Note: Descriptions are shown in the official language in which they were submitted.
CA 02710823 2010-08-03
Signal Lamps and Apparatus
The present invention relates to signal lamps and apparatus and particularly,
although not exclusively, to railway signal lamps and apparatus and
particularly to lamps
and apparatus utilising Light Emitting Diodes (LEDs) as light emitters instead
of normal
filament bulbs.
An LED signal consist of a multiplicity of LEDs which collectively produce a
monochromatic light emitting from a viewing aperture equivalent in size to a
conventional
filament lamp light signal aperture. Since the source is not a single filament
as in a bulb,
the LEDs are arranged in a pattern of points over the aperture. Use of LEDs
has the
advantage over single filament bulbs that, whilst individual LEDs may fail,
this does not
cause complete failure of the signal lamp as occurs with a bulb single
filament failure. A
failure in the control supply to the LEDs would, however, cause a complete
failure.
According to one aspect of the present invention an LED signal lamp comprises
at
least two separate LED arrays which have separate power feeds and wherein the
LEDs of
the arrays are positioned with respect to each other such that when lit they
provide a
composite light signal output and such that when the LEDs of only one of the
two arrays
are lit they provide a light signal with a visible distinctive pattern.
According to one embodiment of the invention an LED signal lamp is formed with
two LED arrays, each forming half of the signal display and each having
separate control
electronics supplied from the signalling supply. Hence if either half fails,
either in the
electronics or some of the LEDs such that current ceases to flow in the array,
then half of
the LEDs extinguish. The LEDs of the two arrays are arranged such that, on
extinguishing
of one array with the remaining half of the LEDs formed by the other array
remaining
alight, a distinctive pattern is revealed, either lit or dark. Typically this
pattern may be
formed as a letter such as "X" or "F" or may be formed as a striped effect,
for example. A
viewer (typically a train driver) of a signal in this state will interpret the
displayed signal
CA 02710823 2010-08-03
2
as a valid signal, but a signal that has to be reported as defective in
appearance, resulting
in a maintenance alert where the defective aspect of the signal can be
replaced.
An LED signal lamp typically takes less power (6 Watts) than an equivalent
filament lamp type signal(30 Watts). Hence when replacing Filament lamp
signals with
LED signal lamps in the existing railway signalling, the LED signal current
needs to be
ballasted to equate with that of a Filament lamp when lit, to enable the
existing signal
interlocking circuitry to detect a dark signal failure. The ballasting is
effected utilising a
ballast resistor in parallel with the LED signal across the signal supply.
With the typical
levels of power consumption mentioned above, this ballast resistor will take
approximately
80% of the supplied current.
In the existing railway signalling network, it is substantial cessation of
supply
current during a signal operation phase that indicates signal failure. It is,
therefore,
imperative that some form of interlock be applied to ensure that, if LED
current stops, the
ballast load is also disconnected from the supply. This has typically been
performed by a
fuse blow circuit. However because of the active nature of this circuit, it is
inherently less
reliable than the dropped relay version as applied to a filament lamp which is
inherently
fail safe.
According to a second aspect of the present invention, an LED signal apparatus
comprises input signal power supply terminals for the apparatus; a series
connection of
switch means and a ballast load connected across the supply terminals; an LED
signal lamp
connected to the terminals to be supplied with current therefrom; and switch
operating
means, in the supply path to the LED lamp, for controlling the state of the
switch means in
the series connection, whereby, during operation of the apparatus, total
failure or
substantially total failure of the current to the LED signal lamp results in
said switch
operating means causing said switch means to open to disconnect the ballast
load from
power from the supply terminals.
CA 02710823 2010-08-03
3
Advantageously, the switch operating means may comprise an optocoupled diode
for controlling an electronic switch such that, if electric current flows
through the diode,
the electronic switch closes and vice versa.
