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BattleMaster posted:Knoll's Radiation Detection and Measurement Thanks for the name of this book. Looks great!
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May 10, 2017 23:39
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Aurium posted:Thanks for the name of this book. Looks great! It's essentially the Bible of radiation detection, but just be warned that it doesn't offer an incredible amount to EE types who just want to design circuits and don't care as much about what's going on inside the detectors. However, it does go deep into a the physics behind radiation, its interaction with matter, and the mechanisms that different types of detectors exploit to detect and measure it. For example, a lot of my effort post earlier was repeating stuff from chapter 6 (gas proportional counters) and chapter 7 (G-M counters.) Plus, every chapter is incredibly lavishly-cited so if you have some way to access journals you have a good lead on more information.
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May 11, 2017 00:03
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Zero VGS posted:I looked that up and it seems to be "beta-value", which is essentially how the resistance scales to temp. Is there an easy way to figure out if the BMS and Tesla thermistors are the same b-value? Can I just set my multimeter to 20k ohms, and test the battery pack indoors and outdoors to see if I get equal values with both thermistors? Short answer: No. Longer answer: Specific thermistors have a temperature-resistance curve that should be roughly linear, but isn't. Beta is the slope of that (somewhat) linear curve. It's likely that the manufacturer(s) chose thermistors whose curves are linear in the areas they cared about, but that the areas don't match, so that straight-up beta isn't useful. Your best bet is to measure resistance at 0C (water with ice mixed in), and at the boiling point of water (100C at sea level, but adjust for your altitude/barometric pressure). This will give you a very crappy beta value. If the two numbers are "close enough" then go hog wild.
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May 11, 2017 01:23
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Zero VGS posted:I'm hooking my Tesla battery modules up to my aftermarket Orion battery management system, and I noticed that the Tesla modules have built-in thermistors. Googling around, people have confirmed they are 10k thermistors. Thermistor curves are more accurately described by high order polynomials (usually 5th order, in my experience). Beta values are a decent approximation, but can't tell you whether two thermistors are identical. I especially wouldn't assume two matching data points at moderate temperatures means an identical curve at the extremes, which is where your BMS needs to be accurate, for safety reasons. When it comes to safety circuitry, never assume. Do an experiment at the temperatures of interest and modify the circuit if you need to, such that the critical temperatures produce the correct behavior, or design a whole new system if need be, so you can be sure. If one or more parts of your safety system is undocumented, you've already hosed up. Don't compound that by assuming.
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May 11, 2017 03:39
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Given that it's temperature monitoring for a high-voltage battery pack I wouldn't feel really safe about it unless I'd pulled one out, stuck it on a hot plate while measuring the value at various temperatures, and built a lookup table (or at least measured a bunch of test points and done a regression). Can you remove one of the thermistors for testing?
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May 11, 2017 06:27
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Even though I didn't ask that question - the answers were really useful. Thanks. Does the same theory apply to type- (K, etc.) thermocouples?
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May 11, 2017 10:25
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Jamsta posted:Even though I didn't ask that question - the answers were really useful. Thanks. Theoretically, no. A K-type thermocouple has electrical characteristics defined by the metals used in the junction, and shouldn't change much between manufacturers.
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May 11, 2017 11:24
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Sagebrush posted:Given that it's temperature monitoring for a high-voltage battery pack I wouldn't feel really safe about it unless I'd pulled one out, stuck it on a hot plate while measuring the value at various temperatures, and built a lookup table (or at least measured a bunch of test points and done a regression). I'll see if I can remove one... I remembered my boyfriend has thermocyclers at his lab so I could use that as a precision hotplate. I think they're in there pretty good though.
