Abstract: A system and method for improving the accuracy of a speckle-based image correlation displacement sensor provides ultra-high accuracy by ensuring that, in the absence of motion, the speckle image does not vary over time. In one embodiment, the speckle image is stabilized by reducing or compensating for laser diode wavelength changes. Various methods for stabilizing the wavelength include thermoelectric temperature control, measuring and correcting the wavelength by any suitable means, or providing a specific wavelength of light feedback from an external grating. Image stabilization may also be accomplished by monitoring the warm-up process of the system. Once the system is determined to have completed the warm-up process, an indicator is provided to the user to indicate that the system is ready for use. Sensor geometric configurations that reduce or eliminate wavelength-related errors are also disclosed.

Abstract: An inductive transducer system for use in high accuracy applications such as linear or rotary encoders, employs two members movable relative to each other. A first, active member induces eddy currents in a second, passive member that lacks a power source or electrical wires connected thereto. The first, active member contains both a transmitter for generating a magnetic field and a receiver for receiving the field. The receiver has a plurality of symmetric loops. Electronic circuitry coupled to the receiver evaluates the relative position between the two members as the passive member disrupts the magnetic field received by the receiver. The inductive transducer can be readily manufactured using known printed circuit board technology, and is substantially immune to contamination by particles, including ferromagnetic particles, oil, water and other fluids.

Abstract: A speed sensor for a ship, more particularly, a thin speed sensor which can be mounted in the hull of the ship and remain flush with the outer surface of the hull. The transducer assembly for the speed sensor is composed of two thin piezoelectric transducers mounted in a spacer plate that locates them in an exact position relative to each other. A baseplate and a coverplate are affixed by appropriate adhesive techniques to each side of the transducers to create a single transducer assembly. Holes through the baseplate and spacer plate permit electrical contact to each side of the transducers so that they may be stimulated to generate acoustic waves. The entire transducer assembly is significantly thinner than the hulls of most watercraft. Thus, a large hole completely through the hull is not necessary. Rather, a shallow recess approximately equal to the thickness of the transducer assembly is made in the hull to countersink the transducer assembly flush with the hull.

Abstract: A speed sensor for a ship, more particularly, a thin speed sensor which can be mounted in the hull of the ship and remain flush with the outer surface of the hull. The transducer assembly for the speed sensor is composed of two thin piezoelectric transducers mounted in a spacer plate that locates them in an exact position relative to each other. A baseplate and a coverplate are affixed by appropriate adhesive techniques to each side of the transducers to create a single transducer assembly. Holes through the baseplate and spacer plate permit electrical contact to each side of the transducers so that they may be stimulated to generate acoustic waves. The entire transducer assembly is significantly thinner than the hulls of most watercraft. Thus, a large hole completely through the hull is not necessary. Rather, a shallow recess approximately equal to the thickness of the transducer assembly is made in the hull to countersink the transducer assembly flush with the hull.

Abstract: A combined speed and depth transducer adapted to be mounted flush in the hull of a ship. An acoustic depth transducer is mounted piggyback on top of an acoustic speed transducer within a single housing. A base plate is sandwiched between the depth transducer and the speed transducer. The dimensions and frequency of transmission of the transducers are selected to prevent ringing in one transducer that may be caused by the acoustic wave of the other transducer. The base plate 40 is constructed to damp the acoustic wave transmitted by the speed transducer and be transparent to the acoustic wave transmitted by the depth transducer. Having the depth and speed transducers mounted within a common housing, and flush with the hull of the ship, provides the advantage of having to make only a single hole in the hull as well as having a low drag.