Abstract: A method for calibrating a gas measurement device which includes a gas sensing element having an electrical signal output dependent upon concentration of the gas being measured and a diffusion barrier to limit gas entry to the gas measurement device. The gas sensing element is exposed to gas and a steady state current is measured, and then the diffusion barrier is placed in front of the gas measurement device to reduce diffusion, and a second steady state signal is measured. A diffusivity is determined from a coefficient of diffusion of the gas and the physical dimensions of the gas path, and this diffusivity is used together with the first and second steady state outputs to calculate the test concentration of the gas. Subsequent measurements of gas can be corrected using the calculated test concentration.

Abstract: An oxygen sensor based on a metal-air cell, typically a commercially available zinc-air battery of the type used in hearing aids. The cell, which admits oxygen to generate electric current at its cathode is disposed in a mechanical housing which restricts the flow of oxygen to the cell, and is connected to an electrical circuit which provides a variable resistance load, the load increasing as current flow through the circuit decreases, to prevent hydrogen evolution at the cathode. Current flow through the cell is measured, and is proportional to oxygen concentration.

Abstract: A method and apparatus for determining the concentration of a gas using nondispersive infrared absorption. The method includes measuring the output signal for a plurality of instantaneous time periods, calculating the change of the output signals (CS), calculating the change of the change of the output signal (CCS) which creates a pattern of CCS data and comparing the CCS data with corresponding CCS data for a known reference gas at a known concentration and at a range of known temperatures. The apparatus for determining the concentration of a known gas in a sample gas mixture is a gas chamber, a light source, a detector, a signal converter, and a data acquisition and microprocessor unit which measures the output signal and has a memory with a program to calculate the change of the signal (CS) and the change of the change of the signal (CCS), and compare the CCS data generated from the gas sample mixture to CCS data of known gases with known concentrations and at known temperature ranges.

Abstract: Portable gas sensing devices practicing the present invention include a fault protective battery cap to interrupt flow of battery current exceeding a preselected-threshold level. In normal operation, the battery cap is engaged with a compartment of the gas sensing device which maintains the battery used to power gas sensing circuitry therein. When installed in the gas sensing device in this manner, the battery cap defines a current path from at least one terminal of the battery to internal gas sensing circuitry. As with prior art battery caps, the battery cap of the invention is removable to facilitate replacement of the battery. Unlike prior art battery caps, however, battery caps constructed in accordance with the invention include a fuse electrically connected interposing the current path. The fuse functions to interrupt current flow from the battery if the current exceeds a preselected threshold level.