CA1222046A - Automatic control system for acoustic logging - Google Patents
Automatic control system for acoustic loggingInfo
- Publication number
- CA1222046A CA1222046A CA000468936A CA468936A CA1222046A CA 1222046 A CA1222046 A CA 1222046A CA 000468936 A CA000468936 A CA 000468936A CA 468936 A CA468936 A CA 468936A CA 1222046 A CA1222046 A CA 1222046A
- Authority
- CA
- Canada
- Prior art keywords
- acoustic
- signal
- output
- operational amplifier
- input
- 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
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers without distortion of the input signal
- H03G3/20—Automatic control
- H03G3/30—Automatic control in amplifiers having semiconductor devices
- H03G3/3052—Automatic control in amplifiers having semiconductor devices in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver
- H03G3/3073—Circuits generating control signals when no carrier is present, or in SSB, CW or pulse receivers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/24—Recording seismic data
- G01V1/245—Amplitude control for seismic recording
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers without distortion of the input signal
- H03G3/20—Automatic control
Abstract
AUTOMATIC CONTROL SYSTEM FOR ACOUSTIC LOGGING
Abstract of the Disclosure A circuit is disclosed for use in an acoustic logging tool incorporating a transmitter sending an acoustic pulse which is received by acoustic receivers.
In the preferred and illustrated embodiment hereof, an automatic gain control (AGC) circuit controls the receiver amplification to enable the output range to be limited for input to a digital graphic recorder, typically having a limited number of output signal levels, coordinating with data processing equipment.
The AGC times the peak operation to thereby limit the dynamic range.
Abstract of the Disclosure A circuit is disclosed for use in an acoustic logging tool incorporating a transmitter sending an acoustic pulse which is received by acoustic receivers.
In the preferred and illustrated embodiment hereof, an automatic gain control (AGC) circuit controls the receiver amplification to enable the output range to be limited for input to a digital graphic recorder, typically having a limited number of output signal levels, coordinating with data processing equipment.
The AGC times the peak operation to thereby limit the dynamic range.
Description
~22a~46 18C/722~PA/DR4/~40913 ATTORNEY DOCKET NO. WPC-77 AUTOMATIC ~ONTROL SYSTEM FO~ ACOUSTIC L~GGING
Background of the Disclosure This apparatus is directed to an AGC for use in an acoustic logging tool. This type of tool features an acoustic pulse transmitter. Acoustic pulses are transmitted into the well fluid and pass into the adjacent formations. Acoustic signals are observed at receivers mounted on the logging tool.
Typically, more than one acoustic receiver is used.
One arrangement features a first spaced receiver and an identical receiver which is spaced even further away from the acoustic transmitter. This receiver system enables a comparison to be made between the received signals at the two receivers. Data reduction is simplified by procedure which is known as acoustic amplitude ratio logging. This involves the use of signals from two acoustic receivers. The ratio of the signals is more important than the absolute valves in this two receiver system. Other data processing procedures involving the signal from a single receiver are enhanced by the ~GC of the present disclosure.
The method of operation of an acoustic logging tool normally involves the propagation of an acoustic burst transmitted from a piezoelectric or magnetostrictive transducer. The transmitted pulse is typically very short. The signal at receivers in the acoustic logging tool has a wide dynamic range. The pulse return to the receiver is relatively dynamic in light of this fact. Typically, the dynamic range of the received signal is quite wide, easily having a range of 1,000 fold or greater.
9~Z2204~
While it is possible to utilize A5C circuits with dynamic ranges up to one million to one, it is equally difficult to have only a limited AGC gain range to accommodate a wide dynamic range. Such a limit is 5 in part imposed by data processing apparatus. One such requirement arises in the display of the received data in a display form utilizing the system known as Micro-Seismogram, a service mark identifying such a display system. A typical range of data presentation is about 16 gray levels. This data handling format has achieved a high degree of popularity.
To accommodate the more limited dynamic range exemplified by 16 levels, or any other limited dynamic range, the AGC system must provide a relatively limited response. It is desirable that the AGC have a limited dynamic range. In addition to that, this apparatus limits the dynamic range only for a specified interval or window of time. The window is tied to the event being observed. In this instance, it is preferably to determine the window based on the incoming signal at the receiver. With this in mind, a window is thus defined based on increase in the signal at the receiver, thereby outputting data in a compressed data range where the time window limits the operation of the circuit to a time when data is more relevant.
