Communications – electrical: acoustic wave systems and devices – Testing – monitoring – or calibrating
Patent
1989-09-13
1991-03-19
Lobo, Ian J.
Communications, electrical: acoustic wave systems and devices
Testing, monitoring, or calibrating
324202, G01V 1300, H04B 1700
Patent
active
050016750
ABSTRACT:
A phase and amplitude calibration system for an electromagnetic propagation based earth formation evaluation tool is presented. In accordance with the present invention, improved phase and amplitude logs of a borehole section are provided by an automatic calibration system which compensates for errors caused by temperature and pressure variations in the borehole. This improvement is accomplished by applying in-phase, equal-amplitude reference signals to both measurement channels of a two channel system to thereby characterize system errors for correction of data used for logging. The reference signals are applied by tightly coupling a calibration signal to each receiving antenna. In a first embodiment, this is accomplished by adding a second antenna (a calibration antenna) to each of the two spaced receiving antennas. Each of the calibration antennas communicates with an attenuator which acts to make the calibration antenna transparent or invisible to the receiving antenna when the receiving antenna is in the measurement mode. The attenuator also sets the signal level delivered to the calibration antenna to a value that the receiving antenna would normally see in a measurement mode. In a second and preferred embodiment, the electrostatic shield surrounding each receiving antenna is used as a calibration antenna. The attenuator is then connected across the gap of the shield.
REFERENCES:
patent: 2633484 (1953-03-01), Zimmerman
patent: 4613821 (1986-09-01), Sternberg et al.
patent: 4876511 (1989-10-01), Clark
Lobo Ian J.
Teleco Oilfield Services Inc.
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