CA1128129A - Method for measuring low capacities - Google Patents
Method for measuring low capacitiesInfo
- Publication number
- CA1128129A CA1128129A CA313,113A CA313113A CA1128129A CA 1128129 A CA1128129 A CA 1128129A CA 313113 A CA313113 A CA 313113A CA 1128129 A CA1128129 A CA 1128129A
- Authority
- CA
- Canada
- Prior art keywords
- output
- measured
- capacitance
- input
- amplifier
- Prior art date
- Legal status (The legal status 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 status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2605—Measuring capacitance
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Resistance Or Impedance (AREA)
- Transmission And Conversion Of Sensor Element Output (AREA)
- Amplifiers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides a method for measuring low capacities with the elimination of the influence of stray capacitances, which method makes use of an RC oscillator circuit, whose output impedance depends on the measured capacitance;
wherein the measured capacitance is connected between a low-impedance generator and a circuit measuring only current.
The present invention provides a method for measuring low capacities with the elimination of the influence of stray capacitances, which method makes use of an RC oscillator circuit, whose output impedance depends on the measured capacitance;
wherein the measured capacitance is connected between a low-impedance generator and a circuit measuring only current.
Description
2~
The present invention relates to a method for measuring low capacitances, in whlch -the influence of the stray capacitan-ces is eliminated which method uses an RC oscillator circuit, whose output frequency depends, preferably inversely proportion-ally, on the measured capacitance.
~here has been difficulties in measuring low capaci-tances par-ttcularly because, when using conventional methods, capacitances of the measuring wires and stray capacities, which may be in the same size order as the measured low capacities, have an influence on the measurement.
The present invention provides a method in which these drawbacks are essentially eliminated and low capacitances can be meallsred without any influence oE stray capacities. The present invention also provides a method in which small variations in the voltage the measuring circuit i9 supplied with, have es-sen-tially no influence on the accuracy of the measurement. The presen~ invention provides a mel:hod that is suitable Eor tele-metrical use Eor instance in radiosondes and a method that can be achieved with simple and inexpensive equipment.
Acc~rding to the present innvention there is provided an apparatus for measuring low capacitance while minimizing the ef-fect on stray capacitance, comprising an inverting amplifier hav-ing an input and output, leads connected to said input and output o~ the inverting amplifier for connection to the capacitance to be measured, ~ bistable oscillator circu~t having an input con-nected to the output of said invertin~ amplifier and an output con-nected to the input of said inverting amplifier through a resis-tance, said bistable oscillator circuit generating an output frequency dependent on said capacitance to be measured.
Thus the principal characteristic feature of the in-vention is that in the method the capacitance to be measured is connected between a low-impedance generator and a circuit measur-ing only cu:r:rent, for instance between the input and ou-tput oE the invextlng arnpliEier.
The rnethod oE the present i.nvention is particularly .
~' - la -~,g~Q~
neant for telemetrical use, in which there are several measured capacities, which are connected one by one with the measuring circuit, by means of an electronic selector switch. In accor-dance with the invention, the electronic selector switches to be used preferably comprise a CrlOS differential amplifier pack-age or the like, the outputs of each of various amplifiers of this package being connected with the capacitance to be measured, and their inputs being connected with the stepping circuit, whereas the measured signal is directed to the output oE the measuring circuit from the voltage supply of the CMOS package or the like.
The present invention will now be further described with reference to the schematic Figures in the accompanying drawings in which:
Figure 1 is a block diagram of a clrcuit in which the method of the present invention is used;
Figure 2 is an embodiment, of the present invention in which the measured capacitance is remotely connected with the measuring circuit by means o:E two coaxial cables;
Figure 3 is an embodiment of the present invention in which there are several measured capacitances connected one by one with the measuring circuit by rneans of a special selector switch in accordance with the invention; and Figure 4 is a detailed representation of the basic structure of the CMOS differential amplifiers shown in Fig. 3.
