# Measurement with High Voltage Differential Probe

I am doing a measurement with this a 100 MHz high voltage differential probe with voltage derating. As per datasheet of TT-SI 9110 probe, the derating curve looks like below.

What impact this voltage derating can have on my measurement when I am measuring voltage up to 800 V?

Thanks

The derating curve is to avoid damage due to heating of the capacitors used in the input of the probe. This heating is a result of resistive and dielectric losses, and is proportional to the RMS voltage and frequency.

To stay within the power dissipation limit of the capacitors, the derating curve effectively plots the line of constant power, with a low frequency voltage limit driven by the breakdown voltage of the capacitors.

Specifically for this probe, if you are measuring an 800V RMS signal, the frequency must be below approximately 3MHz. Short term operation above this limit may be possible, but will be outside of the approved operation range, and "mileage may vary".

Measurements of sharp 1-off pulses is very unlikely to be an issue, despite containing high frequency elements, because average power is limited. It is the heating due to constant HF AC that is the key concern.

• If this answers you question, please mark as answered to help other looking for similar information. Commented Mar 6, 2023 at 18:13

It us highly unlikely you will be testing 800 V rms above 2 MHz so no impact. However you can convert the breakpoint to risetime for impulses or switching characteristics. I recall the conversion as T = 0.35 / f.

This is just like any scope probe rated for RMS voltages with a certain bandwidth due to the quality of the cable voltage rating, the capacitance /m and compensation for say a 50:1 or 100:1 probe divider. Except it may have fins for added moisture creepage protection.

The cable geometry is a normal effect on bandwidth low pass filtering even with simple compensation adjustments with higher impedance and voltage comes a lower bandwidth.

If one wanted to extended bandwidth then a different probe or built-in capacitance divider to a 50 ohm transmission line might be considered for fast spike measurements and attenuation.

• I am not sure i understood your valuebale comment. Could you please eloborate. Thanks Commented Feb 28, 2023 at 15:25