In preferred embodiments of the invention, the LED signal lamp comprises at
least
two separate LED arrays arranged jointly to provide a signal light output for
the lamp and
wherein each of said arrays has an individual switch control means in its
supply path and
said ballast load is connected to said supply terminals through a plurality of
switch means
each controlled by a respective one of the switch control means and the
arrangement is
such that provided current flows to one of said arrays, the corresponding
switch control
means controls its respective switch means to permit current to flow through
the ballast
load. Preferably, in such an arrangement, detection means are provided to
detect that not
all the switch means are permitting flow of current to the ballast load and to
provide a non-
urgent alarm signal to that effect. Such an alarm signal would normally
indicate failure of
current flow through the array associated with the corresponding switch
control means.
The detection means may comprise a relay with its relay coil connected between
switch
means controlled points, in the supply to the ballast load, that are at
substantially the same
voltage during closure of all switch means but which are at different
voltages, in the event
of opening of only one of the switch means, such that relay operating current
flows through
the relay coil.
Preferably, a pair of switch control means are connected in parallel in the
supply to
an array such that supply of current to the array is not interrupted solely as
the result of
failure of a single switch control means. Additionally there may be a pair of
switch means
each associated with a respective one of the pair of switch control means.
For a better understanding of the present invention, reference will now be
made to
the accompanying drawings, in which, solely by way of example:
Figure 1, shows diagrammatically the circuit of one embodiment of railway
signal
lamp apparatus in accordance with the second aspect of the invention; and
CA 02710823 2010-08-03
4
Figure 2, shows diagrammatically the circuit of a second embodiment of railway
signal lamp apparatus in accordance with the second aspect of the invention.
In both figures, the same references have been used for the same or
corresponding
elements.
The circuit arrangement of Fig.1 has two LED arrays 1 and 2, housed together
in
the same lamp (not shown) and designed to provide together the output signal
light for the
lamp. LED array 1 is connected to an array control electronics unit 3 through
two supply
lines, in one of which there are two optocoupled diodes D l and D2. Similarly,
LED array
2 is coupled to control electronics unit 4 through two separate supply lines,
of which one
includes parallel connected optocoupled diodes D3 and D4.
Two signal power terminals for the apparatus are referenced 7 and 8 and the
signal
supply voltage and current are shown as V and I respectively. These supply
terminals are
connected directly, to supply signal power thereto, to the control electronics
units 3 and 4.
A ballast load 6 is connected across terminals 7 and 8, one end being
connected directly to
terminal 8 with the other end being connected to terminal 7 through two pairs
of switches
S 1, S4 and S3, S2. The switches of each pair of switches are connected in
series between
terminal 7 and said other end of the ballast load 6. The junction between the
switches of
each pair of switches are connected via the coil of a relay 5. Switch contacts
S5 of relay 5
are coupled to a "non-urgent alarm" output 9. The switching state of each of
the switches
S I to S4 is controlled by the correspondingly numbered optocoupled diodes D 1
to D4.
As indicated, the LED signal lamp is formed with two LED arrays I and 2, each
forming half of the signal display and each having separate control
electronics supplied
from the signalling supply. Hence, if either half fails, either in the
electronics or in the LED
array such that current ceases to flow in the array, then half of the LEDs
extinguish. The
LEDs of the two arrays are arranged such that, on extinguishing of one array
with the
remaining half of the LEDs formed by the other array remaining alight, a
distinctive pattern
CA 02710823 2010-08-03
is revealed, either lit or dark. Typically this pattern may be formed as a
letter such as "X"
or "F" or may be formed as a striped effect, for example. As a result, a
viewer (typically a
train driver) of a signal in this state will interpret the.displayed signal as
a valid signal but
one that has to be reported as defective in appearance, resulting in a non-
urgent
5 maintenance alert where the defective aspect of the signal can be replaced.
