This is for an ion sensing system for an automobile engine.
I have a voltage source of 200-400V (final voltage to be determined by testing). This is applied to the spark plug. Under certain conditions the spark gap will break down and current will flow. I have a circuit to measure this current as drawn from my supply. Based on current flow vs time I can determine certain operating conditions of the engine.
Problem is that when the ignition coil fires I will get a short voltage spike on the same lead going to the spark plug which could hit 20kv. I want to prevent that from going back into my power supply.
I found a school paper from someone who built a functioning circuit. He didn't post schematics but stated he used 20 x 1kv avalanche rated diodes in series between his power supply and the spark plug. This seems a little hokey to me.
Does anyone know a better way I could prevent high voltage from the ignition coil from entering my circuit? FYI, my current measurements don't start until about 1ms after ignition, so perhaps some sort of "switch" would be possible to turn on the supply after ignition rather than have it permanently connected with diodes.
I have a voltage source of 200-400V (final voltage to be determined by testing). This is applied to the spark plug. Under certain conditions the spark gap will break down and current will flow. I have a circuit to measure this current as drawn from my supply. Based on current flow vs time I can determine certain operating conditions of the engine.
Problem is that when the ignition coil fires I will get a short voltage spike on the same lead going to the spark plug which could hit 20kv. I want to prevent that from going back into my power supply.
I found a school paper from someone who built a functioning circuit. He didn't post schematics but stated he used 20 x 1kv avalanche rated diodes in series between his power supply and the spark plug. This seems a little hokey to me.
Does anyone know a better way I could prevent high voltage from the ignition coil from entering my circuit? FYI, my current measurements don't start until about 1ms after ignition, so perhaps some sort of "switch" would be possible to turn on the supply after ignition rather than have it permanently connected with diodes.
