Horizontal loop electromagnetic prospecting system with temperature composition

Claim 2

A horizontal loop electromagnetic prospecting system comprising a. a transmitter including a tuned loop transmitting coil, for generating a primary magnetic field, said transmitter including oscillator and amplifier means connected to said transmitting coil for driving said transmitting coil, b. said transmitter including temperature stabilizing means for maintaining the amplitude of said primary field substantially independent of changes in ambient temperature said temperature stabilizing means comprising a reference coil inductively coupled to said transmitting coil for generating a reference signal representative of the field produced by said transmitting coil, means for providing a fixed reference voltage, means for comparing said reference voltage and said reference signal to produce an error signal, and means responsive to said error signal and coupled to said oscillator and amplifier means to vary the gain of the latter to maintain the magnetic moment of said transmitting coil substantially independent of temperature changes, c. and a receiver including i. a tuned loop receiving coil for generating a received signal dependent on the field received at said receiving coil, ii. a compensation coil inductively coupled to said receiving coil such that temperature induced changes in area of the receiving coil will cause corresponding changes in the mutual inductance between the compensation and receiver coils, iii. means for generating and feeding into said compensation coil a cancellation signal to oppose that portion of the received signal caused by the portion of said primary field at said receiver coil, iv. and means connected to said receiver coil for measuring substantially the remaining component of said received field in time phase with said primary field and for measuring substantially the component of said received field that is out of phase with said primary field.

Claim 3

A system according to claim 1 wherein said reference coil is coaxial with and of approximately the same diameter as said transmitting coil, and said compensation coil is coaxial with and of approximately the same diameter as said receiving coil.

Claim 4

and a receiver including a. a tuned loop receiving coil for generating a received signal dependent of the field received at said receiving coil, b. a compensation coil inductively coupled to said receiving coil such that temperature induced changes in area of the receiving coil will cause corresponding changes in the mutual inductance between the compensation and receiver coils, c. means for generating and feeding into said compensation coil a cancellation signal to oppose that portion of the received signal caused by the portion of said primary field at said receiver coil, d. and means connected to said receiver coil for measuring substantially the remaining component of said received field in time phase with said primary field and for measuring substantially the component of said received field that is out of phase with said primary field.

Claim 5

and a receiver including a. a tuned loop receiving coil for generating a received signal dependent of the field received at said receiving coil, b. a compensation coil inductively coupled to said receiving coil such that temperature induced changes in area of the receiving coil will cause corresponding changes in the mutual inductance between the compensation and receiver coils, c. means for generating and feeding into said compensation coil a cancellation signal to oppose that portion of the received signal caused by the portion of said primary field at said receiver coil, d. and means connected to said receiver coil for measuring substantially the remaining component of said received field in time phase with said primary field and for measuring substantially the component of said received field that is out of phase with said primary field.

Claim 6

A system according to claim 1 wherein said transmitter includes means for generating a reference signal of phase representative of the phase of said primary field, and means for transmitting said reference signal to said means (c.) (iii.) of said receiver to act as a phase reference for the generation of said cancellation signal, said means (c.) (iii.) including a voltage standard source, and means coupled to said voltage standard source and responsive to said reference signal for generating said cancellation signal.

Claim 7

A horizontal loop electromagnetic prospecting system comprising a. a transmitter, including a tuned loop transmitting coil, for generating a primary magnetic field, b. said transmitter including means for maintaining the amplitude of said primary field substantially independent of changes in ambient temperature, c. and a receiver including i. a tuned loop receiving coil for generating a received signal dependent on the field received at said receiving coil, ii. a compensation coil inductively coupled to said receiving coil such that temperature induced changes in area of the receiving coil will cause corresponding changes in the mutual inductance between the compensation and receiver coils, iii. means for generating and feeding into said compensation coil a cancellation signal to oppose that portion of the received signal caused by the portion of said primary field at said receiver coil, iv. and means connected to said receiver coil for measuring substantially the remaining component of said received field in time phase with said primary field and for measuring substantially the component of said received field that is out of phase with said primary field, d. said transmitter also including means for generating a reference signal of phase representative of the phase of said primary field, and means for transmitting said reference signal to said means (c.) (iii.) of said receiver to act as a phase reference for the generation of said cancellation signal, e. said means (c.) (iv.) including a self-nulling servoloop coupled between said receiving coil and said compensation coil, said servoloop including means for detecting the in-phase and out-of-phase components of said received signal, means for integrating such components, means for generating in-phase and out-of-phase signals from such integrated components, means for adding said in-phase and out-of-phase signals to form a sum signal, and means for injecting a predetermined portion of said sum signal into said compensation coil in a direction to reduce said received signal, and means for measuring the level of said integrated components.

