AIR FLOW DETECTION APPARATUS

摘要

An air flow detection apparatus useful in operating an accessory item in an HVAC system includes a sensor printed circuit board assembly having a first thermistor adapted to be exposed to an air flow and associated with a first pair of heating resistors. A second thermistor is placed in parallel with the first thermistor and is adapted to be hidden from the air flow and is associated with a second pair of heating resistors. A control printed circuit board assembly is interconnected with the sensor printed circuit board assembly and has a voltage regulator circuit for applying a DC voltage source to a power regulator circuit and a sensor monitoring circuit interfaced therewith. The power regulator circuit enables the first thermistor and the second thermistor to be heated to a target temperature greater then a highest specified operating ambient temperature and maintains a temperature of the second thermistor regardless of the actual ambient temperature, and the sensor monitoring circuit responds to the cooling of the first thermistor in the presence of air flow to output a signal operating the HVAC accessory item.