U.S. patent number 3,797,003 [Application Number 05/259,822] was granted by the patent office on 1974-03-12 for warning circuits for intermittently flashable lamp.
This patent grant is currently assigned to C.A.V. Limited. Invention is credited to Anthony John Ramshaw.
United States Patent |
3,797,003 |
Ramshaw |
March 12, 1974 |
WARNING CIRCUITS FOR INTERMITTENTLY FLASHABLE LAMP
Abstract
A warning circuit for use with a lamp which in use is connected
to an intermittent source of electric supply, the warning circuit
comprising means for sensing the current flow through the lamp
during the on period of the supply and further means operable when
the current falls below a predetermined value, indicative that the
lamp has failed for providing an indication of such failure.
Inventors: |
Ramshaw; Anthony John (Hayes,
EN) |
Assignee: |
C.A.V. Limited (Birmingham,
EN)
|
Family
ID: |
10131691 |
Appl.
No.: |
05/259,822 |
Filed: |
June 5, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Jun 9, 1971 [GB] |
|
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19577/71 |
|
Current U.S.
Class: |
315/136; 340/331;
340/641 |
Current CPC
Class: |
B60Q
11/005 (20130101) |
Current International
Class: |
B60Q
11/00 (20060101); G08b 021/00 () |
Field of
Search: |
;340/251,67,81R,80,331
;307/310 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Myer; Daniel
Attorney, Agent or Firm: Holman & Stern
Claims
1. A warning circuit for a lamp which in use, is connected to an
intermittent source of electric supply the circuit comprising in
combination a resistor connected in series with said lamp and the
intermittent source of electric supply, switch means for sensing
the voltage developed across said resistor during the on periods of
said supply, an electromagnetic relay, said switch means switching
on to energise said relay when the voltage drop due to current flow
developed across said resistor falls below a predetermined value
during an on period of said supply, a pair of relay contacts
forming part of said relay, said relay contacts when said relay is
energised maintaining current flow through said resistor from a
further source of supply during the off periods of said first
mentioned supply and a warning lamp for providing an
2. A warning circuit as claimed in claim 1 in which said switch
means comprises a transistor having the operating coil of said
relay connected
3. A warning circuit as claimed in claim 2 in which the operating
coil of the relay and the collector emitter path of the transistor
are connected
4. A warning circuit as claimed in claim 3 including means for
determining the base potential of the transistor whereby the
voltage across the
5. A warning circuit as claimed in claim 4 in which the means for
determining the base potential of the transistor comprises a
potential divider network connected in parallel with said first
mentioned supply.
6. A warning circuit as claimed in claim 5 in which said potential
divider network includes a diode to provide compensation for
changes in the operating characteristics of the transistor with
temperature variations.
7. A warning circuit as claimed in claim 6 in which said potential
divider network includes a Zener diode whereby compensation for
varying lamp current will be obtained as a result in fluctuation of
the voltage of said
8. A warning circuit as claimed in claim 1 in which said warning
lamp is
9. A warning circuit as claimed in claim 8 in which said first
mentioned source of supply comprises an interrupter switch
connected in series with
10. A warning circuit as claimed in claim 9 in which said relay
contacts are of the normally open type and are connected in
parallel with said interrupter switch.
Description
BACKGROUND OF THE INVENTION
This invention relates to warning circuits for use with lamps which
in use, are connected to an intermittent source of electric supply
whereby the lamp or lamps will flash.
The object of the invention is to provide a warning circuit for
such a lamp or lamps whereby an indication will be given upon
failure of the or one or more of the lamps.
DESCRIPTION OF THE PRESENT INVENTION
A warning circuit in accordance with the invention comprises in
combination means for sensing the current flow through the lamp or
lamps during an on period of said supply and further means operable
when the current flow falls below a predetermined value indicative
that the lamp or one or more of the lamps has failed, for providing
an indication of such failure.
More specifically a warning circuit in accordance with the
invention comprises in combination a resistor for connection in
series with said lamp or lamps and the intermittent source of
electric supply, switch means for sensing the voltage developed
across said resistor during the on periods of said supply, said
switch means being arranged to switch on and thereby energise a
relay, when the voltage developed across the resistor falls below a
predetermined value during an on period of said supply, a pair of
relay contacts operable when said relay is energised to maintain
current flow through said resistor during the off periods of said
supply and a warning lamp for providing an indication of the
operation of the relay.
