Built-in seismometer amplifier

Claim 2

In an improved noise-suppressing seismic system of the type having a plurality of individual seismometers each of which generate an electrical signal proportional to the ground motion at said individual seismometers, said seismometers each having two output terminals, a remote multichannel amplifying and recording apparatus to separately amplify and record said electrical signals from a group of at least one of said individual seismometers, said apparatus having a pair of input terminals for each said group, a means for transmitting said electrical signals from said individual seismometers to said multichannel amplifying and recording apparatus, said transmitting means having a pair of input terminals for each individual seismometer and a pair of output terminals for each group connected to the pair of input terminals corresponding to that group on said amplifying and recording apparatus, the improvement comprising:

Claim 3

an impedance-buffering monolithic operational amplifier, having a positive and a negative power supply terminal, a separate quiescent current control terminal, an inverting differential input terminal and a separate non-inverting differential input terminal as well as an output terminal; b. means for connecting said differential input terminals to said individual seismometer''s output terminals; c. battery means adjacent said operational amplifier and connected to said power supply terminals for supplying a predetermined voltage thereto, said battery means having an intermediate point for output coupling; d. means interposed between said battery means and said quiescent current control terminal of said operational amplifier for adjusting the quiescent current drain of said amplifier without appreciably altering said predetermined voltage at said positive and negative power supply terminals; e. means for connecting said operational amplifier''s output terminal to said transmission mean''s first input terminal; f. means for connecting said intermediate battery point to said transmission means'' second input terminal; and g. means including at least two resistors for providing a balanced feedback signal from said first operational amplifier''s output to said first operational amplifier''s differential input said balanced feedback signal being within an order of magnitude equal to said seismometer electrical signal such that the AC impedance at said output terminals is substantially less than the AC input impedance of said transmission means both measured at seismic frequencies.

Claim 4

an impedance-buffering monolithic operational amplifier, having a positive and a negative power supply terminal, a separate quiescent current control terminal, an inverting differential input terminal and a separate non-inverting differential input terminal as well as an output terminal; b. means for connecting said differential input terminals to said individual seismometer''s output terminals; c. battery means adjacent said operational amplifier and connected to said power supply terminals for supplying a predetermined voltage thereto, said battery means having an intermediate point for output coupling; d. means interposed between said battery means and said quiescent current control terminal of said operational amplifier for adjusting the quiescent current drain of said amplifier without appreciably altering said predetermined voltage at said positive and negative power supply terminals; e. means for connecting said operational amplifier''s output terminal to said transmission mean''s first input terminal; f. means for connecting said intermediate battery point to said transmission means'' second input terminal; and g. means including at least two resistors for providing a balanced feedback signal from said first operational amplifier''s output to said first operational amplifier''s differential input said balanced feedback signal being within an order of magnitude equal to said seismometer electrical signal such that the AC impedance at said output terminals is substantially less than the AC input impedance of said transmission means both measured at seismic frequencies.

Claim 5

A system as recited in claim 1 in which said operational amplifier, said battery means, said quiescent current adjusting means, and said feedback means are located within said individual seismometers.

Claim 6

A system as recited in claim 1 including a. means for controlling the gain of said operational amplifier by changing the ratios of input and feedback signals summed at said inverting and non-inverting differential input terminals, while substantially maintaining a balanced condition in said seismometer output-operational amplifier input circuit, said gain control means having a pair of input terminals and a pair of output terminals; b. means for connecting said individual seismometers to said pair of said gain control means'' input terminals; and c. means for connecting saId gain control means'' pair of output terminals to said differential input terminals of said operational amplifier.

Claim 7

A system as recited in claim 3 in which said gain control means is located within said individual seismometer being manually adjustable by an external knob.

Claim 8

A system as recited in claim 3 in which said gain control means comprises: a. an array of essentially equal valued pairs of fixed resistors chosen to provide a series of predetermined gains for said operational amplifier; and b. means for externally selecting one of said essentially equal valued pair of resistors from said array of fixed resistors between said input and said output terminals to adjust the ratio of input to feedback signals to a predetermined value, whereby a plurality of said seismometers and their associated operational amplifiers may be employed for spatial filtering.

