WEBVTT - How Metal Detectors Work 0:00:00.280 --> 0:00:02.960 Brought to you by the reinvented two thousand twelve Camray. 0:00:03.160 --> 0:00:08.920 It's ready. Are you get in touch with technology with 0:00:09.000 --> 0:00:17.640 tech Stuff from how stuff works dot com. Hello again, everyone, 0:00:17.720 --> 0:00:20.119 Welcome to tech stuff. My name is Chris Polett and 0:00:20.120 --> 0:00:22.840 I'm an editor at how stuff works dot com. I 0:00:22.880 --> 0:00:27.320 worked with a person across from me pretty often. Uh. 0:00:27.360 --> 0:00:29.920 He has a senior writer at how stuff works dot com. Also, 0:00:30.040 --> 0:00:34.280 his name is Jonathan Strickland. New Wave tried to kill 0:00:34.320 --> 0:00:37.159 the Metal but they failed as they were stricken down 0:00:37.240 --> 0:00:41.960 to the ground. The second time I've quoted this band. Really, 0:00:42.479 --> 0:00:45.760 at least it isn't from Tron, that's true. Not from Tron, 0:00:46.200 --> 0:00:50.680 not from war games. Um. So today we are going 0:00:50.720 --> 0:00:53.280 to talk about you know what, This was a topic, 0:00:53.720 --> 0:00:56.920 uh that I don't know that anyone has ever requested. Um. 0:00:56.960 --> 0:01:00.680 It came to me actually as I was looking through 0:01:00.800 --> 0:01:04.560 stuff in my basement and went metal detectors you should 0:01:04.560 --> 0:01:07.479 talk about We've never talked about metal detective Actually, we've 0:01:07.520 --> 0:01:10.480 sort of talked about metal detectors because metal detectors use 0:01:10.520 --> 0:01:14.000 a lot of the technology we talked about before, especially 0:01:14.319 --> 0:01:19.399 the relationship of magnetism to electricity. Yeah, um, but yeah, 0:01:19.400 --> 0:01:22.600 I mean it's something that we run into very often, 0:01:22.680 --> 0:01:25.280 especially if we travel and walk through the metal detectors 0:01:25.280 --> 0:01:27.960 at the airport. If we're not getting back scattered or 0:01:28.160 --> 0:01:31.120 uh you know, dropping stuff that you can't find, losing 0:01:31.160 --> 0:01:36.000 your wedding ring and the maltch outside. Yikes, that's good stuff. 0:01:36.040 --> 0:01:39.120 I've done that. I still have it, so there you go. 0:01:39.280 --> 0:01:43.560 I've never lost my wedding ring. Alright, Well it was 0:01:43.600 --> 0:01:47.840 only temporary. So anyway, metal detectors talk about what they are. 0:01:48.160 --> 0:01:51.240 We're mostly going to be talking about the kind that 0:01:51.280 --> 0:01:54.040 you would you would carry with you, you know, the 0:01:54.320 --> 0:01:57.960 portable metal detectors that you would use when looking for say, 0:01:58.000 --> 0:02:01.680 loose change on the beach, or you know, searching for 0:02:01.760 --> 0:02:07.640 that rare civil war uh bullet or a gun that 0:02:07.800 --> 0:02:09.920 might be part of you know, in an area that 0:02:09.960 --> 0:02:12.520 you knew the battle happened here, so there may very 0:02:12.520 --> 0:02:15.240 well be stuff here. Yeah, we we should definitely talk 0:02:15.280 --> 0:02:18.160 about some of the applications of the technology. UM and 0:02:18.200 --> 0:02:19.880 I would like to point out that we have an 0:02:19.919 --> 0:02:22.160 excellent article on how stuff works dot com if you're 0:02:22.160 --> 0:02:27.119 interested in learning more. UM it's called how metal Detectors Work. Yeah, 0:02:27.120 --> 0:02:29.120 it should be