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P6015A kV probe max frequency

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bacon117
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Joined: May 23rd, 2011, 6:38 am

P6015A kV probe max frequency

Post by bacon117 » May 23rd, 2011, 8:07 am

My question is general in nature, but it applies to our use of the P6015A high voltage probe. Please excuse me if it sounds simple, I'm originally a mechanical engineer, so some of this electrical stuff is magic to me. :lol:

In general, when we discuss the frequency limitations of signal measurement equipment, is it the actual frequency that matters or the voltage change per unit time (dv/dt).?

For example, the P6015A instruction manual states that the rated voltage is 20kv unless the frequency exceeds 460kHz. (from page 1-11 and 1-12). The maximum dv/dt at 20kv and 460kHz is 9.2E+9 v/s. From my basic understanding, as long as you do not exceed this dv/dt, there will be no problems. We are measuring the sparking voltage of an automobile ignition system and the impulse can have a maximum of 40kv, but the dv/dt is around 8.05E+8 v/s, which is less than the maximum of 9.2E+9 v/s. So this is acceptable, correct?

My question also extends to a more general realm. Will the measurement of a single event impulse that has a certain dv/dt be affected the same way as a sine wave that has a peak and frequency to produce the same dv/dt? (When I say affected, I mean affected by factors in the measurement circuit, say impedance, probe calibration, etc.)

Thanks in advance for any help.

Chris B
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Tektronix Applications
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Joined: December 17th, 2010, 3:17 pm

Re: P6015A kV probe max frequency

Post by Chris B » May 23rd, 2011, 1:22 pm

To the first question, both matter, as for pulses, the duty cycle/on time also are important.

For your second question, if you are dealing with a non-sinusoidal signal then there is going to be frequency content in addition to just that of the sine wave with a frequency causing the maximum dv/dt to match that of the pulse. Each piece of this content will behave differently. For example, if you look at a square wave on a scope, you will notice that the corners of the square wave are rounded off, and the lower the bandwidth of the scope, the more they will be rounded.

bacon117
Posts: 2
Joined: May 23rd, 2011, 6:38 am

Re: P6015A kV probe max frequency

Post by bacon117 » May 23rd, 2011, 2:46 pm

Thanks for the reply. I think I get it.

Just to make sure I do, please allow me to try out a hypothetical situation. Let's say I have a piece of equipment that says you cannot exceed a 500kHz frequency at 100v. This creates maximum dv/dt of 50x10^6 v/s. If I am using this equipment to measure an impulse, I will be ok as long as my impulse does not exceed 50x10^6 v/s, correct?

Chris B
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Tektronix Applications
Posts: 657
Joined: December 17th, 2010, 3:17 pm

Re: P6015A kV probe max frequency

Post by Chris B » May 23rd, 2011, 3:30 pm

I would argue that this is a definite maybe. Most equipment will specify a maximum RMS value that can be applied, and a maximum pulse that can be applied. They may or may-not be equal in the dv/dt values, depending on safety regulations.

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