Title:
PIT TRACKING RECORDER
Document Type and Number:
Japanese Patent JPS63100365
Kind Code:
A
Abstract:
A well casing potential measuring tool including an improved first stage amplifier for precise amplification of small DC voltages between first and second points 18,20 on the well casing. A differential amplifier 28 has its inputs 30,32 coupled to the pair of voltage sensing electrodes, 18,20 by switching arrangement for alternately reversing the polarity of the connection of the input voltages to the differential amplifier. A unity gain inverter has its input connected to the differential amplifier output. In similar fashion a switching network alternately connects the output of the differential amplifier directly and via the output of inverter 36 to the input of a low-pass filter 46. A clock 50 drives the switches synchronously. As a result, the low-pass filter removes that portion of the signal which results from amplified offset voltages in the differential amplifier. The output of the low-pass voltage contains essentially only the desired amplified voltage signal. In an alternative embodiment (Fig. 4) in which the potentials to be measured result from a correct being driven through the casing, the direction of the driven current is alternately reversed to reverse the input to the differential amplifier.
Inventors:
MIKAERU EFU GAADO
Application Number:
JP18464387A
Publication Date:
May 02, 1988
Filing Date:
July 23, 1987
Export Citation:
Assignee:
ATLANTIC RICHFIELD CO
International Classes:
G01R19/165; E21B47/00; G01N17/02; G01N27/20; (IPC1-7): G01N27/20; G01R19/165
Attorney, Agent or Firm:
Akizawa Masamitsu