Personnel-carried dosimeter

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. The alarm signal is produced when the count reaches a value C=LnT, where n is the frequency converter output in pulses per second for a concentration of 1 ppm, T is a certain extended time duration, and L is the threshold limit value.