Path: Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Wed, 10 Apr 2024 15:46:54 +0000 From: John Larkin Newsgroups: sci.electronics.design Subject: Re: Inductance meter for BIST Date: Wed, 10 Apr 2024 08:45:09 -0700 Organization: Highland Tech Reply-To: xx@yy.com Message-ID: <27cd1jhkj6f02vmlpgk4tlc1t5d0ojeban@4ax.com> References: X-Newsreader: Forte Agent 3.1/32.783 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 80 X-Trace: sv3-p9QuDiRkvnWNzMDFPMSKMmwYQCcjnUINMRIbb21TbsNKQn/2jZITW+8HA6jrNURzgr4/f0c4LnAhEqW!NVNEEX+Ij9UIifjzXLR6FJ9L33XjgbLdzwDPv5QprktWQkuUyH7LgxC+Bs+7JaH9w0ZVk1yoV9u/!fgdraA== 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: 4414 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 https://www.dropbox.com/scl/fo/d9qffkwqzikd9visdt0zi/h?rlkey=mdon4i9xblxkerk470umdbsw3&dl=0 This is charmingly bizarre. There are 41 (prime number!) of commutator segments. If I pick one arbitrarily, and call it #1, and go clockwise with an ohmmeter, resistance goes up to about 8 ohms in steps and goes back down to about 1 ohm at commutator 17, 26, and 34. This is an NOS motor from ebay. It's an older style with brushes and alnico magnets. Imagine designing this 50 years ago without a computer.