How smoke detectors work
ฝัง
- เผยแพร่เมื่อ 5 มี.ค. 2011
- Bill takes apart a smoke detector and shows how it uses a radioactive source to generate a tiny current which is disrupted when smoke flows through the sensor. He describes how a special transistor called a MOSFET can be used to detect the tiny current changes.
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That got technical real quick.
That's how I like it
As an engineer, I truly appreciate the level of detail in this video. As technical as it all sounds, its actually a rather simple design.
For the people who cannot comprehend, just think about the smoke as a genie that flips a magic switch inside a circular box on your ceiling. When the genie (smoke) appears you're either in trouble or annoyed.
Didn't sound simple to me.
Are you kidding? This is like pre-preschool level stuff, in the engineering world. (That is, if you are a fairly competent engineer.)
But it is simple. Basically, it's two circuits working to interfere with the other.
1. Circuit A is designed to sound the alarm.
2. Circuit B is designed to stop circuit A from working.
When smoke enters the system, it interferes with circuit B, making it unable to stop circuit A from working, thus allowing it to sound the alarm.
Sounds like you, are not
drkjk took a condensed matter and analog electronics course, it was pretty well explained.
There are other types of smoke detectors as well: they are build around the effect that smokes disperses light. So if you have smoke detectors like he does, they would have light rays inside which are pointed (sometimes via mirrors) at a photo sensor. If the intensity of the light that reaches the sensor drops the smoke detectors "says" alarm.
Another type of optical smoke detectors analyzes the amount of laser beams that are being reflected back into the emitter. Same logic, if the amount of laser beams that are coming back drops there should be smoke between the emitter and the reflector. The last method works even at greater distances up to 100m.
By the end my eyes had glazed over and all I could think was, "wat".
***** From the beginning I was completely fascinated.
+Chiki McBallin By the end I was completely confused.
+adizmal amen, brother
+adizmal Yep, the tangent into a MOSFET obscured the original point. The relevant point seemed that this type of transistor was a key to detecting the tiny change in current, that the MOSFET and the ion-based detection scheme worked together to make a very tiny change be reliably detectable. The older bipolar type of transistor doesn't have the sensitivity to work in this case.
gblargg .........wat
As an electrical engineer thanks for this video, and I want to say everyone interested in the slightest bit should take the opportunity to learn some electronics. It has become even easier and accessible in the recent years to learn electronics. There are a plethora of great introductory books written for all ages. If you have ever wanted to know how a computer really works or learn electronics, I recommend getting into it as a hobby.
Hey! email me at. I would love some more advise. Dsilvaroyed70@gmail.com
I clicked on this video while I had some food cooking and had the volume full blast. I immediately ran to my kitchen
I opened this video with high volume too but I had headphones on. Not a pleasant experience.
same here lol
I turned my volume down to 10% of usual before loading it, because I knew it was coming - and it was still bloody startling!
Countless hours mucking with redstone gates has allowed me to understand what just happened lol.
Same lol
relatable
newonaginnalf When they say Minecraft is for kids only
@@w5527 When it comes redstones, it can become educational regarding electronics.
One of the most concise explanation (that doesn't exclude any crucial details) for how MOSFETs work
With your demonstration, it took me 5 mins to learn hos a smokedetector Works. Tnx Bill 👍😊
the only yt videos where the annotations are actually useful instead of annoying.. thanks for keeping it that way Bill! :)
Agree!! engineering at its best, simple, reliable, and inexpensive stuff that helps people, great words Bill.
Very smooth explanation.
I must say, I thoroughly enjoy your well-thought-out responses to questions. The fact that you answer questions period, choose the best ones which people will likely have, and answer them in a full yet concise manner demonstrates an absurd amount of rational thought. Well done sir, well done. You.. are approaching Bill Nye territory :)
Bill,
Great work! It's nice to see quality educational videos on TH-cam.
Thank you,
Steven
This reminds me of the "Radioactive Boyscout" a kid who in 1994 managed to build a nuclear breeder reactor using radioactive material from smoke detectors and old clocks!
Science is awesome!!!
I hope Mr. Engineer Guy is planning on making more videos. :)
seriously when those diagrams started displaying i was like WHO, WHAT the hell. confused. i had to pause and call my brother who explained them to me. nice diagram. my brother loved it
Thank you for reminding how stuff works in a simple way! Definitely will show it to my kids!
Always get a kick out of your videos, Bill. Thanks a lot.
My god, you make everyone smarter in less then 4 minutes with everyone of your videos.
i lost
I just love the background music.
And the show itself, of course.
The videos are fantastic ... Thank you so much!
thx for video... is very nice this simply design of MOSFET and it helps to understand better the construction
Typo: Simplied Circuit
Should be Simplified.
Otherwise, wonderfully informative video. I learn something new every time you post a video.
All of your videos are really great! This one has me looking deeper to learn more about base knowledge of electricity and electronic circuits so I can actually understand this video completely. Do you have any good resources I should look at?
