Abstract: A dosimeter includes an electrochemical sensing cell and circuitry which provides a first alarm when the contaminant concentration exceeds a short-term exposure limit, and a second alarm when the time weighted average concentration level over a relatively longer term exceeds a different threshold limit value. In one sensing cell embodiment, the gas sample flows through a circuitous recess on the interior surface of the cell body, which recess is covered by the sensing electrode. A downstream pump urges the gas sample through the cell. In an alternative embodiment, not utilizing a pump, the gas sample enters the cell by diffusing through a sintered porous plate into contact with the sensing electrode. In each cell, the output current is proportional to the contaminant concentration level.To obtain a time weighted concentration level alarm signal, the circuitry employs a frequency converter that produces output pulses at a rate proportional to the cell output current level. These pulses are counted.

Abstract: An electrochemical sensing cell includes a planar sensing electrode clamped between a manifold cap and a cover for a container housing the counterelectrode and electrolyte. In the manifold cap, the gas being analyzed flows through a shallow recess into contact with one side of the sensing electrode. The cover includes an opening across which is supported a porous disc saturated with electrolyte. When the cap is secured to the cover, the disc presses against the other side of the sensing electrode to ensure good electrolyte contact therewith. A vent hole in the cover also permits replenishing of the electrolyte without major disassembly of the cell.