Note: Descriptions are shown in the official language in which they were submitted.
59fl
This invention relates to communication between
vehicles and road side installations, and more particularly
though not exclusively to communication between tank vehicles
and stationary filling installations for such vehicles.
It is well known to provide a tank vehicle with liquid
level detectors in the or each tank of the vehicle so as to warn
of overfilling during a filling operation. Such detectors are
particularly necessary when the liquid being filled is flammable
or otherwise hazardous. The detectors are connected to a monitor
unit associated with the filling installation which responds to
an alarm condition by cutting off the supply of liquid being
filled. A number of such detecting systems are known, and the
construction of the detectors themselves forms no part of the
present invention. The principal shortcoming of known systems
resides in the means used to transmit the alarm signals from the
vehicle to the stationary installation. This is normally a flex-
ible cable plugged into a receptacle on the vehicle, and it is
found that the plug-in connection is a prolific source of prob-
lems whilst the cable is subject to considerable wear and tear.
Moreover, plugging in the cable is an additional step in the
filling operation. Further problems arise from the use of in-
compatible connectors in different detection systems, and the
special precautions needed when establishing electrical connec-
tions in the vicinity of highly flammable liquids.
Conventional methods of wireless communication are un-
suitable for establishing the link since filling installations
are normally arranged to service several vehicles simultaneously
at closely spaced locations and it is essential that the moni-
toring signals transmitted by each vehicle are reliably received
at the correct station but at no other station. This problem is
difficult to solve by encoding the signals to identify individual
5~
vehicles, since any vehicle may be received to fill at any loca-
tion and thus each receiver would have to be programmed indivi-
dually for each vehicle scheduled to use its associated filling
location. There are strict limits to the extent that the sig-
nals can be beamed, since the transmitters on different vehicles
during use may be in widely differing locations relative to the
receivers, and even if satisfactory control of the beam charac-
teristics could be achieved at an economic price, scattering and
reflection of the signal might still cause reception by the wrong
receiver.
We have now found that a satisfactory and reliable com-
munications link may be established between land vehicles and a
stationary vehicle service installation in respect of which
vehicles are required to assume a restricted range of locations,
by means of a particular form of modulated optical link, inclu-
ding an optical transmitter mounted on a vehicle at approximately
a first height above grade comprising a modulatable source of
submillimetric electromagnetic radiation and means restricting
radiation from said source to a comparatively narrow angle in a
first dimension and a comparatively wide angle in a second
dimension, an optical receiver mounted in a fixed position rela-
tive to said stationary installation at a second substantially
different height above grade, and comprising a sensor responsive
to radiation from said source and means concentrating on said sen-
sor radiation from said source received in a comparatively narrow
angle in said first dimension and a comparatively wide angle in
said second dimension, said receiver being directed so that its
field of view includes all possible locations of a transmitter
on a vehicle located anywhere in said range of locations, and said
transmitter being oppositely directed relative to the vehicle
whereby to establish an optical path between said source and
said sensor when the vehicle is anywhere in said range of
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locations. Preferably the submillimetric electromagnetic radi-
ation is infrared radiation. The term service installation is
intended to embrace any installation which a group or class
of vehicles may be required to visit at frequent intervals, such
as filling installations for tank vehicles, loading bays, in-
spection stations and the like. A second similar transmitter
and receiver pair may be mounted on the service installlation and
the vehicle respectively to establish two way com~unication, and
information is transmitted by modulation of the source. In the
simplest form of the invention, information may be transmitted
simply by the presence of absence of modulated light from the
source. For example, the transmitter may be arranged so that
the source cannot be energized to emit modulated radiation unless
overfill sensors on a tank vehicle indicate a non-overflow con-
dition, and the vehicle ignition system is also switched off,
and a monitor associated with the receiver may be arranged to
prevent the supply of liquid to the tanks of the vehicle unless
a modulated signal is received, thus providing a fail-safe sys-
tem. Additional information, such as data captured by an on-
vehicle computer or recorder may also be transmitted, as by fre-
quency shift keying of the modulating frequency. The restricted
transmission and reception angles, together with the different
heights of the transmitter and receiver and the opposite direc-
tion of these units, can readily be selected to prevent any pos-
sibility of the wrong signal being received, whilst the modula-
tion of the signal enables substantial elimination of interfe-
rence from noise in the form of ambient light.
