An optical velocimeter probe a device to illuminate a volume of measurement in which there may pass particles, and an optical detector to produce an electrical signal x(t) in response to the passage of a particle in the illuminated volume. It also includes a device to extract information representing the velocity v of particles from the electrical signal, including, in particular, a device to convert the electrical signal x(t) into a complex signal .sub.x (t), an apparatus to set up a self-correlation function r.sub.x (m) of the signal x(t), and a device to estimate the velocity v from the computation of the phase .phi..sub.x (m) of the function r.sub.x (m).

An allergen particle detecting apparatus has a passageway through which environmental air is directed. A light beam is directed across the passageway so that portions of the beam will be scattered if any particles are present in the path of the beam. A beam blocking device on the opposite side of the passageway blocks any non-scattered portion of the beam while transmitting any scattered portions of the beam along a light path in the apparatus. Any light scattered by allergen size particles will be traveling in a predetermined angular range, and a pinhole device is positioned in the light path so as to transmit only light traveling in that angular range. Light transmitted through the pinhole device is detected by a light detector and an alarm output signal is produced if the detected amount of light is above a predetermined level.

The present invention describes an optical technique for analyzing undiluted, multi-phase fluid flows as typically encountered inside reactor vessels or flow lines in the chemical industries. In particular the technique uses a pulsed, coherent light source and measures the back-scattered light collected over a wide scattering angle. A light beam is relayed via a set of lenses down a long probe tube, through a window at a probe tip to illuminate the material that is passing past the window. The light beam is pulsed to "freeze" the motion of the particles streaming past the window. The backscattered light is collected by the same set of optics and is focused on the front surface of a CCD chip. The lens closest to the front window has a short focal length with a large numerical aperture to collect the back-scattered light over a wide range of backward angles, thereby increasing the detection sensitivity to larger particles, which lie behind and are partially obscured by the myriad of smaller particles closest to the window. The probe tube is inserted through an insertion assembly so that the front viewing window is in direct contact with the material flow, and can be positioned so that the flow will provide a continuous and representative stream of material past the window. Best measuring conditions are obtained by placing the probe window at a modest angle of 30.degree.-45.degree. into the flow. The preferred embodiment combines imaging technology with a specific probe configuration, which is optimized for use in the chemical process industries.

A light beam is directed from a light source through an air sample so that portions of the beam will be scattered if any particles are present in the path of the beam. A beam blocking device on the opposite side of the air sample is arranged to block all light except light scattered in a predetermined angular range corresponding to a predetermined allergen particle size range. A light focusing lens in front of the light source is arranged to focus the unscattered part of the light beam onto the blocking device. Light transmitted through the blocking device is detected by a light detector and an alarm output signal is produced if the detected amount of light is above a predetermined level. The signal may be used to activate filtering or air conditioning devices.

An optical measurement system is presented that offers precision on-line monitoring of the quality of steam. Multiple wavelengths of radiant energy are passed through the steam from an emitter to a detector. By comparing the amount of radiant energy absorbed by the flow of steam for each wavelength, a highly accurate measurement of the steam quality can be determined on a continuous basis in real-time. In an embodiment of the present invention, the emitter, comprises three separate radiant energy sources for transmitting specific wavelengths of radiant energy through the steam. In a further embodiment, the wavelengths of radiant energy are combined into a single beam of radiant energy for transmission through the steam using time or wavelength division multiplexing. In yet a further embodiment, the single beam of radiant energy is transmitted using specialized optical elements.