U.S. patent number 3,858,223 [Application Number 05/436,036] was granted by the patent office on 1974-12-31 for device for photographic monitoring of road intersections controlled by a traffic light.
This patent grant is currently assigned to Robot Foto und Electronic GmbH & Co. KG. Invention is credited to Jurgen Holzapfel.
United States Patent |
3,858,223 |
Holzapfel |
December 31, 1974 |
DEVICE FOR PHOTOGRAPHIC MONITORING OF ROAD INTERSECTIONS CONTROLLED
BY A TRAFFIC LIGHT
Abstract
At an intersection controlled by a traffic light, a first sensor
provides an electric signal when a vehicle enters the intersection
against the red light. That electric signal causes a first
photograph to be immediately taken of the intersection and a second
photograph of the intersection to be taken after a time delay. If
that vehicle illegally entering the intersection turns right, it
activates a second sensor which sends a signal to cause another
picture to be taken. A second vehicle illegally entering behind the
first will not interrupt the sequence of pictures initiated by the
first, but will result in another picture being taken after a
predetermined time lapse.
Inventors: |
Holzapfel; Jurgen (Neuss,
DT) |
Assignee: |
Robot Foto und Electronic GmbH
& Co. KG (Dusseldorf-Benrath, DT)
|
Family
ID: |
5871885 |
Appl.
No.: |
05/436,036 |
Filed: |
January 24, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Feb 14, 1973 [DT] |
|
|
2307217 |
|
Current U.S.
Class: |
396/263; 396/310;
346/40; 396/502; 340/937 |
Current CPC
Class: |
G08G
1/0175 (20130101) |
Current International
Class: |
G08G
1/017 (20060101); G08g 001/10 () |
Field of
Search: |
;346/17UP,40 ;340/31C
;354/76,105,106,354 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hartary; Joseph W.
Attorney, Agent or Firm: Darbo, Robertson &
Vandenburgh
Claims
I claim:
1. An improvement for an apparatus for photographically monitoring
an intersection of two roads, at which there is a traffic light, by
making photographs of vehicles entering the intersection against
the stop signal of the traffic light, said apparatus including a
first sensor positioned along one of the roads to produce a signal
when a vehicle passes the first sensor, a first device to produce a
first camera-actuating pulse in response to said signal for taking
an initial photograph, and a second device to produce a second
camera-actuating pulse a predetermined delay time after said
initial photograph for taking a second photograph, said improvement
comprising:
a second sensor positioned along the other of the two roads to
produce a signal when a vehicle passes the second sensor; and
means connected to said second sensor and to said apparatus for
producing a camera-actuating pulse when a signal from the second
sensor occurs within said given period of time after the signal
from the first sensor.
2. An apparatus and improvement as set forth in claim 1,
wherein
said second device comprises means defining a control path for said
second camera-actuating pulse and including a first gate means,
and
said first device comprises a first monostable multivibrator
triggered by the signal from the first sensor and connected to said
first gate means to open the gate means for the passage of said
second pulse.
3. An apparatus and improvement as set forth in claim 2,
wherein
said first multivibrator changes from its stable to its metastable
state by said triggering, remains in its metastable state for said
predetermined period of time and then returns to its stable state;
and
said means defining said control path being connected to said first
multivibrator to produce said second camera-actuating signal upon
said multivibrator returning to its stable state.
4. An apparatus and improvement as set forth in claim 2,
wherein said first sensor comprises an induction loop;
including a detection circuit connected to the first sensor for
producing a detection pulse in response to the signal from the
first sensor which detection pulse has a duration of at least the
time required by the vehicle to pass the first sensor; and
wherein said first device comprises a second monostable
multivibrator which remains in its metastable state for a shorter
period of time than the duration of said detection pulse, means
connecting said second multivibrator to said detection circuit to
trigger the second multivibrator from its stable state to its
metastable state by the initiation of said detection pulse, and
means connecting said second multivibrator to the first
multivibrator to normally trigger the latter when the second
multivibrator returns to its stable state.