Claim 9

A system as recited in claim 1 where said feedback means comprises: a. at least two essentially identical networks of capacitors and resistors chosen to provide a predetermined frequency response transfer function for said operational amplifier; and b. a means for substituting said networks into said operational amplifier''s balanced feedback circuit

Claim 10

A system as recited in claim 1 further comprising: a. An active filter stage containing at least one additional monolithic operational amplifier for adjusting the frequency response of said individual seismometer signal, each said additional operational amplifier having a positive and a negative power supply terminal, a separate quiescent current control terminal, an inverting input terminal, a non-inverting input terminal, and an output terminal; b. additional battery means connected to said power supply terminals for supplying predetermined voltages to each said additional operational amplifier, each said additional battery means having an intermediate point for coupling to a succeeding stage; c. means for connecting said input terminals of each additional operational amplifier to said output and said intermediate battery point of the preceding operational amplifier; d. means for connecting said output terminal and said intermediate battery point of the final additional operational amplifier to said transmission means; e. at least one additional quiescent current adjusting means for controlling the quiescent current drawn by each said additional operational amplifier without appreciably altering said predetermined voltage at said positive and negative power supply terminals of each of said additional operational amplifiers, each said quiescent current adjusting means connected between said separate quiescent current control terminal of said additional operational amplifier and said battery means; and f. at least one additional network of capacitors and resistors for providing a predetermined frequency response transfer function of said active filter stage, each said network providing an unbalanced feedback signal between said output terminals and said inverting input terminals of one of said additional operational amplifiers said unbalanced feedback signals being of sufficient magnitude to reduce the AC impedance at said final operational amplifiers output terminals to a value substantially less than the AC input impedance of said transmission means both measured at seismic frequencies.

Claim 11

A system as recited in claim 7 where said additional operational amplifiers, said additional batteries, said quiescent current adjusting means, and said feedback networks are located within said individual seismometers.

Claim 12

A system as recited in claim 7 including: means for substituting one of said capacitor and resistor feedback networks for another, thereby changing said additional feedback networks'' resistor and capacitor values to permit on-site alteration of said frequency response transfer function of said active filter stage.

Claim 13

In a method of seismic surveying of the Type wherein electrical signals are generated by a plurality of seismometers in response to impinging seismic waves, said electrical signals are transmitted to a remote location by a transmission means, amplifying and recording said electrical signals at said remote location, the improvement comprising: a. buffering the impedance between said seismometers and said transmission means prior to transmission of said electrical signals by increasing the feedback to electrical input signal ratio in monolithic operational amplifiers located adjacent to said seismometers, such that the output impedance of said amplifiers are substantially less than the input inpedance of said transmission means; and b. isolating said seismometers one from another and from the variable damping resistances characteristic of said transmission means by said monolithic operational amplifiers.

Claim 14

In a method of seismic surveying of the Type wherein electrical signals are generated by a plurality of seismometers in response to impinging seismic waves, said electrical signals are transmitted to a remote location by a transmission means, amplifying and recording said electrical signals at said remote location, the improvement comprising: a. buffering the impedance between said seismometers and said transmission means prior to transmission of said electrical signals by increasing the feedback to electrical input signal ratio in monolithic operational amplifiers located adjacent to said seismometers, such that the output impedance of said amplifiers are substantially less than the input inpedance of said transmission means; and b. isolating said seismometers one from another and from the variable damping resistances characteristic of said transmission means by said monolithic operational amplifiers.

Claim 15

A method of seismic surveying as recited in claim 10 further comprising controlling the gain of said monolithic operational amplifier by changing the ratio of feedback to electrical input signals summed at said amplifiers differential input terminals such that input circuit balance is maintained thereby permitting adjustment of the individual amplitudes of said electrical signals from said seismometers for spatial filtering.

Claim 16

A method of seismic surveying as recited in claim 10 further comprising substituting one capacitor resistor feedback network for another thereby adjusting the frequency response of said monolithic operational amplifier to provide frequency filtering of said electrical signal prior to transmission by said transmission means to said remote amplifying and recording location.