Neil Brown Instruments Systems, Inc.

USA As Represented by Secretary of the Navy

Woods Hole Oceanographic' Institution

Ziba Design, Inc.

Falmouth Scientific Incorporated

Neil Brown Instrument Systems, Inc.

Eg&g International, Inc.

Neil L Brown

Kenneth D Lawson

Joshua King Hoyt

William D Leppo

Kenneth W Doherty

Daniel Frye

Alan Fougere

Alan J Fougere

The present invention provides a subsurface instrument and a system for the collection and transmission of deep ocean data utilizing standard buoy mooring lines. The system includes a moored surface buoy and a submerged data collection instrument both inductively coupled to the buoy cable. The instrument has a transducer responsive to the characteristics of seawater. A slave modem is interconnected to the transducer through an A/D converter allowing analog transducer signals to be converted to standard telephone modem signals. The modem signals are inductively coupled into the mooring cable and received by a master modem located in the buoy. The buoy may contain a satellite transceiver allowing transmission of the signals to a remote location. The subsurface instrument is battery powered and battery life is extended by powering down when the instrument is not in use. Upon receipt of a signal from the master modem or an internal timer, a wake-up circuit in the instrument is activated causing the transmission of ocean data to be initiated.

Inductively coupled underwater modem

The fluid conductivity sensor disclosed herein is adapted for the non-contacting measurement of fluid conductivity and utilizes first and second insulating tubes, each of which is provided with both the driving transformer and the sensing transformer. The sensor is immersed in the fluid to be tested so that the tubes fill with the fluid. The driving transformer's are oppositely poled so that the current induced in one tube tends to return through the other tube. Shrouds are provided which link the corresponding ends of the tubes and operate to obstruct in-fluid current flow not linking both of the tubes. Accordingly the influence of objects nearby in the fluid is substantially eliminated.

Fluid conductively sensor

A multiple axis joystick employs positionable and fixed electrode assemblies having mutually orthogonal sets of spaced apart electrodes. The electrode spacings depend on the rotational and translational movements of the positional electrodes relative to the fixed electrodes. A signal generator applies an electromagnetic signal to one set of the electrodes. The signal is coupled to the closest associated electrodes of the other set of electrodes to a degree dependent on the rotation- and translation-induced spacings. A controller sequentially detects and processes each coupled signal voltage to determine a degree of deflection in the X-, Y-, Z-, roll-, pitch-, and yaw-axis directions of one set of the electrodes relative to the other set of electrodes.

Multiple axis data input apparatus and method employing positionable

A capacitively coupled, six axis joystick (320) employs a sensor electrode (310) having a perpendicular pair of slots (312, 314) and a fixed electrode assembly (300) having capacitor electrodes (C.sub.S) formed on three mutually orthogonal surfaces of planar circuit boards (302, 304, 306) that are complementarily nested within the slots of the sensor electrode. When nested together, the capacitor electrodes are separated from faces of the sensor electrode by spacings that depend on the rotational and translational movements of the sensor electrode relative to the electrode assembly. A signal generator (352) and address decoder (354) sequentially apply an alternating signal to the capacitor electrodes. The alternating signal is coupled to the closest associated faces of the sensor electrode to a degree dependent on the rotation- and translation-induced spacings. A controller (350) detects and processes each coupled signal voltage to determine a degree of deflection of the sensor electrode in the X-, Y-, Z-, roll-, pitch-, and yaw-axis directions.

Capacitively coupled multiple axis data input apparatus and method

A system for determining a property, such as conductivity, of a material in which a sensor provides a square wave sensor output signal the value if which is selected to the proper in response to a square wave driver signal. The sensor output signal is compared with a feedback signal to produce an error signal. A forward circuit responds to the error signal and provides an in-phase component thereof which is integrated to provide an integrated DC output signal. A feedback signal provides an in-phase square wave feedback signal the peak-to-peak amplitude of which has a precisely selected relationship with the integrated DC output signal for comparison with the square wave sensor output signal to reduce the error signal to zero. The integrated DC output signal can be digitized and suitably processed to provide a signal which represents the property of the material to a high degree of accuracy.

System for measuring properties of materials

An acoustic current meter in which a CW burst is transmitted first in one direction along each acoustic path and then in the reverse direction along such path so that a single receiver system may be used and phase shift and/or d.c. offsets canceled. Four orthogonal components of current are measured so that the axis contaminated by the center support strut may be eliminated from further computation. A direction sensor includes a 3 axis magnetometer using feedback to minimize current requirements and a two axis accelerometer aligned therewith as a tilt sensor.

Acoustic current meter

A pressure transducer capable of measuring very high pressures with great accuracy. The transducer includes a metal structure enclosing a volume which forms a resonant cavity to provide the tuning element in a UHF oscillator. The resonant cavity provides an inductance and a variable capacitance, the capacitance being variable as a function of the pressure to be measured. A transistor oscillator is very loosely coupled to the tuned circuit and provides positive feedback to maintain the oscillation. Due to the loose coupling between the transistor and the tune circuit, changes in the input reactance of the oscillator circuit have very little affect on the frequency of the tuned circuit. The frequency varies as a function of the pressure and provides an indication thereof. Two embodiments of the transducer are described. A first embodiment includes two concentric tubes, a section at the center of the outer tube being reduced in diameter to form an annular gap to provide the variable capacitance. A second embodiment includes a flat diaphragm-like member in close proximity to an opposing flat section. The capacitance between the diaphragm and the section is variable in response to an external pressure.

