Short pulse detection

[JimW]

Hi all,

I'm using a spark gap and length of coax to create short, high voltage
pulses, 2-6KV 40-300nS range (Blumlein line). Currently I ramp up the
voltage on the power supply using a potentiometer, wait until I hear
the spark then turn the power off. This system works ok but I was
hoping to automate it some how.

I had planned to use an RC circuit connected to a length of wire
wrapped around the coax (12 times) - in principal, when the pulse
occurs a voltage is induced which charges the capacitor. After the
pulse, the cap discharges over a longer time(mS) and is able to be
detected by a microprocessor etc.

So far I've been unable to find any R-C combination that gives me a
sufficiently long decay time. I tried 10uF and 4.7Kohm which should
give a time constant of 47mS – but in practice this gave me a no more
than a few uS of detectable voltage. I was wondering if any one has an
better ideas or perhaps where my idea is going wrong?

Thanks for any help,

Jim W

 

[John Larkin]

On 3 Feb 2005 06:27:40 -0800, jimwalsh142@hotmail.com (JimW) wrote:

Hi all,

I'm using a spark gap and length of coax to create short, high voltage
pulses, 2-6KV 40-300nS range (Blumlein line). Currently I ramp up the
voltage on the power supply using a potentiometer, wait until I hear
the spark then turn the power off. This system works ok but I was
hoping to automate it some how.

I had planned to use an RC circuit connected to a length of wire
wrapped around the coax (12 times) - in principal, when the pulse
occurs a voltage is induced which charges the capacitor. After the
pulse, the cap discharges over a longer time(mS) and is able to be
detected by a microprocessor etc.

Is there a diode in the circuit? The pickup coil will produce a fast
ringing with no DC component, and that won't charge the capacitor.

It would be easier to separate the detection from the timing
functions. A pickup of some sort could fire a one-shot which would
time out whatever interval you need.

Or have an oscillator (or a pushbutton) set a flipflop that starts the
charging, and have a picked-off fire pulse reset it.

John