GB2214033A - Transponder system for identifying railway vehicles - Google Patents

Description

9214033 -_ 1 - APPARATUS FOR READING INFORMATION OFF RAILWAY VEHICLES The

present invention relates to automated management and control systems, and'more part'icularly it relates to apparatus for reading information off movable objects of railway trans- 1 port, i.e. off railway vehicles.

The invention can be utilized in traffic control systems of railway transport and othertransport systems.

There is widely known a system f.Or automatic reading of information off railway vehicles (Quarterly Reports, Vo. 23, No. 4 /Japan/T.Yuge "Automatic Identification of Cars on JaPan National Railways". pp. 145-150), comprising a data sender or pickup with receiving and transmitting elements, made in the form of a marker sign carrying information on the railway rolling stock, attached to the side of a car in a train. The marker includes two horn aerials for receiving electromagnetic energy and one horn aerial for radiating signals containing information identifying vehicle, mixers connected to the aerials, a low-frequency oscillator connected to a mixer, and a logic circuit connected to the low-frequency oscillator. In this system the data identifying the car of the train are stored in a read-only memory built into the marker. The system includes a mear for transmitting electromagnetic energy directing electromagnetic energy at a 2.45 GHz frequency onto the marker, and a means for receiving data signals adapted to respond to the information coming from the ma ker. The electromagnetic energy transmitting mean includes a main transmitting unit situated at the side of a railway track and two aerials directed onto each other across the railway track for transmitting signals differentiated by their polarization type. The mean for receiving data signals includes a.series 2 connection of a frequency demodulator, an amplifier, filters and mixers.

A signal in the microwave range generated in the main transmitting unit is supplied to the two aerials through a diffe- rential circuit. As a railway train passes by the information reading post., a-continuoua microwave i3mmodulated signal Is radiated towards a goods van, polarized in a horizontal plane.

The marker receives the energy of this signal and produces the information at the third aerial as a signal polarized in a vertical-plane.

In this known apparatus electromagnetic energy is tran mitted in the microwave band, which requires relatively complicated and costly hardware. The operability of a microwave system is dependent on the degree of contamination of the receiv- ing and transmitting aerials, so that the known apparatus would not ensure fully reliable performance under such adverse conditions as heavy rains and snowfalls.

Widely known is also an apparatus for automatically responding to the arrival of a full train (Avtomatika, telemellianika No. 99 1971, Svyaz /Moscow/, B.L.Razumovsky "Avtomatichesky.kontrol pribytiya poyezda v polnom sostavie", pp. 10-15), comprising an information pickup mounted on the automatic coupling of the last van in a train, mean for tran mitting electromagnetic energy and means for receiving data signals, mounted at a railway station where arrival of a full train is being monitored.

The data pickup includes a serial connection of a receiving element, a rectifier, a sine-wave oscillator and a transmitting element, both the receiving and transmitting elements being in the form of inductance coils.

c The means for transmitting electromagnetic energy includes a sine-wave oscillator situated at the post for reading information off railway vehicles, connected to a transmitting element accommodated between the rails of a railway track. The means for receiving data signals includes a power amplifier connected to the receiving element in the form of an inductance coil. The sine-wave oscillator of the means for tran mitting electromagnetic energy operates in a longwave band, at a 22 kHz frequency. As an information pickup mounted on the last van of the train passes over the tran mitting element of the means for transmitting electromagnetic energy, the information pickup receives the energy of the electromagnetic field, a signal is fed to the sine-wave oscillator of the information pickup operating at a 9 kHz frequency and connected to the transmitting element which emits a response signal to be received by the mean for receiving data signals. The information pickup of the apparatus being described stores and transmits information on the arrival of a full train, which can be transmitted as a single signal. The apparatus is incapable of tran mitting information in a greater volume, e.g. identifying the consecutive numbers of vans in the train.

The energy transmitted from the track floor-mounted induc- tance coil of the means for transmitting electromagnetic energy to the receiving Inductance coil of the information pickup is limited and can be transmitted over a distance short of 5 cm. This limitation of the distance between the pickup and the track-mounted part of the apparatus creates a situation when, under such adverse conditions as the trackmounted part of the apparatus getting buried under sand or snow, the information pickup and the track-mounted part alike might experience impacts causing their substantial damage, which impairs the performance reliability of the apparatus.