Claim 8

A horizontal loop electromagnetic prospecting system comprising a. a transmitter, including a tuned loop transmitting coil, for generating a primary magnetic field, b. said transmitter including means for maintaining the amplitude of said primary field substantially independent of changes in ambient temperature, c. and a receiver including i. a tuned loop receiving coil for generating a received signal dependent on the field received at said receiving coil, ii. a compensation coil inductively coupled to said receiving coil such that temperature induced changes in area of the receiving coil will cause corresponding changes in the mutual inductance between the compensation and receiver coils, iii. means for generating and feeding into said compensation coil a cancellation signal to oppose that portion of the received signal caused by the portion of said primary field at said receiver coil, iv. and means connected to said receiver coil for measuring substantially the remaining component of said received field in time phase with said primary field and for measuring substantially the component of said received field that is out of phase with said primary field, d. said transmitter also including means for generating a reference signal of phase representative of the phase of said primary field, and means for transmitting said reference signal to said means (c.) (iii.) of said receiver to act as a phase reference for the generation of said cancellation signal, e. said means (c.) (iv.) including a self-nulling servoloop coupled between said receiving coil and said compensation coil, said servoloop including means for detecting the in-phase and out-of-phase components of said received signal, means for integrating such components, means for generating in-phase and out-of-phase signals from such integrated components, means for adding said in-phase and out-of-phase signals to form a sum signal, and means for injecting a predetermined portion of said sum signal into said compensation coil in a direction to reduce said received signal, and means for measuring the level of said integrated components.

Claim 9

A system according to claim 4 wherein said means for detecting the in-phase and out-of-phase components of said received signal comprise first and second phase detectors each coupled to said receiver coil, said means for integrating comprising first and second integrators coupled respectively to the outputs of said first and second phase detectors, said means for generating in-phase and out-of-phase signals from said integrated components comprising first and second multipliers connected respectively to the outputs of said first and second integrators for providing chopped outputs representative respectively of the in-phase and out-of-phase portions of the integrated signals from said integrators, said sum signal being the sum of said chopped signals.

Claim 10

A system according to claim 4 wherein said means for measuring said integrated components comprises a digital voltmeter.

Claim 11

A system according to claim 6 wherein said transmitter includes means for switching off transmission of said primary field while continuing generation of said reference signal to permit continued generation of said cancellation signal, and wherein said voltmeter is calibrated so that in the absence of transmission of said primary field but with continued generation of said cancellation signal, said voltmeter will read -100 percent when measuring the integrated in-phase component of said received signal and will read zero when measuring the integrated out-of-phase component of said received signal.

Claim 12

A system according to claim 5 wherein said means (c.) (iv.) further includes a dIgital voltmeter, and switching means for connecting said voltmeter to a selected one of the outputs of said integrators for measuring the output of either integrator.

Claim 13

A system according to claim 8 wherein said means for injecting a predetermined portion of said sum signal includes adjustable attenuator means for attenuating the amount of said sum signal injected into said compensation coil, said attenuator means being switchable to vary its attenuation dependent upon the frequency of said transmitter and the separation of said transmitter and receiver coils.

Claim 14

A system according to claim 9 wherein said phase detectors are digital phase detectors each of which provides an output which becomes smaller in amplitude as the size of the in-phase and out-of-phase components of said received signal becomes smaller relative to the noise in said received signal, and wherein said means (c.) (iv.) further includes a long time constant filter, and means for switching said filter in series with said voltmeter to reduce fluctuations in the readings of said voltmeter.

Claim 15

A system according to claim 9 wherein said transmitter includes means for switching off transmission of said primary field while continuing generation of said reference signal to permit continued generation of said cancellation signal, and wherein said voltmeter is calibrated so that in the absence of transmission of said primary field but with continued generation of said cancellation signal, said voltmeter will read -100 percent when measuring the integrated in-phase component of said received signal and will read zero when measuring the integrated out-of-phase component of said received signal.

Claim 16

An electromagnetic prospecting system comprising:

Claim 17

An electromagnetic prospecting system comprising:

Claim 18

Apparatus according to claim 12 wherein said means (d.) (ii.) comprises means for providing a fixed reference voltage, means for comparing said reference signal with said fixed reference voltage to produce an error signal, and means responsive to said error signal and coupled to said oscillator and amplifier means to vary the gain of the latter.

Claim 19

Apparatus according to claim 12 wherein said reference coil is coaxial with and of approximately the same diameter as said transmitting coil.

Claim 20

Apparatus accOrding to claim 12 wherein said reference coil is wound around said transmitting coil.