CA1237807A - Seismic detection method and apparatus - Google Patents
Seismic detection method and apparatusInfo
- Publication number
- CA1237807A CA1237807A CA000471139A CA471139A CA1237807A CA 1237807 A CA1237807 A CA 1237807A CA 000471139 A CA000471139 A CA 000471139A CA 471139 A CA471139 A CA 471139A CA 1237807 A CA1237807 A CA 1237807A
- Authority
- CA
- Canada
- Prior art keywords
- amplifier
- pick
- series
- resistance
- damping resistance
- 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
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Acoustics & Sound (AREA)
- Environmental & Geological Engineering (AREA)
- Geology (AREA)
- Remote Sensing (AREA)
- General Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Geophysics (AREA)
- Geophysics And Detection Of Objects (AREA)
Abstract
A B S T R A C T
SEISMIC DETECTION METHOD AND APPARATUS
Seismic detection apparatus in accordance with the invention comprises a seismic pick-up made of one or more geophones, a damping resistance, and an amplifier, wherein said damping resistance is essentially constituted by a resistance connected in series between the said pick-up and said amplifier.
In a preferred embodiment, the damping resistance is made of two equal resistances, one of which is connected in series with the positive input of the amplifier while the other one is connected in series with the negative input of the amplifier.
A seismic detection method in accordance with the invention in which the electrical signals generated by a pick-up made of one or more geophones connected in series are damped and the damped electrical signals are amplified, consists in making all of the current delivered by the pick-up participate in the amplification.
(Figure 2).
SEISMIC DETECTION METHOD AND APPARATUS
Seismic detection apparatus in accordance with the invention comprises a seismic pick-up made of one or more geophones, a damping resistance, and an amplifier, wherein said damping resistance is essentially constituted by a resistance connected in series between the said pick-up and said amplifier.
In a preferred embodiment, the damping resistance is made of two equal resistances, one of which is connected in series with the positive input of the amplifier while the other one is connected in series with the negative input of the amplifier.
A seismic detection method in accordance with the invention in which the electrical signals generated by a pick-up made of one or more geophones connected in series are damped and the damped electrical signals are amplified, consists in making all of the current delivered by the pick-up participate in the amplification.
(Figure 2).
Description
~ 7~ 7 SEISMIC DE~ECTION ME~HOD AND APPARA~US
- The present invention relates to the acquisition of seismic signals, and more particularly to a seismic detection method and apparatus using a seismic pick-up composed of one or more geophones.
Seismic interpretation, whether of surface data or of deep data, is of capital importance in oil prospecting, and the quality of the result depends ~or the most part on the quality of the seismic signal as picked up together with its initial processing.
Seiæmic waves are very often picked up using pick-ups made of one or more electromagnetic type geophones. These geophones essentially comprise a coil and a magnet, one of which i8 fixed relative to the Earth, while the other is suspended by a spring from a fixed support. Any relative displacement between the coil and the magnet generates an electromotive force (e.m.f.) across the terminals of the coil proportional to the speed of the movement.
In conventional manner, the e.m.f. is fed through a damping resistance connected directly in parallel with the geophone so as to produce damping which is typically between 60% and 70%. Seen from the geophone, the damping resistance is in series with the internal resistance of the geophone, and consequently acts as a voltage divider, thus reducing the signal presented to the voltage preamplifier. The input impedance of the preamplifier iB high enough not to modify the damping.
The voltage divider circuit has the drawback of reducing the geophone's sensitivity. This first drawback can be 3 remedied either by connecting a plurality of geophone~ in series, or by increasing the number of turns in the coil.
Each o~ these solutions has its own drawback: namely increasing the volume of the pick-up per se and/or increasing its internal resistance.
When seismic signals are being picked up at depth, the pick-ups are situated inside an elongate sonde of outside diameter which is less than 100 mm, and which is suitable for ~;~3'~ 7 being suspended at the end of an electric cable inside a _ borehole. Until very recently, single axis pick-ups comprising four geophones in series have been used. However, progress in seismic interpretation has lead very rapidly to consideration of acquiring seismic signals along three orthogonal axes.