Extraneous or system noise occurs between signals and is blanked off by the time window determined by the circuit, thereby limiting operation of the equipment only to those intervals at which time signal data will be processed.
The present apparatus is summarized as an AGC
control circuit including an input operational amplifier with a suitable full wave rectifier. The rectified positive and negative peaks are amplified and applied to the output of the circuit. PeaXs are then ~ILZ22~
detected by a peak detector, including both positive and negative peaks. This output is supplied through an amplifier-then to a sample and hold amplifier. The sample and hold ampli-fier forms a feedback control signal applied to the input ampli-fier, altering its gain and hence the gain of the closed feed-back loop.
More specifically, the invention relates to an automaicgain control system for use in an acoustic well logging system having an acoustic transmitter for transmitting acoustic pulses in a well borehole and a plurality of longitudinally spaced apart acoustic receivers for receiving acoustic pulses travers-ing the well borehole and the earth formations between the trans-mitter and each of the receivers. The automatic gain control system comprises means for inputting signals from at least one of the acoustic receivers to a gain controlled operational amplifier, the operational amplifier having at least one input acoustic signal terminal and a feedback control signal input terminal. The system also includes differential amplifier means connected to the output of the gain controlled operational amplifier for amplifying the output of the operational amplifier and providing a system output acoustic signal and for providing a sample output signal to a feedback control signal generating loop circuit. There is a timing circuit for providing reset signals a predetermined length of time following each successive acoustic pulse from the acoustic transmitter, the time interval between the acoustic pulses and the reset signals defining an operating cycle of the automatic gain control system. The system also includes full wave rectifying means responsive to the output of the differen-tial amplifying means for generating a pulsating D.C. signal representative of the differential amplifier sample output signal; peak detector means responsive to the pulsating D~C. signal and to the reset signal from the timing circuit for -3a-generating a peak output signal representative of the peak value of the pulsating D.C. signal in the operating cycle of the automatic gaill con-trol system; sample and hold amplifier means having an input connected to the output of the peak detector means for holding and providing an output representa-tive of the peak signal representative of the peak value of the pulsating D.C. signal; and filter means having an input terminal connected to the ou-tput of the sample and hold amplifier to limit the high frequency content of the output signal, the filter having an output connected to the feedback control terminal of the gain controlled operational amplifier to thereby provide a galn control signal tl~reto.
Brief Description of the Drawings So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention rnay admit to other equally effective embodiments.
Fig. 1 is a view of an acoustic well logging tool in a well bore including an acoustic transmitter and several acoustic receivers;
Fig. 2 is a schematic block diagram of an automatic gain control circuit for use with an acoustic receiver in the logging tool shown in Fig. 1: and Fig. 3 discloses an alternate block diagrarn schematic of an AGC circuit modified for cooperation with ~wo receivers to provide a ratio of the signals.
jl ~2~2~46 ~ -3b-Detailed Description of the Preferred ~mbodiments Attention is directed to Fig. 1 of the drawings. In Fig. 1, an acoustic well logging tool 10 is suspended in a well bore 12.. I~ is supported on a logging cable 14 which incorporates suitable electrical ~ZZZ(~ 6 conductors extending to the surface to operate the acoustic logging tool 10. The tool 10 is lowered to the bottom of the well to enable data to be gathered through the use and operation of the tool. Briefly, the tool is operated as it is raised along the well borehole 12 to obtain acoustic data. The acoustic logging tool is constructed with a transmitter 16 which transmits acoustic pulses into the adjacent formation.
There are several receivers on the acoustic logging tool 10. One is receiver 18 at the upper end. In addition, there is a lower receiver 20 and a receiver - 22 which is located even further along the tool. The receivers are generally similar in construction and operate in substantially the same fashion. That is, an lS acoustic pulse of a few milliseconds duration is transmitted into the formation adjacent to the transmitter 16 and a received signal is observed at the various receivers. The signals that are observed indicate the nature of the formations along the signal propagation path.