As shown in Figures 1, 2 and 3, a measuring circuit in accordance with the method of this invention, comprises an inverting amplifier 1 between points A and B. Inverting ampli-fier 1 is connected through resistor Rl to output C of bistable oscillating circuit 4. As shown/ bistable circuit 4 comprises two inverting amplifiers 2 and 3, and its output D is backfed with resistor R3 to its ou-tput. Said bistable circuit 4 is for ~z~
instance a Schmitt trigger~ ~hose action typically fea-tures two voltage levels and hysteresis between these levels.
Measured capacitance CM is connected between input A
and outp~lt B of an inverting amplifier 1. Frequency f=l/T is acquired from output D of bistable circuit 4, this frequency is the measuring unit for measuring capacitance CM preferably so that in said RC oscillator circuit its output frequency is in-versely proportional to measuring capacitance CM. An essential feature of the circuitry is that output D of bistable circuit 4 is fed back res1stively via resistor R2 to input A of inverting amplifier 1. It is also important that input A of inverting amplifier 1 be sufficiently isolated (low capacitance) from its output B. It is also important to have a sufficiently high re-sistive input impedance at point A~
The circuitry described above operates as follows:
Assume that, initially, point D is the positive side of the in-put voltage. Then current throuyh resistor R2 tends to raise voltage at point A. As amplifier 1 is inverting, the raising tendency of the voltage at point A has a tendency to lower vol-tage at point B, and via measured capacitance CM, this alsoLends to lower the voltage at point A. The result is that, in the ideal case, voltage at point A does not change at all. The measured capacitance CM is charged with constant current which is determined by resistance R2 and voltage between points D and A. As voltage at point B has reduced to the lower triggering level of the bistable circuit in figures Schmitt-trigger 4, the state of the bistable circuit changes and voltage at point D
falls suddenly to the negative side of the supply voltagel from which moment the circuit goes on functioning as described above Now the currents only have opposite directions.
It is important to note in what is descri~ed above,
The present invention relates to a method for measuring low capacitances, in whlch -the influence of the stray capacitan-ces is eliminated which method uses an RC oscillator circuit, whose output frequency depends, preferably inversely proportion-ally, on the measured capacitance.
~here has been difficulties in measuring low capaci-tances par-ttcularly because, when using conventional methods, capacitances of the measuring wires and stray capacities, which may be in the same size order as the measured low capacities, have an influence on the measurement.
The present invention provides a method in which these drawbacks are essentially eliminated and low capacitances can be meallsred without any influence oE stray capacities. The present invention also provides a method in which small variations in the voltage the measuring circuit i9 supplied with, have es-sen-tially no influence on the accuracy of the measurement. The presen~ invention provides a mel:hod that is suitable Eor tele-metrical use Eor instance in radiosondes and a method that can be achieved with simple and inexpensive equipment.
Acc~rding to the present innvention there is provided an apparatus for measuring low capacitance while minimizing the ef-fect on stray capacitance, comprising an inverting amplifier hav-ing an input and output, leads connected to said input and output o~ the inverting amplifier for connection to the capacitance to be measured, ~ bistable oscillator circu~t having an input con-nected to the output of said invertin~ amplifier and an output con-nected to the input of said inverting amplifier through a resis-tance, said bistable oscillator circuit generating an output frequency dependent on said capacitance to be measured.
Thus the principal characteristic feature of the in-vention is that in the method the capacitance to be measured is connected between a low-impedance generator and a circuit measur-ing only cu:r:rent, for instance between the input and ou-tput oE the invextlng arnpliEier.
The rnethod oE the present i.nvention is particularly .
~' - la -~,g~Q~
neant for telemetrical use, in which there are several measured capacities, which are connected one by one with the measuring circuit, by means of an electronic selector switch. In accor-dance with the invention, the electronic selector switches to be used preferably comprise a CrlOS differential amplifier pack-age or the like, the outputs of each of various amplifiers of this package being connected with the capacitance to be measured, and their inputs being connected with the stepping circuit, whereas the measured signal is directed to the output oE the measuring circuit from the voltage supply of the CMOS package or the like.
