a
resistor R39 to the ground terminal and is also connected directly
to the base electrode of the switching or drive transistor Q7. The
collector electrode of transistor Q7 is connected in multiple to
the cathodes of a series of light emitting diodes D10 to D15 which
are each part of a different insulated signal coupler of a bank of
six such couplers included in the pulse source circuitry. It is to
be noted that, in the subsequent description, any diode or
transistor whose reference character includes a suffix between 10
and 31 is a light emitting or light responsive element,
respectively, and is part of an insulated signal coupler logic
element. The anode electrodes of diodes D10 through D15 are each
connected through a current limiting resistor and thence in
multiple to terminal B of the local source through the upper plate
of capacitor C30.
The alternate conductive and nonconductive conditions of transistor
Q6 periodically turn transistor Q7 on and off. This periodic
conduction and nonconduction of transistor Q7 causes the light
emitting diodes to alternately emit illumination and extinguish as
current flows through them in multiple. As the light emitting
diodes are pulsed on and off in phase with the frequency of the
multivibrator, each associated light responsive transistor is
alternately conducting and nonconducting, also in phase with the
frequency of the multivibrator and with each other transistor of
the bank of signal couplers. Thus the pulse circuit operates to
produce isolated pulse switching by mutually isolated semiconductor
devices, that is, the transistors Q10 and Q15 of these signal
couplers. This switching of these transistors is identical, i.e.,
in phase. It will be appreciated shortly that such phase coherence
is necessary for all contacts of static relaying circuits included
in any interlocked scheme for operating a particular control
circuit, here the logic circuitry of the highway crossing
protection system. As will be apparent in the subsequent
description, these pulse transmitters are used to provide the
modulated switching inputs for the various relay coil circuits and
other contact arrangements of the logic circuitry in FIG. 1.
I now refer to FIG. 1 and to the crossing protection system shown
therein using solid state logic elements of the static relay type.
Across the stop, again illustrated by a two-line symbol, is the
same or at least an equivalent stretch of railroad track
intersected by a highway H. A highway warning device HS, as used in
FIG. 2, is also provided although here illustrated at the crossing
only by a dotted symbol since the control circuit is shown
elsewhere in the circuit diagram. Two overlay track circuits are
provided to detect the approach of trains in the same manner as
shown and described in FIG. 2. Each overlay track circuit has a
transmitter and receiver unit connected to the rails with an
overlap portion between the circuits at the highway. The same
reference characters for the transmitters and receivers are used as
in FIG. 2. However, the track relay energized or supplied by the
output signal of each track receiver unit is now of the static type
shown in FIG. 3, each designated by a similar reference character
but with the suffix A to distinguish between the electromechanical
relays of FIG. 2 and the static relays of this figure.
The coil circuit portion for each static relay is represented by a
conventional block, labeled with the associated reference
character. The control input terminals D and E and the output
terminals X and Y leading to the contact circuit portions are
illustrated. The coil circuitry, including the direct current
supply from terminals B and N, is as shown in FIG. 3 and described
in connection therewith. The direct current output signal from each
overlay track receiver is applied to the control input terminals of
the associated relay through an insulated coupler circuit. For
example, the output of receiver 1TRU is coupled to input terminals
D and E of relay 1TRA through an insulated signal coupler comprised
of diode D16 and transistor Q16. In series with diode D16 is the
collector-emitter path of light responsive transistor Q10 which
provides the modulation or pulsing source for this relay input.
Transistor Q10, of course, is part of a signal coupler shown in the
pulse source arrangement of FIG. 4. Only the transistor elements of
the pulse source couplers are shown in FIG. 1 for convenience and
to simplify the circuit diagram.
Therefore, when the left approach warning track section crossing is
unoccupied, the output from receiver 1TRU is applied through an AND
circuit, including circuit coupler D16-Q16 and transistor Q10, to
input terminals D and E of relay 1TRA. The alternate conducting and
nonconducting conditions of transistor Q10, as a result of the
operation of the pulse source multivibrator, modulates the output
from receiver 1TRU to provide the necessary modulated switching
input which the relay requires in order to assume its so-called
energized condition. Thus, with the track unoccupied and the
switching input to terminals D and E thus modulated, relay 1TRA is
activated to its energized condition so that its output terminal X
is positive with relation to the associated terminal Y.
