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Path: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Klaus Vestergaard Kragelund <klauskvik@hotmail.com> Newsgroups: sci.electronics.design Subject: Re: Inductance meter for BIST Date: Wed, 10 Apr 2024 01:01:55 +0200 Organization: A noiseless patient Spider Lines: 57 Message-ID: <uv4hd3$glt2$1@dont-email.me> References: <go191jli8laisgsbhrrp3fmn113fi5p578@4ax.com> <jnia1j1t40g4ldpk5tkbj6ori2ej13d9ls@4ax.com> <uv3na4$a5pd$1@dont-email.me> <qkta1j1d6rssgifim5vldca5c72ofcgstc@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Tue, 09 Apr 2024 23:01:56 +0200 (CEST) Injection-Info: dont-email.me; posting-host="f8cd8510adcfb1b492c07d9ac7c6e7a5"; logging-data="546722"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/AhD3Dp1wemcHpMW7QZJzloq4MeCRe+LU=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:QeLuTyQXBtmHU6rut6cRtvdxU6s= Content-Language: en-US In-Reply-To: <qkta1j1d6rssgifim5vldca5c72ofcgstc@4ax.com> Bytes: 3475 On 09-04-2024 19:17, john larkin wrote: > On Tue, 9 Apr 2024 17:36:28 +0200, Jeroen Belleman > <jeroen@nospam.please> wrote: > >> On 4/9/24 16:19, John Larkin wrote: >>> On Mon, 08 Apr 2024 17:17:15 -0700, john larkin <jl@650pot.com> wrote: >>> >>>> I can build this into my new programmable inductor module, for >>>> self-test. With a 1% cap, it should be plenty good. L range will be >>>> 750 mH down to maybe 10 mH, part of simulating solenoids and torque >>>> motors and such. >>>> >>>> If I add a switch to open R3 and run some current through R1, it can >>>> measure series resistance too. >>>> >>>> https://www.dropbox.com/scl/fi/tn8lpk38677ioylhdkget/P955_L-meter.jpg?rlkey=xynqyzfc2x020llr3a945c0td&raw=1 >>>> >>>> https://www.dropbox.com/scl/fi/gojlqxj23r4m57ke9jhui/Ind_Meter_1.asc?rlkey=if40kmtiz49gp62bacfvju3uv&dl=0 >>> >>> Most L-meters, the AADE sort, lie or don't work with big Ls. >>> >>> This is better: >>> >>> https://www.dropbox.com/scl/fi/9tex1slpnaqz4n2cbxp3n/Ind_Meter_Apr_9.jpg?rlkey=52vbyylc5ax48w54qdxm9r9cq&raw=1 >>> >>> Given a small uP, like the Rasp Pi thing, it could measure L and Rl >>> pretty easily. One could get compusive and math out the small >>> inductance measuring error from the inductor copper resistance. >>> >>> I need repeatability more than accuracy, and don't have time to >>> explore this very deep, but it's interesting. >>> >>> I've been buying shaftless torque motors off ebay, to understand them >>> electrically. We need to simulate a torque motor. >>> >>> >> >> What's R1 (1G to +5) for? > > It can be switched in, and R2 switched out, to make an ohmmeter. Then > the opamp is a DC amplifier into an ADC. > >> >> Are torque motors actually predominantly inductive? Just >> because it has coils doesn't necessarily mean it is so. > > One case is used in some jet engines, for controlling fuel flow I > think. 750 mH and maybe 200 ohms.. > > Unlike steppers, they seem to have no detent torque and I suspect L > doesn't change much with angular position. Gotta machine a test setup > and verify that. > I did some tests on that maybe 10 years back. I can't remember the details, but I am pretty sure there is a significant change in the inductance vs position