FILTER CONDITION SENSOR AND INDICATOR.

摘要

A filter condition sensor and indicator for responding to the presence of a predetermined collection of material in a filter operatively positioned in a output air flow path comprising: a small by-pass air flow path connected to the output air flow path and separate from the filter; a heated thermistor in the by-pass air flow path; and an indicator light electrically connected in series in a circuit with the heated thermistor sheet illuminates when the resistance in the circuit is decreased due to predetermined cooling of the heated thermistor; whereby a predetermined collection of material in the filter increases the flow of air in the small by-pass air flow path for cooling the heated thermistor and lowering resistance in the circuit to illuminate the indicator light.