A sheave 24 supports the logging cable 14.
The cable is stored on a supply drum or reel 26. A
logging cable is typically longer then the well and are commonly as long as Z5,000 feetO The logging cable is connected by means of suitable conductors with a data processing apparatus 28. The data is processed and provided to a data recorder 30. A mechanical or electronic depth measuring system connected to the sheave 24 is identified at 32 and it provides the depth of the logging tool 10 in the well to the recorder 30.
This enables the data to be recorded as a function of depth.
Going now to Fig. 2, it should be recalled that the output of each receiver is a pulse occurring after the transmitted pulse. The pulse has a duration ~z~zo~
and shape determined by the formations along the path of propagation from transmitter to receiver. In Fig.
Background of the Disclosure This apparatus is directed to an AGC for use in an acoustic logging tool. This type of tool features an acoustic pulse transmitter. Acoustic pulses are transmitted into the well fluid and pass into the adjacent formations. Acoustic signals are observed at receivers mounted on the logging tool.
Typically, more than one acoustic receiver is used.
One arrangement features a first spaced receiver and an identical receiver which is spaced even further away from the acoustic transmitter. This receiver system enables a comparison to be made between the received signals at the two receivers. Data reduction is simplified by procedure which is known as acoustic amplitude ratio logging. This involves the use of signals from two acoustic receivers. The ratio of the signals is more important than the absolute valves in this two receiver system. Other data processing procedures involving the signal from a single receiver are enhanced by the ~GC of the present disclosure.
The method of operation of an acoustic logging tool normally involves the propagation of an acoustic burst transmitted from a piezoelectric or magnetostrictive transducer. The transmitted pulse is typically very short. The signal at receivers in the acoustic logging tool has a wide dynamic range. The pulse return to the receiver is relatively dynamic in light of this fact. Typically, the dynamic range of the received signal is quite wide, easily having a range of 1,000 fold or greater.
9~Z2204~
While it is possible to utilize A5C circuits with dynamic ranges up to one million to one, it is equally difficult to have only a limited AGC gain range to accommodate a wide dynamic range. Such a limit is 5 in part imposed by data processing apparatus. One such requirement arises in the display of the received data in a display form utilizing the system known as Micro-Seismogram, a service mark identifying such a display system. A typical range of data presentation is about 16 gray levels. This data handling format has achieved a high degree of popularity.
To accommodate the more limited dynamic range exemplified by 16 levels, or any other limited dynamic range, the AGC system must provide a relatively limited response. It is desirable that the AGC have a limited dynamic range. In addition to that, this apparatus limits the dynamic range only for a specified interval or window of time. The window is tied to the event being observed. In this instance, it is preferably to determine the window based on the incoming signal at the receiver. With this in mind, a window is thus defined based on increase in the signal at the receiver, thereby outputting data in a compressed data range where the time window limits the operation of the circuit to a time when data is more relevant.
Extraneous or system noise occurs between signals and is blanked off by the time window determined by the circuit, thereby limiting operation of the equipment only to those intervals at which time signal data will be processed.
The present apparatus is summarized as an AGC
control circuit including an input operational amplifier with a suitable full wave rectifier. The rectified positive and negative peaks are amplified and applied to the output of the circuit. PeaXs are then ~ILZ22~
detected by a peak detector, including both positive and negative peaks. This output is supplied through an amplifier-then to a sample and hold amplifier. The sample and hold ampli-fier forms a feedback control signal applied to the input ampli-fier, altering its gain and hence the gain of the closed feed-back loop.
