Depth Sensitive Transducer

摘要

1,175,553. Seismic prospecting; microphones. SCHLUMBERGER TECHNOLOGY CORP. 17 Jan., 1967, No. 2353/67. Headings H4D and H4J. [Also in Division G1] A transducer for measuring hydrostatic pressure variations and acoustical pressure waves, produced, e.g. by underwater explosion and reflected from earth formations on the water bed, comprises a sealed housing 14, (Fig. 1) of which two opposite walls are formed by diaphragms 16, 18 carrying iron or steel armatures 20, 22. U-shaped magnetic polepieces 24, 26 fixed in the housing are provided with coils 34, 36 connected in series in one arm of a bridge (Fig. 2) in parallel with a variable capacitor 60. Initially the capacitor and a resistor in arm 50 are varied to balance the bridge at a known pressure. Changes in the inductance of the coils due to movement in opposite directions of armatures 20, 22 modulates the bridge output at a frequency of the order of 1500 c/s for acoustic pressure waves and at a frequency of less than 1 c/s. for hydrostatic pressure changes occurring as a result of variations in the depth of the transducer. The bridge output is demodulated to remove the carrier frequency then fed through a high pass filter, which selects signals due to the acoustic waves which are amplified and re. corded, and also through a low pass filter, which records depth signals. In operation a plurality of transducers are towed behind a boat, the hydrostatic pressure measurements enabling the operator to keep the transducers at a required depth. The transducer construction automatically cancels signals produced by displacement of the transducer as a whole in the liquid medium. In modifications permanent magnets may be attached to the diaphragms, movement of the magnets inducing currents in coils 34, 36: or one plate of a capacitor may be mounted on each diaphragm with a second plate fixed in the housing; of the wiper arm of a potentiometer may be connected to the diaphragm to vary the impedance of the potentiometer dependent on pressure.