The present invention resides in an apparatus for reading information off railway vehicles, comprising mean for trans- mitting electromagnetic energy including a generator of sinewave oscillations situated at a post for reading information off railway vehicles and connected to a transmitting element situated between the rails of a railway track, and a-data pickup with receiving and tran mitting elements, accommodated on a railway vehicle and including a generator of clock pulses,, a unit for shaping and storing data signals having its inputs connected to the output of the generator of clock pulses, a carrier frequency generator having its input connected to the output of the unit for shaping and storing data signals and its output connected to the transmitting element of the pickup, and a power supply unit having its input connected to the receiving element tuned to the frequency of the generator of sine-wave oscillations of the means for transmitting electromagnetic energy, and its output connected to the generator of clock pulses, to the unit for shaping and storing data signals and to the carrier frequency generator; the apparatus further comprising mean for receiving data signal.% including a power amplifier connected to a receiving element, situated at the post for reading information off railway vehicles.

It is expedient that the receiving element of the data pickup should include a loop aerial having one its end connected to the frame of a railway vehicle directly and its other end through an insulating member.

It is further expedient that the unit for shaping and sto- ring data signals of the data pickup should include a NA' gate having its input connected to the generator of clock pulses, a flip- flop having its input connected to the output of the NAND gate, a first AND-NOR gate having its inputs connected. respectively, to the output of the NAND gate and to the direct and inverted outputs of the flip-flop, a shift reglater having its address inputs connected to a zero bus in accordance with the information pertaining to the railway vehicle, its count inputs connected to the output of the flipflop and its output connected to the input of the first AND- NOR gate, a univibrator Including two NAND gates of which one has its input connected to a resistance-capacitance network and its output connected to the enable input of the shift re gister. and the other has its input connected through a capacitor to the output of the flip-flop, and should further in- clude a second AND-NOR gate having its respective inputs connected to the output of the first AND-NOR gate and to the inverted output of the flip- flop, and its output connected to the carrier frequency ge,!jepator.

It is alternatively expedient that the unit for shaping and storing data signals of the data pickup should include two serially connected pulse counters of which the respective enable inputs are interconnected and grounded, the count input of the first counter being connected to the first output of the generator of clock pulses, two NAND gates of which one has its input connected to the output of the first pulse counter and the other has its f-lrat input connected to the other output of the generator of clock pulses and its other input connected to the output of the first NAND gate. and should further include a programmable storage having its address in- Puts connected to the outputs of the pulse counters, its ac- 6 cess input grounded, its enable input connected to the output of the first NAND gate and its output connected to the carrier frequency generator.

It is also expedient that the power supply unit should in- elude an oscillatory circuit connected to the receiving ele- ment,-and a step-down transformer of which the primary winding is the inductance of the oscillatory circuit and the secondary winding has connected thereto diodes wired into a full-wave rectifier circuit with a midpoint output.

In the presently disclosed apparatus electromagnetic energy is transmitted and received in a short-wave band, which provi des for simplifying the apparatus and enhancing its perform ance reliability.

The present invention will be further described in connec- tion with its embodiments in apparatus for reading information offrailway vehicles,, with reference being made to the accompanying drawings,, wherein:

FIG. 1 is a block unit diagram of an apparatus for reading information off railway vehicles, embodying the invention; FIG. 2 is a circuit diagram of one version of the data pick up of the apparatus embodying the invention; FIG. 3 is a circuit diagram of another version of the data pickup of the apparatus embodying the invention; FIF. 4 is a diagram plotting voltage versus time in the first version of the data pickup in the apparatus embodying the invention; FIG. 5 is a diagram plotting voltage versus time in the other version of the data pickup in the apparatus embodying the invention.

The apparatus for reading information off railway vehir-L45 t comprises a data sender/pickup 1 (FIG. 1) with a receiving element 2 a-ad a transmitting element 3.

The receiving element 2 of the data pickup 1 is in the form of a loop aerial of which one end is directly attached to the frame knot shown) of a vehicle 4,, while its other end is attach6d to the frame through an insulating member. The transmitting element 3 of the data pickup 1 is in the form of a rod aerial mounted on the railway vehicle 4,e.g. a goods vagon, on its frame.

At a post for reading information off vehicles 4, spaced from the track by a distance within 20 m, there is situated a means 5 for transmitting electromagnetic energy, including a generator 6 of sine-wave oscillations, connected to a trans mitting element 7 mounted between the rails of the railway track.

The transmitting element 7 of the means 5 for transmitting electromagnetic energy is in the form of an inductor having an inductance coil wound on bushing insulators, and a capacitor connected to the terminals of the inductance coil (not shown in the drawing).

The generator 6 of sine-wave oscillations is of a generally known design (cf. "Spravochnik radiolyubitelya-konstrt7,ktoralI /Moscow/, R.N. Perischuk, K.I.Perischuk, S.A.Sedov, 1977,, pp. 395-399).

The information reading post also accommodates a means 8 for receiving data signals, including a power amplifier 9 con nected to a receiving element 10 in the form of a rod aerial.

The power amplifier 9 of the means 8 for receiving data signals is of a generally known design (of. op.cit. "Spravoch- nik radiolyubitelya-konstruktora!', pp. 128-129).

8 The data received are further transmitted to a computer, printer. display devices. etc. (not shown).

The data pickup 1 (FIG. 2) includes a generator 11 of clock pulses. a unit 12 for shaping and storing data signals,, having its inputs connected to the output of the generator 11 of clock pulses, a carrier frequency generator 13 having its input connected to the output of the unit 12 for shaping and storing data signals and its output connected to the transmitting element 3 of the data pickup 1. The data pickup 1 fur tber includes a power supply unit 14 having its input connected to the receiving element 2 tuned to the frequency of the generator 6 (FIG. 1) of sine-wave oscillations of the means 5 for transmitting electromagnetic energy. The output of the power supply unit 14 (FIG. 2) is connected to the generator 11 of clock pulses. to the unit 12 for shaping and storing data signals. and to the generator 13 of carrier frequency.

The generator 11 of clock pulses of the data pickup 1 inc ludes two NAND gates 15. 16, each having its respective outputs connected to the respective inputs of the other gate, and an oscillatory circuit 17 including a capacitor 18 and an inductance coil 19 with a ferrite core 20, connected to the inputs of the NAND gates 15, 16, as shown in the circuit diagram in FIG. 2.

The unit 12 for shaping and storing data signals of the data pickup 1 includes a NAND gate 21 having its input connected to the output of the NAND gate 15 of the generator 11 of clock pulses. The output of the NAND gate 21 has connected thereto the first input 22 of an AND-NOR gate 23. Also connected to the output of the NAND gate 21 is the input of a J-K flip-flop 24 of which the direct and inverted outputs are egn- - 9 nected, respectively. to the second and third inputs 25, 26 of the AND-NOR gate 23.

The unit 12 further includes a shift register 27 of a generally known design (cf. "Spravochnik po mikroskhemam", M.Tarabarin et al., 1984, Radio i Svyaz /Moscow/g P. 59). The count inputs of the shift register 27 are connected to the inverted output of the flip-flop 24. The address inputs of the shift register 27 are connected to the zero bus in accordance with the data identifying the respective railway vehicle 4.

The output of the shift register 27 is connected to the fourth input 28 of the AND-NOR gate 23.

The unit 12 still further comprises a univibrator 29 with two NAND gates 30, 31. The output of the NAND gate 30 is connected to the first input of the NAND gate 31 and to the in- verted output of the J-K flip-flop 24.

The first input of the NAND gate 30 is connected to the inverted output of the J-K flip-flop 24 through a capacitor 32. The output of the NAND gate 31 is connected to the other input of the NAND gate 30 and to the enable input of the shift register 27.

The other input of the NAND gate 31 is connected through a resistor 33 and a grounded capacitor 34 to the positive terminal of the power supply unit 14.

Connected to the output 35 of the AND-NOR gate 23 a-ire two joined inputs 36, 37 of the second AND-NOR gate 38 of which two other inputs 399 40 are connected to the inverted output of the J-K flip-flop 24.

The carrier frequency generator 13 includes two NAND gates 411 42. the output of the NAND gate 41 being connected to the first input of the NAND gate 42. and the output of the N' - 10 gate 42 being connected to the first input of the NAND gate 41 and to the output 43 of the AND-NOR gate 38. The respective other inputs of the NAND gates 41, 42 are connected to an oscillatory circuit 44 including a capacitor 45 and an inductance in the form of the primary winding 46 of a transformer 47. The secondary winding 48 of the transformer 47 is connected to the aerial serving as the transmitting element 3 of the data pickup, 1.

The power supply unit 14 of the data pickup 1 includes an oscillatory circuit 49 with an inductance in the form of the primary winding 50 of a transformer 51, and a capacitor 52. The oscillatory circuit 49 is connected in series with the loop aerial serving as the receiving element 2 of the data pickup 1. Connected to the terminals of the secondary winding 53 of the transformer 51 are resistors 54, 55 connected with the respective anodes of diodes 56, 57. The cathodes of the diodes 56, 57 are interconnected and connected to the cathode of a stabilizer diode 58 of which the anode is grounded and connected to the midpoint of the secondary winding 53 of the transformer 51, connected with a capacitor 59 of which the other terminal is connected to the cathodes of the diodes 56.

57-In another version of the data pickup, 1, the generator 11 (PIG. 3) of clock pulses includes two NAND gates 60, 61. The output of the NAND gate 60 is connected through a capacitor 62 to the input of the NAND gate 61. also connected to a grounded resistor 63. The output of the NAND gate 61 is connected through a capacitor 64 to the input of the NAND gate 60. also connected to a grounded resistor 65.

The unit 12 for shaping and storing data signals in thi ,I 11 version of the data pickup 1 includes a series connection of two pulse counters 66, 67 of which the enable inputs are interconnected and grounded. The first count input of the pulse counter 66 is connected to the output of the NAND gate 60 of 5 the generator 11 of clock pulses. The unit 12 further includes two NAND gates 68, 69. the input of the NAND gate 68 being connected to the.output of the first flip-flop and to the other count input of the pulse counter 66. The NAND gate 69 has its first input connected to the output of the NAND gate 61 of the generator 11 of clock pulses, its second input connected to the output of the NAND gate 68, and its output connected through a resistor 70 and diode 71 to the output of the last flip-flop of the pulse counter 67.

The unit 12 further includes a read-only progranunable sto- rage 72 of a generally known design (11Spravochnik po mikrookhemam", M. Tarabarin et al., 1984,, Radio i Svyaz /Moscow/,, P. 310). The address inputs of the storage 72 are connected to the outputs of the pulse counters 66, 67. The access input of the storage 72 is grounded, and its enable input is connec- ted to the output of the NAND gate 68. The output of the storage 72 is connected to the anode of the diode 71 and to the input of the carrier frequency generator 13.

The carrier frequency generator 13 includes three transistors 73, 74, 75. The base of the transistor 73 is the input of the carrier frequency generator, connected to the output of the storage 72. The emitter of the transistor 73 is grounded. and its collector is connected through respective resistors 76, 77 to the emitter and base of the transistor 74, and through respective resistors 78, 79 to the emitter and base of the transistor 75. The bases of the transistors 72:

- 12 are interconnected and connected to inductances 80, 81, likewise interconnected. The interconnection point 82 of the inductances8O, 81 is connected through a resistor 83 to the positive terminal of the power supply unit 14. The inductances 80, 81 are the primary winding of a transformer 84 of which the secondary winding 85 serves as the inductance of an oscillatory circuit 86 having a capacitor 87. The midpoint of the secondary winding 85 of the transformer 84 is connected through a resistor 88 to the positive terminal of the power supply unit 14. The rod aerial serving as the transmitting element 3 of the data pickup 1 is connected to the oscillatory circuit 86 via a transformer coupling in the form of an inductance coil 89.

The apparatus for reading information off railway vehicles operaies, as follows.

