WO1987004527A1 - A method and a device for measuring a distance by means of ultrasonic pulses - Google Patents

A method and a device for measuring a distance by means of ultrasonic pulses Download PDF

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Publication number
WO1987004527A1
WO1987004527A1 PCT/FI1987/000014 FI8700014W WO8704527A1 WO 1987004527 A1 WO1987004527 A1 WO 1987004527A1 FI 8700014 W FI8700014 W FI 8700014W WO 8704527 A1 WO8704527 A1 WO 8704527A1
Authority
WO
WIPO (PCT)
Prior art keywords
transceiver
measuring
lvb
lva
counter
Prior art date
Application number
PCT/FI1987/000014
Other languages
French (fr)
Inventor
Esko Jukkala
Original Assignee
Mikrovalmiste Oy U.J. Pulkkanen Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mikrovalmiste Oy U.J. Pulkkanen Oy filed Critical Mikrovalmiste Oy U.J. Pulkkanen Oy
Priority to GB8816812A priority Critical patent/GB2207504B/en
Publication of WO1987004527A1 publication Critical patent/WO1987004527A1/en
Priority to NO873982A priority patent/NO873982L/en
Priority to DK504887A priority patent/DK504887D0/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/74—Systems using reradiation of acoustic waves, e.g. IFF, i.e. identification of friend or foe