Further features of the invention will become apparent
from the following description of preferred embodiments thereof.
Figure 1 is a diagrammatic view of a typical tank
vehicle filling installation, equipped with the system of the
invention;
Figure 2 is a diagrammatic elevation of a vehicle in
such an installation;
Figures 3 and 4 are orthogonal sections through the
essential portions of a transmitter unit used in the system;
Figure S is a plan view of a receiver unit used in the
system;
Figure 6 is a block diagram of a circuit controlling
the transmitter;
Figure 7 is a block diagram of a circuit associated
with the receiver; and
Figure 8 is a schematic diagram of the power supply
for the transmitter unit.
Referring first to Figures 1 and 2, a typical terminal
for loading tank vehicles 2 is shown in plan. The terminal has
several double sided islands 4 with fuel outlets 6 which can be
connected to filler tubes 8 on the vehicles during filling of
the latter. The vehicles 2 shown in the figures are illustrative
of the range of vehicle types and vehicle positions that can
typically occur. Since several vehicles may be in the terminal
at one time, it is essential that any wireless signalling link
employed to transfer data between a vehicle and an island when
the vehicle is standing at the latter should not be subject to
interference from links established between other vehicles and
islands or between another vehicle on the other side of the is-
land and the same island.
With this in view, each vehicle is equipped with a
directional transmitter unit 10 mounted at an elevated position
on the vehicle, typically at the front of the tank immediately
behind the vehicle cab 12. As will be described in more detail
below, radiation from the transmitter is directed to one side of
the vehicle only, typically being restricted in azimuth to about
1350 of arc. Usually this will be the same side as the filler
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Tubes 8, i.e., the right hand side in countries which drive on
the right of the road. Radiation from the transmitter is also
severely restricted so far as its vertical angle is concerned,
typically to about 12 of arc, centred on an elevation of about
35 from the horizontal.
Each filling location to either side of each island
is provided with a mast 14 on the island carrying a receiver
unit 16 at an elevation above grade greater than that of the
transmitter units 10 on the trucks, the height of the masts 14
being such that each receiver unit is within the beam from the
transmitter unit of a truck at any position within the filling
location at which its filler tubes 8 may be coupled to the
outlets 6. The angle of reception of the receiver is similarly
restricted in azimuth and elevation to the beam from the
transmitter, but its recept~on axis is angled downwardly rather
than upwardly, the axis of the receiver and its angles of recep-
tion being selected so far as possible so as to receive radiation
from anywhere within an area in which the transmitter may be
located on a vehicle properly located for filling with its
associated filling location, but not from outside that location.
Similarly, each transmitter is arranged so that when its associa-
ted vehicle is properly located within a filling location, the
receiver will fall within its beam. Typically, if the average
transmitter height is about 12 feet above grade, then the average
receiver height is about 20 feet above grade, with the receiver
spaced about 12 feet from the vehicle centre line.
Beam control of radio waves, even at microwave fre-
quencies to the accuracy required by the present invention,
requires sophisticated, costly and bulky equipment, and even then
the radiation pattern is likely to have lobes in unwanted direc-
tions. Similar considerations apply to ultrasound. However,
radiation at wavelengths in the submillimetric range is amenable
to optical techniques and can be accurately beamed and focussed
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because the wavelengths involved are very small compared to the
physical dimensions of the apparatus. As the wavelength shor-
tens, such radiation becomes more subject to the atmospheric ab-
sorption and scattering, and optimum results in the present in-
vention are achieved by the use of infra-red radiation. This is
less subject to atmospheric absorption and scattering (as by mist,
rain or snow) than visible or ultraviolet light, and easily
modulated sources of such radiation are readily available at
reasonable prices in the form of infra-red emitting diodes.
Complementary sensor devices are also readily available. It is
of course known to use such devices for the establishment of the
line-of-sight communication links, but normally the transmitter
diode at least is associated with focussing means to produce a
narrow pencil beam, and the transmitter and receiver are care-
fully aligned to ensure reception of a significant proportion
of the energy of the transmitter. I have determined that it is
possible to maintain reliable communication over significant
distances (50 feet or more) under adverse weather conditions,
with the transmitter located anywhere within a substantial area,
provided that the source is modulated, the radiation is beamed
only into the general area where reception is required, and
angle of reception of the receiver is similarly restricted whilst
its effective aperture is made large.