When the railway vehicle 4 (FIG. 1) comes to the post for reading information off railway vehicles 4, the generator 6 of sine-wave oscillations of the means 5 for transmitting electromagnetic energy is automatically turned on, and the inductor of the transmitting element 7 of the transmitting means 5 irradiates electromagnetic energy at a frequency within the short-wave band, e.g. at about 800 kHz. As the railway vehicle 4 passes above the location of the inductor 7 - the transmitting element of the energy- transmitting means 5 - between the rails of the railway track, the receiving element 2 of the data pickup 1 responds to the energy of the electromagnetic field. The current flowing in the loop aerial of the receiving element 2 of the data pickup 1 flows through the oscillatory circuit 49 (FIG. 2) and the primary winding 50 of the transformer 51. Rectified current is supplied to the 1 - 13 generator 11 of clock pulses, to the unit 12 for shaping and storing data signals and to the generator 13 of carrier frequency. The moment the power is supplied to the resistor 33 and capacitor 34. the charging current of the latter causes a "0" signal at the respective input of the NAND gate 31, held until the capacitor 34 Is fully charged '.(PIG. 4f). This sets the flip-flops of the shift register 27 (FIG. 2) in accordance with the encoded data identifying the vehicle 4. With the capacitor 34 charged, a clock pulse triggers the NAND gates 30, 31 of the univibrator 29, and a "0" signal is set at the output of the NAND gate 31, enabling output of information from the shift register 27. The output of the NAND gate 30 sends a 11111 signal to the respective input of the AND-NOR gate 38, enabling transfer of the data through this gate. The gene- rator 11 of the clock pulses is supplied and shapes square pulses (FIG. 4a) at a frequency dependent on the parameters of the oscillatory circuit 17 (FIG. 2). The operation of the oscillatory circuit 17 causes alternating reversal of the states of the NAND gates 15, 16, in which way clock pulses are sent out. Clock pulses are fed by the output of the NAND gate 21 to the input of the AND-NOR gate 23 and to the input of the J-K.flip-flop 24. Pulses are fed from the respective direct and inverted outputs of the J-K flip-flop 24 to the inputs 25, 26 of the AND-NOR gate 23 (PIGS 4b,, 4c). The inverted output of the J-K flip-flop 24 (FIG. 2) feeds pulses to the count inputs of the shift register 27, so that encoded information is fed out to the input 28 of the AND-NOR gate 23 (FIG. 4d), e.g. as a "101100111 message. The pulses coming to the inputs 22,, 25 26,1 28 (PIG. 2) of the AND-NOR gate 23 are added up, a--dl the AND-NOR gate 23 forms at its output 35 a summed 1 - 14nal (FIG. 4e). The pulses are inverted by the AND-NOR gate 38 (FIG. 2), and fed for modulation to the Input of the NAND gate 41 of the carrier frequency generator 13. The carrier frequency.generator 13 Is similar in its structure to the generator 11 of clock pulses. although the oscillatory circuit 44 of the carrier frequency generator 13 is tuned to a higher frequency than the oscillatory circuit 17 of the generator 11 of clock pulses. Por example. the generator 11 of clock pulses operates at a 40-200 kHz frequency, whereas the carrier frequency generator 13 operates at a 30-40 MHz frequency (in the short- wave band). The aerial serving as the receiving element 10 (FIG. 1) of the mean 8 for receiving data signals responds to the information identifying the railway vehicle 4. The power amplifier 9 of the means 8 amplifies the information which can be subsequently directed into a computer, a printer, a display device. etc.

With the apparatus incorporating the data pickup 1 with another version of the unit 12 for shaping and storing data signal, illustrated in PIG. 3, the operation is basically si- milar to the abovedescribed.

Upon receiving power supply from the power supply unit 14 (PIG. 3), the generator 11 sends out clock pulses (FIG. 5a). The resistance-capacitance networks 64, 65 and 62,, 63 connected to the inputs of the respective NAND gates 60, 61 (FIG. 3) dictate by their parameters the frequency of the sending of the clock pulses. and with the capacitors 62, 64 going through successive charging/discharging cycles, the state of the NAND gates 60, 61 is alternatingly reversed.

Pulses coming from the output of the NAND gate 60 of the generator 11 of clock pulses are fed to the count input of R 4 1 the pulse counter 66. Pulses (FIG. 5b) of the first flip-flop of the counter 66 (FIG. 3) are fed to the enable input of the programmable read- only storage 72.

The signal formed at the output of the NAND gate 61 of the 5 generator 11 of clock pulses is fed to the other input of the NAND'gate 69, where the pulses are added up or superimposed (FIG. 50). The output of the NAND gate 69 (FIG. 3) feeds the resulting signal through the resistor 70 to the base of the transistor 73. Pulses coming from the outputs of the pulse counters 66, 6? are fed to the address inputs of the programmable read- only storage 72 which feeds out one bit of encoded data per two clock pulses. A logical 11111 signal is fed out with a duration of a full single clock pulse, and a logical 11011 is likewise fed out with a duration of a full single clock pulse, at the corresponding 11111 and 11011 levels (FIG. 5d). Pulses coming from the output of the NAND gate 69 (FIG. 3) and from the programmable read-only storage 72 are added up or superimposed at the base of the transistor 73, the duration of a logical 11111 being three times that of a logical 11011 (FIG. 5e).

The generator 13 (FIG. 3) of carrier frequency is of a self-exciting type with the transistors 74, 75 being supplied from the transistor 73 turned on and off in accordance with the data signals coming from the programme le read-only sto- rage 72. When a logical 110" signal is formed at the output of the last flip-flop of the pulse counter 67, this signal is sent through the diode 71 to the base of the transistor 73, so that the latter is turned off, and a silence clock period follows a clock period of sending the data signal.

Data signals coming from the carrier signal generator are irradiated by the aerial of the transmitting element 3 of the -data pickup.

The present invention provides for transmitting augmented volume of information identifying a railway vehicle, such as the own weight of the vehicle, the number of axles, the date of manufacture, the proprietor or operator of the vehicle, and the like, and also for significantly reducing the operating cost.

0 1

Claims (6)

CLAIMS:

1. An apparatus for reading information off railway vehicles, comprising means for transmitting electromagnetic energy including a generator of sine-wave oscillations situated,at a post for reading information off railway vehicles and connected to a transmitting element situated between the rails of a railway track, and a data pickup with receiving and transmitting elements, accommodated on a railway vehicle and including a generator of clock pulses, a unit for shaping and storing data signals having its inputs connected to the output of the generator of clock pulses, a carrier frequency generator having its input connected to the output of the unit for shaping and storing data signals and its output connected to the transmitting element of the pickup, and a power supply unit having its input connected to the receiving element tuned to the frequency of the generator of sine-wave oscillations of the means for transmitting electromagnetic energy,, and its output connected to the generator of clock pulses, to the unit for shaping and storing data signals a-ad to the carrier frequency generator; the apparatus further comprising means for receiving data signals, including a power amplifier connected to a receiving element, situated at the post for reading information off railway vehicles.

2. An apparatus as claimed in Claim 1, wherein the receiving element of the data pickup includes aloop aerial having its one end connected to the frame of the vehicle directly and its other end through an insulating member.

3. An apparatus as claimed in Claim 1, wherein the unit I for shaping and storing data signals of the data pickup inclu- 4 1 1 1 - 18 des a NAND gate having its input connected to the generator of clock pulses, a flip-flop having its input connected to the output of the NAND gate. a first AND-NOR gate having its inputs connected, respectively. to the output of the NAND gate and to the direct and inverted outputs of the flip-flop. a shift register having its address inputs connected to a zero bus In accordance with the information pertaining to the railway vehicle., its count inputs connected to the output of the flip-flop and its output connected to the input of the first AND-NOR gate, a univibrator including two NAND gates of which one has its input connected to a resistance-capacitance network and its output connected to the enable input of the shift register. and the other has its input connected through a capacitor to the output of the flip-flop, the unit further inc- luding a second AND-NOR gate having its respective inputs connected to the output of the first AND-NOR gate and to the inverted output of the flip-flop, and its output connected to the carrier frequency generator.

4. An apparatus as claimed in Claim 1, whereih the unit for shaping and storing data signals of the data pickup includes two serially connected pulse counters of which the respective enable inputs are interconnected and grounded, the count input of the first counter being connected to the first output of the generator of clock pulses, two NAND gates of which one has its input connected to the output of the first. pulse counter and the other has its first input connected to the other output of the generator of clock pulses and its other input connected to the output of the first NAND gate, the unit further including a programmable storage having its address inputs connected to the outputs of the pulse counte 1 21 4 4 1. 1 V - 19 - its access input grounded, its enable ipput connected to the output of the first NAND gate and its output connecttd to the carrier frequency generator.

5. An apparatus as claimed in Claim 1. whereinthe power supply unit includes an oscillatory circuit connected to the receiving element, and a step-down transformer of which the primary winding is the inductance of the oscillatory circuit and the secondary winding has connected thereto diodes wired into a full-wave rectifier circuit with a midpoint output.

6. An apparatus as claimed in any one of the preceding Claims 1 to 5, substantially as hereintofore described with reference to the appended drawings.

Published 1988 at The Patent Office, State House, 66.71 High Holborn, London WC1R 4TP_ Further copies may be obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington, Rent BfL5 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Kent. Con- 1.187.