The present invention will now be further described with reference to the schematic Figures in the accompanying drawings in which:
Figure 1 is a block diagram of a clrcuit in which the method of the present invention is used;
Figure 2 is an embodiment, of the present invention in which the measured capacitance is remotely connected with the measuring circuit by means o:E two coaxial cables;
Figure 3 is an embodiment of the present invention in which there are several measured capacitances connected one by one with the measuring circuit by rneans of a special selector switch in accordance with the invention; and Figure 4 is a detailed representation of the basic structure of the CMOS differential amplifiers shown in Fig. 3.
As shown in Figures 1, 2 and 3, a measuring circuit in accordance with the method of this invention, comprises an inverting amplifier 1 between points A and B. Inverting ampli-fier 1 is connected through resistor Rl to output C of bistable oscillating circuit 4. As shown/ bistable circuit 4 comprises two inverting amplifiers 2 and 3, and its output D is backfed with resistor R3 to its ou-tput. Said bistable circuit 4 is for ~z~
instance a Schmitt trigger~ ~hose action typically fea-tures two voltage levels and hysteresis between these levels.
Measured capacitance CM is connected between input A
and outp~lt B of an inverting amplifier 1. Frequency f=l/T is acquired from output D of bistable circuit 4, this frequency is the measuring unit for measuring capacitance CM preferably so that in said RC oscillator circuit its output frequency is in-versely proportional to measuring capacitance CM. An essential feature of the circuitry is that output D of bistable circuit 4 is fed back res1stively via resistor R2 to input A of inverting amplifier 1. It is also important that input A of inverting amplifier 1 be sufficiently isolated (low capacitance) from its output B. It is also important to have a sufficiently high re-sistive input impedance at point A~
The circuitry described above operates as follows:
Assume that, initially, point D is the positive side of the in-put voltage. Then current throuyh resistor R2 tends to raise voltage at point A. As amplifier 1 is inverting, the raising tendency of the voltage at point A has a tendency to lower vol-tage at point B, and via measured capacitance CM, this alsoLends to lower the voltage at point A. The result is that, in the ideal case, voltage at point A does not change at all. The measured capacitance CM is charged with constant current which is determined by resistance R2 and voltage between points D and A. As voltage at point B has reduced to the lower triggering level of the bistable circuit in figures Schmitt-trigger 4, the state of the bistable circuit changes and voltage at point D
falls suddenly to the negative side of the supply voltagel from which moment the circuit goes on functioning as described above Now the currents only have opposite directions.
It is important to note in what is descri~ed above,
- 3 2~
that voltage at point A did not chanye at all in any phase during the cycle. An important result of-thisfact is that stray capacitance CEIl, shown with broke~ lines in Figure 1, earthed at point A, has no influence on output frequency f because voltage at point A does not change and consequently stray capacitance CHl is neither charged or discharged. The situation is the same when stray capacitance is connected with point B, as output frequency f does not change o~er, due to the fact that in the ideal case inverting amplifier 1 is able to take or provide a sufficiently high current so to be able to, in addition to its other functions, charge and discharge said stray capacitance CH2.
What is described above is the reason why, as shown in Fig. 2, measured capaci-tance CM can be taken for instance with two coaxial cables 5a and Sb relatively far from the actual meas-~ uring circui~- In practice~ this is a remarkable advantage as in _ radiosondes, for instance, measured capacitances are shaped ' A apart from each other and, using the method of the invention, various capacitances can be connected by means of coaxial cables, ~or instance, with the measuring circuit in question without any loss of measuring accuracy. In previous methods for measuring low capacitances this kind of arrangement has been completely !. impossible.
Another important advantage of the invention is that the capacitance being measured can be changed to other capaci- -tances by means of a selector switch that is either a mechanical or electronic switch without any danger of stray capacitance influence on measuriny circuits. These other capacitances can be for instance references.
Figures 3 and 4 show a desirable electronic selector switch ~or said use. As shown in Fig. 3, in the selector switch there is a CMOS differential amplifier package in which there is si~ amplifier units 7I-7VI The unique and new feature of an ,1 electronic selector switch is that the ampliflers have been connected "in the wrong way" i e. ou~puts bl-b7 of various amplifiers 7I-7VI are connected with measured capacitances CMl-CM6, and inputs al-a6 are connected with a conventional stepping circuit 8, said circuit ~ giving through path indica-ted with arrow 9, impulse Pl alternatingly to each input terminal al-a6 of amplifier package 6.
