FLUKE 8845A 8846A & 34401A AC Filter bandwidth

[Kiriakos GR]

Back in time a FLUKE employ made the thought to hide FLUKE 8845A 8846A AC Filter bandwidth information at the calibration document, instead this information be at User Manual.

Today I was exploring HP/Agilent/Keysight 34401A user manual and this AC Filter bandwidth information was clearly described.   
The new information this is that both brands they use at that class of benchtop DMM,  three identical AC Filter bandwidth options.

Instead of me reinventing the wheel, I will simply copy/paste the relative text:   

AC Voltage Specifications

AC Voltage specifications are for ac sinewave signals >5 % of range.
 For inputs from 1 % to 5 % of range and <50 kHz, add an additional error of 0.1 % of range, and for 50 to 100 kHz, add 0.13 % of range.

Maximum Input:
750 V rms or 1000 V peak (8845A)
1000 V rms or 1414 V peak (8846A) or 8 x 10 7 volts-Hertz product (whichever is less) for any range.

Measurement Method AC-coupled true-rms.
Measures the ac component of input with up to 1000 V dc bias on any range.

AC Filter Bandwidth:
Slow         3 Hz -300 kHz
Medium    20 Hz -300 kHz
Fast          200 Hz -300 kHz

[Kiriakos GR]

Other than bandwidth specifications, Fluke manual this deliver and practical explanations.

3 Hz Slow =  Provides higher measurement accuracy on ac signals between 3 Hz and 20 Hz
20 Hz = Provides higher measurement accuracy on ac signals between 20 Hz and 200 Hz.
200 Hz = Provides accurate measurements on ac signals 200 Hz and above.

If I decode this information, in to actual applications that we can use them.
3 Hz and 200 Hz filters, they are useful at audio equipment diagnosis and measurements
While 20 Hz Filter, this is useful for ACV and ACI Mains.

What both FLUKE and Agilent skipped to mention, that Filtering this is to assist when we measure very small quantities.
Audio Pre-amplifier has a range of input voltages starting from 150 mV up to 250 mV.

And also regarding ACI currents, these Filters it can make a difference, at the 400 mA input.
(Input Connection for Current Measurements Below 400 mA).

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At digital power meter analyzer, the accurate measurement at 20 mA and below, this is a major challenge.
8846A current ranges: 100 uA, 1 mA, 10 mA, 100 mA and 400 mA.

AC Filter Bandwidth
Slow .................................................................... 3 Hz to 10 kHz
Medium ............................................................... 20 Hz to 10 kHz
Fast..................................................................... 200 Hz to 10 kHz

Now everything makes more sense, a high precision DMM along a digital power meter analyzer, they both need Filters, so to remove any noise or interference when they do attempt to measure very low quantities of mV and mA.
And especially the AC component of non-linear loads. 

At characterization of audio systems, most specifications they are delivered by tests performed at the frequency range of 1 KHz.
The 200Hz filter, this might assist at filtering any ACV noise that possibly exist at 50/60 Hz power line, at the application of
Audio Pre-amplifier development.

In conclusion, an high precision DMM this is configured and includes filters, that they can assist at very specific electrical applications.
If you never come close dealing with such specific applications, then the Default selection 20 Hz filter at 8846A, this is all that you will ever need.