pretty easy for people to find, written 0:02:29.120 --> 0:02:32.760 by Jeff Tyson, and it is a very good article 0:02:32.919 --> 0:02:37.400 and very uh simple to follow, easy to understand. I 0:02:37.440 --> 0:02:39.840 would say this is this is one of those really 0:02:40.000 --> 0:02:43.240 great how stuff works articles. Yeah, by the time you 0:02:43.240 --> 0:02:45.400 get through it and you're like, oh, yeah, no, that 0:02:45.480 --> 0:02:48.639 totally makes sense, especially if you have a little bit 0:02:48.639 --> 0:02:54.920 of grounding in the way electromagnetism works and conductors and inducers. 0:02:55.960 --> 0:02:58.840 So we'll we'll cover that. I mean, we've talked about 0:02:58.840 --> 0:03:01.160 an in previous podcast, but we'll will will do a 0:03:01.240 --> 0:03:03.960 quick brush up so that we can explain it. Um, 0:03:04.000 --> 0:03:07.520 so you wanna, let's let's talk about the the Jeff 0:03:07.560 --> 0:03:09.679 does a great job at breaking down what the typical 0:03:10.680 --> 0:03:15.000 portable metal detector, the four main parts of one, what 0:03:15.040 --> 0:03:17.520 they would be. Yeah, I mean, if you've ever seen 0:03:17.520 --> 0:03:20.720 people walking around with a metal detector, you you sort 0:03:20.720 --> 0:03:22.200 of know what they look like. They have a round 0:03:22.280 --> 0:03:26.000 dish part that's used close to the ground, right, that's uh, 0:03:26.200 --> 0:03:31.720 that's called the coil. Yes, and then you have the stabilizer, um, 0:03:32.840 --> 0:03:35.200 which is the part that you actually hold onto, that 0:03:35.400 --> 0:03:37.560 holds onto your rope, that that you see on your 0:03:37.640 --> 0:03:40.640 arm because you know, frankly having used a metal detector, 0:03:40.800 --> 0:03:43.720 it's not the lightest thing, right, This this helps, This 0:03:43.760 --> 0:03:47.040 helps distribute the weight somewhat so that you're not you 0:03:47.040 --> 0:03:49.800 don't feel like you're carrying around a you know, ten 0:03:49.880 --> 0:03:53.800 pound brick the whole time, because without that then you 0:03:53.800 --> 0:03:56.480 would get very tired, very quickly. Yeah. And the the 0:03:56.560 --> 0:03:59.200 ten pound the aforementioned ten pound brick, which probably isn't 0:03:59.240 --> 0:04:01.360 ten pounds, but it's certainly can feel that way after 0:04:01.400 --> 0:04:04.400 a while. That's the control box, uh, And you've got 0:04:04.440 --> 0:04:07.360 all your your electronics in there. And and then the 0:04:09.200 --> 0:04:13.280 connect yes, the long skinny part that's the shaft. Yes, 0:04:13.400 --> 0:04:16.159 it connects the coil at the base to the part 0:04:16.200 --> 0:04:18.600 that you're holding. And the of course the control box. 0:04:18.960 --> 0:04:21.600 So those are your four basic parts of your basic 0:04:21.760 --> 0:04:24.680 metal detector. Yes. And then you know you have your 0:04:24.680 --> 0:04:28.360 headphones because this is one of our episodes of stuff 0:04:28.400 --> 0:04:31.440 that beeps and stuff what beat? Stuff? What beeps? And 0:04:31.520 --> 0:04:34.480 it it does in fact beep. Yeah, there's usually some 0:04:34.520 --> 0:04:40.279 sort of audible alert that you have in fact detected metal. Yeah. Now, 0:04:40.440 --> 0:04:43.640 more sophisticated uh, metal detectors will tell you a lot 0:04:43.680 --> 0:04:47.040 more often with uh, well, sometimes with with an audible tone, 0:04:47.040 --> 0:04:50.880 but also with a visual uh, some kind of visual analysis. 