Figure 4 shows a detailed example of the structure of a CMOS differential amplifier in its simplest Eorm. In this case it comprises two transistors Tp and TN, Tp being a P-channel-MOS-transistor and T~ an N-channel-MOS-transistor. The resistance of conducting transistor Tp, TN is in the order of 500Q and in non-conducting transistor TN,Tp several decades higher. As shown in Fig. 3, in one package 7 there are six amplifiers of the descri-bed type, and all VDD's of these amplifiers 7 are interconnected - as all VSS's are also in-terconnected.
An essential feature of -the selector switch described above is, firstly, as said before, that amplifiers 7 are connec-ted "in thewrongway"and that measured signal isdirected tothe des-cribed measurin~ circuit fromthevoltagesupply ofCMOS package6, notfor instance from its VDD. As shown in Fig. 3, this takes place so that resistor R4 brings drive voltage +U to the selector switch, and said voltage is separated with capacitance Cl from the RC oscillator circuit in accordance with the invention.
- Resistor R4 is preferably in the order of 150 kQ, and capacitance Cl preferably in the order of 10 nF. Said capacitance Cl must of course be high enough in order to keep its influence on the fre-quency being measured insignificant. Said value of capacltance Cl, appro~. 10 nF, is suitable, if measured capacitances CM are in the order of from a few pFis to a few tens pF's. A typical operational feature of the electronic selector swi-tch described above is that, as one of capacities CMl~CM6 is connected with L2~3 the measurin~ circuit as shown in Figure 3, other capacities are earthed.
that voltage at point A did not chanye at all in any phase during the cycle. An important result of-thisfact is that stray capacitance CEIl, shown with broke~ lines in Figure 1, earthed at point A, has no influence on output frequency f because voltage at point A does not change and consequently stray capacitance CHl is neither charged or discharged. The situation is the same when stray capacitance is connected with point B, as output frequency f does not change o~er, due to the fact that in the ideal case inverting amplifier 1 is able to take or provide a sufficiently high current so to be able to, in addition to its other functions, charge and discharge said stray capacitance CH2.
What is described above is the reason why, as shown in Fig. 2, measured capaci-tance CM can be taken for instance with two coaxial cables 5a and Sb relatively far from the actual meas-~ uring circui~- In practice~ this is a remarkable advantage as in _ radiosondes, for instance, measured capacitances are shaped ' A apart from each other and, using the method of the invention, various capacitances can be connected by means of coaxial cables, ~or instance, with the measuring circuit in question without any loss of measuring accuracy. In previous methods for measuring low capacitances this kind of arrangement has been completely !. impossible.
Another important advantage of the invention is that the capacitance being measured can be changed to other capaci- -tances by means of a selector switch that is either a mechanical or electronic switch without any danger of stray capacitance influence on measuriny circuits. These other capacitances can be for instance references.
Figures 3 and 4 show a desirable electronic selector switch ~or said use. As shown in Fig. 3, in the selector switch there is a CMOS differential amplifier package in which there is si~ amplifier units 7I-7VI The unique and new feature of an ,1 electronic selector switch is that the ampliflers have been connected "in the wrong way" i e. ou~puts bl-b7 of various amplifiers 7I-7VI are connected with measured capacitances CMl-CM6, and inputs al-a6 are connected with a conventional stepping circuit 8, said circuit ~ giving through path indica-ted with arrow 9, impulse Pl alternatingly to each input terminal al-a6 of amplifier package 6.
Figure 4 shows a detailed example of the structure of a CMOS differential amplifier in its simplest Eorm. In this case it comprises two transistors Tp and TN, Tp being a P-channel-MOS-transistor and T~ an N-channel-MOS-transistor. The resistance of conducting transistor Tp, TN is in the order of 500Q and in non-conducting transistor TN,Tp several decades higher. As shown in Fig. 3, in one package 7 there are six amplifiers of the descri-bed type, and all VDD's of these amplifiers 7 are interconnected - as all VSS's are also in-terconnected.