More specifically, the invention relates to an automaicgain control system for use in an acoustic well logging system having an acoustic transmitter for transmitting acoustic pulses in a well borehole and a plurality of longitudinally spaced apart acoustic receivers for receiving acoustic pulses travers-ing the well borehole and the earth formations between the trans-mitter and each of the receivers. The automatic gain control system comprises means for inputting signals from at least one of the acoustic receivers to a gain controlled operational amplifier, the operational amplifier having at least one input acoustic signal terminal and a feedback control signal input terminal. The system also includes differential amplifier means connected to the output of the gain controlled operational amplifier for amplifying the output of the operational amplifier and providing a system output acoustic signal and for providing a sample output signal to a feedback control signal generating loop circuit. There is a timing circuit for providing reset signals a predetermined length of time following each successive acoustic pulse from the acoustic transmitter, the time interval between the acoustic pulses and the reset signals defining an operating cycle of the automatic gain control system. The system also includes full wave rectifying means responsive to the output of the differen-tial amplifying means for generating a pulsating D.C. signal representative of the differential amplifier sample output signal; peak detector means responsive to the pulsating D~C. signal and to the reset signal from the timing circuit for -3a-generating a peak output signal representative of the peak value of the pulsating D.C. signal in the operating cycle of the automatic gaill con-trol system; sample and hold amplifier means having an input connected to the output of the peak detector means for holding and providing an output representa-tive of the peak signal representative of the peak value of the pulsating D.C. signal; and filter means having an input terminal connected to the ou-tput of the sample and hold amplifier to limit the high frequency content of the output signal, the filter having an output connected to the feedback control terminal of the gain controlled operational amplifier to thereby provide a galn control signal tl~reto.
Brief Description of the Drawings So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention rnay admit to other equally effective embodiments.
Fig. 1 is a view of an acoustic well logging tool in a well bore including an acoustic transmitter and several acoustic receivers;
Fig. 2 is a schematic block diagram of an automatic gain control circuit for use with an acoustic receiver in the logging tool shown in Fig. 1: and Fig. 3 discloses an alternate block diagrarn schematic of an AGC circuit modified for cooperation with ~wo receivers to provide a ratio of the signals.
jl ~2~2~46 ~ -3b-Detailed Description of the Preferred ~mbodiments Attention is directed to Fig. 1 of the drawings. In Fig. 1, an acoustic well logging tool 10 is suspended in a well bore 12.. I~ is supported on a logging cable 14 which incorporates suitable electrical ~ZZZ(~ 6 conductors extending to the surface to operate the acoustic logging tool 10. The tool 10 is lowered to the bottom of the well to enable data to be gathered through the use and operation of the tool. Briefly, the tool is operated as it is raised along the well borehole 12 to obtain acoustic data. The acoustic logging tool is constructed with a transmitter 16 which transmits acoustic pulses into the adjacent formation.
There are several receivers on the acoustic logging tool 10. One is receiver 18 at the upper end. In addition, there is a lower receiver 20 and a receiver - 22 which is located even further along the tool. The receivers are generally similar in construction and operate in substantially the same fashion. That is, an lS acoustic pulse of a few milliseconds duration is transmitted into the formation adjacent to the transmitter 16 and a received signal is observed at the various receivers. The signals that are observed indicate the nature of the formations along the signal propagation path.
A sheave 24 supports the logging cable 14.
The cable is stored on a supply drum or reel 26. A
logging cable is typically longer then the well and are commonly as long as Z5,000 feetO The logging cable is connected by means of suitable conductors with a data processing apparatus 28. The data is processed and provided to a data recorder 30. A mechanical or electronic depth measuring system connected to the sheave 24 is identified at 32 and it provides the depth of the logging tool 10 in the well to the recorder 30.
This enables the data to be recorded as a function of depth.
Going now to Fig. 2, it should be recalled that the output of each receiver is a pulse occurring after the transmitted pulse. The pulse has a duration ~z~zo~
and shape determined by the formations along the path of propagation from transmitter to receiver. In Fig.
2, the input 36 is from one of the receivers to the system 35. The pulse is supplied to an AGC operational amplifier 38. This amplifier has an input gain control signal which controls the gain of the amplifier 38.
The amplifier 38 forms an output which is proportional to the gain and input signal. The output has the form of a signal applied on two conductors to a differential amplifier 40. This amplifier forms an output on a conductor 42 which is the output of the system. The system however includes a feedback loop which is connected from the output to obtain the AGC function.
