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advice on capturing spikes with a Rigol scope

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jahonen:

--- Quote from: Simon on May 01, 2010, 07:28:48 pm ---well as these are single shotr spikes the dissipation should not be an issue, but if the probe is 10 Mohm series resistance, how can it at any frequency come down to 200 ohms ?

--- End quote ---

Common 1:10 probes also typically have about 10 pF of capacitance, so at about 80 MHz, the probe input impedance has dropped to 200 ohms.

Regards,
Janne

Simon:
so the capacitor is first in line and then the resistor so the full signal goes accross the capacitor, i was thinking it was round the other way

alm:
The capacitor and resistor are in parallel. At low frequencies, the resistor is the dominant part in the impedance, at high frequencies, it's the capacitor. This capacitor is there to compensate for the capacitance in the scope and the probe cable, and is the one you adjust when you compensate your probe with the 1kHz square wave. Some probes use more complex compensation schemes, but this is the basic idea.

rf-loop:
Here some very simple educational basics: http://www.box.net/shared/de5b3paxxn

By Andy Frost, Don Whiteman, and Jason Tsai, Hewlett-Packard
Are you measuring your circuit or your scope probe?

Simon:
so if I read that right having two seperate wires may prove better ?

another thought came to mind, isn't back EMF spikes negative ?, how do I set up the trigger in this case, if i'm after a negative peak the scope will run non stop at the power supply will be over the trigger voltage

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