An analog VLSI microchip which uses moments to determine the position and orientation of an object in a scene is disclosed. The imaging sensors are implemented on the chip itself using standard fabrication processes. The method allows very high speed computation in a small, low cost, and low power device. The first moments determine the centroid of the image, which provides the position. The second moments, together with the first moments, determine the axis of least inertia, which provides the orientation. The method uses a resistive grid with nodes containing intensity data (in the form of voltages) corresponding to the image. The moment extraction method is a two-stage dimensional reduction of data. First, the two-dimensional array of intensity data is reduced to a one-dimensional array of data (in the form of currents) by the resistive grid. Second, the one-dimensional data array, which is available at the periphery of the grid, is reduced to a data vector, the size of which is independent of the grid size.

An infrared detector includes process and circuitry for detecting the direction of movement of a radiation source with a predetermined resolution. Four radiation-sensitive elements defining a square are provided in the detector, each connected to an evaluation circuit which compares the output signals from the elements. A normalized pulse is generated upon the occurrence of the maximum of the output signal from each of the elements. The direction of movement of the radiation source is identified from the chronological sequence and spacing of the normalized pulses.

A conductivity sensor for measuring hematocrit and a sensor housing for a blood analysis instrument using the conductivity sensor are described. The conductivity sensor includes a seven-electrode conductivity measurement cell in which three symmetric pairs of electrodes are arranged on opposite sides of a central electrode. The central electrode is connected to an AC source and the outermost pair of electrodes, which provide a return path for the current, are maintained at a ground or reference potential. The two inner pairs of electrodes measure the voltage drop along the current flow path. This arrangement confines the measurement current and potential within the sensor chamber, thereby preventing the sensor from interfering with other electrochemical sensors that may be provided in the blood analysis instrument. The sensor housing provides a linear arrangement of flow cells defining a fluid flow path through the housing. The conductivity and other sensors are each located within an associated cell to form a wall portion of the flow path. The housing arrangement is simple to assemble and provides a flow path which resists fouling and is readily flushed out.