An essential feature of -the selector switch described above is, firstly, as said before, that amplifiers 7 are connec-ted "in thewrongway"and that measured signal isdirected tothe des-cribed measurin~ circuit fromthevoltagesupply ofCMOS package6, notfor instance from its VDD. As shown in Fig. 3, this takes place so that resistor R4 brings drive voltage +U to the selector switch, and said voltage is separated with capacitance Cl from the RC oscillator circuit in accordance with the invention.
- Resistor R4 is preferably in the order of 150 kQ, and capacitance Cl preferably in the order of 10 nF. Said capacitance Cl must of course be high enough in order to keep its influence on the fre-quency being measured insignificant. Said value of capacltance Cl, appro~. 10 nF, is suitable, if measured capacitances CM are in the order of from a few pFis to a few tens pF's. A typical operational feature of the electronic selector swi-tch described above is that, as one of capacities CMl~CM6 is connected with L2~3 the measurin~ circuit as shown in Figure 3, other capacities are earthed.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An apparatus for measuring a low capacitance while minimizing the effect of stray capacitance, comprising an in-verting amplifier having an inupt and output, leads connected to said input and output of the inverting amplifier for connection to the capacitance to be measured, a bistable oscillator circuit having an input connected to the output of said inverting ampli-fier and an output connected to the input of said inverting am-plifier through a resistance, said bistable oscillator circuit generating an output frequency dependent on said capacitance to be measured.
2. An apparatus as claimed in claim 1, wherein the input of said inverting amplifier functions as a low impedance generator having a low internal resistance and the output of said amplifier functions as a circuit responsive only to current.
3. An apparatus as claimed in claim 1, wherein bi-stable circuit comprises a bistable multivibrator.
4. An apparatus as claimed in claim 1, wherein said bistable circuit comprises a Schmitt trigger.
5. An apparatus as claimed in claim 1, wherein said leads comprise a pair of coaxial cables for connecting said capacitance to be measured to the input and output of said in-verting amplifier.
6. A radiosonde comprising an apparatus as claimed in claim 1 and several capacitances to be measured which are arran-ged to be connected one by one across said inverting amplifier by means of an electronic selector switch, said electronic switch comprising a CMOS differential amplifier package, the outputs of the various amplifiers of the package each being con-nected to the capacitances to be measured and inputs thereof being connected to a stepping circuit, the input and output of said inverting amplifier being connected respectively to the voltage supply terminal of the CMOS package and the side of said capacitances to be measured remote from the side thereof connected to the differential amplifiers of the CMOS package.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI773063A FI57319C (en) | 1977-10-14 | 1977-10-14 | ADJUSTMENT OF CAPACITY IN CAPACITY |
| FI773063 | 1977-10-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1128129A true CA1128129A (en) | 1982-07-20 |
Family
ID=8511140
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA313,113A Expired CA1128129A (en) | 1977-10-14 | 1978-10-11 | Method for measuring low capacities |
Country Status (10)
| Country | Link |
|---|---|
| JP (2) | JPS5498696A (en) |
| AU (1) | AU523345B2 (en) |