Damn, I was asked this exact question a week ago. I was struggling to explain the specifics. If only I'd consulted TH-cam.
Nice vid.
Good work Bill!
It's amazing they are able to make it so reliable, im surprised they aren't beeping all the time due to random chance
Wow.....thanks. I've always wondered how smoke detectors worked. Thanks!
*This channel never disappoints.*
Bill Hammack is amazing.
I really learnt something, well invested time.
The same device principle applies to photoelectric smoke alarms as well but with an LED and photodetector or photo transistor in place of the ionization chamber.
I have a reasonable understanding of circuitry and I still had to re-watch some of this to fully grasp the concepts.
🤗Wonderful presentation Webster... 🙄🤔🥽🧬🧪📝2️⃣✖️7️⃣
Can you elaborate more on the voltage source for the detector?
This is 100% more informative than how its made
ty this help my project on engineering do you mind if i show this vid in class? pl
this guy gives extra credit to engineers, i mean we ALL are grateful for them, but understanding what they do give it much more value.
pretty much like art, you appreciate its beauty (usefulness on engineers) but it has more value when you comprehend the process of creation.
I get the weirdest happy nerd smile every time I watch one of these vids. So smart it's hypnotizing!
Nice video.. Another version of the same pupose detectors use beer lambert law for smoke detection
Should the resistor not be 1GOhm in order to counter the 4.5 V battery ?
Would placing the alarm in an atmosphere of pure Helium also trigger the alarm? as there would be no formation of ions to complete the circuit?
A link to this playlist should come with every purchase of pot
This video committed a cardinal sin: playing the sound of a smoke alarm at a loud volume with no warning
I think it was only a venial sin, but we did learn from this video how many of our viewers use headphones and so changed our practice accordingly.
1:54 That's what a diode does? Man I was so confused on my phys exam talking about the current flow in diodes. Intresting to learn about it now.
Thank you for you explanation and very nice video. I think there is a small imperfection on your circuit diagram: for the detecting part it should be a constant current source across (100 pico amo like you say) and you use a battery symbol there which is constant voltage.
Lol I was scratching my head at that circuit diagram, too. Thanks for clarifying.
So, unless I'm misunderstanding, if current flows through the ionizing detector when the air is clean, then very little current will be going through the resistive divider, and therefore the gate voltage will be low. Since this is a PMOS device, that means that there will be current flowing from source to drain.
If there is smoke, very little current will flow through the detector, and most of it will pass through the resistive divider, pulling the gate of the MOSFET high, stopping the flow of current from source to drain.
As for the signal going into the electronics to signal the horn....
Clean air: 4.5V
Smoky air: 0V
A wonderful and educative video. Thank you!!!. The Planetary Society of Patagonia, Argentina.
That very interesting. I've always been wondering about this.
@engineerguyvideo,
Okay, thank you. How much did your smoke detector cost?
For photoelectric ones, they use an infared beam and a infared sensor, when the smoke gets to the detector, it cuts the infared beam
In this video, you actually helped me understand how the power section of high wattage automobile amplifiers work LOL. You know, the ones that have the word MOSFET on the outside, like any average person would know what it meant. LOL I know it's an actual semiconductor device, but I feel they use it as a marketing ploy.
@sharrynuk His explaination was simple, but it gave the basic idea of a MOSFET. If you have done any diode and MOSFET analysis you will note they have very similar reactions from the p-substrate to the drain/source. In fact the energy band diagram for a MOSFET in depletion involves the same structure as a diode.
@PCFPSGamer @engineerguyvideo yes but now they have ones that only go off when they detect thicker particle disruption ie smoke.
Does that mean that a smoke detector alarm could sound during say, a sandstorm? Or any other event that could release a fine particulate?
Bill,
Thank you for one of the BEST explanations of a MOSFET and how it works. I have been a ham for 55 years but still am amazed at how those tiny thingies work. Just had a MOSFET blow (or was defective) in a QRP transmitter (IRF510) used as as a polarity protecting device and had to ask for help in learning its function. Also using an IRF510 as a final for up to 5 watts output, so they have many uses. I finally replaced the defective one and things are good again. Also, am impressed in how smoke detectors work and check them at home and at my kids regularly. They are so ubiquitous that many folks forget about checking them until the battery goes weak. I see now that many have a 10 year battery and it is not replaceable, just replace the whole unit.
Dave K8WPE
Awesome stuff!!
delicious and nutritious ... I love these and I loved the detail in this one (admittedly, I am a physicist)
Bill, we have five A/C powered smoke detectors wired together. When one triggers, all sound the alarm. Through the years we have had one of these malfunction, and I can't tell which one is generating the false alarm, because all make noise. Making things more complicated, it's hopelessly intermittent, usually on a cold evening when I suspect dew is forming. Can you help me to decide which is the detector causing the false alarm? I have a multimeter and an oscilloscope.