The feedback loop incorporates a full wave rectifier 44. The system is therefore able to handle both positive and negative signals. They are rectified, thereby forming a procession of pulses from the full wave rectifier and which pulses are input to the peak detector 46, The peak detector 46 detects a specified peak during its operation. If it operates for the entire cycle of the pulse train input to the detector 46, it will normally select the largest peak. The duration of operation of the peak detector is controlled by a timing circuit 48 to be described in detail hereinafter. The timing circuit forms a signal input to the peak detector 46 which gates the detector 46 off and on. The detector 46 is held on for a specified interval, thereby defining the portion of the received data to be evaluated for peak value. The peak signal is detected and supplied through an amplifier and input to a sample and hold amplifier 50. An amplifier 52 is at the input of the amplifier 50. The sample and hold amplifier 50 is operated at a timed moment. It is operated for a specified interval as determined by the timing circuit 48.
~L22:2~ 6 The timing circuit ~8 triggers the sample and hold amplifier 50 to operate to thereby fix a specified output signal. This output signal is supplied to a filter circuit 54. This circuit limits the harmonic content of the sample and hold signal passed through it; in fact, the filter provides a signal passband as a function of frequency, thereby enabling the Eilter circuit 54 to determine a feedback signal to be applied to the AGC operational amplifier 38. The operational amplifier 3~ is operated at gain level determined by the gain control signal input to it.
Consider some examples of operation. Assume that the transmitted pulses have a uniform length of N
time units. Assume that it is stretched to propagation to a length of 4~. Assume further that the information of interest is located after a time of 3N. In this event, the timing circuit 48 operates the peak detector for a specified time interval of sufficient length to observe the data of interest. The timing circuit 48 will operate the sample and hold amplifier 50 to evaluate only the portion of the received signal which has data of interest. The timing circuit 48 causes the sample and hold circuit 50 to form a feedbacX signal which is applied by the feedback loop to the AGC
operational amplifier 38, thereby regulating the timing of its operation to the specified interval. This timed operation then limits the dynamic range of the feedback loop. While the received signal may have a dynamic range frorn the smallest readible input to the largest peak of 1,00~ times larger or perhaps even greater, the range exceeds the dynamic range of some data reduction or data handling systems. Through the use of this apparatus, the specified interval of interest is located and the gain of the system is controlled in that interval so that the signal ~ynamic range is 41~
within specified limits. To cooperate with the equipment featuring the Micro-Seisogram, it is desirable that the output data have sixteen gray levels. This limited response range enables the sixteen levels to be obtained.
Attention is next directed to Fig. 3 of the drawings. There, two receivers are shown. They are conveniently the receivers 20 and 22 shown in Fig. 1.
They form input signals to the same AGC circuit shown in Fig. 2 and which is now found in Fig. 3. That circuit was previously identified as the AGC system 35.
Again, in Fig. 3 the system 35 is included. It is arranged somewhat differently. There are two input signals, one each from the receivers 20 and 22. That is, the output signals from the receivers 20 and 22 are input to the AGC operational amplifier 40. The filter 54 is also shown in Fig. 3. In ïike fashion, the timing circuit 48 is connected to a timed source. The timing or firing signal is timed by receiver operation.
In this instance, it is connected to the receiver 20 as a trigger source.
In Fig. 3, the switched signals for the AGC
are processed wherein the gain of the AGC circuit is set by the signal from the first receiver and the gain isheld at the same level for the signal for the second receiver. At each transmitter firing, the switch alternates, passing alternate signals from the two receivers.
The foregoing sets forth one embodiment of the AGC control systern and an alternate arrangement in which it is used with different inputs. Modifications can be accommodated without departing from the structure which is set forth. For instance, one modification is substitution of a halfway rectifier for the full rectifier. This can be done where the signal ~2~)46 of interest is substantially unidirectional. The peak detector 46 is typically gated by the timing circuit 48. The gating signal is variable in the system as shown. If circumstances permit, it can be fixed by the time of the transmitted pulse. That is, the timing circuit 48 might be simplified by simply tying the input of the timing circuit 48 to the acoustic pulse transmitter, thereby timing operation of the AGC
control system of this invention on occurrence of a transmitted pulse. Another important factor is to note the incorporation of the filter 54. This limits the frequency content input to the AGC operational amplifier. This limitation prevents destabilized operation of the feedback loop as a result of feeding excessive rate of change through the feedback loop, thereby altering the gain in an uncontrollable fashion.
