#garfield Logs

Jun 03 2020

08:56 AM rue_mohr: ARG
09:02 AM rue_mohr: again with the dupont connector failures on a printer
09:30 AM rue_mohr: https://i.imgur.com/S0HuPuN.png
09:31 AM rue_mohr: polprog, we need to fix the integrator, real ones have a resistor across the cap
09:36 AM rue_mohr: http://info.ee.surrey.ac.uk/Workshop/advice/coils/BHCkt/BH_circuit.svg
09:36 AM rue_mohr: that looks right
09:40 AM rue_mohr: polprog, the input wave can be any shape, as long as it does not have high frequencies in it
09:41 AM rue_mohr: https://meettechniek.info/passive/magnetic-hysteresis.html
09:41 AM rue_mohr: interesting, its integrated the other way
09:41 AM rue_mohr: oh their using the digital scope to postprocess
09:41 AM rue_mohr: nevermind
10:01 AM polprog: yeah a 10M is good for puting across the cap
10:02 AM polprog: gotta write up this lab on magnetic stuff
10:02 AM polprog: then another lab on.. diffraction gratings
10:02 AM polprog: also, test tomorrow
10:02 AM polprog: and i have weekend!
10:07 AM polprog: im tired
10:14 AM polprog: https://polprog.net/rozne1/ircjunk/various/les_terminals/nethack.jpg
10:16 AM polprog: these are thin clients
10:16 AM polprog: 4 out of 5 have dead SMPS units inside
10:16 AM polprog: they run off 5V internally
10:18 AM polprog: i think the caps are dead, but im not sure what to probe to tell that.. i also dont have a fitting isolation transformer (the one i have has C13/C14 connections)
12:57 PM polprog: weird, so im getting the same DMM readings in DC+AC mode across the big cap on both the working and dead one
02:23 PM rue_mohr: I wonder what a BH looks like on paramagnetic material
02:24 PM polprog: ill try to check that on friday i hope
02:24 PM rue_mohr: make an in-circuit capacitor tester
02:24 PM polprog: yes! that too
02:25 PM rue_mohr: you need to use it with a scope tho
02:25 PM polprog: i know
02:25 PM rue_mohr: its the dv/dt you need to look at
02:25 PM polprog: dont you still have it pinned on the twitter page
02:25 PM rue_mohr: a new one
02:25 PM polprog: hmm, weird. i thought it looked at the voltage across the cap
02:25 PM rue_mohr: no, you look at the dv-dt
02:25 PM rue_mohr: the votlage doesn't matter
02:26 PM polprog: isnt dv/dt current
02:26 PM rue_mohr: your looking for the instantanious votlage change
02:26 PM rue_mohr: which is resistance
02:26 PM polprog: ah no
02:26 PM polprog: current is dq/dt
02:26 PM rue_mohr: ----/\/\/\/\-----||------ <-- non-ideal capacitor
02:27 PM rue_mohr: the normal resistance is from a few mR to maybe 0.25R
02:27 PM rue_mohr: when you put a square wave across it, you see the resistance as a sudden change
02:27 PM rue_mohr: the cap will cause a slope
02:28 PM rue_mohr: the amplitude of the sudden shift will tell you how much reisitance there is
02:28 PM rue_mohr: thats why I did the 1R for scale
02:29 PM polprog: ah.. right
02:29 PM rue_mohr: make a BH tester, ask if the school has any paramagnetic material you can use it on
02:29 PM polprog: so the shift is when the slope changes direction?
02:29 PM rue_mohr: yes
02:29 PM polprog: right!
02:29 PM rue_mohr: you will see
02:29 PM rue_mohr: \/\/\/\/\/\/\/ on a cap with no resistance
02:30 PM rue_mohr: the point will come apart with resistance
02:30 PM rue_mohr: |\
02:30 PM rue_mohr: | |
02:30 PM rue_mohr: | /
02:30 PM rue_mohr: hmm
02:30 PM rue_mohr: not ascii art worthy
02:31 PM rue_mohr: on the bad cap image, you see the slope of charge, but the HUGE vertical slip
02:31 PM polprog: yeah makes sense.. a suddent shift of current direction will cause a resistive voltage drop - and that drop will change polarity
02:31 PM rue_mohr: mmmm
02:31 PM rue_mohr: a capacitor cant instantaniously change votlage
02:32 PM rue_mohr: so, instantanious changes are resistance
02:32 PM rue_mohr: the more resistance, the more instantanious change
02:32 PM rue_mohr: oh I'll make a video tonight if I can
02:33 PM polprog: todays lab report.. finding the curie temperature of a simulated material
02:33 PM polprog: https://polprog.net/rozne1/ircjunk/curie.svg
02:33 PM polprog: thats the chart..
02:33 PM rue_mohr: hmm
02:33 PM rue_mohr: what was the material?
02:33 PM polprog: hmm.. good question
02:33 PM polprog: not that it matters, this was a LabView simulation because the school is closed
02:34 PM polprog: were all having remote classes
02:34 PM rue_mohr: hmm
02:34 PM rue_mohr: who is tiwake ?
02:34 PM polprog: yeah.. not very much fun innit
02:34 PM polprog: tiwake: show yourself :P
02:35 PM rue_mohr: anyhow polprog, ask about paramagnetic material eh?
02:35 PM polprog: ill do
02:35 PM rue_mohr: I want to know what a BH curve looks like :)
02:35 PM rue_mohr: maybe its left-right mirrored
02:35 PM polprog: oxygen is :)
02:36 PM polprog: Aluminum
02:39 PM rue_mohr: aluminum!?!
02:39 PM rue_mohr: I think I know oxygen is
02:39 PM rue_mohr: bit hard to work with
02:39 PM rue_mohr: aluminum must be really weak
02:40 PM rue_mohr: so, that should mean if I make a magnetic motor with molten aluminum, it'll turn the wrong way...
02:40 PM polprog: really?
08:37 PM rue_mohr: http://info.ee.surrey.ac.uk/Workshop/advice/coils/BHCkt/BH_circuit.svg
11:42 PM rue_mohr: ruemohr.org/~ircjunk/projects/resistorbox/
11:42 PM rue_mohr: updated