FILTER MONITORING SYSTEM USING A THERMISTOR

摘要

A system (figure 3) for monitoring a percentage of filter life remaining of a filter assembly (18) of filter-fan devices. The system uses a single thermistor (RT1) that is operated in two separate modes for monitoring the filter assembly. The thermistor (RT1) is positioned in the airflow of the filter-fan device (2) adjacent to the air outlet. A first current is applied to the thermistor (RT1) for determining the temperature of the airflow from a first thermistor voltage. The first thermistor voltage is responsive to the first current applied to the thermistor. A second current that is greater than the first current is applied to heat the thermistor. The temperature of the thermistor is determined from the second thermistor voltage which is responsive to the second current applied to the thermistor. The percentage of filter life remaining of the filter assembly is determined from the temperature of the airflow and the second thermistor voltage.