Abstract: A method and apparatus for measuring relative humidity including condensing environmental conditions using a circuit with a capacitive humidity sensor and a reference resistor each connected to an input of a switch device and thence a quadrature sampling circuit. A sinusoidal source is first connected to the reference resistor and secondly to the capacitive humidity while a signal ground is first connected to the capacitive humidity sensor and secondly to the reference resistor. This produces a first voltage and a second voltage that are each sampled in quadrature. A complex ratio of the sampled voltages is calculated and converted into a representation of relative humidity.

Abstract: A method and apparatus for measuring relative humidity including condensing environmental conditions using a circuit with a capacitive humidity sensor and a reference resistor each connected to an input of a switch means and thence a quadrature sampling circuit. A sinusoidal source is first connected to the reference resistor and secondly to the capacitive humidity while a signal ground is first connected to the capacitive humidity sensor and secondly to the reference resistor. This produces a first voltage and a second voltage that are each sampled in quadrature. A complex ratio of the sampled voltages is calculated and converted into a representation of relative humidity.

Abstract: A multi-beam tool is disclosed which can perform square, plumb, and level function which may be required in a construction environment. The tool can generate in a preferred embodiment up to five orthogonal beams with two beams being plumb and three beams being leveled. Combinations of two level beams, or a level and a plumb beam in orthogonal arrangement can produce a square alignment set of beams. The tool includes in a preferred arrangement a self-leveling pendulum to which a laser and quad-mirror arrangement is secured. The self-leveling pendulum is dampened in order to allow the tool to settle down and provide alignment after the tool is positioned as desired.

Abstract: A multi-beam tool is disclosed which can perform square, plumb, and level function which may be required in a construction environment. The tool can generate in a preferred embodiment up to five orthogonal beams with two beams being plumb and three beams being leveled. Combinations of two level beams, or a level and a plumb beam in orthogonal arrangement can produce a square alignment set of beams. The tool includes in a preferred arrangement a self-leveling pendulum to which a laser and quad-mirror arrangement is secured. The self-leveling pendulum is damped in order to allow the tool to settle down and provide alignment after the tool is positioned as desired. The quad-mirror, the magnetic damping, and the coiled wire allowing power to be provided to the laser assembly, each separately, and also in combination, provide for a compact tool.

Abstract: A breath sensor utilizes optical fibers to detect the flow of a patients respiratory airstream. As it has no conductive or magnetic parts, it can be used on patients within the bore of a magnetic resonance imaging system for simple, safe, and rapid assessment of a patient's breathing.

Abstract: A fiber optic pressure sensor suitable for use in measuring, for example, arterial blood pressure, is taught. A catheter tip is formed utilizing the phenomena of collision quenching or Foerster energy transfer quenching of fluorescence in order to measure the pressure exerted by the medium in which the sensors are placed. When utilizing a collision-quenching type of sensor, the change in concentration of a quencher is measured, the quencher being enclosed in the sensor tip, which is in hydrodynamic equilibrium with its ambient environment. Foerster-quenching type sensors measure the change in distance between the quencher and the fluorophore, which in turn are caused by pressure changes caused by the ambient environment in which the sensor is placed.

Abstract: Oxygen determination based on luminescence quenching of fluorescent dye is effected by using the frequency output of an offset-phase locked loop to calculate the time constant for the exponential decay of fluorescence. An offset phase angle between a periodic stimulus signal used to excite the dye and a response signal based on fluorescence detection is predetermined to optimize signal-to-noise ratio for a wide range of time constants. An offset-phase locked loop is used to vary the frequency of a periodic stimulus signal until the predetermined phase relationship is established. Where the stimulus and response signals are substantially sinusoidal, the offset phase angle is ideally about 49.3.degree., although substantially optimal performance is achieved using a more conveniently generated 45.degree.. The 45.degree. angle offset can also be used with a square-wave stimulus signal.