~urther, in deviation boreholes it is desirable for one of the three axes to be vertical, which naturally leads to the use of suspended pick-ups being considered. The use of three orthogonal suspended pick-ups, with each pick-up being made up of four geophones in series, requires a complex and voluminous mechanical structure.
Recent studies have shown that the weight of a seismic sonde should be as light as possible so as to obtain better acoustic coupling between the pick-up and the wall of the borehole. This weight condition is in direct opposition to the above-mentioned line of development.
~ urther, increasing the number of turns in the coil, and hence the internal resistance of the pick-up leads to increasing input impedance for the amplifier and hence of its negative feedback resistance, thus very rapidly reaching values that are high and not recommended for connection to an amplifier. ~he constraints of this upper limit are made even more onerous by the fact that the amplifier circuit is subjected to temperatures as high as 200C.
One aim of the invention is thus to guarantee optimal transfer of the energy generated by a geophone to the input of a preamplifier.
Another aim of the invention is to minimize the effect of noise at the input to the preamplifier.
Seismic deteotion apparatus in accordance with the invention comprises a seismic pick-up made of one or more geophones, a damping resistance, and an amplifier, wherein said damping resistance is essentially constituted by a resistance connected in series between the said pick-up and said amplifier.
In a preferred embodimentl the damping resistance is made of two equal resistances, one of which is connected in series 0~
with the positive input of the amplifier while the other one is ~ connected in series with the negative input o~ the amplifier.
A seismic detection method in accordanee with the invention in which the electrical signals generated by a pick-up made of one or more geophones connected in series are dampedand the damped electrical signals are amplified, consists in making all of the current delivered by the pick-up participate in the amplification.
The following description will facilitate understanding 0 the invention.
Figure 1 is a circuit diagram of a prior art preamplifier circuit;
Figure 2 is a circuit diagram of a preamplifier circuit in which the dampïng resistance is connected in series between the pick-up and the amplifier; and ~ igure 3 is a circuit diagram of a preferred embodiment of a preamplifier circuit.
A conventional preamplifier circuit is briefly de~cribed to begin with. The electromagnetic or speed-sensitive seismic pick-up is symbolized in ~igure 1 by a voltage source 1 delivering an electromotive force (e.m.f.) el and having a corresponding internal resistance 2 of value R2. A damping resistance 3 of value R3 is connected in parallel with the pick-up, and one of its terminals is grounded.
~his conventional circuit constitutes a voltage divider, with the voltage across the terminals of the damping resistance being equal to:
V(R3) _ el.R3/(R2 ~ R~) 3~
~he volt~ge V(R3) is applied via an input resi~tance 4 of value R4 to the negative input of an amplifier 9. ~he amplifier is provided with a negative feedback loop constituted by a resi~tance 5 of value Rs which is much greater than R3, such that the gain g1 Of the amplifier 9 is equal to:
gl = - R5/R4 1~3t7~0~
A voltage source 6 placed at the negative input to the _ amplifier 9 symbolizes a voltage Vn1 equivalent to the the electrical noise of the circuit preceding the amplifier 9.
The output volta~e sl from the amplifier can thus be expressed as a function o~ e1 and Vn1:
s1 = g1~e1-R3/(R2 + R3) + g1.Vn1 The ratio R3/(R2 + R3) i8 obviously less than 1, and is typically about 60~, such that the contribution of the e.m.f. e1 to the signal s1 is considerably reduced to the detriment of the electrical noise Vn1. In other words the following expression may be written:
The Gain of e1 R~
_______________ _ <
The Gain of Vn1 R2 + R3 It is thus essential, in the above-described arrangement, to keep the electrical noise as low as possible, ie. to use relatively low values of resistance R2 and R3 in the range of about 300 ohms to 1000 ohms.
lhis condition obviously limit~ the sensitivity of the pick-up, since it determines the maximum number turns in the coil.
With reference to Figure 2, the damping resistance 13 of value R13 is connected in series with the pick-up which is represented by a voltage source 11 delivering a voltage e2 and having an internal resi~tanoe 12 of value R12. ~he re~iatances R12 and R13 thus con~titute the input resi~tance to the amplifier 19 whose gain is marked g2.
