Wyatt Technology Corporation

Other

The United States of America As Represented by the United States

Electro-craft Corporation

David T Phillips

Gary R Janik

Virgil B Elings

Steven P Trainoff

Douglas W Shepard

A method and apparatus is disclosed for measuring the refractive index difference between a reference and sample liquid based on an interferometric design. The resultant device has an almost unlimited range of operation in contrast to a conventional interferometric refractometer of the so-called polarization type whose dynamic range is restricted to a relatively narrow range of refractive indices. The measurement of the refractive index difference between a sample and reference cell is achieved by measuring the angle through which the plane of polarization of a combined beam has rotated. For the conventional device, this angle is restricted to about .pi. radians which corresponds to a half wavelength shift between the reference and sample components of said combined beam. The extended range device disclosed permits this angle to be tracked and measured accurately over many rotations. The rotation tracking is achieved by one of three embodiments, the preferred of which involves the use of a liquid crystal retarder. The other two techniques incorporate, respectively, a rotating polarizer and a doubly split beam. All three embodiments permit the measurement of both the sine and cosine of the rotation angle and, thereby, allows a four quadrant arctangent calculation to yield the rotation angle directly. The error associated with such measurements is not a function of the rotation angle of the combined beams.

Extended range interferometric refractometer

The incorporation of certain classes of solid state lasers into light scattering instrumentation is desirable because of their compact structure. However, mode hopping often causes the output power produced by such lasers to be unstable. The frequency of such output power fluctuations is often so broad that output power monitoring means, characteristic of the light scattering instrumentation into which such lasers are incorporated, cannot track accurately the temporal output power fluctuations. A method, and associated apparatus, is described whereby the laser drive current is modulated at low frequency and amplitude sufficient to induce and thereby control mode hopping so as to permit accurate measurement of the ratio of light scattering signals to the laser output power.

Control of laser light power output for use in light scattering

An optical shaft angle encoder which provides sensor output voltages having waveform characteristics modified for use with 'multiplication type' tachometer converter circuits to provide improved servo control system performance by reducing step changes in the tachometer output voltage due to phase error and reducing tachometer output voltage ripple. The geometry of the encoder mask combination provides a non-sinusoidal sensor output voltage comprised of linear and parabolic segments having a trapezoidal derivative.

Optical shaft angle encoder

A data acquisition system capable of resolving transient pulses in the subnanosecond range. A pulse in an information carrying medium such as light is transmitted through means which disperse the pulse, such as a fiber optic light guide which time-stretches optical pulses by chromatic dispersion. This time-stretched pulse is used as a sampling pulse and is modulated by the signal to be recorded. The modulated pulse may be further time-stretched prior to being recorded. The recorded modulated pulse is unfolded to derive the transient signal by utilizing the relationship of the time-stretching that occurred in the original pulse.

Data acquisition system

A thermodilution cardiac output computer uses an autobalancing temperature-measuring circuit which adjusts the initial voltage derived from a thermistor and then holds constant the current through the thermistor as the thermistor responds to different temperatures in a blood-injectate mixture. The initial voltage is adjusted to a predetermined constant so that the response from thermistors of different initial resistance is the same. A Wheatstone bridge is not used. Before the temperature measurement, the voltage derived from the thermistor is adjusted to be equal to a predetermined constant either by varying the current through the thermistor or, with a constant current through the thermistor, by varying the gain of the amplifier sensing the voltage across the thermistor. During the temperature measurement this current or gain is held constant. The voltage change derived from the thermistor is integrated in a conventional integrator, and the integration is stopped at the tail of the decay of the temperature-time curve by an automatic timer. This termination point is calculated not as a percentage of the peak value of the curve or at a particular slope of the curve, but as a function of the time of two points high on the decay curve where the artifacts causing undulations in the curve are small compared to the temperature height of the curve. In this fashion, the triggering of the cutoff point by undulations in the curve is avoided.

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Santa Barbara, CA, United States of America

David T Phillips