Its a very good video. I would like to do a video about intelligent smoke devices in commercial applications. 120 smoke detectors wired together on a single pair of wires, plus, minus and data all on one. Its part of the BACnet protocol. Then when a smoke detector alarms, the main control panel (micro controller with RAM and ROM) determines the exact location of the alarm and signals the appropriate signalling devices, fan shut downs, elevator sequence, fire department dispatch etc. I will accomplish all of this with an arduino micro-contoller. It will take me a bit of time to produce this. I started about a month ago.
How does the test function work? Does it just test the horn, or the electronics as well?
it just tests the horn. not the electronics.
Some will interrupt the smoke detector current and allow the alarm circuit to activate. Thus when you release the test button , it take a moment to silence the alarm.
Hello, do you have any idea like how to work other kind of gas or smell detector? Or can we change the idea or parameters to find out other molecules or element under this technic?
How quickly it detects the smoke? Can the smoke firstly sufficate sleeping person before it reaches the smoke detector?
Ok so i worked for a painter and sometime we to sand the drywall after patch. My boss would freak out if we sanded near a smoke detector without covering it. Is it possible the to set off the alarm with dust or other particles other then smoke? I kinda thought he was crazy but he might be right
This guy is awesome! Hope we see even more like him :)
try Technology Connection, their style is pretty similar
Awesome!! Thank you very much!
Thks ,easy to understand
I do too! there's crazy advanced science in the most unassuming things. Like smoke detectors!
that ratio of the small resistor in series with the 45 MOhm resistor is important because it creates a voltage divider; the current source of 100 picoAmps times the 45 MOhms matches the source voltage from the battery.
I get 45 10^9 Ohms x 100 10^-12 A=4.5 V, so should it not be 45 GOhms ?
so say if you would vacuum all the air particles out of a space wit a smoke detector, would the alarm go off?
@TheJonititan Some detectors use optical detectors to sense the smoke, but combustion products at first may not have any visible smoke, so the gases kill you and, while it does, you can plainly see your alarm clock to note what time you are dying. :-)
so because when the battery is running low, there is not enough of a current running between the two electrodes causing the alarm to go off?
I really love your videos
10 points to you,for being x10 as smart as i ever will be!
Really cool!
Engineer guy... your wife and children are very lucky to have you :)
so all the resistor does is to discharge the most but the current coming from the detector is greater then the current that can flow trough thee resistor so it chatges the gate of the mosfet
if it is radioactive, then does it means that after some time the metal will disappear??
How do you feel about tickets being issued by the municipality for every false alarm? It seems counterproductive because the dis-efficiency lies in the responders of the alarm rather than the alarm itself.
I always thought they relied on current from the smoke to activate, not the other way around! Thanks
@engineerguyvideo name of the Gel?
@engineerguyvideo,
Oh. Excuse me. I've been trying to find these with Americium inside them, but couldn't do so. Everywhere they told me that those are old and now smoke detectors are optical (a chamber of air with a photo-something in it that detects when the air gets "foggy").
yay! a new video! I've been waiting for one!
I'm trying to follow your explanation of how the MOSFET works, but I get lost at the part where a voltage difference between the source and the gate allows current flow between the source and the drain. If the gate is attached to an insulator, how does it have any effect on the transistor at all. It seems the same to me as attaching the gate to the air or the wall. I'm really confused.
OK, disregard my last question. I listened more carefully this time and heard the word "field", so now I get it---"Field Effect Transistor" So what's the electrode attached to the substrate about?
very helpful
I love this channel.
@timerider4 The physics involved isn't going to change over time, so why wouldn't it be reliable? How else would you sense invisible gases of combustion?
Bill hammak is best engineer
can u do a video on things that have gone wrong in chemical industries and explain stuff like idk say flooding...?
Cool, for some reason this only showed up under new videos today.
wow nice........keep up the good work
@Soldier842 It's also somewhat difficult for anyone who is not involved in the engineering field. I'm English first language, and I don't know everything he's talking about. Look up terms on the net; that might help. :)
@PCFPSGamer Yeah they do. We used to have a detector just down the hall from our upstairs shower. If my shower was too hot and I opened the door.. the steam countless times set off the alarm.
*****
Wouldn't it be better for them to use a JFET instead of a MOSFET? JFETs have higher input impedance - though I suppose a MOSFET might just suffice in this situation.
Thank you
@crasherball Note each thing you don't understand and then ask questions. There are dozens of forums on the Web where people gather to talk about electricity and electronics. Of course you can do it the old-fashened way like I did: get a copy of ARRL's Amateur Radio Handbook from the library and read the basics.
I always thought these detect heat and not smoke. And that poses another question, what happens if fire produces little to no smoke? What about cigarettes, they would probably trigger the alarm?
The beep at the start scared the crap outta me
I need another video Explaining why the resistors create a pull up