Re: Differential probes

Chris Carlen wrote:
Hi:


I have a Tek P5205 1:50/1:500 100MHz probe. I just tested it with a 1MHz square wave and it gives nice clean edges with little ringing.

However, a Fluke DP120 20MHz 1:20/1:200 probe loaned to me by an Agilent sales rep. gives miserably ringing edges. The Fluke is kind of silly in having 4 ft. long heavy cables with huge probes that look suitable for heavy duty power distribution probing. Not very convenient for little stuff.

But worse, the Fluke gives horribly ringing edges. I tried making the test cables into a twist-pair, which helped a little but not much. Do the designers ever really think that the thing can give meaningful measurements of 20MHz signals with such a huge pickup loop area! Also, the FP120 is about 4x more noisy than the Tek. The Fluke must have a power supply in there to generate a negative supply, whereas the Tek just pulls clean power from the scope.

Ugh!

The problem with the Tek is it can only work with the scope. But I need to look at a filtered signal to get better RMS measurements of PWM BLDC motor terminal voltages.

Although the FLuke gave a little better 1MHz CMRR of about -66dB vs. Tek -49dB.


There are also a bunch of probes on the market that look like this:

http://www.probemaster.com/activedifferential.html
http://www.linkinstruments.com/adf25.htm

I wonder how they perform?


Oh well, just deliberating in public.

Thanks for input.

Hi Chris,

Tek make the P5200, its essentially the same thing as the 5205 sans scope power. 50R output Z too, whichis kinda handy. I made a bunch of 8th order 50R Bessel LPFs so I can directly measure PWM messes with them.

there is also a crowd who make the best damn diff probe there is. Alas I forget their name, they are a bunch of ex-tek engineers. Maybe Jim Yanik will tell us. not cheap though.

your comments wrt loop area are spot on.

Cheers
Terry
.

Relevant Pages

  • Re: Differential probes
    ... 1MHz square wave and it gives nice clean edges with little ringing. ... The Fluke is kind ... the FP120 is about 4x more noisy than the Tek. ... there is also a crowd who make the best damn diff probe there is. ...
    (sci.electronics.design)
  • Differential probes
    ... a Fluke DP120 20MHz 1:20/1:200 probe loaned to me by an Agilent sales rep. gives miserably ringing edges. ... The Fluke is kind of silly in having 4 ft. long heavy cables with huge probes that look suitable for heavy duty power distribution probing. ... The Fluke must have a power supply in there to generate a negative supply, whereas the Tek just pulls clean power from the scope. ...
    (sci.electronics.design)
  • Re: Differential probes
    ... the Fluke gives horribly ringing edges. ... the FP120 is about 4x more noisy than the Tek. ... The problem with the Tek is it can only work with the scope. ...
    (sci.electronics.design)
  • Re: Differential probes
    ... the Fluke gives horribly ringing edges. ... the FP120 is about 4x more noisy than the Tek. ... The problem with the Tek is it can only work with the scope. ...
    (sci.electronics.design)
  • Re: Differential probes
    ... the Fluke gives horribly ringing edges. ... the FP120 is about 4x more noisy than the Tek. ... The problem with the Tek is it can only work with the scope. ...
    (sci.electronics.design)
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