Definitions

  • the invention relates to a method and a device for measuring a distance between two points by means of ultrasonic pulses.
  • the distance between two points can be measured in various ways. It is known to send an electromagnetic, acoustic or optical signal from a point of origin so that it is reflected back from a target point to the point of origin. The distance between the points is determined on the basis of the to-and-fro transmission time. In this way of measuring, a passive echo from the target point is not usually sufficient, but the target has to be provided with a reflector in order that the magnitude of the echo to be received would be sufficient.
  • U.S. Patent Specification 4,254,478 dis ⁇ closes a method for the determination of a distance by means of ultrasonic pulses, in which method the target point is provided with a transmitter which sends the pulse back to its point of origin after a determined delay.
  • the function of the delay is to eliminate possible disturbing echos from the surroundings.
  • a drawback of this known method for the determina ⁇ tion of a distance by means of ultrasonic pulses is that the transmitting and the receiving means are separate, and they are designed to function according to whether they are positioned at the point of origin or at the target point of the measuring interval. Furthermore, the measuring result can be read only at one end of the measuring interval. On account of the rigid nature of the measuring methods, it is not easy to observe a varying distance between measuring points.
  • the object of the invention is to eliminate the above drawbacks and to provide a method for the measure ⁇ ment of distances, which method enables a more flexible operation than known methods. This is achieved by means of the method disclosed in the prior art portion of claim 1 by means of the operational steps described in the characterizing portion of the claim.
  • the basic idea of the invention is to provide a method for measuring a d- ' stance in such a manner that devices positioned at different points interact with each other continuously and that the measuring result is visible in both devices.
  • the object of the invention is to provide a measuring device which is suitable for the measuring method and which ensures the simplest possible use. This is achieved in accordance with the characterizing portion of claim 4.
  • Figure 1 is a simplified view of transceiver units used in the method according to the invention and the interaction therebetween,
  • Figure 2 illustrates on a time axis the significant events of the measuring procedure according to Figure 1 ,
  • FIG 3 is a block diagram of the structure of the transceiver unit used in the method according to the invention.
  • the transceiver (transmitter-recei ⁇ ver) units LVA and LVB are positioned at a determined distance from each other.
  • the transceiver unit LVA com ⁇ prises a transmitter L and a receiver V.
  • the transceiver unit LVB correspondingly a transmitter _ o and a receiver V
  • the measuring can be started at either end of the measuring interval.
  • the measuring is started by means of the device LVA by sending with the transmitter L an ultrasonic pulse to the device LVB, the counter of the device LVA being started simultaneously (the counter is not shown in Figure 1 for the sake of clarity).
  • the upper time axis, indicated LVA illustrates the signifi ⁇ cant events of the device LVA
  • the lower time axis, indicated LVB illustrates the significant events of the device LVB.
  • the pulse is received by the receiver Vi_s at a moment t ? , the delay means of the device LVB being started simultaneously (said means is not shown in Figure 1).
  • the transmission time from the device LVA to the device LVB is indicated by T in Figures 1 and 2.
  • the delay is intended to delay the transmission until any possible disturbing reflections are fatigued.
  • the trans- mitter L ⁇ After the delay time at ⁇ t of the device LVB is pased, the trans- mitter L ⁇ sends an ultrasonic pulse USP ⁇ at a moment t, , the counter of the device LVB being started simultaneous ⁇ ly (the counter is not shown in Figure 1).
  • the pulse sent is received after the transmission time T at a moment t. in the device LVA, the delay means of the device LVA being started simultaneously (the means is not shown), and the counter which was started earlier at the moment t. is stopped, whereafter the measuring result calculated on the basis of the time interval measured by the counter can be read in the device LVA.
  • the transmitter L A After the delay time ⁇ t of the device LVA, preferably equal to that of the device LVB, the transmitter L A sends an ultrasonic pulse USP, at a moment t,-, which pulse is received by the receiver V prepare of the device LVB after the transmission time T at a moment t g , as a result of which the delay means of the device LVB is started, and the counter which was started earlier at the moment t, is stopped, whereafter the measuring result is visible in the device LVB, too.
  • the device again sends an ultrasonic pulse and the measuring procedure continues as described above, the devices interacting continuously with each other.
  • the length of the ' delay time ⁇ t of the devices has to be selected so that it is sufficiently long in view of the largest operating range between the devices and the speed of travel of the pulse in the medium.
  • the distance between the devices can, of course, be calculated from the measured time interval.
  • Figure 3 illstrates more closely the structure of the transceiver unit LVA or LVB according to the inven ⁇ tion.
  • a transceiver sensor 1 operating at equal transmission and reception frequencies is connected to a transceiver component 2 the reception side of which comprises a reception amplifier 3 connected after the sensor 1 , and a detector circuit 4 and a pulse shaping circuit 5 connected after the reception amplifier.
  • a pulse is applied to the sensor 1 through a transmission amplifier 6.
  • the transceiver component 2 is connected through a bus 7 to a counter and control gate component 8 which communicates through a two-way bus 10 with a processor component 9 controlling the operations of the apparatus.
  • the processor component 9 controls a display unit 11 through a bus 12.
  • a cali ⁇ bration component 13 is connected both the the counter and control gate component 8 and to the processor compo ⁇ nent 9.
  • the programmability of the device is represented by a program component 14 attached to the processor component 9.
  • Figure 3 also shows a current source component 15 supplying current to the device.
  • the speed of travel of the ultrasonic pulse varies, depending on the medium and its tempera- ture, for example, it is necessary to calibrate the device for the operating conditions in each particular case.
  • This measuring of the speed of travel by means of the calibration component 13 can be .carried out in many ways, e.g. manually over a known distance, or automa- tically, whereby the processor component 9 corrects the measuring result.
  • the calibration is not within the scope of the inventive idea, so it is not more closely discussed here.
  • the delays ⁇ t essential to the devices, can be effected by the processor 9, which controls the opera ⁇ tions of the device, on account of which no separate delay means are shown in Figure 3.
  • the processor 9 is informed of a received pulse through the control gates and the channel 10, and it gives a transmission signal to the transceiver component after the delay time.
  • the compensation of the delay for obtaining a correct measuring result can also be carried out by the processor 9 so that the delay is taken into account with the pro ⁇ cessor calculates the measuring result.
  • the compensation can be carried out in the counter and control gate component 8 so that the counter does not start the effective counting until the delay time has passed after the reception of the starting pulse by the counter.
  • Desired measuring results can be stored in the memory of the processor component 9; further, it is possible to display on the display 11 not only the measured distance but also the change of a distance, for instance. Naturally, it is also possible to carry out other calculating operations by the processor 9 and display them on the display unit 11.
  • the invention has been described above with reference to the example of the attached drawing, it is self-evident that the invention is not restricted thereto, but it can be modified in various ways. For example, if no response is obtained to a sent ultrasonic pulse in a determined period of time, the sending of the pulse can be continued until a response pulse is obtained from the other device.
  • the structural details of the transceiver unit can be varied considerably within the inventive idea set forth in the following claims. It is also possible to use more than two devices simultaneously by synchronizing the devices with each other, i.e. by alternately measuring the distance between any two of the devices.

