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NNTP-Posting-Date: Sun, 23 Mar 2025 05:47:21 +0000
From: john larkin <jlArbor.com>
Newsgroups: sci.electronics.design
Subject: Re: Wideband ammeter
Date: Sat, 22 Mar 2025 22:47:14 -0700
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On Sun, 23 Mar 2025 03:59:46 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:

>Bill Sloman <bill.sloman@ieee.org> wrote:
>> On 23/03/2025 12:49 pm, john larkin wrote:
>>> 
>>> How about thermal imaging a surface-mount resistor?
>> 
>> Why bother? Measuring the voltage drop across the same device is easier, 
>> and just as fast, if not faster.
>
>That depends on what you actually want to measure. And "wideband" makes it
>even more difficult.
>
>Wideband current shunts made for AC-DC transfer are all of very special
>costruction and cost arm and leg. If you want to measure the voltage drop
>over those resistors, without making AC-DC transfer, you're up to another
>challenge, measuring the AC voltage. Should start from the definition, what
>IS the AC voltage? What the actual number your measurement shows means and
>so on.
>
>Look at e.g. not all that precise but much better than most LT1088 chip,
>long obsolete. There is another one, proprietary and much better precision
>inside e.g. Fluke 5790A Standard (which is a misnomer -- it is actually an
>AC and DC voltmeter, 10x more precise that the venerable HP/Agilent/Keysight
>3458A).
>
>---
>******************************************************************
>*  KSI@home    KOI8 Net  < >  The impossible we do immediately.  *
>*  Las Vegas   NV, USA   < >  Miracles require 24-hour notice.   *
>******************************************************************

Many otherwise great DVMs have an AC bandwidth that doesn't even
handle the audio range.

The resistor has great common-mode rejection too.