Monitoring the waveform of a low frequency squarewave, built into unit, with bnc output to scope

Question

I want to monitor the waveform of a high voltage (8kV) 3Hz to 1000Hz DC pulse form. It has been suggested that I use 1pf capacitor in series with a 1000pf capacitor, then put the scope across the 1000pf capacitor for a 1000 to 1 voltage divider.

I have a few questions:

• Will a 3 Hz DC pulse with a 50% duty cycle, look true, (i.e. flat tops without droop) with a capacitive divider?
• How will the 10X scope probe load such a circuit and alter the waveform and amplitude?I will alter values as needed.
• Would I be better off using a resistive divider?

I want to keep the current low, under 0.5 uA.

Answer 1

Don't mess with Mickey Mouse solutions because you'll never know whether the divided waveform is a true representation of the actual high-voltage waveform. If the 1 pF capacitor breaks down, it will destroy your scope. Also, it could be dangerous.

Instead buy a high-voltage scope probe: reliable, accurate, well built.

EDIT:

OP added "build it into the unit".

In that case, the correct way to do this is with 21 resistor and 21 capacitors:

1. Build a parallel set of 1 MOhm 1/2 W resistor and 1 nF 1 kV capacitor.
2. Make 19 more of them
3. Connect them in series in a string
4. Place the whole string across the voltage to be sampled
5. Place the monitor port across the last set, the one connected to ground.

That will give you a 20:1 divider that is faithful from DC to high frequencies.

^{simulate this circuit – Schematic created using CircuitLab}