In the Fig. I circuit, when power is applied to the input terminals 7,8, both
control
electronics units Sand 4 provide independent power to LED arrays I and 2 via
the diodes
Dl and D2 (for LED array-1) and D3 and D4 (for LED array-2). These four
optocoupled
diodes, control switches SI, S2, S3 and S4 respectively such that if current
flows through
DI electronic switch S 1 closes. Normally, on application of signal power,
current flows
through all 4 diodes Dl-D4 and hence S 1-S4 are closed. This results in the
ballast load 6
being in circuit, connected across the power supply terminals 7 and 8, and the
combined
effect of the ballast load 6 and the LED current, via the 2 sets of control
electronics are
arranged to be equivalent in load to that of a normal filament signal lamp.
Hence, the
normal hot filament proving circuit, in the standard existing control signal
interlocking
arrangement, will detect what it believes to be a normally operating filament
signal lamp
and react correctly. In this normal condition the voltage across the coil of
the non-urgent
alarm relay 5 is effectively zero and hence the contact S5 (which is normally
closed)
remains closed.
In the case where current stops flowing through one or other LED array
(causing it
not to be lit), then two switches will open. For example if LED array I fails,
then S I and
S2 open and current then flows via S3, the relay coil and S4 to the ballast
load 6. Similarly
if LED array 2 fails then S3 and S4 open and current then flows via S 1, the
relay coil 5 and
S2 to the ballast load 6. Hence in either of these partial failure cases, the
non-urgent alarm
output 9 is signalled by the opening of contact S5. However the signal load
current,
although reduced slightly, is still sufficient to indicate to the interlocking
control that the
lamp is operational. This is equivalent to the first filament failure alarm in
a conventional
signal.
CA 02710823 2010-08-03
6
In the very rare event that current stops being supplied to both LED arrays,
then all
4 switches SI to S4 open and the ballast load is removed from circuit. This
effect, plus the
loss of current to both arrays results in a loss of load current from the
interlocking control
arrangement sufficiently to guarantee the asserting of an Urgent Alarm in the
interlocking
control, which sets safe operation of the signalling. In this case the non-
urgent alarm is not
set but that is not a problem since it is overridden by the Urgent Alarm. The
operation of
the Urgent Alarm circuit is thus fault tolerant, and hence very reliable.
Combined with the
duplex operation of the LED arrays this arrangement may enable the meeting of
a UK
specified railway signalling reliability target of <1 undetected dark signal
lamp in 10"
hours.
The arrangement of Fig. 2 differs from that of Figure 1 solely in the
arrangement of
the switches S I to S4 and by the addition of two resistances RI and R2. In
this
arrangement switches S 1 and S2 form one pair and S3 and S4 form another.
Switch pair
SI,S2 is connected in series with resistance RI between supply line 7 and said
other end of
the ballast load 6. Similarly switch means pair S3,S4 is connected in series
with resistance
R2 between supply line 7 and said other end of ballast load 6.
This circuit arrangement provides a reliable switch S I in series with S2,
respectively operated optically by DI and D2 passing current. In the case of
LED array I
stopping taking current (either by the LED array I or the control electronics
unit 3 failing),
a voltage is generated across R2 sufficient to cause activation of the non-
urgent alarm relay
5 with current flowing through the coil via resistance RI. Similarly, if LED
array 2 stops
taking current then S3 and S4 are opened and a voltage is generated across RI
sufficient to
activate the non-urgent alarm relay 5 via R2.
The circuit arrangement of Fig.2 has the advantage that if any of the four
switches
S I to S4 fails short-circuit, the circuit continues operation correctly,
whereas if any of the
four switches fails open-circuit, it activates the non-urgent alarm. In both
cases, the signal
continues to operate correctly with the ballast load connected. In all other
respects the
CA 02710823 2010-08-03
7
operation of the second variant is the same as the first
In combination with the distinctively patterned LED arrays, which will alert
drivers
to a partially failed lamp for these to be independently reported, reliability
is further
enhanced.