In the accompanying drawings forming a part of the
specification:
FIG. 1 is a circuit diagram showing one example of a circuit in
accordance with the invention, and
FIG. 2 shows a circuit diagram of a modification to the circuit of
FIG. 1.
With reference to FIG. 1 there is provided a lamp 10 the failure of
which or of one of a plurality of such lamps connected in parallel
is required to be indicated. The lamp 10 is connected to the
negative terminal of an accumulator 11. The positive terminal of
the accumulator is connected by way of a switch 12 and an
interrupter switch 13 connected in series. The switches 12, 13
together with the accumulator constitute a source of intermittent
supply. One end of a sensing resistor 14 is connected to the switch
13 and the other end of the resistor is connected to the other
terminal of the lamp 10.
Also provided is a p-n-p transistor 15 having its emitter terminal
connected to a point intermediate the resistor 14 and the lamp or
lamps 10 and having its collector terminal connected by way of a
resistor 16 and a relay coil 17 to the negative terminal of the
accumulator.
The base terminal of the transistor 15 is connected to the negative
terminal of the accumulator by way of a resistor 18 and to a point
intermediate the switch 13 and resistor 14 by way of a further
resistor 19 and a diode rectifier 20 having its cathode connected
to the base terminal of the transistor. In addition there is
provided an indicator lamp 21 which is connected in parallel with
the switch 13 and in parallel with the indicator lamp is a pair of
normally open relay contacts 22.
Such a system can form part of the direction indicator system of a
road vehicle. The switch 13 is a switch which is closed and opened
in sequence, when the switch 12 is closed, and during its on period
causes current to flow to the lamp 10 by way of the sensing
resistor 14. In normal circumstances therefore when the switch 13
is closed the lamp or lamps 10 is illuminated and when the switch
13 is open or off the indicator lamp 21 will be illuminated. The
current flowing in the lamps 10 flows through the sensing resistor
14 and as with all tungsten filament lamps the initial flow of
current through the lamp or lamps is high but falls to a steady
value after a comparatively short time. The voltage developed
across the resistor 14 will therefore initially be high but will
gradually fall as the current flowing through the lamps decreases.
In the event that the lamp 10 or one of such lamps fails, then the
current will fall to a much lower value and the transistor 15 which
constitutes a switch means, will turn on.
The value of current flow in the lamps at which the transistor 15
turns on is determined by the base potential of the transistor and
this in turn depends upon the relative values of the resistors 18
and 19 and the forward volt drop of the diode 20. When the
transistor 15 is turned on current will flow through the relay coil
17 and the relay contacts 22 will be closed thereby to effectively
short circuit the warning lamp 21 and the interrupter switch 13.
When this occurs the warning lamp 21 will cease to flash thereby
providing an indication that the lamp 10 has failed or that one or
more of such lamps has failed. Once failure has occurred and whilst
the switch 12 is closed the remaining lamps 10 will remain
illuminated. The diode 20 is provided to compensate for the changes
in the characteristics of the transistor with varying
temperature.
The circuit of FIG. 1 is able to tolerate variations in the voltage
of the source since the base terminal of the transistor is
connected to a potentiometer network effectively across the supply
terminals. However, where the voltage of the source can vary over
fairly high values the biasing circuit of the transistor is
modified as shown in FIG. 2. In this circuit the resistor 19 and
diode 20 are as before but the cathode of the diode as well as
being connected to the base terminal of the transistor 15 is
connected to the negative terminal of the supply through a pair of
resistors 23, 24 connected in series. Moreover, a point
intermediate the resistors 23 and 24 is connected to the anode of a
zener diode 25 the cathode of which is connected to the interrupter
switch 13. In addition a further resistor 26 is connected between a
point intermediate the resistor 19 and the diode 20 and the
negative terminal of the source of supply. The voltage which is
applied to the base terminal of the transistor therefore does not
vary directly in accordance with the supply voltage and therefore
takes into account the fluctuations in the current flowing in the
lamps 10 resulting from variation in the supply voltage.
* * * * *