Capacitive pressure transducer

A two-stage band-pass amplifier filter circuit which uses a bi-quad amplifier in each stage, the bi-quad amplifier being connected between an AC feedback amplifier in the signal transmission path and ground. The bi-quad amplifiers each provide a variable impedance and effectively operate as series-resonant circuits such that, during closed loop operation, the overall amplifier-filter circuit has a high gain at or near resonance and a very low gain off-resonance and has a phase shift of 0.degree. at resonance and .+-.90.degree. substantially off-resonance. The bi-quad amplifiers are connected to the feedback resistance of the signal path amplifier via a coupling resistance, the signal path amplifier feedback resistance being greater than the coupling resistance, normally by a factor as high as 20 to 1, so that the bi-quad amplifier is thereby prevented from overloading during operation.

Band-pass amplifier filters

An analog-to-digital converter for performing extremely accurate measurements of AC voltages. In the conversion process, the most significant bits are determined using a precision ratio transformer having multiple, binary-weighted windings which are selectively connected in series during a first interval to provide an approximation to the input voltage to be measured via a successive approximation conversion technique. The digital value so determined is clocked into a bi-directional counter. The transformer output signal at the end of the first interval is subtracted from the input signal to give an AC residue signal which represents the round-off error from the successive approximation conversion performed during the first interval. The residue signal is synchronously detected and applied to a dual slope type of converter during a second interval, the digital output thereof being accumulated in the counter. The circuit inherently provides for filtering of the input signal and accurately measures the average value of the input signal over the measurement interval even when the input signal varies during the measurement.

Analog to digital converter for precision measurements of A.C. signals

The drive signal applied to the drive winding of a magnetometer is provided by a voltage controlled oscillator. The average current flowing through the drive winding is monitored, and a signal representative of the average current is applied to the input of the voltage control oscillator. The sense windings of the magnetometer are connected to a servo-loop which causes a current to flow in the sense windings which produces a magnetic field cancelling the sensed components of the earth's magnetic field. The magnetometer uses a drive signal which saturates the core for only a short duration of time thereby reducing the power required by the magnetometer while ensuring complete saturation of the core.

Low-power magnetometer circuit with constant current drive

A circuit for measuring the relative phase of two periodic signals. Two analog waveforms are applied to limiting amplifiers which provide digital output signals. The output signals therefrom are applied to digital circuitry which provides an analog voltage representative of the phase difference between the two input signals over a 360 degree range. The digital circuitry compensates for any offset errors which may be introduced by the limiting amplifiers.

Phase measuring circuit

An acoustic current meter in which two channels have acoustic paths oriented at right angles to each other to measure orthogonal components of a current velocity. Each channel includes two transducers aimed at an acoustic mirror so that the reflected acoustic signal from each transducer impinges upon the opposite transducer. Periodically, a burst of high frequency acoustic energy is simultaneous emitted by each transducer. A current flowing produces a relative phase shift between the received signals representative of the current velocity. The output signal produced by each of the transducers is mixed with a common reference signal to provide two, low frequency, beat frequency signals having a phase difference proportional to the current velocity. Due to the reduction in frequency, the phase shift is expanded in time with respect to the phase shift of the acoustic signals and may be easily measured.

An active filter which can achieve extremely high attenuation of frequencies outside the passband while maintaining a very low phase shift of signals within the passband. A preferred embodiment is described in which two, second-order, multiple-feedback, active filter circuits are cascaded and the output of the second filter is fedback to the input of the first filter to realize a fourth-order filter which has very high attenuation of signals falling outside the passband while providing very low phase shifts of signals within the passband.

Bandpass filter having low passband phase shift

A phase detector which utilizes an amplifier that has the input signal coed by resistive elements to both its non-inverting and inverting input terminals operates with an amount of negative feedback determined by the magnitude of the resistive element associated with the inverting input terminal. The reference signal controls a switching device which grounds the non-inverting terminal during the time when this signal has a particular polarity. As a consequence, the gain of the amplifier shifts between equal, positive and negative values in synchronism with changes in the polarity of the reference signal, and the average value of the output signal of the amplifier is indicative of the phase relationship between the input and reference signals when these signals have the same frequency.

Phase sensitive detector

A four electrode T-shaped conductivity cell has one pair of external elecdes affixed to opposite sides of the stem member and one pair of internal electrodes affixed to diametrically opposite arcuated portions of the inner wall surface of an open-ended tube which serves as the crosshead member of the T. The 'voltage' electrodes of the cells are connected in the input circuit of a high gain amplifier which has a negative feedback loop in which the 'current' electrodes are connected. An AC reference signal is coupled to this input circuit and is canceled by the voltage developed across the 'voltage' electrodes. The feedback current, which is responsible for this condition and is proportional to the conductivity of the electrolyte, is converted to an output voltage whose magnitude with respect to that of the reference signal yields a ratio which is linearly proportional to the conductivity.

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Falmouth, MA, United States of America

Neil L Brown