Path: ...!2.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Bill Sloman Newsgroups: sci.electronics.design Subject: Re: Inductance meter for BIST Date: Wed, 10 Apr 2024 17:38:00 +1000 Organization: A noiseless patient Spider Lines: 69 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Wed, 10 Apr 2024 07:38:07 +0200 (CEST) Injection-Info: dont-email.me; posting-host="41d675878fb95553b5a898130949587e"; logging-data="877128"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+PbC8EKQ6FB+sJQhu6bz6mCl6FMzC2dJ8=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:XhDDAVu2k6GhDBzsYVgKHc5HWmI= Content-Language: en-US In-Reply-To: Bytes: 3903 On 10/04/2024 4:29 pm, piglet wrote: > john larkin wrote: >> On Tue, 9 Apr 2024 17:36:28 +0200, Jeroen Belleman >> wrote: >> >>> On 4/9/24 16:19, John Larkin wrote: >>>> On Mon, 08 Apr 2024 17:17:15 -0700, john larkin 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. >> >> If the brushes short windings sometimes, it could get weird. Why would you need brushes in a torque motor? > They won’t have nice linear ferrite cores but nasty lumps of iron so > measured inductance could depend on test frequency, AC amplitude, amount of > DC flowing, rotor position, temperature etc etc etc. Precision is futile? Not futile but probably difficult to achieve. Lots of variables to measure and correct for, and non-linear correction equations. -- Bill Sloman, Sydney