| 摘要 |
PROBLEM TO BE SOLVED: To make always measurable a correct peak voltage by measuring an offset voltage in a state that a common potential is given to an operational amplifier on the front stage side by a changeover switch, and subtracting the offset voltage from the peak voltage. SOLUTION: Changeover switches S2, S3 are shifted to their contacts (b) sides before and after the measurement of a peak voltage DX, and a non- inverting input terminal of an operational amplifier A1 is connected to a common potential side. An output terminal of the amplifier A1 is disconnected from a diode D2, and a diode D1 of a peak detecting circuit PA is short- circuited. An output voltage V2 of an operational amplifier A2 is measured in this state, and stored as an offset voltage DAZ in a CPU. Then, the switches S2, S3 are shifted to their contacts (a) sides. An input terminal Tin is connected to the non-inverting input terminal of the amplifier A1, and an output terminal is connected to as cathode of the diode D2. Then, the peak voltage DX is measured, and the offset voltage DAZ is subtracted from the voltage DX. Thus, even when the voltage DAZ is slightly changed, it can be accurately removed.
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