Patent ID: 6507282
Filing Date: 2003-01-14
Classification: B01D,F24F

Abstract:
A method of operating a thermistor within a filter-fan device to monitor a percentage of filter life remaining of a filter assembly, the filter-fan device having a fan that generates an airflow that passes through the filter assembly and exits through an air outlet, the airflow having a temperature, said method comprising the steps of:(a) positioning the thermistor in the airflow within the filter-fan adjacent to the air outlet; (b) applying a first current to the thermistor; (c) determining the temperature of the airflow from a first thermistor voltage, the first thermistor voltage being responsive to the first current applied to the thermistor; (d) applying a second current to the thermistor to heat the thermistor, the second current being greater than the first current; (e) determining the temperature of the thermistor from a second thermistor voltage, the second thermistor voltage being responsive to the second current applied to the thermistor; and (f) determining the percentage of filter life remaining of the filter assembly from the temperature of the airflow and the second thermistor voltage.