The voltage amplifier 19 may, for example, be an HA-5130 type low-noise operational amplifier manufactured by Harris Co.
The pick-up thus delivers current into a damping re~istance R13, to obtain damping of 60% to 70%, but the same current participates in the amplification.
~3 -~30~
As in the preceding circuit, the electrical noise i~
represented by a voltage source 16 delivering a voltage Vn2 which is added to the negative input of the amplifier 19. A
resistance 15 of value R15 provides the amplifier 19 with 5 negative ~eedbac~.
The gain g2 f the amplifier is given, in practice, by the ratio of the feedback resistance 15 divided by the sum of the internal resistance 12 of the pick-up plus the damping resistance 13. ~he output voltage s2 can thus be expressed as follows:
S2 = - (e2 ~ Vn2).Rls/(R12 + R13) ~he output voltage s2 is thus not degraded by the electrical noise to the same extent as in the conventional circuit, which may be expressed as follows:
~he Gain of e2 ____________ = 1 .
~he Gain of Vn2 It is thus quite possible, by means of such a circuit, to increase the sensitivity of the pick-up, by adding turns to the coil, for example, without thereby increasing the contribution o~ the electrical noise to the signal s2-~igure 3 shows a more elaborate embodiment. As befere, the pick-up is represented by voltage source 21 delivering a voltage e3 and having an internal resietance 22 of value R22. In thi~ cirouitl the damplng re~i~tance i~ co~po~ed of two reeistance~ 231 and 232 equal to half the value o~ the damping resistance R13, with each o~ them being connected in series with a respective one of the output~ ~rom the pick-up.
~he output~ from the two resistances 231 and 232 are connected to respective input~ of the amplifier 29.
~urther, the connection between the pick-up and the amplifier is fitted uith a guard ring 30 to improve electrical noise immunity with temperature. ~he voltage applied to the __ _.. _.. ~ . , . ,__, __ .___ __ __,_ . .~, .. .. . ., ,.. , .. _ .. . _ __ .
guard ring is equal to s3/2 and is taken from a voltage divider formed by two equ~l resistances 27 and 28.
Negative feedback for the amplifier 29 is provided at its negative input by a resistance 251 connected in parPllel with a capacitance 261. Common mode rejection is assured by a differential circuit comprising a resistance 252 connected in parallel with a capacitance 262 and connected to the positive input. ~he resistances 251 and 252 are equal and determine the gain of the amplifier 29. The capacitances 261 and 262 are equal and determine its upper cut-off frequency.
~ his differential circuit provides improved immunity to common modes.
~ he gain g3 of such a circuit may be expressed as follows:
e3 . R251 3 --____ R231 + R22/2 The gain g3 is chosen in such a manner as to ensure that the signal S3 has a sensitivity of 2500 V/m/s. Such a circuit makes it possible to use an electromagnetic pick-up having an internal impedance of about 3.5 Kohms ar.d whose sensitivity is about 80 V/m/s. A damping resistance of 12 Kohms, ie. 6 Kohms for each of the resistances 231 and 232, combined with a feedback resistance of 220 Kohms provides a gain of about 30.
~he use o~ such a det0ction device m~kes it po~ible to reduce appreciably the number of geophones that need to be connected in series; it providee an eleeant solution to the problems of bulk and electrical noise de~cribed above.
- The present invention relates to the acquisition of seismic signals, and more particularly to a seismic detection method and apparatus using a seismic pick-up composed of one or more geophones.
Seismic interpretation, whether of surface data or of deep data, is of capital importance in oil prospecting, and the quality of the result depends ~or the most part on the quality of the seismic signal as picked up together with its initial processing.
Seiæmic waves are very often picked up using pick-ups made of one or more electromagnetic type geophones. These geophones essentially comprise a coil and a magnet, one of which i8 fixed relative to the Earth, while the other is suspended by a spring from a fixed support. Any relative displacement between the coil and the magnet generates an electromotive force (e.m.f.) across the terminals of the coil proportional to the speed of the movement.
In conventional manner, the e.m.f. is fed through a damping resistance connected directly in parallel with the geophone so as to produce damping which is typically between 60% and 70%. Seen from the geophone, the damping resistance is in series with the internal resistance of the geophone, and consequently acts as a voltage divider, thus reducing the signal presented to the voltage preamplifier. The input impedance of the preamplifier iB high enough not to modify the damping.
