Watch crystals run at 32[.768] kHz because you can divide with a binary counter by 2^16 and get 1 pps to drive the Lavet stepper driving the seconds hand.
Watch crystals are also commonly used by MCUs for their RTC (real time, very low power clock), but never used to produce the main clock of a SoC or something like that. Mostly because that'd need an insanely high multiplication through a PLL (higher frequency multiplication ~ higher phase noise). Base clock crystals are typically 20-50 MHz.
Quartz crystals used to be hermetically sealed.
Are they sealed against helium though? It can get through a lot of materials that more common gases can't.
The sealing is mostly because of humidity. I wouldn't expect quartz crytals to be overly sensitive to some gas, since they're basically tuning forks; the crystal physically vibrates in a resonance mode caused by and inducing an electric current across the crystal.
"The sun makes energy by fusing hydrogen atoms, each with one proton, into helium atoms, which contain two protons. Helium is the byproduct of this reaction. Although it does not threaten the environment, it wreaks havoc upon the materials needed to make a fusion reactor.
"Helium is an element that we don't usually think of as being harmful," said Dr. Michael Demkowicz, associate professor in the Department of Materials Science and Engineering. "It is not toxic and not a greenhouse gas, which is one reason why fusion power is so attractive."
However, if you force helium inside of a solid material, it bubbles out, much like carbon dioxide bubbles in carbonated water.
"Literally, you get these helium bubbles inside of the metal that stay there forever because the metal is solid," Demkowicz said. "As you accumulate more and more helium, the bubbles start to link up and destroy the entire material.""
This led - in addition to lots and lots of eardrum-splitting workshop pranks - the occasional kids' party balloons being inflated with hydrogen. (As it was free, which He definitely isn't. HS&E be damned.)
A then colleague of mine claimed they'd cracked a window and caused instant panic at his son's birthday party when a bright spark decided to put a balloon to a lit candle to show the other kids it'd pop.
I doubt the cracked window (given a standard party balloon is pretty small - and a cracked window would likely mean lots of -ahem- eardrum deficiency in the assembled crowd) - but I can imagine it got the kids' attention all right when the balloon more or less exploded.
(We did crack a couple of windows in the workshop, though - you'd be amazed at the bang a litter bag filled with a hyd/ox mixture can produce if set alight.)
>you'd be amazed at the bang a litter bag filled with a hyd/ox mixture can produce if set alight.
Try a large garbage bag with oxyacetylene mix (do not try this at home).
Maybe I'll have to do some empi research one of these days - we do have a few bottles of oxygen and acetylene in the workshop at my current employer.
Hey ho, time for an engineer to pay our welders a visit.
Early Zeppelins used rubberised cotton for the gasbags, but most later craft used goldbeater's skin, made from the intestines of cattle
Edit: looked it up and yes, helium is smaller than atomic hydrogen.
Fairly standard technique to run the watchdog off the RTC clock, because that might still work if the main clock is wonky.
I said "historically" because I don't know is if these are still important issues on a modern system relative to all of the other things that are probably using the main system clock during sleep mode, and the more generous battery.
Hydrogen would be even better of course but it is rather dangerous when mixed with air.
They don't form compounds easily but there exist molecules containing at least xenon, radon. Even helium can be made to participate in reactions if pressure is high enough.
The noble gases have complete electron shells and are quite satisfied with themselves, not needing any bonds with anything else. However, the larger the atom, the more flexibility it has with how many electrons it can hide down the back of the sofa. Xenon is the largest non-radioactive noble gas, so it was the first to have a noble gas compound discovered. Fluorine is just desperate to acquire an electron to complete its electron shell, and will do it by whatever dirty tricks it can manage, which is why it is able to wrest one from Xenon's tight grasp.
This sort of thing (along with Derek Lowe's blog) makes chemistry interesting for me.
Edit: Never mind, all the nobel gasses.
