| 摘要 |
2114033 9309383 PCTABS00022 A circuit for detecting whether the level of an electrical signal having a preselected polarity is above a preselected value, is powered by DC of the opposite polarity. This prevents current leakage within the detector (20) circuit from simulating the level of the electrical signal. Such a circuit is particularly suited for detecting the current level provided by a flame sensor in a combustion control system. The preferred embodiment has a capacitor (55) which is charged by the circuit and then discharged by the electrical signal. The time required to discharge the capacitor (55) to a preselected level indicates the level of the electrical signal. A second embodiment uses a comparator (42) in a feedback loop which allows sensing the level of a voltage outside of the voltage range defined by the comparator's (42) power supply.
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