The voltage divider circuit has the drawback of reducing the geophone's sensitivity. This first drawback can be 3 remedied either by connecting a plurality of geophone~ in series, or by increasing the number of turns in the coil.
Each o~ these solutions has its own drawback: namely increasing the volume of the pick-up per se and/or increasing its internal resistance.
When seismic signals are being picked up at depth, the pick-ups are situated inside an elongate sonde of outside diameter which is less than 100 mm, and which is suitable for ~;~3'~ 7 being suspended at the end of an electric cable inside a _ borehole. Until very recently, single axis pick-ups comprising four geophones in series have been used. However, progress in seismic interpretation has lead very rapidly to consideration of acquiring seismic signals along three orthogonal axes.
~urther, in deviation boreholes it is desirable for one of the three axes to be vertical, which naturally leads to the use of suspended pick-ups being considered. The use of three orthogonal suspended pick-ups, with each pick-up being made up of four geophones in series, requires a complex and voluminous mechanical structure.
Recent studies have shown that the weight of a seismic sonde should be as light as possible so as to obtain better acoustic coupling between the pick-up and the wall of the borehole. This weight condition is in direct opposition to the above-mentioned line of development.
~ urther, increasing the number of turns in the coil, and hence the internal resistance of the pick-up leads to increasing input impedance for the amplifier and hence of its negative feedback resistance, thus very rapidly reaching values that are high and not recommended for connection to an amplifier. ~he constraints of this upper limit are made even more onerous by the fact that the amplifier circuit is subjected to temperatures as high as 200C.
One aim of the invention is thus to guarantee optimal transfer of the energy generated by a geophone to the input of a preamplifier.
Another aim of the invention is to minimize the effect of noise at the input to the preamplifier.
Seismic deteotion apparatus in accordance with the invention comprises a seismic pick-up made of one or more geophones, a damping resistance, and an amplifier, wherein said damping resistance is essentially constituted by a resistance connected in series between the said pick-up and said amplifier.
In a preferred embodimentl the damping resistance is made of two equal resistances, one of which is connected in series 0~
with the positive input of the amplifier while the other one is ~ connected in series with the negative input o~ the amplifier.
A seismic detection method in accordanee with the invention in which the electrical signals generated by a pick-up made of one or more geophones connected in series are dampedand the damped electrical signals are amplified, consists in making all of the current delivered by the pick-up participate in the amplification.
The following description will facilitate understanding 0 the invention.
Figure 1 is a circuit diagram of a prior art preamplifier circuit;
Figure 2 is a circuit diagram of a preamplifier circuit in which the dampïng resistance is connected in series between the pick-up and the amplifier; and ~ igure 3 is a circuit diagram of a preferred embodiment of a preamplifier circuit.
A conventional preamplifier circuit is briefly de~cribed to begin with. The electromagnetic or speed-sensitive seismic pick-up is symbolized in ~igure 1 by a voltage source 1 delivering an electromotive force (e.m.f.) el and having a corresponding internal resistance 2 of value R2. A damping resistance 3 of value R3 is connected in parallel with the pick-up, and one of its terminals is grounded.
~his conventional circuit constitutes a voltage divider, with the voltage across the terminals of the damping resistance being equal to:
V(R3) _ el.R3/(R2 ~ R~) 3~
~he volt~ge V(R3) is applied via an input resi~tance 4 of value R4 to the negative input of an amplifier 9. ~he amplifier is provided with a negative feedback loop constituted by a resi~tance 5 of value Rs which is much greater than R3, such that the gain g1 Of the amplifier 9 is equal to:
gl = - R5/R4 1~3t7~0~
A voltage source 6 placed at the negative input to the _ amplifier 9 symbolizes a voltage Vn1 equivalent to the the electrical noise of the circuit preceding the amplifier 9.