Edit: apparently even helium can form compounds it’s just freaking hard to force it to play nice with others - https://en.m.wikipedia.org/wiki/Noble_gas_compound
You can find the formulas in a typical college chemistry textbook.
They don't - even knowing He is more expensive that H, because helium is better at leak testing than hydrogen is
Repeated bouts of guessing where the leak might be and trying to plug it (usually by welding or re-machining some part), cooling down, checking if it worked, warming up, ripping some more of your hair out, repeat.
Just having fun with your typo...
Added bonus: if the metals in question form chemical bonds with hydrogen, (titanium in particular) it will happily do so, even if it's deep inside the metal. The metal will turn very brittle very quickly if it's exposed to molecular hydrogen.
After debating late nights about whether to pony up for the new better-sealed clock, someone said "Screw it, throw it in the user agreement."
but don't trust me, see the "advantages" of manufacturers promotion https://www.electronicdesign.com/analog/look-inside-programm...
The air’s usual O2 concentration is ~20.5% and it looks like safety monitors trigger at 19.5% and 18%: https://www.pureairemonitoring.com/all-categories-gas-monito...
Helium makes up less than 0.0005% of air naturally. I’m guessing that increasing He concentration 1000 times to 0.5%, for example, is enough to cause problems for iPhones, but not enough to trigger the alarm or pose any danger to people.
That's why it seems like oxygen concentration monitors are a good idea for hospitals with liquid He. They don't really need to monitor helium levels since that's not the direct cause of problems. It's only an issue (but a big issue) if there's so much He released that it displaces enough air to meaningfully dilute O2 concentrations.
Our atmosphere does not contain mostly O2 and N2 in the middle, with a layer of CO2, Ar, etcetera near the surface. The sugar in a bottle of coke does not spontaneously sink to the bottom.
Likewise, if you release helium in air, it goes up first, and then (quickly) dissolves in the air.
The author's cavalier "I bet the nurse’s voices were higher pitched that day!" was incredibly inappropriate given the potential danger.
While technically correct in theory, in any real world environment Helium will not displace Oxygen unless you are dumping orders of magnitude more helium than in this scenario.
> Heliox still contains enough oxygen to breathe (at sea level it's 21% oxygen just like normal atmosphere, and when diving the partial pressure of oxygen is the same as oxygen in normal atmosphere).
There’s so much wrong with this (and the rest of your post) I can’t think of a polite way to respond, so I’ll just wish you a good day.
The point is to keep partial pressure of oxygen below that of maximum safe limit of 1.2 to 1.6. For example, 100% oxygen at surface is 1.0 and thus safe but will very fast reach maximum when you increase the pressure just by a few meters. Regular air with 21% oxygen will start to be a problem at 50 meters, so divers that need to go deeper need to use mixes that has less than 21% oxygen. When a mix is less than 18% oxygen they become hypoxic and cannot safely be used at shallow depth.
So the point is not to get "the same as oxygen in normal atmosphere". It is to keep the partial pressure of oxygen within safe limits, usually between 0.18 pp02 and 1.4 pp02 depending on a multitude of factors and safety margins.
If thier voices were rising, id suspect helium but would be worried that some reaction released hydrogen. Same squeeky voices but a serious fire hazard.
What makes you think you can’t (other than it being hypoxic)? You most certainly can breath Heliox, in fact, it has been used medically for almost 100 years, far longer than used for commercial diving.
In fact, Heliox would usually not be used for dives to 200m due to HPNS risk. Usually it would be Trimix for that.
Either way, GP is mostly wrong on the points they made.
The article I linked mentioned that O2 monitors are legally required for hospitals in NYC. That regulation might have been created because in 2000 someone working on an MRI machine died from a Nitrogen leak (it's also used for cooling and like He, the only risk is that it displaces O2). It's likely this person wouldn't have died if an O2 monitor was in place that sounded an alarm fast enough for the victims to leave the area. http://www.nydailynews.com/archives/news/nitrogen-gas-leak-k...
edit: googling a bit more found some interesting references on dealing with "oxygen-displacing gases". O2 monitors are on the long list recommendations/requirements. One thing I found interesting is that at one laboratory part initial assessment involves a controlled release of the maximum amount of gas that will be stored and then measuring the drop in O2.