Accordingly, front contact circuits of this relay will be active,
that is, will be in the so-called closed circuit condition. If
there is no output from receiver 1TRU, usually because the
corresponding track section is occupied, relay 1TRA is deenergized,
terminal Y is positive with relation to terminal X, and back
contact circuit couplers are active. If there is any circuit fault
in transistor Q10 or transistor Q16, so that this circuit either is
open or remains continuously completed, relay 1TRA also assumes its
deenergized state so that terminal Y is positive and back contacts
are active. This is a fail-safe operation since the deenergized
condition of the track relay is the safe condition. A similar
operation of relay 3TRA in accordance with the output of track
receiver 3TRU through transistor Q13 and the insulated coupler
including diode D21 and transistor Q21 will be apparent from a
study of the drawings taken in connection with the immediately
preceding description.
Each of the track relays TRA is provided with two back and two
front contact circuit couplers. For example, relay 1TRA has two
back contact circuit couplers including diodes D17 and D18 and the
associated transistors Q17 and Q18. These diodes are forward biased
when output terminal Y has a positive potential. The front contact
circuit couplers, which become active when terminal X has a
positive potential, include diodes D19 and D20 and their associated
transistors Q19 and Q20, respectively. The back and front contact
couplers are controlled separately, to provide a pulsed output, by
transistors from the pulse source of FIG. 4. For example, diodes
D17 and D18 in multiple are connected in series with the
collector-emitter path of transistor Q11, while diodes D19 and D20
of the front contacts are similarly connected to the
collector-emitter path of transistor Q12. Referring to relay 3TRA,
its back contacts include diodes D22 and D23 with their associated
transistors Q22 and Q23. For pulse operation, these diodes, in
multiple, are connected in series with the collector-emitter path
of transistor Q14 from the pulse source. Front contact circuit
couplers of this relay 3TRA include diodes D24 and D25 and their
associated transistors Q24 and Q25. Diode D24 is connected in
series with transistor Q15 to provide a pulse output from this
front contact. However, it is to be noted that diode D25 is
connected in series with the collector-emitter path of transistor
Q20 in one of the front contact circuits of relay 1TRA, so that
relay 1TRA must also be in its energized condition with front
contacts active for any switching output to occur from transistor
Q25 of this front contact circuit coupler of relay 3TRA. The
pulsing for this output is provided by transistor Q12, which action
is in cooperation with the front contact coupler of relay 1TRA.
Therefore, an output from transistor Q25 represents the logic AND
function (1TR.sup.. 3TR), which is one element of equation (8)
previously discussed.
In this crossing protection arrangement, the directional stick
relays are also of the static type and their coils are
conventionally indicated by the blocks designated by references
1XSA and 3XSA. The directional and stick logic control is then
provided by contact circuit couplers of the various relays TRA and
XSA. Each XSA relay has two front and one back contact circuit
couplers but each coupler also includes control from other contacts
as well as from the associated relay coil circuit portion. Pulsing
in each case is accomplished at the other relay contacts and not
direct from the pulse source of FIG. 4. Since the XSA relays are
used as set, reset flip flop logic elements, these functions are
implemented by supplying the relay control input from its own
output through other reset devices, the latter of which may be, for
example, relay contact circuits of the other XSA relay. As a
specific example, the switching input connected across terminals D
and E of relay 3XSA is provided by transistor Q26 which is a part
of a back contact circuit coupler of relay 1XSA. However, it will
be noted that the circuit through diode D26 of this back contact
circuit coupler is connected in series with the collector-emitter
paths of transistors Q17 and Q30 in multiple. Said in another way,
diode D26 is connected in series with the collector-emitter path of
transistor Q17 or transistor Q30 to provide an alternative OR
function. Transistor Q17, of course, is part of a back contact
circuit coupler of relay 1TRA and represents the function 1TR,
i.e., the left approach warning track section occupied. Transistor
Q30 is part of a front contact coupler of relay 3XSA but its
associated diode D30 is also in series with the collector-emitter
path of transistor Q23. Since transistor Q23 is part of a back
contact circuit of relay 3TRA, transistor Q30 then represents the
function (3TR.sup.. 3XS). In other words, transistor Q30
periodically conducting represents the right track section occupied
by a train moving left to right.
Combining the various functions which are represented in diode D26
with the basic function of transistor Q26 as a back contact of
relay 1XSA, transistor Q26 then represents the function, in symbol
form, 1XS[1TR + (3TR.sup.. 3XS)]. The (1XS.sup.. 1TR) portion of
this function (as expanded) represents the pickup circuit for relay
3XSA, with reference to equation (10) and the prior art circuit for
relay 3XS in FIG. 2. The other portion of the expanded function.