While the foregoing sets forth the preferred embodiment, the scope is determined by the claims which follow.
The amplifier 38 forms an output which is proportional to the gain and input signal. The output has the form of a signal applied on two conductors to a differential amplifier 40. This amplifier forms an output on a conductor 42 which is the output of the system. The system however includes a feedback loop which is connected from the output to obtain the AGC function.
The feedback loop incorporates a full wave rectifier 44. The system is therefore able to handle both positive and negative signals. They are rectified, thereby forming a procession of pulses from the full wave rectifier and which pulses are input to the peak detector 46, The peak detector 46 detects a specified peak during its operation. If it operates for the entire cycle of the pulse train input to the detector 46, it will normally select the largest peak. The duration of operation of the peak detector is controlled by a timing circuit 48 to be described in detail hereinafter. The timing circuit forms a signal input to the peak detector 46 which gates the detector 46 off and on. The detector 46 is held on for a specified interval, thereby defining the portion of the received data to be evaluated for peak value. The peak signal is detected and supplied through an amplifier and input to a sample and hold amplifier 50. An amplifier 52 is at the input of the amplifier 50. The sample and hold amplifier 50 is operated at a timed moment. It is operated for a specified interval as determined by the timing circuit 48.
~L22:2~ 6 The timing circuit ~8 triggers the sample and hold amplifier 50 to operate to thereby fix a specified output signal. This output signal is supplied to a filter circuit 54. This circuit limits the harmonic content of the sample and hold signal passed through it; in fact, the filter provides a signal passband as a function of frequency, thereby enabling the Eilter circuit 54 to determine a feedback signal to be applied to the AGC operational amplifier 38. The operational amplifier 3~ is operated at gain level determined by the gain control signal input to it.
Consider some examples of operation. Assume that the transmitted pulses have a uniform length of N
time units. Assume that it is stretched to propagation to a length of 4~. Assume further that the information of interest is located after a time of 3N. In this event, the timing circuit 48 operates the peak detector for a specified time interval of sufficient length to observe the data of interest. The timing circuit 48 will operate the sample and hold amplifier 50 to evaluate only the portion of the received signal which has data of interest. The timing circuit 48 causes the sample and hold circuit 50 to form a feedbacX signal which is applied by the feedback loop to the AGC
operational amplifier 38, thereby regulating the timing of its operation to the specified interval. This timed operation then limits the dynamic range of the feedback loop. While the received signal may have a dynamic range frorn the smallest readible input to the largest peak of 1,00~ times larger or perhaps even greater, the range exceeds the dynamic range of some data reduction or data handling systems. Through the use of this apparatus, the specified interval of interest is located and the gain of the system is controlled in that interval so that the signal ~ynamic range is 41~
within specified limits. To cooperate with the equipment featuring the Micro-Seisogram, it is desirable that the output data have sixteen gray levels. This limited response range enables the sixteen levels to be obtained.
Attention is next directed to Fig. 3 of the drawings. There, two receivers are shown. They are conveniently the receivers 20 and 22 shown in Fig. 1.
They form input signals to the same AGC circuit shown in Fig. 2 and which is now found in Fig. 3. That circuit was previously identified as the AGC system 35.
Again, in Fig. 3 the system 35 is included. It is arranged somewhat differently. There are two input signals, one each from the receivers 20 and 22. That is, the output signals from the receivers 20 and 22 are input to the AGC operational amplifier 40. The filter 54 is also shown in Fig. 3. In ïike fashion, the timing circuit 48 is connected to a timed source. The timing or firing signal is timed by receiver operation.
In this instance, it is connected to the receiver 20 as a trigger source.
In Fig. 3, the switched signals for the AGC
are processed wherein the gain of the AGC circuit is set by the signal from the first receiver and the gain isheld at the same level for the signal for the second receiver. At each transmitter firing, the switch alternates, passing alternate signals from the two receivers.
