Path: news.eternal-september.org!eternal-september.org!feeder3.eternal-september.org!border-3.nntp.ord.giganews.com!nntp.giganews.com!Xl.tags.giganews.com!local-3.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Sun, 23 Mar 2025 05:47:21 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: Wideband ammeter Date: Sat, 22 Mar 2025 22:47:14 -0700 Message-ID: <4s7vtjpl393277u0mvrg8o6sqc00ld6o9l@4ax.com> References: User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 38 X-Trace: sv3-ANg4G0hOuJU3lCUGHd5oZn31aFLKTFRnr7oKnKpONx5CKv6ToffK1YTOapgMhE7W/j9GPeiuBHWcru3!AUfCxluE/7i63SUMDjBJWXvBip9j6D1PzyPMYOdk6sDurXkniVNtoGJUHZN5XR/Iuts41xPkCz50!0EALhQ== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 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.