Abstract

Method and device for measuring a distance by means of an ultrasound. A drawback of this type of known methods for measuring a distance is that the transmitting and the receiving devices are separate, and they are designed to function according to whether they are positioned at a point of origin or at a target point of a measuring interval. For solving this problem, transmitter-receiver units (LVA, LVB) at the ends of a measuring interval are identical and interact continuously with each other so that the measuring result can be read in both devices.

Description

A method and a device for measuring a distance by means of ultrasonic pulses
The invention relates to a method and a device for measuring a distance between two points by means of ultrasonic pulses.
It is well-known that the distance between two points can be measured in various ways. It is known to send an electromagnetic, acoustic or optical signal from a point of origin so that it is reflected back from a target point to the point of origin. The distance between the points is determined on the basis of the to-and-fro transmission time. In this way of measuring, a passive echo from the target point is not usually sufficient, but the target has to be provided with a reflector in order that the magnitude of the echo to be received would be sufficient.
Further, U.S. Patent Specification 4,254,478 dis¬ closes a method for the determination of a distance by means of ultrasonic pulses, in which method the target point is provided with a transmitter which sends the pulse back to its point of origin after a determined delay. The function of the delay is to eliminate possible disturbing echos from the surroundings. A drawback of this known method for the determina¬ tion of a distance by means of ultrasonic pulses is that the transmitting and the receiving means are separate, and they are designed to function according to whether they are positioned at the point of origin or at the target point of the measuring interval. Furthermore, the measuring result can be read only at one end of the measuring interval. On account of the rigid nature of the measuring methods, it is not easy to observe a varying distance between measuring points. However, it would often be desirable that obser¬ vers at different points would be able to easily follow the movements of each other and to control continuously the distance between the locations. This is necessary for, for example, policemen, divers, and in the field of land surveying and building. The object of the invention is to eliminate the above drawbacks and to provide a method for the measure¬ ment of distances, which method enables a more flexible operation than known methods. This is achieved by means of the method disclosed in the prior art portion of claim 1 by means of the operational steps described in the characterizing portion of the claim.
Thus, the basic idea of the invention is to provide a method for measuring a d-' stance in such a manner that devices positioned at different points interact with each other continuously and that the measuring result is visible in both devices.
On the other hand, the object of the invention is to provide a measuring device which is suitable for the measuring method and which ensures the simplest possible use. This is achieved in accordance with the characterizing portion of claim 4.
Since the devices positioned at the different points are identical, even a layman unfamiliar with the measuring techniques finds it easy to use them, and he does not need to know whether he should have with him a device intended for the point of origin or a device intended for the target point. The identical structure of the devices also makes them easier to realize and produce industrially. In the following the invention will be described in more detail with reference to the attached drawing, wherein
Figure 1 is a simplified view of transceiver units used in the method according to the invention and the interaction therebetween,
Figure 2 illustrates on a time axis the significant events of the measuring procedure according to Figure 1 ,
Figure 3 is a block diagram of the structure of the transceiver unit used in the method according to the invention. In Figure 1, the transceiver (transmitter-recei¬ ver) units LVA and LVB are positioned at a determined distance from each other. The transceiver unit LVA com¬ prises a transmitter L and a receiver V., and the transceiver unit LVB correspondingly a transmitter _ o and a receiver V The measuring can be started at either end of the measuring interval. In the following example, the measuring is started by means of the device LVA by sending with the transmitter L an ultrasonic pulse to the device LVB, the counter of the device LVA being started simultaneously (the counter is not shown in Figure 1 for the sake of clarity). In Figure 2, the upper time axis, indicated LVA, illustrates the signifi¬ cant events of the device LVA, and the lower time axis, indicated LVB, illustrates the significant events of the device LVB. The moment when the device LVA sends an ultrasonic pulse USP1 as indicated by t. on the time axis. The pulse is received by the receiver Vi_s at a moment t?, the delay means of the device LVB being started simultaneously (said means is not shown in Figure 1). The transmission time from the device LVA to the device LVB is indicated by T in Figures 1 and 2. The delay is intended to delay the transmission until any possible disturbing reflections are fatigued. After the