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May 11, 2017 16:31
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I took a quick video of the tube glowing, though I don't really have a youtube account I want to put it up on so I just made it into a gif and put it on imgur: Note that this is with the 50M resistor, the 10M one was brighter and emitted an audible hiss (still audible now but much quieter)
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May 11, 2017 17:28
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Jamsta posted:Even though I didn't ask that question - the answers were really useful. Thanks. For a given thermocouple type, (defined by the 2 dissimilar metals that meet at the thermocouple junction), this voltage should always be consistent with other thermocouples of the same type. If you want to know thermocouple tables, just get data from NIST, no sense in trying to measure it yourself. like this: https://srdata.nist.gov/its90/download/type_k.tab
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May 11, 2017 18:27
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ate all the Oreos posted:I took a quick video of the tube glowing, though I don't really have a youtube account I want to put it up on so I just made it into a gif and put it on imgur: Looks like the colour of neon to me. Neon or any of the other noble gases can be used to fill a G-M tube. I was under the impression that argon was the most common but I suppose neon wouldn't be all that out there. I took my G-M counter with pancake probe to a dark room and I saw a similar neon glow when I put a source near it. I never looked up what its fill gas was but I guess it's neon as well. The fact that you also only see the glow when it picks up counts tells me that it probably isn't anything to be alarmed about. I guess it follows that with so much ionization and excitation going on you don't just get ionizing UV photons that create more avalanches but that you can also get visible light emitted. I had never really thought about it before. The dependence on the resistor value of the brightness is most likely due to the fact that the tube recovers faster with a lower value resistor. It's probably not that the individual counts are brighter but that it can detect more counts when you use a proper resistor for the job. I think the only time you should worry is if it glows like a neon bulb while idle.
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May 12, 2017 00:20
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BattleMaster posted:Looks like the colour of neon to me. Neon or any of the other noble gases can be used to fill a G-M tube. I was under the impression that argon was the most common but I suppose neon wouldn't be all that out there. Ah cool, thanks. I've been kinda nervous to run it for any length of time just in case it was doing something nasty. Now I can actually have some fun with it 
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May 12, 2017 00:23
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How would you know if its spitting out enough UV to be an eye hazard?
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May 12, 2017 04:42
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Foxfire_ posted:How would you know if its spitting out enough UV to be an eye hazard? Would the mica window block UV? I don't know, it's nothing that I've seen discussed anywhere so I assume they aren't eye hazards.
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May 12, 2017 05:33
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It's not enough to make my self-darkening glasses darken at all and they're very touchy (about lower-frequency UV, at least). I'm pretty sure that in order to be ionizing the UV needs to be way up in the range that gets quickly absorbed by the atmosphere anyway but I could be wrong.
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May 12, 2017 05:38
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I don't have any numbers but I have this instinct that the UV production isn't terrible intense. A different type of tube exists called a proportional gas tube that works like a G-M tube except that the out of control Geiger discharge caused by UV photons causing additional avalanches is not desired. Fill gas for proportional gas tubes include a component that preferentially absorbs the UV. A common mix is P-10 gas which is 90% argon and 10% methane, and the methane is enough to stop all of the UV. The result is a weaker signal, but one that is proportional to the amount of ionization that the radiation caused (i.e. you can work backwards and determine what the energy lost by the particle in the gas was.) So I feel like if 10% methane at half an atmosphere or less is enough to stop all the UV there must not be a whole lot of it.
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May 12, 2017 05:53
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A good metric for whether the UV is in the "holy poo poo look away and turn it off" range is if you smell ozone.
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May 12, 2017 08:03
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Could you use something fluorescent (e.g. a bank note or the rear of a visa card) to get a feeling for the amount of UV?
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May 13, 2017 01:08
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Does the tube even have enough power going through it to constitute a major UV hazard, even if it were relatively good at turning that power into ultraviolet photons?
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May 13, 2017 01:15
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Platystemon posted:Does the tube even have enough power going through it to constitute a major UV hazard, even if it were relatively good at turning that power into ultraviolet photons? Well it has enough energy to be emitting visible light, and if the UV it emits is in the far UV range where it's basically more like x-rays than UV, and it's emitting that at the same sort of intensity as it's emitting the visible light it could be a problem... But judging by the amount of current it's spec'ed to use the max power in the thing total is only like 1.2 mW so it's proobably fine.
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May 13, 2017 02:11
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Computer viking posted:Could you use something fluorescent (e.g. a bank note or the rear of a visa card) to get a feeling for the amount of UV? I actually have some neat fluorescent uranium minerals I can use which I think are the most appropriate thing to test with 
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May 13, 2017 02:14
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I had a secondary school lab where we tested sunscreens using cyanotypes.
