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I worked at a television station years back that was designed in such a way that the lights going up the tower were powered by the separate phases of three phase AC with the one at the top powered from all three combined. This was pretty normal but what the engineer had done was rotate them at every level so that if a phase was dropped you could count the lights and quickly see from a distance that the power wasn't right. 4 lights was good, 3 meant you dropped a phase, and so on. I thought it was a pretty clever way of keeping light on all sides of the tower while being able to tell from a distance that a phase was out.
This is best practice for anyone who uses three phase power.
A machine shop should connect 1/3 of their lights to each phase so it is immediately obvious if a phase gets dropped. Lots of equipment will suffer on two of three phases but with lower performance or even damage.
> This is best practice for anyone who uses three phase power.
No, it’s not. It’s a neat trick that visually reveals when the utility drops a phase, but there are better ways to handle avoiding equipment damage.
Best practice is to use phase monitoring relays that can de-energize a motor when a phase is dropped/reversed to prevent damage. The trip time is adjustable and it’s more reliable than manually hitting an e-stop. It also won’t let a motor with incorrect phasing start up either. You see phase loss relays on a lot of compressor motors and other large motors.
I was told that you want lights on all 3 phases so that you can see spinning things spin. If the lights are on single phase, they will dim 120 times a second, and the strobe effect can cause spinning things to appear stationary. With 3 phase, at least 1/3 of the lights are lit all the time.
That's a valid reason too. In an industrial environment full of rotating machines, thinking something is stationary because it's on the grid's natural frequency can be lethal.
It's way less of a problem with modern machinery, and leds will blink in uncorrelated phases in a frequency that is different from the grid's anyway.
For residential lighting running off a single-phase supply, there are some annoying LED bulbs with simple half-wave rectification that strobe at the grid frequency with less than a 50% duty cycle (often seen with bulbs emulating vintage exposed-filament bulbs with no frosted glass). It would be interesting to see how much less annoying that kind of flicker is when you have a three-phase supply to a light fixture, so that at least one set of LEDs was illuminated at all times.
There are no light fixtures that use three-phase power. At least that’s my belief, as I’ve never heard of one or seen one and I’ve been working in the electrical industry for almost a decade. You could theoretically arrange three lampholders like a delta or wye transformer [0] and connect a phase to each one and all three lamps will be lit, but the lampholders will be energized, so make sure to wear voltage-rated gloves when changing out the lamps ;) This is how three-phase resistive heaters are wired, the drop in ampacity and large resistive heating loads make it worth using three phase since ampacity is 1.73 times lower than it would be on a three-phase circuit than it would be at the same voltage as a single-phase circuit.
In the US, there are 208V single-phase and 480V single-phase lights that use two of the three phases. In practice, indoor lighting is either 277V (line to neutral on a 480V service) or 120V (line to neutral on a 208V service). Most commercial LED fixtures can use any voltage between 120V to 277V single-phase.
480V single phase is used for some pole lighting with long runs of conductors to handle voltage drop. Anything over 277V has to be elevated at least 22 feet off the ground per the NEC.
Back in the analog TV days, I could see the flicker on the 50hz PAL/SECAM signals whenever I visited Europe, especially when the screen was white and in my peripheral vision. I always wondered why it didn't drive everybody nuts, but then I got used to it. I did always wonder if there was a way they could have eliminated that (maybe they did in more expensive TVs that fired off at double the reference signal and not in cheap TVs in hotels/bars?).
The 100 Hz TVs weren’t that common and had other issues. They weren’t strictly superior. TVs were supposed to use a different set of phosphors for 50 Hz that were less flickery at 60 Hz but in practice I don’t know if tube producers bothered to have different sets for the different markets.
simple answer is grid frequency in europe is 50hz, in the US and Canada it's 60hz.
Early TV's synchronised to the grid frequency (and drew the entire screen on each cycle) - also remember TV's where analogue to start with (and operated at large voltages/transformers) so if they didn't sync with the grid electrical noise becomes a big problem with the power supply.
Are/were there 3-phase fluorescent tubes available?
Or are we relying on the spinny-thing that is to be observed to somehow be illuminated by all three phases, with three lamps or fixtures, simultaneously? Without such malarcky as shadows or inverse-square to muddy our vision?
Or maybe a multiplicity of single fixtures with 3 tubes -- one tube per each phase?
And even then: Doesn't it still strobe somewhat at (50*3*2)=300 or (60*3*2)=360Hz, instead of the 100- or 120-Hz that a shop lit by a single phase might provide?
(LEDs are out-of-scope of this question, of course: Line-voltage LED lamps can have integrated electronics and can therefore have diode elements that are driven by things that approach [or even achieve] DC, which changes the rules.
And, of course: Incandescent lamps have enough persistence that stroboscopic effects are generally not an issue with a human eye.)
You typically connect 1/3 of lamps on one phase, one third on another and so on.
In the UK we use a 230V single phase system for most things (industrial/commercial often use 400V) (if all three phases are in use it's 400V - you may see it as 415V but we harmonised with Europe to 400V) so lighting expects that 230V anyway, you still have a common ground, you just run the live for each phase to the lamp/light.
Power delivery to homes is in effect a single phase out of a three phase supply with each house (often but not always) wired in sequence, so house 1 is Phase 1, house 2 is Phase 2, house 3 is Phase 3, house 4 is phase 1 and repeat.
We have standard colors for this as well (as do most jurisdictions), neutral is always blue but the phases are Brown, Black and Grey
When I trained as an industrial electrician they where different colors, they changed in 2006 so that just makes me feel old (used to be Red, Yellow, Blue with Black for Neutral).
> We have standard colors for this as well (as do most jurisdictions), neutral is always blue but the phases are Brown, Black and Grey
Never even thought about the fact that different regions may have different colour standards. This explains some of the power cables I've torn apart over the years and the strange colours I found inside!
> When I trained as an industrial electrician they where different colors, they changed in 2006 so that just makes me feel old (used to be Red, Yellow, Blue with Black for Neutral).
Making a mental note of that one... a black neutral would be a nasty surprise coming from North America.
Indeed, half my house is blue/brown, the other half is black/red since reg changes where grandfathered in and the wiring has been added to (some places clearly by a knowledgeable individual others..not so much).
I spent the first day after we bought it and moved in going around with a screw driver, side cutters a notepad and enough swearing to make a pirate with Tourette’s blush.
It’ll need a full rewire at some point, while I can do it myself to a commercial standard our regs require a currently qualified electrician sign off (mine expired many years ago) so I’ll just pay someone to do the lot.
It’s annoying but I’ve seen enough horror shows to see why it’s nescessary.
> Or are we relying on the spinny-thing that is to be observed to somehow be illuminated by all three phases, with three lamps or fixtures, simultaneously?
That's exactly what they mean, yes. Some lights on L1, some L2, some L3.
> And even then: Doesn't it still strobe somewhat at (5032)=300 or (6032)=360Hz, instead of the 100- or 120-Hz that a shop lit by a single phase might provide?
No, because the phases are overlapping, there is no point in time where they're all off. There'd be local dimming of course, depending on their position etc., but light for all of the second.
They're saying that you have 3 banks of lights, each connected to one phase of the 3 phase input. That way, when only 1 bank goes out, it's easy to see that one phase is out.
At work we run a lot of machinery with motors and its obvious when phase loss happens. From my office I can tell if the lights go out/dim and the usual shop "hum" becomes a buzzing grunt that is immediately identifiable. Older machines have to be manually powered down but the machines I rebuilt have phase loss protection in the PLC thanks to a power monitoring terminal in the IO (Beckhoff EL3453.) Since the PLC is on 24V DC I have a capacitor backup module fronted by a 24V PSU that takes the 480V three phase power which tolerates a phase loss. The machine safely stops the process and shuts down the pumps and any other AC loads, then waits to be manually powered off as the PSU and DC side doesn't care.
Clever! I know I talked to the folks at Masterclock in St. Louis recently about one of their clock displays; they intentionally default the separators to flash if the clock is not synced to NTP, and then they go solid once the connection is established.
It's a quick way to know if something is down, using context clues that are already there to begin with!