Hospitals of reasonable size typically have an on-site clinical engineering team that handles those kinds of situations. Important (that is, capital expense category) hospital equipment will typically emit all kinds of warnings and alarms way before anything's actually a problem, because everyone would rather rely on the on-site engineering spending a little extra time silencing false positives then leave anything to chance.
> “An analysis of alarms at The John Hopkins Hospital, Baltimore, Maryland, revealed a total of more than 59 000 alarm conditions over a 12-day period-or 350 alarms per patient per day.1,2”
Alarms are mostly ignored or turned off.
Not for superconducting magnets they don’t. They may be involved with MR scanners somewhere, but that would be extremely uncommon.
"So, i noticed some of the workers' iwatch's weren't registering the users' heart-rates. At first, I thought it was because they had all died from suffocation from the massive gas leak. But, then I discovered something interesting... it was actually the helium molecules worming their way into the internal clock chip! Amazing day."
Nobody could adequately explain to those of us in the CS dept why we had to take 3 semesters of Chemistry. Bits of it hung on and from other sources such as space exploration articles I recall this much:
Fires and lungs both operate on partial pressure of oxygen. As long as nothing else in the air is toxic, your body cares that it gets X oxygen molecules per cubic centimeter of air in your lungs, not Y parts per million. Those deep sea submariners are breathing mostly helium with a small fraction of oxygen in it. If you just compressed surface air there would be so much oxygen that your hair would explode when you ran your hand through it. Assuming the electronics didn't burst into flames first. And if you didn't set yourself on fire, that much nitrogen would kill you pretty quick.
So the question is, does helium displace air or mix in with it? I believe the answer is 'some of both'. If that's the case (and I think we can infer that from "the alarms didn't go off") then a good amount of helium might reduce the oxygen partial pressure less than going to 3000 feet above sea level. So what's the Venn diagram of COPD sufferers, in a hospital wing near the MRI machine, that aren't currently on supplemental oxygen?
Even outdoors, large amounts of CO2 tend to sink to the ground and suffocate people in low-lying areas. Look up Lake Nyos for a particularly grizzly example of that.
I meant that it's disturbing that the amount of He needed to disable the iPhone is low enough that the standard sensors around He (which measure 02 levels) don't regard it as a major leak for He to be at that level.
Presumably, the sensors exist to protect humans, not electronics.
Yes, I'm allowed to be disturbed by that; why wouldn't you be?
The devices are tested for usual STP. Nothing else, unless specified. They are done so not for human comfort, but for tested conditions. No more.
If you want extreme conditions, pay through the nose.
In addition, unlike carbon monoxide, helium doesn't bind to, well, anything and certainly not hemoglobin, so it doesn't present a momentary exposure hazard either.
> Yeah, but at the same time, it wasn't enough to set off the alarms for low oxygen content, which is at least a little disturbing, right?
First, alarms for low oxygen content are set for people and no other reason. There can be alarms for high oxygen content, but they are extremely rare and would likely not be present in very many places in a hospital.
Second, why in the world would low oxygen be a danger to an iPhone?
You can't make a complete non-sequitur of a logic leap and then expect everybody to be on board your train of thought.
Furthermore, comments were rolling in assuring me of the nonthreat to humans after I clarified.
And yes, I get it, the sensor exists to detect for threats to life, not threats to iphones. But that's the point: this is a threat we're not set up to watch for at all -- hence why it took so much investigation to root-cause it!
Are you still going to make it your hill-to-die-on that it's "not disturbing"?
Come to think of it, did that "lack of faith" scene in Star Wars (1977) also seem confusing to you?