| BR (1) | BR7806786A (en) |
| CA (1) | CA1128129A (en) |
| DE (1) | DE2844121C2 (en) |
| FI (1) | FI57319C (en) |
| FR (1) | FR2410280A1 (en) |
| GB (1) | GB2006442B (en) |
| IT (1) | IT1100121B (en) |
| ZA (1) | ZA785694B (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2475231A1 (en) * | 1980-02-04 | 1981-08-07 | Testut Aequitas | CAPACITY MEASURING DEVICE, IN PARTICULAR FOR A WEIGHTING INSTRUMENT |
| JPS56166411A (en) * | 1980-05-27 | 1981-12-21 | Yokogawa Hokushin Electric Corp | Capacity type displacement transducer |
| DE3117808A1 (en) * | 1981-05-06 | 1982-11-25 | Robert Bosch Gmbh, 7000 Stuttgart | CIRCUIT ARRANGEMENT FOR MEASURING INDUCTIVE CHANGES |
| DK4383A (en) * | 1983-01-07 | 1984-07-08 | Nils Aage Juul Eilersen | oscillator circuit |
| FI69932C (en) * | 1984-05-31 | 1986-05-26 | Vaisala Oy | MAINTENANCE FOUNDATION CAPACITORS SPECIFIC FOR SMAR CAPACITORS VID VILKER MAN ANVAENDER TVAO REFERENSER |
| JPS6114578A (en) * | 1984-06-30 | 1986-01-22 | Suzuki Shigeo | Capacity meter |
| FI74549C (en) * | 1986-02-13 | 1988-02-08 | Vaisala Oy | MAETNINGSFOERFARANDE FOER IMPEDANSER, SAERSKILT SMAO KAPACITANSER. |
| DE4039006C1 (en) * | 1990-12-06 | 1992-03-12 | Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung Ev, 8000 Muenchen, De | |
| JP2007187509A (en) | 2006-01-12 | 2007-07-26 | Denso Corp | Physical quantity sensor of capacitance type |
| US8604809B2 (en) | 2008-11-02 | 2013-12-10 | Siemens Aktiengesellschaft | Current sensor capacity measuring system |
| FR2977950B1 (en) * | 2011-07-13 | 2014-11-07 | Jean Noel Lefebvre | CAPACITIVE DETECTION DEVICE |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3518537A (en) * | 1967-11-28 | 1970-06-30 | Richard Mcfee | Apparatus and method for determining the capacitance and conductance of capacitors |
| US3626287A (en) * | 1969-02-10 | 1971-12-07 | C G I Corp | System for responding to changes in capacitance of a sensing capacitor |
| FR2142732B1 (en) * | 1971-06-24 | 1975-02-07 | Commissariat Energie Atomique | |
| FR2208121B1 (en) * | 1972-11-29 | 1978-12-29 | Commissariat Energie Atomique | |
| US4083248A (en) * | 1975-09-04 | 1978-04-11 | Simmonds Precision Products, Inc. | Digital liquid-level gauging systems |
-
1977
- 1977-10-14 FI FI773063A patent/FI57319C/en not_active IP Right Cessation
-
1978
- 1978-10-09 ZA ZA00785694A patent/ZA785694B/en unknown
- 1978-10-10 DE DE2844121A patent/DE2844121C2/en not_active Expired
- 1978-10-11 CA CA313,113A patent/CA1128129A/en not_active Expired
- 1978-10-12 AU AU40675/78A patent/AU523345B2/en not_active Expired
- 1978-10-12 IT IT28692/78A patent/IT1100121B/en active
- 1978-10-13 FR FR7829343A patent/FR2410280A1/en active Granted
- 1978-10-13 BR BR7806786A patent/BR7806786A/en unknown
- 1978-10-13 JP JP12521278A patent/JPS5498696A/en active Pending
- 1978-10-16 GB GB7840632A patent/GB2006442B/en not_active Expired
-
1987
- 1987-06-08 JP JP1987087613U patent/JPH056544Y2/ja not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| FI773063A (en) | 1979-04-15 |
| JPS5498696A (en) | 1979-08-03 |
| JPH056544Y2 (en) | 1993-02-19 |
| FI57319C (en) | 1980-07-10 |
| ZA785694B (en) | 1979-09-26 |
| FR2410280A1 (en) | 1979-06-22 |
| DE2844121A1 (en) | 1979-04-19 |
| IT7828692A0 (en) | 1978-10-12 |
| FR2410280B1 (en) | 1984-01-06 |
| GB2006442A (en) | 1979-05-02 |
| DE2844121C2 (en) | 1981-09-24 |
| BR7806786A (en) | 1979-05-15 |
| GB2006442B (en) | 1982-04-28 |
| FI57319B (en) | 1980-03-31 |
| IT1100121B (en) | 1985-09-28 |
| JPS62201074U (en) | 1987-12-22 |
| AU523345B2 (en) | 1982-07-22 |
| AU4067578A (en) | 1980-04-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |