Path: ...!news.misty.com!weretis.net!feeder6.news.weretis.net!news.cmpublishers.com!usenet.blueworldhosting.com!diablo1.usenet.blueworldhosting.com!feeder.usenetexpress.com!tr3.iad1.usenetexpress.com!69.80.99.22.MISMATCH!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Tue, 09 Apr 2024 20:57:47 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: Inductance meter for BIST Date: Tue, 09 Apr 2024 13:57:47 -0700 Message-ID: References: User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 69 X-Trace: sv3-u7tBBxYMNqMebxrOW4Z5O8Nr3j7a4epSy6F+MDyxTOYfdjgg8D60IIx97jFU8TaGN4+33XQN0oqrkqz!aa2osmDEs9BuCRj5phKEmEnXkRYnSanTOto7yB5+aNSiTz80pRj40OtiXZBSihn4nVXweibN42N0!F5fBJQ== 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 Bytes: 4219 On Tue, 9 Apr 2024 21:13:30 +0200, Jeroen Belleman wrote: >On 4/9/24 19:17, 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. > >At first sight, if they're like brushed DC motors, the equivalent >circuit would be a series combination of an inductor, a resistor >and a voltage source, function of rotational speed. There will be >some torque ripple and commutator noise, but there's no telling >how important that may be. > >Jeroen Belleman They behave about like 2-phase stepper motors. DC applied to the two windings sets an angular position, not a speed.