You totally misunderstood my comment.
I mentioned popping a party balloon because it could also disable your phone. And UV light because it can also destroy certain electronics. But sensors that can pick up little bits of UV are normally not set to warn about it, and that's perfectly reasonable and not "disturbing".
We can use a different word if you want. You think it's a [significant] problem and I don't think it's a problem. Is that better?
I'm not here to die on the hill of word choice. I disagree with your underlying opinion.
What made it unnoticed for so long was that it required the much larger MRI He release to trigger. What (I claim) makes it disturbing is that an expensive incident can happen (bricking a hospital's iphones for weeks) at levels that no one currently calibrates sensors to check for, because no one expects that level to have a negative effect of such magnitude.
Regardless of your preferred terminology, it seems odd to take an attitude of "oh, it only deleted everyone's second-brain for week, in a way that was hard to root-cause, no one died, no big deal" and therefore balk at the use of "disturbing".
I mean, do you consider undetectable, inexpensive phone-bricking techniques to be generally "non-disturbing", or just this one?
Some of the tests were just plastic bags with tiny amounts of helium in them. Unless you're asserting some exceptionally strange gas physics here, you can break an iphone with some balloons.
> Regardless of your preferred terminology, it seems odd to take an attitude of "oh, it only deleted everyone's second-brain for week, in a way that was hard to root-cause, no one died, no big deal" and therefore balk at the use of "disturbing".
> I mean, do you consider undetectable, inexpensive phone-bricking techniques to be generally "non-disturbing", or just this one?
Hang on. You were calling the calibration of the air quality sensors disturbing. That's what I objected to. I wasn't making any claims about the iphone bug itself.
Ideally you would pressure test and purge new work with nitrogen as well in order to prevent a potentially combustible mixture from forming inside the pipe while the air is being purged from it.
As to the safety of purging natural gas directly indoors, obviously that carries some risk but it's not as dangerous as you might assume. Below a certain concentration (5% by volume) natural gas mixed with air actually won't burn freely. Also above 15% natural gas by volume won't burn freely. The risk of an explosion is only present in that 10% range. If you're putting in a new gas stove in your kitchen and you crack open the valve with the hose off of the stove until you smell gas, that's not a ton of natural gas that you've let out into a room with a relatively huge volume. The pressure of a natural gas pipe in a house is actually very low, only around 0.25 psi. It's coming out slow enough that you've got plenty of time to turn off the gas before you come anywhere close to hitting that lower explosion limit where things get extremely dangerous.
I discovered that the helium leakage occurred while the new magnet was being ramped. Approximately 120 liters of liquid He were vented over the course of 5 hours. There was a vent in place that was functioning, but there must have been a leak. The MRI room is not on an isolated HVAC loop, so it shares air with most or all of the facility. We do not know how much of the 120 liters ended up going outdoors and how much ended up inside.
I've seen multiple vents of ~1500l of liquid helium (~1,050,000l of gaseous) in a single day from a couple bad MRI units when I worked at a company that makes them
Only "dangerous" place to be was in the fragmentation path of the burst disc (which was enclosed in the top of the unit (at the time)), or directly in the path of the nearly-liquid (ie extremely cold) helium as it vented
It dissipates extremely rapidly
But there are plenty of things to help you out here. First is that helium is very light. So if you pass out and fall down you will be in a lower concentration of helium (assuming you are not in a sealed room). (Labs with heavy gases have vents on the floor) If the room is reasonable ventilated you should be fine. It dissipates fairly quickly. Helium permeates through most things, but this is a slow process so probably won't save you.
Venting even a full MRI's worth of LHe (~1500l) as most will make you a little lightheaded for a few minutes
The risk of death from quench events is effectively non-existent
Other posters have pointed out that this is false(you will continue producing CO2 while unconscious just fine, chemoreceptors will notice).
I would like to add that I have personally witnessed people falling unconscious from helium. They recovered just fine.
Really, the greatest danger is the fall.
If you displace 30% of the atmosphere with helium, the O2 concentration drops from 21% to 15%. That's low enough that you'll probably start to see mild cognitive impairment, but it's still plenty capable of supporting life. However, a 30/70 mixture of helium and air is about 67% as dense as normal air, which means voices would be pitched more than half an octave higher.
Sadly my immediate reaction to this post on /r/sysadmin was to discount it, or rather attribute it to some external factor that nobody could possibly figure out and entirely unrelated to the MRI. In this case I was quite happy to be proven wrong by the follow up posts and subsequent article.
I'm really curious why something they can generalize to "helium leaking into the quartz oscillator" only affected Apple products. What feat of manufacturing keeps a broad range of OEMs safe on the Android side but so eludes Apple? Worse yet, was some "cost savings" engineered between iphone 5s and 6 that ultimately introduced this issue?
The other phones involved still used quartz.
"But quartz oscillators have some problems. They don’t keep time as well at high (and low) temperatures, and they’re a relatively large component—1×3 mm or so. In their quest for smaller and smaller hardware, Apple has recently started using MEMS timing oscillators from a specialized company called SiTime to replace quartz components.
Specifically, they’re using the SiT512, 'the world’s smallest, lowest power 32 kHz oscillator.' "
So it was size, not cost that led Apple to be using a susceptible component.
Every time my colleague brought his phone to the control room the Cellular stops working for like a day or two, but my 6s worked just fine anywhere even next to a Dewar that's venting Helium. Now the mystery is solved!
BTW, among us there are others who accidentally brought their phones near or even into the MR bore during maintenance, but none of these devices has done any permanent damage to our phones, except one accelerometer on a cheap Chinese phone, even in a 7T magnet. So I never thought that MRI could be causing the problem.
That said - a 120l leak of liquid helium is both stupidly expensive, and highly damaging to the MRI unit: there's a bath of ~1000-1500l of liquid helium in an MRI to keep the superconducting coils at superconducting temperatures. Losing ~10% of that volume probably means the unit won't work
Nope - well, not with any of the ones with which I am familiar: they're shipped full most of the time
Also, this could be a potentially catastrophic tool for terrorists. As trivial as it sounds, it's even worse than a traditional frequency jammer because it renders the device unusable instead of just not being able to communicate with the outside world.
Edit: On the other hand, interesting counter-terrorism tool as well. Is there any precedent for the CIA using this sort thing intentionally?
Liquid helium is rather expensive and would likely draw attention in areas where it's not usually handled. Really doesn't sound like a useful terrorism tool.
I think the infamous Thunderf00t does a decent job of explaning why https://www.youtube.com/watch?v=l6uLUaqgWY0
120 liters of liquid helium is a lot, but it wasn't released at once but over a longer time as far as I understand the story.
One of our multi-practice facilities is having a new MRI installed and apparently something went wrong when testing the new machine.
Say I scored a big truckload of helium, 5000 l. (The contents of my tank will expand to 3750 m3 of He gas.) Then I got access to a ventilation duct into the subway. I manage to hook up my tank and start depleting into the subway. Assuming 20 m2 cross-section for a tunnel: if I could do the emptying at once, I could fill 0.187 km of tunnel completely with He; killing all vermin in that section.
But hey my goal is not to suffocate (that would be boring, right?) but to fritz electronics. So I do it slow and steady into a station. Say I want to keep the concentration of He in the station at around 0.1%. (I assume it would take time for operators to detect this. I don't know how sophisticated gas detection is in subways.) Let's assume an airflow of 5 m3/s into that station. I'd need 0.005 m3/s He or 400 m3 per day to keep the level at 0.1%. So for only one day, I'd need to get around 500 l liquid helium into position.
There are easier pranks to play.
Or if you are some kind of compressed gas terrorist, 5000L of compressed oxygen or acetylene will do a lot more damage than helium.
