Abstract: The density of chlorine dioxide gas in a wet acid atmosphere may be continuously monitored with a photometer energized by a constant voltage incandescent light source illuminating a 0.5 inch thickness, continuous flow sample spaced between quartz glass windows. The emergent light is filtered to pass approximately 4400 Angstrom wavelength light to a selenium photocell. Photocell power output measuring means is calibrated to correspond with chlorine dioxide gas density. The concentration strength of an aqueous solution of chlorine dioxide is continuously monitored with a similar photometer having a 0.125 inch sample space between windows and a 4600 Angstrom filter for the emergent light.

Abstract: In a paper pulp bleach plant, the concentration of residual caustic in solution with the pulp slurry may be measured as a function of the voltage across cathode and anode poles of an electrolytic cell comprising the pulp slurry solution as the electrolyte and ferro-metallic walls of the slurry container as the cathode or anode pole. The opposite cell pole is selected from a group of metals and alloys thereof discretely removed from iron in the electromotive series, the specific pole metal or alloy within the group being selected on the basis of resistance to chemical reactivity at the point of pole placement in the pulp flow stream. Control over the flow of caustic into the slurry flow stream may be exerted in response to an error signal generated from cascade management of the voltage emissions from two such cells positioned early and late, respectively, in the pulp flow stream respective to the caustic injection point.

Abstract: To achieve constant brightness from the chlorine stage of a wood pulp bleaching system, the chlorine addition rate is controlled by two white light photosensors positioned, respectively, 1-5 minutes downstream of the chlorine addition point and immediately prior to the chlorine washers. A relative error signal from the late photosensor is cascaded upon the set-point of a signal differentiator for the early photosensor to generate a chlorine valve control signal. The photosensors comprise selenium photocells positioned against a transparent stock conduit window and reflection illuminated by a low power white light source positioned more remotely from the window than the photocell at a discreet offset angle relative thereto. The white light is directed past the photocells, through the windows and into the flow stream; the photocells being responsive to the relative magnitude of white light reflected from the wood pulp. The power generated from the photocell is correlated to the pulp brightness.

Abstract: The consistency of solid particles in an aqueous fluid suspension may be measured over the range of 0.20 to 20% from the magnitude of electrical power generated by a 0.35 to 1.05 micron light spectrum responsive silicon photocell that is energized by a low, constant power incandescent light source. Light from the source is reflected from the suspension flow stream. The reflected light is filtered to block passage of wave-lengths less than 0.70 microns to the photocell. Angular disposition of the photocell relative to the light path is adjusted to emphasize either a direct relationship between cell power and consistency changes or an inverse relationship thereof.