An electrochemical cell for detecting and measuring an oxidisable or reducible substance in a fluid in which cell the background current is substantially compensated by providing in the cell first and second working electrodes and a counter electrode all in contact with an electrolyte, the first working electrode also being exposed to the fluid, the current through the first working electrode being measured, and the current through the second working electrode which includes the background current being maintained at a constant level. Optionally, the second working electrode may be exposed to a reference fluid, and desirably the current through it may be controlled by an operational amplifier.
The invention is directed to an electrochemical measuring cell 1 for detecting different gas components. The electrochemical measuring cell includes several measuring electrodes (8, 12, 13), a common counter electrode 21 and a common reference electrode 20 in an aqueous electrolyte 3. The measuring electrodes each include a diffusion membrane (7, 11) and individual diaphragms (9, 14) limiting the inflow of gas to the individual measuring electrodes (8, 12). The diffusion membranes (7, 11) cover the measuring electrodes (8, 12, 13). The measuring cell 1 is so improved that the selectivity of the detection of different gas components is improved. An electrolyte barrier 19 is provided at least between one of the measuring electrodes 8 and the remaining measuring electrodes (12, 13). The electrolyte barrier 19 prevents lateral diffusion within the diffusion membrane (7, 11).
An electrochemical gas sensor assembly comprises an electrochemical gas sensor; an electrolyte reservoir (3); and at least one capillary (9) defined by substantially rigid, non-porous walls for conveying electrolyte between the reservoir and the gas sensor.
An electrochemical detection system is disclosed for measuring the amount of carbon monoxide or similar oxidizable gases present in a gas phase mixture wherein the gas phase mixture is brought into contact with a liquid electrolyte through a gas-permeable measuring electrode. The improved electrode is formed of a porous membrane of chemically-inert non-wettable material, on one side of which a layer of gold is specially deposited for contact with an electrolyte of a substantially pure aqueous solution of perchloric acid. An electrical readout system is connected to the electrode for deriving a signal from the resulting oxidation current, which corresponds to a quantitative measure of the oxidation of the gas at the electrode-electrolyte interface. In addition to the special method for forming the electrode, a method for rejuvenating it after each sample measurement is disclosed wherein the electrode is successively impressed with an oxidizing (anodic) voltage, a reducing (cathodic) voltage and a working or reading voltage in an appropriate time sequence.
The present invention is directed to certain modifications to sensor cells to minimize electrolyte dilution or loss and to reduce electrical noise. These objectives are attained by designing and constructing the cell in such a manner as to force the electrolyte to communicate between the anode and cathode by diffusion through a porous plug which is placed adjacent the cathode and in contact with the required porous membrane.
A method and apparatus facilitates the alignment and light sensitivity adjustment of an optical computer input system, which includes a user generated light directed onto a screen bearing a computer generated image, to convey information to the computer interactively by the user, even in a darkened room. The system discriminates between the user generated image, and the computer generated image. Devices facilitate the proper alignment of the system with the screen, as well as proper light sensitivity adjustments.
