| 摘要 |
A detector for monitoring the low levels of differential pressures and the rate of mass flow rate of gas (air, e.g.) in a duct. The sensor's temperature is maintained at a constant gradient above temperature of the flowing gas, typically 4-7° C. higher. The detector consists of two thermally decoupled sensors-one is the air temperature sensor and the other is a temperature sensor coupled to a heater. The sensors are connected to an electronic servo circuit that controls electric power supplied to the heater. The sensors are positioned outside of the air duct and coupled to the duct via a relatively thin sensing tube protruding inside the duct. The end of the tube has an opening facing downstream of the gas flow, thus being exposed to a static gas pressure. The detector can be employed in fuel burners of the HVAC systems, internal combustion engines, medical equipment to control flow of anesthetic gases, in the security systems to monitor minute changes in air pressure resulted from opening and closing of doors and windows in a protected facility.
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