The foregoing sets forth one embodiment of the AGC control systern and an alternate arrangement in which it is used with different inputs. Modifications can be accommodated without departing from the structure which is set forth. For instance, one modification is substitution of a halfway rectifier for the full rectifier. This can be done where the signal ~2~)46 of interest is substantially unidirectional. The peak detector 46 is typically gated by the timing circuit 48. The gating signal is variable in the system as shown. If circumstances permit, it can be fixed by the time of the transmitted pulse. That is, the timing circuit 48 might be simplified by simply tying the input of the timing circuit 48 to the acoustic pulse transmitter, thereby timing operation of the AGC
control system of this invention on occurrence of a transmitted pulse. Another important factor is to note the incorporation of the filter 54. This limits the frequency content input to the AGC operational amplifier. This limitation prevents destabilized operation of the feedback loop as a result of feeding excessive rate of change through the feedback loop, thereby altering the gain in an uncontrollable fashion.
While the foregoing sets forth the preferred embodiment, the scope is determined by the claims which follow.
Claims (3)
1. An automatic gain control system for use in an acoustic well logging system having an acoustic transmitter for transmitting acoustic pulses in a well borehole and a plurality of longitudinally spaced apart acoustic receivers for receiving acoustic pulses traversing the well borehole and the earth formations between said transmitter and each of said receivers, said automatic gain control system comprising:
means for inputting signals from at least one of said acoustic receivers to a gain controlled operational amplifier, said operational amplifier having at least one input acoustic signal terminal and a feedback control signal input terminal;
differential amplifier means connected to the output of said gain controlled operational amplifier for amplifying the output of said operational amplifier and providing a system output acoustic signal and for providing a sample output signal to a feedback control signal generating loop circuit;
a timing circuit for providing reset signals a predetermined length of time following each successive acoustic pulse from said acoustic transmitter, the time interval between said acoustic means and said reset signals defining an operat-ing cycle of the automatic gain control system;
full wave rectifying means responsive to the output of said differential amplifying means for generating a pulsating D.C. signal representative of said differential amplifier sample output signal;
peak detector means responsive to said pulsating D.C. signal and to said reset signal from said timing circuit for generating a peak output signal representative of the peak value of said pulsating D.C. signal in said operat-ing cycle of the automatic gain control system;
sample and hold amplifier means having an input connected to the output of said peak detector means for holding and providing an output representative of said peak signal representative of the peak value of said pulsating D.C.
signal; and filter means having an input terminal connected to the output of said sample and hold amplifier to limit the high frequency content of said output signal, said filter having an output connected to said feedback control terminal of said gain controlled operational amplifier to thereby provide a gain control signal thereto.
means for inputting signals from at least one of said acoustic receivers to a gain controlled operational amplifier, said operational amplifier having at least one input acoustic signal terminal and a feedback control signal input terminal;
differential amplifier means connected to the output of said gain controlled operational amplifier for amplifying the output of said operational amplifier and providing a system output acoustic signal and for providing a sample output signal to a feedback control signal generating loop circuit;
a timing circuit for providing reset signals a predetermined length of time following each successive acoustic pulse from said acoustic transmitter, the time interval between said acoustic means and said reset signals defining an operat-ing cycle of the automatic gain control system;
full wave rectifying means responsive to the output of said differential amplifying means for generating a pulsating D.C. signal representative of said differential amplifier sample output signal;
peak detector means responsive to said pulsating D.C. signal and to said reset signal from said timing circuit for generating a peak output signal representative of the peak value of said pulsating D.C. signal in said operat-ing cycle of the automatic gain control system;
sample and hold amplifier means having an input connected to the output of said peak detector means for holding and providing an output representative of said peak signal representative of the peak value of said pulsating D.C.
signal; and filter means having an input terminal connected to the output of said sample and hold amplifier to limit the high frequency content of said output signal, said filter having an output connected to said feedback control terminal of said gain controlled operational amplifier to thereby provide a gain control signal thereto.
2. The system of claim 1 and further including means for multiplexing several acoustic receiver output signals as input to said gain controlled operational amplifier.
