Image Number 10 for United States Patent #4500391.
An electrochemical detection cell which includes, in the order named, a stack of components constituted by a first membrane, an electrode carrier having reference and counter electrodes thereon, a membrane support, an electrode carrier having a sensing electrode thereon, and a permselective membrane. Whatman filter papers are positioned between the sensing electrode and both the counter electrode and reference electrode, these being positionable in a central rectangular opening of the membrane support. The cell allows air or gas ambient to address the membranes and effects application of an electrolyte to space between the electrodes by, for example, a wick which extends between an electrolyte-containing reservoir and the Whatman filter papers. A system for detecting a gaseous agent uses the aforementioned detection cell coupled with circuitry capable of applying a fixed DC voltage bias to the reference electrode and superimposing a train of DC voltage pulses on the fixed bias. Further circuitry is coupled to and responsive to signals from the sensing electrode. This circuitry determines the difference between the sensing electrode signal at the end of each pulse minus that just before each pulse. The difference is proportional to the concentration of the test gas in the atmosphere adjacent to the sensor, and is a more specific and sensitive indication of the test gas concentration than prior art sensors.