| 摘要 |
PROBLEM TO BE SOLVED: To prevent jamming wave from entering an ignition device body as for as possible. SOLUTION: The jamming wave is reduced or attenuated so that high voltage for ignition hindering charged body current detection and unnecessary voltage wave, that is, the jamming waves do not enter the ignition device body as for as possible through a center electrode of a spark plug of an internal combustion engine, in a preamplifier in the charged body current detecting device for detecting charged body current in gas in a combustion chamber by applying alternation electric field to the gas in the combustion chamber of the internal combustion engine. A semiconductor switch is disposed in a protection circuit of the preamplifier to make current flow to the protection circuit for an intended time from just before the ignition spark is discharged, thereby to reduce the interfering wave. An jamming wave attenuation circuit is additionally disposed to the preamplifier, and thereby attenuates the jamming wave.
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