3. The system of claim 1 wherein two acoustic receiver signals are simultaneously input to multiple input terminals of said gain controlled operational amplifier and the output signal therefrom comprises a signal representative of the amplitude ratio of said two acoustic receiver signals.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/560,294 US4610006A (en) | 1983-12-12 | 1983-12-12 | Automatic control system for acoustic logging |
| US560,294 | 1983-12-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1222046A true CA1222046A (en) | 1987-05-19 |
Family
ID=24237170
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000468936A Expired CA1222046A (en) | 1983-12-12 | 1984-11-29 | Automatic control system for acoustic logging |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4610006A (en) |
| EP (1) | EP0145428A3 (en) |
| AR (1) | AR241167A1 (en) |
| AU (1) | AU3646684A (en) |
| CA (1) | CA1222046A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4855965A (en) * | 1986-11-26 | 1989-08-08 | Shell Oil Company | Time ramped gain for borehole televiewer |
| FR2710757B1 (en) * | 1993-09-30 | 1995-12-15 | Inst Francais Du Petrole | Method and device for acquiring seismic signals. |
| US5844444A (en) * | 1997-02-14 | 1998-12-01 | Macronix International Co., Ltd. | Wide dynamic input range transconductor-based amplifier circuit for speech signal processing |
| US5986749A (en) | 1997-09-19 | 1999-11-16 | Cidra Corporation | Fiber optic sensing system |
| US6137621A (en) * | 1998-09-02 | 2000-10-24 | Cidra Corp | Acoustic logging system using fiber optics |
| US6305227B1 (en) | 1998-09-02 | 2001-10-23 | Cidra Corporation | Sensing systems using quartz sensors and fiber optics |
| US6227114B1 (en) | 1998-12-29 | 2001-05-08 | Cidra Corporation | Select trigger and detonation system using an optical fiber |
| CN102094624B (en) * | 2009-12-14 | 2013-10-30 | 西安威尔罗根能源科技有限公司 | Power supply circuit of main current for microsphere focused logging |
| CN103256044B (en) * | 2012-12-19 | 2016-01-06 | 电子科技大学 | A kind of with brill acoustic signals treating apparatus |
| CN106256989B (en) * | 2015-06-18 | 2020-09-18 | 中国石油化工股份有限公司 | Underground while-drilling noise acquisition system |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3394315A (en) * | 1964-11-23 | 1968-07-23 | Gen Dynamics Corp | Automatic gain control system having wide dynamic range |
| US3289157A (en) * | 1965-12-16 | 1966-11-29 | Dresser Ind | Automatic gain control in acoustic well logging systems |
| FR1506276A (en) * | 1966-01-18 | 1967-12-22 | Inst Francais Du Petrole | Device for automatic binary gain control of an amplifier |
| US3488604A (en) * | 1967-09-01 | 1970-01-06 | Sperry Rand Corp | Automatic pulsed-signal amplitude normalizer |
| US3958213A (en) * | 1975-01-03 | 1976-05-18 | Gte Sylvania Incorporated | Adaptive gain control and method for signal processor |
| US4112384A (en) * | 1977-05-24 | 1978-09-05 | Morgan Industries | Controlled recovery automatic gain control amplifier |
| JPS6059772B2 (en) * | 1979-01-26 | 1985-12-26 | 株式会社日立製作所 | analog to digital converter |
| US4371842A (en) * | 1980-10-24 | 1983-02-01 | Sperry Corporation | Self-adjusting dual mode automatic gain control circuit |
| US4463320A (en) * | 1982-07-06 | 1984-07-31 | Rockwell International Corporation | Automatic gain control circuit |
-
1983
- 1983-12-12 US US06/560,294 patent/US4610006A/en not_active Expired - Fee Related
-
1984
- 1984-11-29 CA CA000468936A patent/CA1222046A/en not_active Expired
- 1984-12-03 EP EP84308371A patent/EP0145428A3/en not_active Withdrawn
- 1984-12-10 AU AU36466/84A patent/AU3646684A/en not_active Abandoned
- 1984-12-12 AR AR298935A patent/AR241167A1/en active
Also Published As
| Publication number | Publication date |
|---|---|
| EP0145428A3 (en) | 1986-08-13 |
| AU3646684A (en) | 1985-06-20 |
| EP0145428A2 (en) | 1985-06-19 |
| AR241167A2 (en) | 1991-12-30 |
| US4610006A (en) | 1986-09-02 |
| AR241167A1 (en) | 1991-12-30 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |