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Fluke 45

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BeBuLamar:
I used the Fluke 45 at work over 30 years ago. Recently I bought one to use on audio work (mainly analog tape decks) because it has better AC voltage specs as compared to the Fluke 289 or 189 that I have. It seems to have good accuracy up to 20kHz. To my surpise the input impedance for AC measurement is only 1 Megaohms and not 10 Megaohms like most other meter.
It's kind of a disappointment.

bdunham7:
Actually that is pretty standard for bench meters.  1M DC-coupled across ~100pF.  Your 189 and 289 have 10M across ~100pF but with an AC blocking cap so infinite DC resistance.  Are the AC specs actually that much better?

hgjdwx:
189 and 289 are all 100khz frequency response

trobbins:
You could make up a 9Meg trimmable interface for a 10:1 divider with 10Meg input, and see what frequency response variation from specs you get using the other 2 flukes for comparison/calibration.

BeBuLamar:

--- Quote from: bdunham7 on November 02, 2022, 11:40:40 pm ---Actually that is pretty standard for bench meters.  1M DC-coupled across ~100pF.  Your 189 and 289 have 10M across ~100pF but with an AC blocking cap so infinite DC resistance.  Are the AC specs actually that much better?

--- End quote ---

In the audio range the AC specs is significantly better while the DC specs isn't.

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