Jeff, it's very cool to hear from you as I have enjoyed your videos for some time. I would like to make one request though. Next time you do a project like "How I almost broke MrBeast's Ages 1-100 video" that involves setting up interactive electronics for an event, you should really call me. I managed interactive technology deployments for the automotive marketing industry for over a decade. It's a niche that has unique challenges which you fell face first into. I would be happy to help make things go much smoother should you ever do something similar. Proof: https://imgur.com/a/5z5JrwT I'm also on Reddit, same screen name if you want to dm me there.
Can someone explain to me how this is different than a simple noise generator based on a PN junction? As in, isn't this just amplifying noise and aren't there less sensational ways of doing nearly the same thing? Does measuring a photon with this method actually get you better randomness? I have some serious gaps in my understanding here and an ELI5 would be neat.
> Although there is only one electronic transition from the excited state to ground state, there are many ways in which the electromagnetic field may go from the ground state to a one-photon state. That is, the electromagnetic field has infinitely more degrees of freedom, corresponding to the different directions in which the photon can be emitted. Equivalently, one might say that the phase space offered by the electromagnetic field is infinitely larger than that offered by the atom. This infinite degree of freedom for the emission of the photon results in the apparent irreversible decay, i.e., spontaneous emission.
I've been told that reverse shot noise from a PN junction is quantum in nature.
It is possible for an electron to spontaneously gather enough voltage to break through a PN junction backwards. This shows up as a very noisy current measured in microamps.
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A forward bias PN junction might not be quantomly random. I'll have to research more. But a reverse bias PN junction is almost certainly quantum in nature.
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IMO, this is all just PN junction noise. Maybe LEDs are better than Zener diodes for noise. I'm pretty sure that noise characteristics are a guess and check methodology, it's all PN junctions of slightly different shapes after all.
The question is whether quantum mechanical noise could have a conceivable advantage over classical noise. I strongly suspect: no. Classical noise is already factually unpredictable, so the theoretical unpredictability (assuming no hidden variable theories I guess) of quantum noise doesn't add anything.
Classical noise is only unpredictable if you are lacking the necessary physical information to make an accurate prediction. Otherwise, it is always predictable.
Quantum noise is not based in any kind of physical information in the same way. It is intrinsically random. The "randomness" isn't merely a side effect of a bunch of physical phenomena. You cannot compromise a QRNG even if you had perfect knowledge of the state of every particle in the system over time.
> Classical noise is only unpredictable if you are lacking the necessary physical information to make an accurate prediction. Otherwise, it is always predictable.
Since you are always lacking that necessary physical information, it is always unpredictable. If it were otherwise, we would already know whether hidden variable theories of quantum mechanics (which lack intrinsic randomness) are correct or incorrect. But we don't know that. So intrinsic randomness doesn't make a difference to us. So quantum noise is useless.
I'm sure I'm overlooking something, but what's the real use-case for true random number generation at that fast of a rate? Even a few Kb/s of random numbers is enough to continually reseed a cryptographic pseudo-random number generator that will generate as much output as you want that's indistinguishable from true randomness. I suppose you aren't reliant on the security of the underlying cryptographic primitives then, but you're still reliant on the particular hardware RNG chip being implemented in a way that's free of bias even if the underlying physics principle is sound.
I thought "Willy Wonka-esque" was tongue in cheek, but they have a yellow brick road leading up to the front door... absolutely bizarre
Those who want to escape the office altogether, can hop on one of the company’s 600 cow-print bikes to take meetings from a treehouse, slide down a rabbit hole or grab lunch in a train car.
I've been to that campus. Never worked there but I got a tour when I was like 18 and it seemed like a cool place to work at the time. They clearly took a page from Google's handbook. Its like a giant adult daycare center.
Their hiring is insane too. Years ago I applied for a Sys admin I position. After 3 rounds of interviews, they gave me a test to take. Except it was something you'd give a senior dev. They specced out a fake language, super esoteric too, it was like a combination of brainfuck and assembly, and asked me to solve problems with it, and debug code written in it. I could have toughed my way through it, but I was so dissatisfied with how much of my time they'd already wasted that I decided I didn't want to work there.
I did one of those once and quickly found out that any display of personality was interpreted as an incorrect answer. It was made clear by the totally unrelated follow ups. I'd like to see the turn over rates of any company that implements this crap.
State-of-the-art for what could survive space. It used 486's for quite a while. You are still very correct, I just think it's funny that the "best" is not always what people think.
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