The output volta~e sl from the amplifier can thus be expressed as a function o~ e1 and Vn1:
s1 = g1~e1-R3/(R2 + R3) + g1.Vn1 The ratio R3/(R2 + R3) i8 obviously less than 1, and is typically about 60~, such that the contribution of the e.m.f. e1 to the signal s1 is considerably reduced to the detriment of the electrical noise Vn1. In other words the following expression may be written:
The Gain of e1 R~
_______________ _ <
The Gain of Vn1 R2 + R3 It is thus essential, in the above-described arrangement, to keep the electrical noise as low as possible, ie. to use relatively low values of resistance R2 and R3 in the range of about 300 ohms to 1000 ohms.
lhis condition obviously limit~ the sensitivity of the pick-up, since it determines the maximum number turns in the coil.
With reference to Figure 2, the damping resistance 13 of value R13 is connected in series with the pick-up which is represented by a voltage source 11 delivering a voltage e2 and having an internal resi~tanoe 12 of value R12. ~he re~iatances R12 and R13 thus con~titute the input resi~tance to the amplifier 19 whose gain is marked g2.
The voltage amplifier 19 may, for example, be an HA-5130 type low-noise operational amplifier manufactured by Harris Co.
The pick-up thus delivers current into a damping re~istance R13, to obtain damping of 60% to 70%, but the same current participates in the amplification.
~3 -~30~
As in the preceding circuit, the electrical noise i~
represented by a voltage source 16 delivering a voltage Vn2 which is added to the negative input of the amplifier 19. A
resistance 15 of value R15 provides the amplifier 19 with 5 negative ~eedbac~.
The gain g2 f the amplifier is given, in practice, by the ratio of the feedback resistance 15 divided by the sum of the internal resistance 12 of the pick-up plus the damping resistance 13. ~he output voltage s2 can thus be expressed as follows:
S2 = - (e2 ~ Vn2).Rls/(R12 + R13) ~he output voltage s2 is thus not degraded by the electrical noise to the same extent as in the conventional circuit, which may be expressed as follows:
~he Gain of e2 ____________ = 1 .
~he Gain of Vn2 It is thus quite possible, by means of such a circuit, to increase the sensitivity of the pick-up, by adding turns to the coil, for example, without thereby increasing the contribution o~ the electrical noise to the signal s2-~igure 3 shows a more elaborate embodiment. As befere, the pick-up is represented by voltage source 21 delivering a voltage e3 and having an internal resietance 22 of value R22. In thi~ cirouitl the damplng re~i~tance i~ co~po~ed of two reeistance~ 231 and 232 equal to half the value o~ the damping resistance R13, with each o~ them being connected in series with a respective one of the output~ ~rom the pick-up.
~he output~ from the two resistances 231 and 232 are connected to respective input~ of the amplifier 29.
~urther, the connection between the pick-up and the amplifier is fitted uith a guard ring 30 to improve electrical noise immunity with temperature. ~he voltage applied to the __ _.. _.. ~ . , . ,__, __ .___ __ __,_ . .~, .. .. . ., ,.. , .. _ .. . _ __ .
guard ring is equal to s3/2 and is taken from a voltage divider formed by two equ~l resistances 27 and 28.
Negative feedback for the amplifier 29 is provided at its negative input by a resistance 251 connected in parPllel with a capacitance 261. Common mode rejection is assured by a differential circuit comprising a resistance 252 connected in parallel with a capacitance 262 and connected to the positive input. ~he resistances 251 and 252 are equal and determine the gain of the amplifier 29. The capacitances 261 and 262 are equal and determine its upper cut-off frequency.
~ his differential circuit provides improved immunity to common modes.
~ he gain g3 of such a circuit may be expressed as follows:
e3 . R251 3 --____ R231 + R22/2 The gain g3 is chosen in such a manner as to ensure that the signal S3 has a sensitivity of 2500 V/m/s. Such a circuit makes it possible to use an electromagnetic pick-up having an internal impedance of about 3.5 Kohms ar.d whose sensitivity is about 80 V/m/s. A damping resistance of 12 Kohms, ie. 6 Kohms for each of the resistances 231 and 232, combined with a feedback resistance of 220 Kohms provides a gain of about 30.