delay time at Δt of the device LVB is pased, the trans- mitter Lβ sends an ultrasonic pulse USP^ at a moment t, , the counter of the device LVB being started simultaneous¬ ly (the counter is not shown in Figure 1). The pulse sent is received after the transmission time T at a moment t. in the device LVA, the delay means of the device LVA being started simultaneously (the means is not shown), and the counter which was started earlier at the moment t. is stopped, whereafter the measuring result calculated on the basis of the time interval measured by the counter can be read in the device LVA. After the delay time Δt of the device LVA, preferably equal to that of the device LVB, the transmitter LA sends an ultrasonic pulse USP, at a moment t,-, which pulse is received by the receiver V„ of the device LVB after the transmission time T at a moment tg, as a result of which the delay means of the device LVB is started, and the counter which was started earlier at the moment t, is stopped, whereafter the measuring result is visible in the device LVB, too. After the delay time lot of the device
LVB, the device again sends an ultrasonic pulse and the measuring procedure continues as described above, the devices interacting continuously with each other. For the sake of clarity, the synchronizing of the devices at the beginning of the measuring procedure has not been described, because it does not belong to the basic idea of the invention. The length of the 'delay time ϋt of the devices has to be selected so that it is sufficiently long in view of the largest operating range between the devices and the speed of travel of the pulse in the medium. When the delay At and the speed of travel of the pulse in the medium are known, the distance between the devices can, of course, be calculated from the measured time interval. Figure 3 illstrates more closely the structure of the transceiver unit LVA or LVB according to the inven¬ tion. As mentioned above, the devices are identical in structure. A transceiver sensor 1 operating at equal transmission and reception frequencies is connected to a transceiver component 2 the reception side of which comprises a reception amplifier 3 connected after the sensor 1 , and a detector circuit 4 and a pulse shaping circuit 5 connected after the reception amplifier. On the transmission side, a pulse is applied to the sensor 1 through a transmission amplifier 6. The transceiver component 2 is connected through a bus 7 to a counter and control gate component 8 which communicates through a two-way bus 10 with a processor component 9 controlling the operations of the apparatus. The processor component 9 controls a display unit 11 through a bus 12. A cali¬ bration component 13 is connected both the the counter and control gate component 8 and to the processor compo¬ nent 9. The programmability of the device is represented by a program component 14 attached to the processor component 9. Figure 3 also shows a current source component 15 supplying current to the device.
Since the speed of travel of the ultrasonic pulse varies, depending on the medium and its tempera- ture, for example, it is necessary to calibrate the device for the operating conditions in each particular case. This measuring of the speed of travel by means of the calibration component 13 can be .carried out in many ways, e.g. manually over a known distance, or automa- tically, whereby the processor component 9 corrects the measuring result. Being known for one skilled in the art, the calibration, however, is not within the scope of the inventive idea, so it is not more closely discussed here. The delays Δt, essential to the devices, can be effected by the processor 9, which controls the opera¬ tions of the device, on account of which no separate delay means are shown in Figure 3. The processor 9 is informed of a received pulse through the control gates and the channel 10, and it gives a transmission signal to the transceiver component after the delay time. The compensation of the delay for obtaining a correct measuring result can also be carried out by the processor 9 so that the delay is taken into account with the pro¬ cessor calculates the measuring result. Alternatively, the compensation can be carried out in the counter and control gate component 8 so that the counter does not start the effective counting until the delay time has passed after the reception of the starting pulse by the counter.
Desired measuring results can be stored in the memory of the processor component 9; further, it is possible to display on the display 11 not only the measured distance but also the change of a distance, for instance. Naturally, it is also possible to carry out other calculating operations by the processor 9 and display them on the display unit 11.
Even though the invention has been described above with reference to the example of the attached drawing, it is self-evident that the invention is not restricted thereto, but it can be modified in various ways. For example, if no response is obtained to a sent ultrasonic pulse in a determined period of time, the sending of the pulse can be continued until a response pulse is obtained from the other device. Correspondingly, the structural details of the transceiver unit can be varied considerably within the inventive idea set forth in the following claims. It is also possible to use more than two devices simultaneously by synchronizing the devices with each other, i.e. by alternately measuring the distance between any two of the devices.

