| 摘要 |
<p>The invention relates to a measuring circuit for sensing ionisation within a combustion chamber of an engine. The measuring circuit is arranged in the grounded end of the secondary winding (5) of an ignition coil (2), and includes a voltage source for measurements having a substantially constant potential. The voltage source for measurements used is a capacitor (13) which is charged by the spark current (SC), and subsequently after the ignition spark goes out will apply a bias voltage over the spark plug gap (3) with a reversed polarity in relation to the spark voltage. The ionisation within the combustion chamber is detected with a measuring resistance (14) arranged in series with the capacitor (13). A rectifying element (11) is connected in parallel with the measuring resistance, which will secure that the spark current is developed in the spark plug gap (4) and that the measurement current is passing through the measuring resistance (14). In accordance with the invention is the rectifying element grounded with a separated ground strap which do not pass the ground plane of the measuring resistance. The interference inducing spark current could then be conducted in a separated circuit without having to pass the ground plane used for the remaining electronic components of the circuitry.</p> |
