| 摘要 |
A detector or measuring bridge (12) and a reference bridge (14) receive input signals from a regulated power source (20) and generate output signals through feedback control circuits (56, 68) to a galvanometer (76). Each bridge (12, 14) Includes a filament (32, 40) exposed to a gas being measured. The detector bridge filament (32) is coated with a catalyst and the reference bridge filament (40) is not. Initially. the bridges are calibrated for operation of the exposed filaments at a preselcted resistance and temperature. In the presence of a gas containing combustibles, the catalyst on the detector filament (32) promotes combustion of the gas thereby increasing the temperature and resistance of the detector filament (32) to unbalance the detector bridge (12) and vary the magnitude of the output signal to the feedback control circuit (56). An operational amplifier (80) of the control circuit (56) is thus actuated at a reduced operating level to switch a transistor (TRI), connected to the power source (20) and an input (44) to the detector bridge (12), from a conductive state to a nonconductive state to thereby adjust the voltage level applied to the detector bridge. The bridge (12) is returned to a balanced condition, and the detector fiiament (32) is returned to its initial temperature. The variation in the voltage supplied to the detector bridge (12) is proportional to the concentration of combustibles present in the gas. The readout of the galvanometer (76) provides a quantitative measurement of the combustibles in the gas. Adjusting the voltage applied to the detector bridge (12) maintains the detector filament (32) at a constant temperature to increase the operating life of the detector filament and reduce evaporation of the catalyst on the filament. |