(1XS.sup.. 3TR.sup.. 3XS), represents the stick circuit for relay
3XSA, again with reference to equation (10) and the FIG. 2
arrangement. The input to terminals D,E of relay 1XSA from
transistor Q29 represents similar logic functions to provide the
pickup and stick energy for relay 1XSA, as may be developed by
reference to the drawings and the preceding description, including
equation (9) and the prior art circuitry shown in FIG. 2.
The crossing relay XR, which is retained in this arrangement as an
electromechanical vital type relay, is directly controlled by an
output buffer circuit. This buffer circuit will accept the pulsed
switching function from the logic circuitry to produce a direct
current output voltage of a fixed polarity in order to energize the
relay winding. Relay XR is the same, or at least serves a similar
function, as the similarly referenced element of the FIG. 2
arrangement. In other words, when the relay is released, upon the
approach of a train, and closes its back contact a, the crossing
signal or other warning device is actuated to protect the highway
traffic. Otherwise, relay XR is energized to interrupt the control
circuit for the protection devices at the crossing. The circuit of
the buffer amplifier includes a four-terminal capacitor C40 which
has two of its terminals connected to terminals B and N of the
local direct current source. The other two terminals of capacitor
C40 are connected, through the ground bus, across the collectors of
a pair of complementary transistors Q32 and Q33 which, in turn, are
connected in emitter-follower arrangement. The common input, i.e.,
the base electrodes connected together, is connected through
resistor R41 to the upper plate of capacitor C40. The common
junction of the emitter electrodes of these two transistors is
connected by a coupling capacitor C42 to the primary winding of
transformer T1, the other terminal of which winding is connected,
in common with the collector electrode of transistor Q33, to the
ground terminal. The secondary winding of this transformer is
coupled by a full-wave rectifier RE to the winding of relay XR.
Thus, a direct current voltage is developed across the rectifier
output to energize the relay when a pulsating switching function
appears across the input electrodes of transistor Q33. This
pulsating input is supplied by transistors Q25, Q28, and Q31 whose
collector-emitter paths are connected in multiple, that is, in OR
function circuit arrangement, across the base and collector
electrodes of transistor Q33.
It was previously described that transistor Q25 represents the
function (1TR.sup.. 3TR). Transistor Q28 is in front contact
relation to relay 1XSA but its associated diode D28 is also
connected in series with the collector-emitter path of transistor
Q24, a front contact of relay 3TRA. Thus transistor Q28 represents
the logic function 1XS and 3TR, i.e., (1XS.sup.. 3TR), which is the
second element of equation (8). Transistor Q31 is in front contact
relationship with relay 3XSA while its associated diode D31 is
connected in series with the collector-emitter path of transistor
Q19, a front contact circuit of relay 1TRA. Therefore, transistor
Q31 represents the logic function (3XS.sup.. 1TR) which is the
final element of equation (8). Therefore, since the
collector-emitter paths of transistors Q25, Q28, and Q31 are
connected in multiple, that is, in OR function association, the
input circuit for transistor Q33 provides the combined logic
function (1TR.sup.. 3TR) + (1XS.sup.. 3TR) + (3XS.sup.. 1TR). This
fulfills the right half of equation (8) and controls the pulse or
switching input which actuates the buffer circuit to energize relay
XR. Relay XR, in turn, controls the crossing warning device,
actuating such device when none of these individual AND functions
of the control logic circuitry controlling this relay are
satisfied.
The arrangement of the invention thus provides a fail-safe crossing
protection system using principally solid state logic elements or
static relays. These relays provide both train detection and
directional logic control. Since the coil circuits of the static
relays require a modulated control switching input to be energized,
any open or short in the light responsive transistors included in
the relay control circuits will interrupt the modulated input and
result in the relay coil circuitry assuming its deenergized state.
Under this condition, back contact circuit couplers only are active
which fulfills the requirements of fail-safe characteristics. The
use of light emitting diodes and light responsive transistors as
insulated circuit couplers for the relay contacts isolates the
various parts of the logic and control circuitry to increase the
fail-safeness by eliminating any cross reactions or interreactions
between circuit elements if circuit faults occur. The resulting
logic control and highway protection system is a safe, efficient,
and economical arrangement.
Although I have herein shown and described but a single arrangement
embodying the features of my invention, it is to be understood that
various changes and modifications may be made within the scope of
the appended claims without departing from the spirit and scope of
the invention.
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