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Development of optical instrumentation to standardize detector tube certification procedures.

NIOSH 1974 Apr; :1-74
Development of an electro optical instrument to enable the certification of gas detector tube units which measure the concentration of toxic gases in the air of the workplace is reported. The gas detector tubes are small diameter glass tubes containing at least one gas permeable substrate impregnated with a chemical reagent which changes color when exposed to a minimum quantity of one or more specific gases. The length of stain produced by reaction between the looked for gas and the tube contents becomes an approximate measure of the specific gas concentration in the air sample drawn through the tube. The instrument developed places the stained detector tube in a holding system similar to an engine lathe. A simultaneous rotation of the sample and relative longitudinal motion between the sample and an optical scanner are held constant. Optical scanning is performed by slowly traversing the useful length of the tube while it rotates. The lead screw and gearing system pitch which causes the relative longitudinal motion between the scanner and the detector tube is chosen so that each rotation of the tube produces a linear motion not more than 1% of the length to be scanned. During each rotation the signal processor samples and holds the integral of the relative contrast (light reflectance transmittance) of the tube's contents. A plot is formed which is a step function graph of the average (integrated) relative contrast of the sample. The ultimate limit of resolution of the system is imposed by the optical reflectance variability of the substrate being scanned.
NIOSH-Contract; Contract-099-73-0030; Air-monitoring; Standards; Measurement-devices; Environmental-hazard-measurement; Atmospheric-monitoring; Analytical-instrumentation; Electronic-equipment; Testing-equipment
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National Institute for Occupational Safety and Health
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division