Importance

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Abstract

A rate of change comparator uses an RC charging circuit and a separate RC discharging circuit to follow a transducer output. The resistor component of each RC circuit is shunted by a diode, each biased in a different orientation so that the charging circuit charges quickly through its diode but discharges slowly through its resistor and the discharging circuit discharges quickly through its diode and slowly through its resistor. The difference in output between the charging and discharging circuits is detected with a comparator, biased off by a threshold bias voltage developed from one of the circuits. The comparator is unaffected by slow changes in transducer signals due to drift, ambient condition and similar changes because the differential voltage between the circuits is minimized for transducer signal changes below the level set by a threshold bias level. When the transducer signal is positive and the rate of change of the transducer signal exceeds the minimum rate of change set by the RC time constant of the discharging circuit, the diode allows the charging circuit to charge faster than the discharging circuit and the differential voltage therebetween triggers the comparator to indicate that an event was detected if the differential voltage exceeds the threshold bias voltage. Similarly, when the transducer signal is negative and the rate of change of the transducer signal exceeds the minimum rate of change set by the RC time constant of the charging circuit, the diode allows the discharging circuit to discharge faster than the charging circuit and the differential voltage therebetween triggers the comparator to indicate that an event was detected if the differential voltage exceeds the threshold bias voltage.

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