5. An apparatus and improvement as set forth in claim 4, wherein
said first device includes a third monostable multivibrator having
an input and an output, said second multivibrator being connected
to said input whereupon the third multivibrator produces a pulse
signal at its output in response to a signal at its input, means
connecting said output of said third multivibrator to the first
multivibrator to trigger the latter by the rear edge of said output
pulse signal, and means connected to said output of said third
multivibrator to use said output pulse signal to form said first
camera-actuating pulse.
6. An apparatus and improvement as set forth in claim 5,
wherein said means defining said control paths for said
camera-actuating pulses includes second gate means; and
wherein said second device includes a fourth monostable
multivibrator having an input and an output, means connecting the
input of the fourth multivibrator to the first multivibrator to
trigger the former by the latter returning to its stable state to
thereby produce a signal at the output of the fourth multivibrator
for forming said second camera-actuating pulse, a fifth monostable
multivibrator having a metastable state duration substantially
equal to the film feed time, means connecting said fifth
multivibrator to the fourth multivibrator to be triggered by the
rear edge of said output signal of the fourth multivibrator, and
means connecting the second gate means to said fifth multivibrator
to close said second gate means when the fifth multivibrator is in
its metastable state to thereby prevent a camera-actuating pulse
from being formed during the film feed time following said
production of said signal at the output of the fourth
multivibrator.
7. An apparatus and improvement as set forth in claim 6
including:
means connected to the first, third, fourth and fifth
multivibrators and defining a third gate means connected between
the second and third multivibrators for blocking signal passage
between the latter during signal passage through said first, third,
fourth and fifth multivibrators;
fourth gate means connected to said first device which is open and
permits a signal to pass therethrough to produce a detection pulse
when said third gate means is blocking,
a pulse delaying sixth monostable multivibrator connected to said
third gate means to delay said passed signal; and
a seventh monostable multivibrator connected to said sixth
multivibrator for producing a camera-actuating pulse in response to
said delayed passed signal.
8. An apparatus and improvement as set forth in claim 1, wherein
said second sensor is positioned on said second road and to the
right of said first road from said first sensor.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to a device for photographic monitoring of
road intersections at which there is a traffic light, in which
device a photographic camera is triggered by a sensor responding to
a vehicle entering the intersection during the stop period of the
traffic light, and in which device there is also provision for
triggering a second camera exposure.
There are prior art devices for photographic monitoring of road
intersections controlled by a traffic light. In the prior art
devices, a sensor is positioned at a point along the road near the
traffic light. This sensor supplies a signal when a vehicle passes
over it. If the signal appears during the "stop" interval of the
traffic light, i.e. a vehicle has entered the road intersection
during the stop interval contrary to traffic regulations, a
photographic camera will be triggered. The field of view of this
camera covers the road intersection. Thereby a photograph is made
of the traffic violation and also of the license plate of the
violating vehicle (German patent 683,658).
At times it will be inevitable that a vehicle driving toward the
road intersection shortly before the traffic lights change from
"go" to "stop" cannot be stopped in front of the traffic lights but
only shortly behind the traffic lights. Usually the driver cannot
be blamed for this. With only a single exposure showing nothing but
the vehicle across or behind the stop mark monitored by the sensor,
the photograph of such a situation would not be different from a
photograph of an occurrence in which the vehicle had actually gone
on and entered the road intersection during the stop interval.
Therefore, care must be taken to distinguish between these two
cases. To this end, there is a prior art device which makes a
second exposure a predetermined delay time after the first
exposure. The second exposure would show whether the vehicle
continued on into the intersection and thus would provide clear
evidence of whether a traffic violation occurred. In addition, a
clock can also be photographed with each exposure, whereby the time
sequence of this event can be recorded conclusively (U.S. Pat. No.
2,871,088).
There is, however, a loophole in the prior art apparatus: If a fast
vehicle enters the road intersection during the stop interval and
immediately turns into the intersecting road, that vehicle may
already have left the field of view of the monitoring camera when
the second exposure is made. On the photograph taken with the
second exposure, no vehicle will be seen. An evidence of a traffic
violation, if any, can be derived therefrom only indirectly. For
example, it can be argued that, when the traffic lights changed to
"stop," the driver had been able to stop his vehicle only beside or
shortly behind the traffic lights (first exposure) and that he then
drove the vehicle backwards to a location in front of the traffic
lights and out of the field of view of the camera at the lower edge
of this field (second exposure).
It is an object of this invention to provide an apparatus of the
type mentioned hereinbefore which will also conclusively record
such vehicles which have entered the intersection during the stop
interval and then have turned into the intersecting road.
According to the invention, a second sensor is positioned in the
road, and an additional exposure is triggered if said second sensor
responds within said delay time. Thus if the vehicle entering the
road intersection during the stop interval turns into the
intersecting road, a second camera exposure will be triggered by
the second sensor before the delay time has expired and before the
vehicle has left the field of view of the camera. The second
exposure will provide a conclusive record of the traffic
violation.
In one embodiment of the invention, a first monostable
multivibrator is connected to be triggered by the first sensor.
This monostable multivibrator opens a first gate circuit in a
control path for a trigger signal from the second sensor to the
camera. The second exposure can be triggered by the first
monostable multivibrator returning to its stable state after said
predetermined delay time. Thus the second exposure will be made at
the end of the delay time in any event and will occur also if the
vehicle continues to go straight ahead and only touches the second
sensor.
Advantageously, the first sensor is an induction loop which
controls a detector circuit. The pulse from the detection circuit
should have a duration of at least the time required by the whole
length of the vehicle to pass over the sensor. A second monostable
multivibrator which remains in its metastable state for a shorter
interval than the duration of said pulse from the detection circuit
is connected to be triggered by the front edge of the detection
circuit pulse in order to reduce the pulse width. The output pulses
of the second monostable multivibrator trigger said first
monostable multivibrator directly or through further intermediate
circuits.
Thus, an initial pulse is produced by the detector circuit. This
pulse continues while the entire length of the vehicle passes over
the induction loop. This makes sure that one vehicle will not
produce a plurality of sensor pulses, for example one for each
axle.
This initial pulse is, however, too long for the actuation of the
processing circuit. Therefore a second pulse of shorter duration is
derived therefrom by the second monostable multivibrator. This
shorter pulse can then be used in a manner whereby the output of
the second monostable multivibrator triggers a third monostable
multivibrator to produce a pulse signal triggering the first camera
exposure. Also, the rear edge of the latter pulse signal is used to
trigger said first monostable multivibrator.
According to a further modification of the invention, the signal
triggering the second exposure is produced by a fourth monostable
multivibrator connected to be triggered by the first monostable
multivibrator returning to its stable state. A fifth monostable
multivibrator is connected to the output of the fourth monostable
multivibrator to be triggered by the rear edge of said exposure
triggering signal, remains in its metastable state for an interval
substantially equal to the film feed time, and blocks a gate
circuit in said control path of said exposure triggering signal.
Thus if a second vehicle passes over the first sensor shortly after
a first vehicle has entered the road intersection, the second
vehicle cannot immediately trigger an exposure. The exposure
triggering pulse produced by the second vehicle is "stored" and
triggers an exposure after a predetermined delay of, for example,
1.3 seconds determined by a sixth monostable multivibrator.
The initial exposure triggered by the first vehicle shows that the
second vehicle was not previously being in the road intersection.
The second picture resulting from the presence of the first vehicle
shows both vehicles in the intersection. This is evidence that the
second vehicle has entered the intersection against the stop
light.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic plan view of a road intersection and the
arrangement of traffic lights, sensors and camera;
FIG. 2 is a schematic diagram of the circuit used in an embodiment
of the invention; and
FIG. 3 is a more detailed wiring diagram.
DESCRIPTION OF SPECIFIC EMBODIMENT
The following disclosure is offered for public dissemination in
return for the grant of a patent. Although it is detailed to ensure
adequacy and aid understanding, this is not intended to prejudice
that purpose of a patent which is to cover each new inventive
concept therein no matter how others may later disguise it by
variations in form or additions or further improvements.
FIG. 1 shows a road intersection formed by two roads 10 and 12
intersecting each other at right angles. The road intersection is
controlled by a traffic light installation, only one of which is
shown. This is light 14 which controls the lane of movement of
vehicles from left to right in road 10. The present description
only describes the apparatus employed in conjunction with this
lane, but it will be understood that corresponding apparatus is
employed in conjunction with the remaining lanes. Pedestrian walks
16 have been marked on the road surface at the road intersection.
There is also a stop mark 18 on the road surface in the lane of
travel controlled by the respective traffic lights. The vehicles
should stop in front of (i.e. immediately before reaching) the stop
mark 18 during the stop interval of the traffic lights.
The road intersection is automatically monitored by a photographic
camera 20, in order to make a conclusive photographic record of all
vehicles which enter or cross the road intersection during the stop
interval. To this end, there is a sensor in the form of an
induction loop I.sub.1 between the stop mark 18 and the pedestrian
walk 16. The induction loop I.sub.1 and the traffic lights 14 are
connected to a control unit 23 which triggers the camera 20.
The technique of producing an exposure triggering pulse when a
vehicle passes over an induction loop disposed on or below the road
surface is well known and, therefore, will not be described in
detail.
The induction loop I.sub.1 is connected to a detector circuit
D.sub.1 which produces a signal when a vehicle passes over the
induction loop (FIG. 2). During the duration of the stop interval
of the traffic lights a signal is applied to a control input 26 of
a NAND-gate N.sub.13. Thus when a signal from detector circuit
D.sub.1 is received by NAND-gate N.sub.13 during the stop interval
that signal triggers a monostable multivibrator MF.sub.1 through an
inverter N.sub.15. The monostable multivibrator MF.sub.1 produces a
trigger signal to be applied to the camera through a control path
28.
By returning into its stable state, the monostable multivibrator
MF.sub.1 triggers a monostable multivibrator MF.sub.2 which changes
to its metastable state for a predetermined delay time. When the
monostable multivibrator MF.sub.2 returns to its stable state it
triggers a monostable multivibrator MF.sub.3 through a NAND-gate
N.sub.23 and an inverter N.sub.24. Monostable multivibrator
MF.sub.3 also applies a triggering signal to the camera through a
control path 30.
Thus a first exposure will be triggered by monostable multivibrator
MF.sub.1, when a vehicle passes the induction loop I.sub.1 during
the stop interval of the traffic lights, and thereafter a second
exposure will be triggered by the monostable multivibrator MF.sub.3
after a delay time determined by the monostable multivibrator
MF.sub.2.
A second sensor in the form of induction loop I.sub.2 is located on
the right-turn lane of road 12. Induction loop I.sub.2 is connected
to a detector circuit D.sub.2 which produces a signal when a
vehicle passes over it. This signal is inverted by the inverter
N.sub.21 and is applied to a second input of the NAND-gate
N.sub.23. Normally (i.e. with no signal from sensor I.sub.2) the
output of the detector circuit D.sub.2 is in the state "O."
Inverted this is a signal "L" at the input of the NAND-gate
N.sub.23. When the monostable multivibrator MF.sub.2 is in its
metastable state, it produces an L-signal at the other input of the
NAND-gate N.sub.23. The output of gate N.sub.23 is then "O," which
is inverted to "L" by inverter N.sub.24. When sensor I.sub.2
produces a signal due to a vehicle passing thereover, detector
circuit D.sub.2 produces a signal "L." This signal is inverted to
"O" by inverter N.sub.21. Thus the output of the NAND-gate N.sub.23
becomes "L," which is inverted to "O" by inverter N.sub.24. Thus
there will be a declining edge of the signal by which the
monostable multivibrator MF.sub.3 is triggered -- the same way as
if the monostable multivibrator MF.sub.3 returns to its stable
state -- so that an additional exposure is triggered through
control path 30.
Thus if a vehicle crosses sensor I.sub.1, enters the road
intersection during the stop interval and turns to the right into
road 12, it could have moved laterally out of the field of view of
the camera at the moment of the normal second exposure. In order to
get a photographic recording of such a vehicle and obtain
unambiguous evidence of its violation of the traffic regulations,
an additional exposure is triggered by sensor I.sub.2 to produce a
photograph of the vehicle turning away.
The triggering of the exposure after the delay time has expired is
effected independently of the additional exposure triggered by
sensor I.sub.2, whereby the vehicle will, for example, be
photographed again if it has actuated sensor I.sub.2 but
nevertheless continues to go straight ahead on road 10.
A more detailed wiring diagram is shown in FIG. 3.
When a vehicle passes over the induction loop I.sub.1, the detector
circuit D.sub.1 produces a signal which is applied to an input
E.sub.1. This signal is maintained during a set time of about 250
milliseconds. This prevents a vehicle from generating a plurality
of pulses, for example one for each axle. The signal thus obtained
is, however, too long to control the subsequent circuit. It must,
therefore, be shortened. To this end, the signal is applied by
detector circuit D.sub.1 to one input of NAND-gate N.sub.13 through
leads 32, 34, and to one input of another NAND-gate N.sub.14
through lead 32 and lead 36. The function of NAND-gate N.sub.14 is
explained below.
At the same time, a monostable multivibrator MF.sub.9 comprising
two transistors T.sub.3, T.sub.4 is triggered by the output signal
of the detector circuit D.sub.1 applied to the base of transistor
T.sub.3. The monostable multivibrator is triggered by the front
edge of the output signal from detector circuit D.sub.1. It applies
a signal through leads 38, 40 and 42 to one input, respectively, of
each of the NAND-gates N.sub.13 and N.sub.14. Multivibrator
MF.sub.9 produces an output pulse to lead 38 which is relatively
short as compared to the duration of the input pulse from detector
circuit D.sub.1.
A signal is applied to an input E.sub.3 when the stop interval of
the traffic light 14 commences. This signal is applied to the base
of a transistor T.sub.8 which operates as an inverter. Transistor
T.sub.8 controls a transistor T.sub.9 operating as an electronic
switch. When the switch is "opened," i.e. the transistor T.sub.9 is
non-conducting, a capacitor C.sub.2 is charged through an
adjustable resistor P.sub.1. The voltage across capacitor C.sub.2
controls a Schmitt trigger comprising transistors T.sub.10,
T.sub.11 and T.sub.12. Thereby a predetermined time interval can be
selected, during which a vehicle passing over the induction loop
I.sub.1 will not trigger an exposure.
The output signal of the Schmitt trigger is applied through an
inverter N.sub.27, the control line 26 and lines 44 and 46 to one
input of each of the NAND-gates N.sub.13 and N.sub.14. The output
of the NAND-gate N.sub.13 is applied through the inverter N.sub.15
to the input of the monostable multivibrator MF.sub.1. The
monostable multivibrator MF.sub.1 supplies a triggering signal for
triggering the first exposure of the camera 20. This triggering
signal applied to line 28 triggers a monostable multivibrator
MF.sub.8 through NAND-gates N.sub.19 and N.sub.20 (the function of
which will be described below) and through lead 48. Monostable
multivibrator MF.sub.8 produces a signal through lead 50 to an
amplifier (not shown) which energize the triggering solenoid of the
camera 20.
When the monostable multivibrator MF.sub.1 returns into its stable
state, a monostable multivibrator MF.sub.2 is triggered through
lead 52. The monostable multivibrator MF.sub.2 remains in its
metastable state during an interval equal to the desired delay time
between the first and the second exposure. The monostable
multivibrator MF.sub.3 is triggered by the rear edge of the output
signal from the monostable multivibrator MF.sub.2 through NAND-gate
23 and inverter 24. Monostable multivibrator MF.sub.3 supplies a
triggering signal to the monostable multivibrator MF.sub.8 through
line 30, NAND-gates N.sub.19 and N.sub.20 and lead 48. Monostable
multivibrator MF.sub.8 supplies a pulse to the triggering solenoid
of the camera through lead 50.
When the monostable multivibrator MF.sub.3 returns to its stable
state, a monostable multivibrator MF.sub.4 is triggered through
lead 54. Monostable multivibrator MF.sub.4 is connected to remain
in its unstable state during an interval substantially equal to the
film feed time. Multivibrator MF.sub.4 is to make sure that no
further pulse can be supplied to the triggering solenoid of the
camera while the film is being advanced. To this end, the
monostable multivibrator MF.sub.4 renders NAND-gate N.sub.20
nonconductive to signals from MF.sub.1, MF.sub.2 or MF.sub.3 and
thereby prevents the triggering of the monostable multivibrator
MF.sub.8. The output of the monostable multivibrator MF.sub.4 is in
the state "O," when the monostable multivibrator MF.sub.4 is in its
metastable state, lead 56 extending from this output. Thus the
output of NAND-gate N.sub.20 is "L," regardless of which signal is
applied to the other input of the NAND-gate N.sub.20. The
monostable multivibrator MF.sub.8 is, however, triggered through
lead 48 by the rear edge of the applied signal, thus by the
transition from "L" to "O."
This output of the monostable multivibrator MF.sub.4 (which is in
the state "O" when the monostable multivibrator is in its
metastable state) and the respective outputs of the monostable
multivibrators MF.sub.1, MF.sub.2 and MF.sub.3 are connected to an
NAND-gate N.sub.18 through leads 58, 60, 62 and 64, respectively.
Thus the output of NAND-gate N.sub.18 is "L," if anyone of the
monostable multivibrators MF.sub.1, MF.sub.2, MF.sub.3 or MF.sub.4
is in its metastable, i.e. triggered, state. This output "L" is
made on "O" by an inverter N.sub.17 and applied through line 66 to
a further input of the NAND-gate N.sub.13. Therefore the NAND-gate
N.sub.13 is rendered non-conductive during the passage of the
signal through the monostable multivibrators MF.sub.1, MF.sub.2,
MF.sub.3 and MF.sub.4. In addition, the output "L" of gate N.sub.18
is directly applied through line 66 to a further input of the
NAND-gate N.sub.14. This results in the gate circuit comprising
NAND-gate N.sub. 14 and the inverter N.sub.16 being rendered
conductive if all leads are on positive potential.
Thus if a second vehicle passes over the induction loop I.sub.1
after a first vehicle passes over the induction loop I.sub.1 and
causes exposure to be triggered through MF.sub.1 and MF.sub.2 and
before the second exposure has actually been made and the film has
been advanced, the pulse generated by the second vehicle is not
supplied to the chain of monostable multivibrators MF.sub.1 to
MF.sub.4 because gate N.sub.13 is blocked. Instead, this second
signal is applied to a lead 70 through the gate circuit N.sub.14,
N.sub.15. A monostable multivibrator MF.sub.5 is triggered through
lead 70. The monostable multivibrator MF.sub.5 remains in its
metastable state for a hold time of, for example, 1.3 seconds.
After this hold time has expired, the monostable multivibrator
MF.sub.6 is triggered through lead 72 by the monostable
multivibrator MF.sub.5 returning into its stable state. The
monostable multivibrator MF.sub.6 generates a triggering signal on
a lead 74, which also triggers the monostable multivibrator
MF.sub.8 through gates N.sub.19 and N.sub.20 and lead 48. This
results in a pulse being applied to the triggering solenoid of the
camera through lead 50.
Signal "O" appears on lead 74 when the monostable multivibrator
MF.sub.6 is in its metastable state. In the stationary state,
signal "L" is applied to lead 74. In the stationary state, there is
also "L"-signal on lead 28 from monostable multivibrator MF.sub.1
and on lead 30 from monostable multivibrator MF.sub.3. Thus "O"
appears at the output of NAND-gate N.sub.19, and consequently "L"
appears at the output of NAND-gate N.sub.20. If one of the
monostable multivibrators MF.sub.5, MF.sub.1 or MF.sub.3 is
triggered and changes over into its metastable state, the signal on
the respective lead 74, 28 or 30 becomes "O." Thus the output of
NAND-gate N.sub.19 becomes "L" and, provided the output of the
NAND-gate N.sub.22 supplies the signal "L," the signal from the
output of NAND-gate N.sub.20, i.e. on lead 48, changes over to "O."
Thereby the monostable multivibrator MF.sub.8 will be
triggered.
The output 76 of the monostable multivibrator MF.sub.6 is applied
to a monostable multivibrator MF.sub.7 to trigger the monostable
multivibrator MF.sub.7, when the monostable multivibrator MF.sub.6
returns into its stable state. The monostable multivibrator
MF.sub.7 has the same function as the monostable multivibrator
MF.sub.4. It is to prevent triggering of the camera during the film
feed operation. Thus the monostable multivibrator MF.sub.7 remains
in its metastable state during a hold time substantially equal to
the time required for the film feed operation. The output from the
monostable multivibrator MF.sub.7, which is in the state "O," when
the monostable multivibrator MF.sub.7 is in its metastable state,
is connected to a NAND-gate N.sub.22 through lead 78. Lead 56 from
the monostable multivibrator MF.sub.4 also is connected to an input
of gate N.sub.22. The output from NAND-gate N.sub.22 is "O," when
neither of the monostable multivibrators MF.sub.4 and MF.sub.7 is
in its metastable state, i.e. when signal "L" is applied to each
input. The output "O"-signal is converted into an L-signal by
inverter N.sub.22a and applied to the input of the NAND-gate
N.sub.20. If one of the monostable multivibrators MF.sub.4 or
MF.sub.7 is triggered, the NAND-gate N.sub.20 will be rendered
non-conductive. The outputs from the monostable multivibrators
MF.sub.5, MF.sub.6 and MF.sub.7, which supply the signal "O," when
the respective monostable multivibrator is in its metastable state,
are applied respectively to the three inputs of a NAND-gate
N.sub.26. The output of this NAND-gate becomes "L," when one of the
three monostable multivibrators MF.sub.5, MF.sub.6 or MF.sub.7 is
triggered. This output "L" is then converted into an "O"-signal by
the inverter N.sub.25, this "O"-signal being applied to the input
leads 82, 84 of the NAND-gates N.sub.13 and N.sub.14 respectively
and rendering these NAND-gates non-conductive. In this case, all
further input pulses with be suppressed.
The second induction loop I.sub.2 similarly actuates a detector
circuit D.sub.2 to produce a signal at input E.sub.2. This signal
triggers a monostable multivibrator MF.sub.10 comprising
transistors T.sub.1 and T.sub.2. Thereby a short pulse, as compared
to the input signal, is produced as has been described in
connection with the monostable multivibrator MF.sub.9. The output
from the monostable multivibrator MF.sub.10 is inverted by an
inverter N.sub.21 and is applied to one input of each of the
NAND-gates N.sub.23 and N.sub.28. The output from the monostable
multivibrator MF.sub.2 is applied to the other input of NAND-gate
N.sub.23. The output from the monostable multivibrator MF.sub.5 is
applied to the other input of the NAND-gate N.sub.28. Normally the
output from the monostable multivibrator MF.sub.10 will be "O." It
is inverted to "L" by inverter N.sub.21. In the stationary state,
the outputs from the monostable multivibrators MF.sub.2 and
MF.sub.5 are in the state "O." Thus there will be a signal "L" at
the outputs of NAND-gates N.sub.23 and N.sub.28 and a signal "O" at
the outputs of the NAND-gates N.sub.24 and N.sub.29.
If the multivibrator multivibrators MF.sub.2 is triggered, the
second input of NAND-gate N.sub.23 also becomes "L," whereby the
output from the inverter N.sub.24 becomes "L." Thus the monostable
multivibrator MF.sub.3, which is triggered by the rear edge of its
input signal, will be triggered, when either the monostable
multivibrator MF.sub.2 returns into its stable state and brings one
input of NAND-gate N.sub.23 into the state "O," or when an output
pulse from the monostable multivibrator MF.sub.10 appears and
through the inverter N.sub.21 brings the other input of the
NAND-gate N.sub.23 into the state "O." In both cases a triggering
signal is applied to line 30 by the monostable multivibrator.
The circuit comprising the monostable multivibrator MF.sub.5,
NAND-gate N.sub.28, inverter N.sub.29 and monostable multivibrator
MF.sub.6 operates in a corresponding manner.
Thus, if a vehicle passes over the sensor comprising induction loop
I.sub.2 during the delay time between the first and the second
exposure (monostable multivibrator MF.sub.2 being triggered) or
during the delay time by which a pulse caused by a second vehicle
is delayed (monostable multivibrator MF.sub.5 being triggered), the
pulse thereby produced will cause an additional exposure to be
triggered, provided none of the interlocking means previously
described becomes operative.
Thus the device of the invention makes it possible to conclusively
record traffic violations at road intersections controlled by
traffic lights even under unfavorable conditions such as with a
plurality of vehicles entering the road intersection in rapid
succession and/or with vehicles turning off.
* * * * *