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May 13, 2017 02:56
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I am trying to make some schematics and wiring diagrams. I would like some software to do this. I am used to schematics like this (apologies to LearJet, all rights reserved, wtf is a lear31, etc)  This has the basic stuff going on; what's connected to what, etc. But the wiring diagrams break down to this:  Wire labels, pin names, connector names, equipment names. Most of everything necessary to actually find a specific physical component. Is there something that does this? I'm fighting with KiCad right now. It doesn't seem to want to label wires how I want. A wire has a designator from beginning to end, and each segment has a different name. The wire starts out as (eg) L1A20 (Lighting, number 1, segment A, 20ga), then is spliced onto another wire, which then becomes L1B20, then goes through a connector, so that wire is L1C20, etc, finally going to ground as L1X20N. KiCad wants to label all electrically contiguous points with the same "net name," regardless of connectors, splices, etc. I realize these Learjet prints are from the 80s, and were hand-drawn, but even modern avionics prints have the same convention and are digitally generated. What is this software?
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May 14, 2017 06:40
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Looks like something more along the lines of a chart tool like Dia, you might try that if you just need to do "lines with labels connecting boxes and symbols" e: Whatever this tool is doing is a biiit fancier than Dia but you could still get close with Dia I think...
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May 14, 2017 08:09
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There are apparently special addons for Visio to do this for simpler schematics/cable assembly drawings too. E3.series is afaik special designed for this kind of thing, but probably pretty expensive. I've never used it myself though.
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May 14, 2017 11:18
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As far as I'm aware there never has been and never will be a good schematic editor. I've done wiring diagrams like this with Visio which is tolerable only if you give up on all its auto-routing features and just draw individual lines with independent text labels.
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May 14, 2017 14:18
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The engineer that used to work for us used an older version of Autocad to draw aircraft wiring diagrams. He had a fantastic library of shapes he'd built up over the years. Ever since he left, we just outsource it because they don't want to pay any of the rest of us to sit around with a ruler and a pencil.
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May 14, 2017 15:46
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You could make a part to represent a splice if you wanted a hacky way to make net names work the way you want.
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May 14, 2017 16:31
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E: I am a idiot.
dad on the rag fucked around with this message at 13:32 on May 16, 2017 |
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May 16, 2017 13:23
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Crossposting from the cooking forum because I figure someone in here may likely know more than the people in the cast iron one.. coyo7e posted:Quick question RE: electrolytic rust removal. So to reiterate: I'm curious about the toxicity of different stuff used as the sacrifical anode, and what I may need to do to ensure that I don't end up killing people in my home if I off-gas some poisonous bullshit (which stainless can do if used as the sac anode, iirc?) OR use something which might contain toxic bullshit that'd gunk up the water and possibly get on my cast iron dutch ovens, etc. Right now I'm experimenting with some ancient tools from my grandfather's toolbox that ended up in mine after he died, but I'd like to move up/on to my cooking stuff sooner rather than later.  Edit: for instance I was curious about used metal cans from food - aren't those steel or galvanized steel I know they can rust..? I have a lot of cans that end up going into the recycle bin but if they're useful and/or safe, I could use them to clean up my tools.
coyo7e fucked around with this message at 06:31 on May 17, 2017 |
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May 17, 2017 06:21
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the cad specialist who works beside me uses AutoCAD for all his electrical drawings, I don't think he uses any special packages.
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May 17, 2017 07:11
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coyo7e posted:Crossposting from the cooking forum because I figure someone in here may likely know more than the people in the cast iron one.. You're actually better off asking chemists i think. I've done my share of chemistry but managed to never apply any of it to real world problems palladium is my metallic specialism so I'll have to leave your general question unanswered. The few minor questions you had I can answer.-there are many stainless steel types, but they all contains chrome. I'll link a reddit post that answers your question better than I can but tbh even if you don't make Cr6+, which is the most dangerous result, there are plenty other Cr-complexes you don't need in your food. However, controlling voltage correctly seems to reduce (lol) the chance of dangerous results. https://www.reddit.com/r/askscience/comments/2ta57z/does_using_stainless_steel_as_an_anode_in/ -food cans can be galvanized, but aluminum or tin (much rarer) are also around. You probably want to check that beforehand. Easiest way to find out is obviously if they're a tad rusty themselves
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May 17, 2017 09:15
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Tin cans were never made primarily of tin. They were made of tin‐plated steel and sometimes still are. Platystemon fucked around with this message at 11:36 on May 17, 2017 |
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May 17, 2017 09:57
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coyo7e posted:Crossposting from the cooking forum because I figure someone in here may likely know more than the people in the cast iron one.. Zinc-plated steel (galvanized) food cans will be OK as anodes. They're just zinc and steel. If you're super super worried about anything, heat it up with a torch in a well-ventilated area until it glows red hot. Once that's done, if a magnet sticks to it, it's OK to use as an anode for electrolytic rust removal. Your best bet is to just use somewhat-coarse steel wool. 100% steel, and large surface area, too.
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May 17, 2017 11:34
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I got my esp8266 based irrigation controller set up pretty well but the moisture readings are a bit wonky, perhaps unsurprisingly for a <$1 sensor. The bit in the middle is fine, it was just off, but what I don't get is why it's so noisy sometimes, to the point of being useless, and other times very consistent. I can smooth it out of course, as shown here with the black moving average, but still. Anything I could do to stabilize it, or is it just fundamentally garbage and I should just bite the bullet and get/diy a capacitive sensor?
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May 21, 2017 19:51
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Is there a cool pre-fab module that can charge 2-, 3-, or 4-in-series lithium cells from a 5V USB-style source? I have a project that gets power via inductive charger that gives USB-style 5V and I need it to charge a higher-voltage lithium pack. I recognize I could get a boost converter hook it to a charger module, but I feel like an all-in-one circuit would be better. That said, I'm trying to avoid doing Real Work and stick to duct-taping prefab stuff.
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May 22, 2017 03:41
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mobby_6kl posted:I got my esp8266 based irrigation controller set up pretty well but the moisture readings are a bit wonky, perhaps unsurprisingly for a <$1 sensor. Can you write up a bit how you've set this up, did you use Arduino or Mongoose, I'm looking to get a cheap sensor to talk to an esp8266 myself with mixed results.
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May 22, 2017 10:18
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Fat Turkey posted:Can you write up a bit how you've set this up, did you use Arduino or Mongoose, I'm looking to get a cheap sensor to talk to an esp8266 myself with mixed results. Sure, this turned out to be pretty trivial all things considered, but my lack of knowledge in the area meant a lot of research and trial and error to get there. I'm using a knockoff NodeMCU board (though a WeMos would probably work better with its compact size) with Arduino libraries. This was a million times easier than trying to program an 12E board directly since you don't have to manually pull up/down half of the pins on the drat board to get it to boot in the right mode. Then the minimal config is the sensor I linked before (or a nicer one for  ), and depending on what you want to do, a logic-level MOSFET like FQP30N06L to control a solenoid valve or pump (i used this one) or a relay. You'd also need a resistor and to be safe, a diode is also a good idea when using a coiled load, hooking everything up like this: Then just analogRead, and turn on the MOSFET based on some pre-defined threshold, you'd probably want to experiment. In my case, consistent readings over 150 or so is pretty dry and needs watering. This can get as complicated as you want to make it, so just ask if this didn't cover it. e: because the moisture sensor tends to corrode in the wet soil very quickly, especially when powered, it's better to toggle it on only when necessary mobby_6kl fucked around with this message at 17:58 on May 22, 2017 |
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May 22, 2017 17:21
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Hopefully this is the right thread, I figured it was more applicable than the home electrical one. In motorcycles or cars, if a connection is dirty sometimes it will melt the connector. The problem I have with the explanation "it has increased resistance" is that it's in series with the load, which increases total circuit resistance and drops current. So I modeled it with this:  14v would be my typical source voltage, 1.2 is a resistance so under normal conditions it draws ~10A. X axis is resistance and Y axis is wattage dissipated in the poor connection. Is this right or am I missing anything? Gonna Send It fucked around with this message at 14:54 on May 23, 2017 |
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May 23, 2017 14:38
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Katosabi posted:In motorcycles or cars, if a connection is dirty sometimes it will melt the connector. The problem I have with the explanation "it has increased resistance" is that it's in series with the load, which increases total circuit resistance and drops current. For one thing, not all loads behave as resistors. Some loads draw more current in response to decreased voltage (e.g the power supply for the ECU), or draw for longer periods of time (e.g. the brake pump). But that’s secondary to the real issue, which applies even to resistive loads. Dirty contacts will decrease total power dissipation, but power dissipation is greatly increased at the dirty connector itself. There is somewhat less current through it, but a much greater voltage drop. You’ve modeled this correctly. If the contacts are really really dirty you’d get to the region to the right of the peak. Nothing would work, but nothing would melt, either. Melting happens when the contacts are the right amount of dirty to end up near that peak. Platystemon fucked around with this message at 20:41 on May 23, 2017 |
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May 23, 2017 20:29
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