A typical transmitter unit 10 is shown in Figures 3
and 4, the case and means for mounting it on the vehicle being
omitted for clarity and simplicity. Two infra-red emitting
diodes 18 are each mounted in a reflector formed by two inclined
mirrors 20 and a vertical mirror 22 which serves to direct most
of its radiation onto a cylindrical lens 24, the two reflectors
being mounted by bases 26 into a lens holder 28 so that each is
optimally located relative to the lens 24, which restricts the
vertical angle of radiation to about 12. Each diode is respon-
sible for one half of the horizontal radiation pattern, the
9-~
reflector arrangement being such as to increase somewhat the
radiation in the angularly outermost portions of the radiation
pattern, where the greatest transmitter range is required.
Typically, the azimuthal angle of radiation is 135.
A receiver unit 16 is shown in Figure 5, the case
again being omitted. Two sensor devices 30 are mounted at the
focus of a fresnel lens 32 which subtends an angle at its focus
equal to the desired azimuthal reception angle, and is narrow
enough to provide the desired elevational reception angle. Ef-
ficiency is improved by providing a mirror surface 38 within theangle of a support member 34. By use of a fresnel lens, which
may be of a moulded synthetic resin transarent to infra-red
radiation, the effective aperture of the receiver may be made
very large. The sensor devices are preferably large area devices
such as silicon solar cells, so as to pick up as much of the
captured radiation as possible, although in some applications
infra-red sensitive photodiodes may be preferred because of their
more rapid response in spite of their effective efficiency being
decreased by their small active area. The receiver incorporates
an optical filter 36 typically as part of the lens 32, so as to
restrict reception substantially to the wavelengths radiated by
the transmitter 10. The characteristics of the transmitter and
receiver are chosen so that the radiation from the transmitter
incident on the receiver sensors under worst case conditions of
maximum range and maximum expected atmospheric absorption will
be at least about 10 nanowatts. With the arrangement described,
a four inch focus lens employed at the receiver, and a maximum
range of 50 feet, this requires a transmitter output of about
10 milliwatts, a figure readily achieved by commercially avail-
able light emitting diodes. A circuit for controlling thetransmitter is shown in Figure 6. Power is applied by a line 40
to an oscillator 42 operating typically at about k~z which
in turn drives an amplifier 44 providing power ~o the transmitter
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diodes 18. The amplifier 44 need be no more than a transistor
switch switching drive current to the diode, which current may
typically be lOOma with a 50~ duty cycle. The current through
the diode is sunk through another electronic switch 46, which
is held on by a signal whose presence is to be monitored. Typi-
cally the signal to be monitored comes from an overfill monitor
48 which monitors one or more liquid level detectors 50 in the
tank or tanks of the vehicle carrying the transmitter. Over-
filling of a tank or failure of the monitor causes the signal
to disappear and thus the transmitter is switched off. Removal
of power on the line 40 has the same effect. As described, the
only information transmitted relates to the presence or absence
of the signal from monitor 48, but other data of a more complex
nature can be transmitted in the presence of the monitor signal,
for example by frequency shift keying of the oscillator 42. As
will be seen, the oscillator frequency may be allowed to change
within a predetermined bandwidth, thus providing for such ~eying,
for example by a modulator 52. Data transmission by this means
is useful for capturing data accummulated for example by an on-
board computer on the vehicle as to deliveries on a previoustrip. A second transmitter-receiver pair could be used to es-
tablish two way communication if desired, with the additional
receiver on the vehicle and the transmitter on the mast. In
case of malfunction of the transmitter-receiver system, and to
allow use of the vehicle at installations without receivers, the
monitor 48 also has a conventional outlet receptacle 49.
A typical power supply unit 54 for the monitor 48, and
for the transmitter control circuit which is conveniently placed
in the same housing 56 as the monitor 48 is shown in Figure 8.