~he use o~ such a det0ction device m~kes it po~ible to reduce appreciably the number of geophones that need to be connected in series; it providee an eleeant solution to the problems of bulk and electrical noise de~cribed above.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Seismic detection apparatus comprising a seismic pick-up made of one or more geophones, a damping resistance, and an amplifier, characterized in that said damping resistance is essen-tially constituted by a resistance connected in series between the said pick-up and said amplifier.
2. Apparatus according to claim 1 characterized in that the value of said damping resistance lies in the range 10 Kohms to 15 Kohms.
3. Apparatus according to claim 1 or 2, characterized in that the value of said damping resistance is three to four times the value of the internal resistance of the pick-up.
4. Apparatus according to claim 1, characterized in that the damping resistance is made of two equal value resistances, one of which is connected in series with the positive input of the amplifier while the other one is connected in series with the negative input of the amplifier.
5. Apparatus according to claim 4, characterized in that the electrical connections between the outputs of the pick-up and the inputs of the amplifier are fitted with a guard ring.
6. Apparatus according to claim 5, characterized in that the potential of the guard ring is equal to half the output potential of the amplifier.
7. Apparatus according to claim 1,2,or 6, characterized in that amplifier negative feedback is provided by two identical networks.
8. Apparatus according to claim 1, 2 or 6, characterized in that it is contained in a logging sonde.
9. A seismic detection method in which the electrical sig-anls generated by a pick-up made of one or more geophones con-nected in series are damped and the damped electrical signals are amplified, characterized in that practically all of the current delivered by said pick-up is made to participate in the amplification.
10. A method according to claim 9, characterized by the fact that said electrical signals are differentially amplified.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8320989A FR2557705B1 (en) | 1983-12-29 | 1983-12-29 | SEISMIC DETECTION METHOD AND DEVICE |
| FR8320989 | 1983-12-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1237807A true CA1237807A (en) | 1988-06-07 |
Family
ID=9295686
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000471139A Expired CA1237807A (en) | 1983-12-29 | 1984-12-28 | Seismic detection method and apparatus |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0149951B1 (en) |
| AU (1) | AU578647B2 (en) |
| CA (1) | CA1237807A (en) |
| DE (1) | DE3470232D1 (en) |
| DK (1) | DK623484A (en) |
| FR (1) | FR2557705B1 (en) |
| OA (1) | OA07915A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19701997A1 (en) * | 1997-01-22 | 1998-02-05 | Erich Lippmann | Damped pre-amplifier for use with electrodynamic seismic transducer |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3412374A (en) * | 1967-06-26 | 1968-11-19 | Teledyne Exploration Co | Short period seismic system with long period response |
| US3863200A (en) * | 1973-01-15 | 1975-01-28 | Amoco Prod Co | Built-in seismometer amplifier |
| US3972001A (en) * | 1975-04-08 | 1976-07-27 | Motorola, Inc. | Common mode rejection dynamic filter circuit |
| DE3307575C2 (en) * | 1983-03-03 | 1984-12-20 | Erich Dipl.-Geophys. 8372 Lindberg Lippmann | Electrodynamic seismometer |
-
1983
- 1983-12-29 FR FR8320989A patent/FR2557705B1/en not_active Expired
-
1984
- 1984-12-21 DK DK623484A patent/DK623484A/en not_active Application Discontinuation
- 1984-12-28 OA OA58494A patent/OA07915A/en unknown
- 1984-12-28 DE DE8484402767T patent/DE3470232D1/en not_active Expired
- 1984-12-28 CA CA000471139A patent/CA1237807A/en not_active Expired
- 1984-12-28 AU AU37215/84A patent/AU578647B2/en not_active Ceased
- 1984-12-28 EP EP84402767A patent/EP0149951B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| OA07915A (en) | 1986-11-20 |
| DK623484A (en) | 1985-06-30 |
| EP0149951A3 (en) | 1985-08-14 |
| EP0149951A2 (en) | 1985-07-31 |
| EP0149951B1 (en) | 1988-03-30 |
| AU578647B2 (en) | 1988-11-03 |
| AU3721584A (en) | 1985-07-04 |
| FR2557705B1 (en) | 1986-07-25 |
| DK623484D0 (en) | 1984-12-21 |
| DE3470232D1 (en) | 1988-05-05 |
| FR2557705A1 (en) | 1985-07-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |