Abstract: An oil and gas well casing inspection tool is disclosed. The casing inspection tool comprises a body; inner and outer contact rollers extending from the body; means for generating a current between the outer contacts; and means for measuring a potential difference between the inner contacts. To enhance the accuracy of the device, capacitance is used downhole to increase the amount of current that can be supplied to the casing. Leaf springs engage the contact rollers to maintain a clean connection between the body and the casing. Signal coders and decoders are also disclosed.

Abstract: A free standing transmitting microphone comprising a hollow holder for enclosing a transmitter and a microphone on a base. A cover of conductive material above the holder functions as an antenna for the transmitter. An acoustic pathway between the holder and the cover directs sounds to the microphone.

Abstract: Phases are measured with a resolution of one degree, and frequencies are measured with a resolution of 0.01 Hz by the same circuitry. An internal voltage-controlled oscillator (VCO) is forced to operate at 360 times the frequency of the incoming test signal by use of a phase-locked loop and a 360 divider. Clock pulses from the VCO are counted throughout an interval of noncoincidence of the original test signal and any phase-shifted version of that test signal, and the count is digitally displayed directly as phase shift in degrees. Clock pulses from the VCO are counted throughout an interval of (1/3.6) second and the resulting count is digitally displayed with the last two digits marked off by a decimal point, as the frequency.

Abstract: This invention relates to an automatic method and apparatus for quick and convenient testing of one or more geophones of a geophysical data acquisition system through the generation and analysis of the impulse response characteristics of such geophones. In particular, geophone response characteristics related to first and second adjacent absolute peak amplitudes associated with the damped equation of motion of the geophone coils are detected and digitally indicated in a surprisingly accurate manner, irrespective of whether or not the testing is carried out in a laboratory or field environment.

Abstract: This disclosure relates to a non-recursive digital synthesizer for producing a surprisingly accurate synthesized sinusoid suitable for testing elements of a geophysical data acquisition system in either a laboratory or a field environment. In accordance with the present invention, [(C/2)+1]-discrete--16-bit binary words are stored in a read-only memory (ROM), representing discrete amplitudes of a digitized sinusoid in a frequency range of 1-500 Hz, and then accessed in succession to a digital-to-analog converter (DAC). A separate suppression circuit means at the output of the DAC is adapted to operate in synchronization with movement of the binary words through the DAC; in that way, glitches generated by the various digital elements of the synthesizer are suppressed. Result: accuracy of the generated sinusoid to the elements under test is assured.

Abstract: An apparatus and a method are described with which the resonance frequencies of seismic detector elements, such as geophones, hydrophones, or sets of geophones or hydrophones, may be automatically determined and displayed with relatively high precision, e.g., to two decimal places. The apparatus is useful under rough field conditions, as well as under laboratory conditions.