Claims

Claims:-N
1. A method for measuring a distance between two points by means of ultrasonic pulses, comprising the 5 steps of
(a) sending an ultrasonic pulse (USP.) at a pre¬ determined frequency by means of a transceiver" (LVA) positioned at a point of origin to a target point, whereby a counter (8) in the transceiver (LVA) is
10 started;
(b) receiving said ultrasonic pulse (USP..) by a transceiver (LVB) positioned at the target point, whereby a determined delay time (Λt) of the transceiver (LVB) is started;
15 (c) sending an ultrasonic pulse at said frequency
(USP-) by the transceiver (LVB) to the point of origin after the passing of said delay time;
(e) receiving said ultrasonic pulse (USP-) by means of the transceiver (LVA) at the point of origin,
20 whereby the delay time (Δt) of the transceiver (LVA) is started simultaneously, the counter (8) thereof is stopped, and the measuring result is displayed in the transceiver (LVA) •
(f) sending an ultrasonic pulse (USP,) at said 25 frequency by the transceiver (LVA) to the target point after the passing of the delay time ( Vt) of said trans¬ ceiver, whereby the counter (8) thereof is started; c h a r a c t e r i z e d in that
(d) the counter (8) of the transceiver (LVB) 30 positioned at the target point is started in step (c),
(g) the ultrasonic pulse (USP,) is received after step (f) by means of the transceiver (LVB) at the target point, whereby a determined delay time (lit) of said transceiver is started simultaneously, the counter (8)
35 thereof is stopped, and the measuring result is displayed in the transceiver (LVB), too; (h) the measuring is continued from step (c) until it is interrupted.
2. A method according to claim 1, c h a r a c ¬ t e r i z e d in that different measuring results are stored in a memory for the processing.
3. A method according to claim 2, c h a r a c - t e r i z e d in that a distance change is optionally displayed in addition to a distance measured between the devices.
4. A device for measuring a distance between two points by means of the transmission time of ultrasonic pulses, c h a r a c t e r i z e d in that transceivers (LVA and LVB) positioned at a point of origin and a target point are identical.
5. A device according to claim 4, c h a r a c ¬ t e r i z e d in that each transceiver (LVA, LVB) comprises as a combination:
- a transmitter (L , L_) and a receiver (V., V ) which operate at the same frequency for sending and receiving ultrasonic pulses;
- a counter component (8) for measuring a time interval dependent on the transmission time of the ultrasonic pulse;
- delay means (8,9) for determing a delay time ( t) between the receiving moment of the ultrasonic pulse and a subsequent sending moment.
PCT/FI1987/000014 1986-01-28 1987-01-27 A method and a device for measuring a distance by means of ultrasonic pulses WO1987004527A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
GB8816812A GB2207504B (en) 1986-01-28 1987-01-27 A method and a device for measuring a distance by means of ultrasonic pulses
NO873982A NO873982L (en) 1986-01-28 1987-09-23 PROCEDURE AND APPARATUS FOR MEASURING A DISTANCE BY ULTRA SOUND PULSES.
DK504887A DK504887D0 (en) 1986-01-28 1987-09-25 METHOD AND APPARATUS FOR MEASURING A DISTANCE USING ULTRASONIC IMPULTS

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI860394A FI75678C (en) 1986-01-28 1986-01-28 FOERFARANDE OCH ANORDNING FOER MAETNING AV AVSTAOND MEDELST ULTRALJUD.
FI860394 1986-01-28

Publications (1)

Publication Number Publication Date
WO1987004527A1 true WO1987004527A1 (en) 1987-07-30

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI1987/000014 WO1987004527A1 (en) 1986-01-28 1987-01-27 A method and a device for measuring a distance by means of ultrasonic pulses

Country Status (8)

Country Link
US (1) US4894810A (en)
DE (1) DE3790018T1 (en)
DK (1) DK504887D0 (en)
FI (1) FI75678C (en)
GB (1) GB2207504B (en)
NL (1) NL8720014A (en)
SE (1) SE458071B (en)
WO (1) WO1987004527A1 (en)

Cited By (6)

