Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Jeff Layman Newsgroups: sci.electronics.design Subject: Re: Wideband ammeter Date: Sun, 23 Mar 2025 08:31:19 +0000 Organization: A noiseless patient Spider Lines: 47 Message-ID: References: <4s7vtjpl393277u0mvrg8o6sqc00ld6o9l@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sun, 23 Mar 2025 09:31:19 +0100 (CET) Injection-Info: dont-email.me; posting-host="8ba4d6f5ab83fc176dcbcdde442291a9"; logging-data="2046143"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX189r1Y1NAtSWlD+OmxXcSSj0gw/YQsc6nY=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:dVpKa5G/UxIAj73YzOwfHyoiimM= In-Reply-To: <4s7vtjpl393277u0mvrg8o6sqc00ld6o9l@4ax.com> Content-Language: en-GB Bytes: 3153 On 23/03/2025 05:47, john larkin wrote: > On Sun, 23 Mar 2025 03:59:46 -0000 (UTC), Sergey Kubushyn > wrote: > >> Bill Sloman 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. There is a skin effect in a surface-mount resistor (see ). If an AC current flows nearer the surface of the resistor, would that make it "hotter" the higher the frequency? In other words, would the ammeter also be a frequency meter? -- Jeff