Anyone who can mount a helium attack can mount much more severe attacks.
I think the probability of some eccentric and well-supplied terrorists trying to ruin Apple devices with helium is so remote as to not be worthy of consideration.
Even if it does come to pass. Oh well, I'll buy another iphone, or an android.
About 3000 people died on 9/11, but we acted like it was the next Pearl Harbor. These 3000 people died needlessly, and it sucks, and my heart goes out to the families who lost someone that day, but statistically was a tiny blip.
9/11, as an act of terrorism, was successful. We now can't get out of the Middle East, it caused a decade long economic depression that snowballed into the housing crash, it ruined our relations with other nations, and hating Muslims is the ordre du jour like it is 1099.
It is, but only in the same sense that a van in the wrong hands could be potentially catastrophic.
A bit of googling on MEMS RTC revealed this slightly dated article which I thought was still interesting: https://www.maximintegrated.com/en/app-notes/index.mvp/id/55...
Turns out one of the main reasons to switch is for the smaller packaging vs quartz oscillators.
But an electromagnetic pulse would have taken out medical equipment in the facility as well, and they were working fine!
I suspect medical equipment is designed to a higher standard of EMP resistance than most other products, especially equipment designed to sustain life. Phones also have antennae specifically designed to pick up EM fields, while medical equipment like an EEG or ECG is specifically designed to reject them.
Likewise, the devices "reviving" after a week is not unusual if they're just resetting due to power loss. Immediately disconnecting and reconnecting the battery would for sure differentiate between helium (device remains dead even after reset) and EMP (device reboots successfully.)
They must have some seal in place and fortunately our air is Nitrogen, O2, and a little bit of Argon. These can’t get through the seal! Helium is only found in minuscule amounts naturally and apparently this concentration is so low it doesn’t matter.
Helium is special because is it has the smallest kinetic diameter of all the noble gases. You can compare its diameter to other gases here: https://en.wikipedia.org/wiki/Kinetic_diameter#List_of_diame...
Helium is frequently used in leak tests since it has a way of working through even the tiniest of leaks. Elemental Hydrogen is of course smaller, but I believe you only find Hydrogen as H2 which is a larger molecule than Helium.
Does that mean that water (in some form) also acts like helium and would be able to get through that seal?
While water’s overall charge is neutral, its charge isn’t distributed symmetrically ans tbis makes it a rather polar molecule. This means part of molecule have different charges which leads to attraction to other water molecules thanks to van der waals forces. Basically water naturally clumps up and won’t squeeze through tiny holes even if it’s kinetic diameter would technically allow it. (Though I believe very high pressure can force it through)
Water’s polarity is what causes surface tension and droplets! For comparison, gasoline is relatively nonpolar, though not as nonpolar as He. If you’ve ever spilled some you can see it spread out immediately and avoid the droplet formation and cohesion you’d see with water. Similarly, water tight containers might not be gasoline tight. (but don’t test this out...)
To correct my comment from earlier:
Helium is special because of its small kinetic diameter AND because it’s naturally found in a monoatomic and nonpolar form, as are all noble gases. This lack of polarity leads to minimal intermolecular attraction that would cause clumping and limit flow.
(I found a reference that helium can be measured flowing through a 1.0nm hole, albeit at a very low rate. I wonder how close to the 0.260nm kinetic diameter a hole can get for He to still flow)
Helium's is 260pm or 0.26nm so that could be the limit. But the actual atomic diameter has a couple different calculated and observed values from 31pm to 140pm so maybe it could fit through holes around that size? My guess is we don't have the technology to make a hole of precisely that size or even measure a single He atom passing through such a hole. Would probably have to find a real expert to know if it's theoretically possible.
It's really hard to contain helium. It'll leak through pretty much any solid material.
That is exactly the case. From the article, helium (and to a lesser degree, hydrogen) have very very small molecules and are able to slip past very small imperfections in hermetic seals.