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GB2235980A (en) * 1989-09-11 1991-03-20 Suparules Ltd Ultrasonic master-slave rangefinder
EP0447783A2 (en) * 1990-02-21 1991-09-25 The Laitram Corporation Hydroacoustic ranging system
US5175695A (en) * 1989-09-11 1992-12-29 Suparules Limited UL trasonic measuring apparatus
US5214617A (en) * 1990-02-21 1993-05-25 The Laitram Corporation Hydroacoustic ranging system
US5385050A (en) * 1992-04-07 1995-01-31 Northrop Grumman Corporation Gap measurement for shim manufacture
GB2508734A (en) * 2012-12-05 2014-06-11 Bosch Gmbh Robert Method and device for determining the relative distance and moement of a plurality of traffic participants

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US5223680A (en) * 1991-05-03 1993-06-29 Otis Elevator Company Measuring elevator car position using ultrasound
US5303206A (en) * 1992-07-17 1994-04-12 Richard Bemb Method and apparatus for measuring distance and determining direction in a fluid medium
US5627800A (en) * 1994-01-28 1997-05-06 Kotler; Seymour R. Method and apparatus for determining position of a moving object in a tank
EP1233281A1 (en) * 2001-02-14 2002-08-21 ISE Ingegneria dei Sistemi Elettronici S.r.l. Apparatus and method for reducing the effects of a fluid motion on measuring distances by means of acoustic waves
DE102004011693A1 (en) * 2004-03-10 2005-09-29 Siemens Ag Sensor node and self-organizing sensor network
US7408839B2 (en) * 2004-09-09 2008-08-05 Siemens Building Technologies, Inc. Distance measurement for wireless building automation devices
US20060063523A1 (en) 2004-09-21 2006-03-23 Mcfarland Norman R Portable wireless sensor for building control
US7378980B2 (en) * 2004-09-29 2008-05-27 Siemens Building Technologies, Inc. Triangulation of position for automated building control components
US7382271B2 (en) * 2004-09-29 2008-06-03 Siemens Building Technologies, Inc. Automated position detection for wireless building automation devices
US7602671B2 (en) * 2007-07-10 2009-10-13 Constantinos Dionysiou Oil heating tank meter for monitoring a plurality of variables

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2235980A (en) * 1989-09-11 1991-03-20 Suparules Ltd Ultrasonic master-slave rangefinder
US5175695A (en) * 1989-09-11 1992-12-29 Suparules Limited UL trasonic measuring apparatus
GB2235980B (en) * 1989-09-11 1993-06-30 Suparules Ltd Ultrasonic master-slave rangefinder
EP0447783A2 (en) * 1990-02-21 1991-09-25 The Laitram Corporation Hydroacoustic ranging system
EP0447783A3 (en) * 1990-02-21 1992-12-09 The Laitram Corporation Hydroacoustic ranging system
US5214617A (en) * 1990-02-21 1993-05-25 The Laitram Corporation Hydroacoustic ranging system
AU644843B2 (en) * 1990-02-21 1993-12-23 Ion Geophysical Corporation Hydroacoustic ranging system
US5385050A (en) * 1992-04-07 1995-01-31 Northrop Grumman Corporation Gap measurement for shim manufacture
GB2508734A (en) * 2012-12-05 2014-06-11 Bosch Gmbh Robert Method and device for determining the relative distance and moement of a plurality of traffic participants
GB2508734B (en) * 2012-12-05 2019-07-10 Bosch Gmbh Robert Method and device for determining the relative distance and the relative movement of a plurality of traffic participants

Also Published As

Publication number Publication date
FI860394A (en) 1987-07-29
FI75678B (en) 1988-03-31
NL8720014A (en) 1988-10-03
US4894810A (en) 1990-01-16
FI75678C (en) 1988-07-11
DK504887A (en) 1987-09-25
GB2207504B (en) 1989-11-01
SE8802737L (en) 1988-07-29
DK504887D0 (en) 1987-09-25
FI860394A0 (en) 1986-01-28
DE3790018T1 (en) 1988-10-27
GB2207504A (en) 1989-02-01
SE458071B (en) 1989-02-20
SE8802737D0 (en) 1988-07-27
GB8816812D0 (en) 1988-09-21

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