Power from the vehicle battery is applied to the circuit only
when the vehicle ignition switch ~8 is switched off so that the
vehicle cannot be operated. Moreover power is cut off from the
line 40 by the normally open contacts of a relay 60. The relay
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is energized by using a momentary contact switch 62 to fire a
thyristor 64 thus completing a circuit through the relay coil
and an indicator lamp 66. Any attempt to turn on the ignition
will turn off the thyristor 64 and thus de-energize the trans-
mitter 10, which cannot then be re-activated except by the switch
62.
The sensors 30 of the receiver 16 provide a signal
which is applied to the signal processing circuit shown in Figure
7. The signal from the sensors is applied to a preamplifier 68
which is matched to the characteristics of the sensors for opti-
mum noise performance and may conveniently be integrated with the
sensors in the receivers 16. The preamplified signal is then
applied to a band-pass filter 70 and thence to a signal processor
72 including a phase locked loop demodulator in which the upper
and lower lock-in limits are appropriately defined. A phase
locked loop will not only act as a product detector to provide
an output proportional to the amplitude of the modulated signal
from the receiver, but can also be used to recover any FSK
modulation of the transmitter frequency. The D.C. signal obtained
from the phase locked loop is applied to a dual limit comparator
which rejects signals above and below predetermined amplitudes,
and thence via an output circuit to a normally open relay 74 which
controls, for example, a pump or shut-off valve in the supply of
liquid to the outlets 6. The action of the comparator results
in rejection of signals of strength too low to have come from a
properly located transmitter, thus providing additional security
against stray radiation from other transmitters in the area.
Excessively high level signals are also rejected since they in-
dicate either a malfunction or that the phase-locked loop is out
of lock. An integrator between the comparator and the relay
provides further protection against spurious signals and signal
drop-outs of short duration. The signal processor 72 and relay
74 are duplicated as a precaution against failure.
1~2S~
In use, a vehicle 2 entering a filling location at
one side of an island 4 will draw up in a location such that
the transmitter 10 is within the field of view of the associated
receiver 16 and vice versa. By turning off the vehicle ignition
switch 58 and operating the switch 62, the transmitter 10 is
activated so as to radiate a 12 kHz modulated signal provided
of course that one of the level detectors, as monitored by the
monitor 48, indicates an overfill condition. A small portion
of the signal is picked up by the appropriate receiver 16, the
pick up of extraneous light being reduced by the filter 36.
Interference from ambient light is further reduced by the band
pass filter 70 and AC coupling to the signal processor 72, which
ensures that only signals corresponding to changes in ambient
light level at approximately the modulation frequency of the
transmitter will be applied to the signal processor. The trans-
mitter signal is detected by the phase-locked loop in the signal
processor, and if the latter verifies the presence of a signal
of appropriate frequency and amplitude, the relay or relays 74
allow filling to commence, provided that all other safety inter-
locks, associated for example with the outlets 6, are in propercondition. An overfill condition of any of the tanks will be
detected by monitor 48, and this or any other failure of the
monitoring system, or any actuation of the ignition switch 58
will result in cessation of the signal from the transmitter 10,
and consequently filling will be interrupted.
Not only the restricted beam dimensions of the trans-
mitter and receiver, but also their different elevations, make
for a minimum of scatter from the filling location associated
with one transmitter into other filling locations, whilst the
amplitude sensitivity of the receivers provides further discrim-
ination. Thus all of the receivers and all of the transmitters
may be made identical, providing a very simple and flexible sys-
tem which nevertheless has the capability of providing a lin~
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for more sophisticated data.
Although the system has been described with specific
reference to overfill alarm systems for tank vehicles, it will
be appreciated that other data could be transmitted from other
types of road or rail vehicles which are required to pass through
an installation along fairly well defined paths. Thus the sys-
tem could for example be used to capture data from an on-vehicle
tachograph or other recorder at an inspection station. Moreover,
whilst in the arrangement described the receiver is to one side
of the vehicle path, it could be supported above or at one end
of the vehicle path provided that suitable support could be
arranged and the geometry of the system was appropriately adjus-
ted. It would also be possible to use more sophisticated opti-
cal systems in order better to match the radiation and reception
patterns of the transmitters and receivers and increase their
efficiency.
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