0:04:51.200 --> 0:04:53.440 We can get into that too in a minute. So 0:04:53.880 --> 0:04:58.200 there are three main types of metal detectors, the ones 0:04:58.240 --> 0:05:03.800 that work, the three three main approaches to to metal detection. 0:05:03.960 --> 0:05:07.760 Let's say, Uh, there's UM, there's the very low frequency, 0:05:07.839 --> 0:05:11.720 which is probably the most um, the most popular or 0:05:11.760 --> 0:05:14.080 the most common type of MEL detector, at least for 0:05:14.160 --> 0:05:18.360 the portable metal detectors. UM. Yeah. When we get into this, 0:05:18.440 --> 0:05:20.720 you'll you'll see that each of these different types has 0:05:20.800 --> 0:05:23.920 its own strengths and weaknesses. And you might say, well, 0:05:23.960 --> 0:05:27.159 the VLF detector sounds great, why would you use the others? 0:05:27.360 --> 0:05:30.960 We'll get into that. The other two are pulse induction 0:05:31.920 --> 0:05:35.920 and beat frequency oscillation. Yeah. I I knew a beat 0:05:35.960 --> 0:05:42.800 frequency oscillator once. He was awesome. Yeah, Anyway, I think 0:05:43.120 --> 0:05:47.200 something else, I guess. So that's the beat boxer frequency oscillator. 0:05:47.600 --> 0:05:51.200 That the uh, the VLF metal detector is the type 0:05:51.200 --> 0:05:57.680 that I have. UM and uh. The the basic differences 0:05:57.800 --> 0:06:01.680 uh and these as you'll see those really in the coils, 0:06:02.120 --> 0:06:05.679 to be honest, because the VLF has two different coils. 0:06:05.800 --> 0:06:11.000 One transmits UM and and the other is basically an 0:06:11.000 --> 0:06:13.880 antenna to pick up the signals, so they're shielded from 0:06:13.920 --> 0:06:16.840 one another so it doesn't pick up because otherwise you 0:06:17.000 --> 0:06:18.960 turn it on, you would just have the receiver saying, 0:06:19.040 --> 0:06:23.360 oh my gosh, there's metal everywhere. Holy crap, you're rich, 0:06:24.040 --> 0:06:27.839 even up in the air. It's it's literally everywhere. Yeah, 0:06:27.839 --> 0:06:30.040 that would that would not be very useful. And taking 0:06:30.040 --> 0:06:32.400 this back to the store where I bought it. It's 0:06:32.440 --> 0:06:35.080 a detector detector. This does not do me any good. 0:06:35.240 --> 0:06:40.160 It's a detector. It's a detected or where's perry? So 0:06:40.800 --> 0:06:47.159 the the the transmitter coil um it's it. Think of 0:06:47.200 --> 0:06:51.320 a circle, all right. It's a this circular part at 0:06:51.320 --> 0:06:54.360 the base of the metal detector. And if you were 0:06:54.400 --> 0:06:56.720 to take it apart, which I do not recommend you do, 0:06:57.320 --> 0:07:00.400 you would see that there is a warrant point warranty 0:07:00.440 --> 0:07:02.599 and it may not work anymore. You will have a 0:07:02.680 --> 0:07:06.359 there's a coil of wire that goes around the perimeter 0:07:06.480 --> 0:07:08.960 of this circle, like it's it's wrapped around. So the 0:07:09.000 --> 0:07:11.120 circle itself is let's say it's like a quarter of 0:07:11.160 --> 0:07:13.280 an inch thick, and you've got this coil of wire 0:07:13.360 --> 0:07:16.080 that's that's coiled around this quarter of an inch all 0:07:16.120 --> 0:07:19.120 the way around the perimeter of this circle. When you 0:07:19.200 --> 0:07:22.960 run electricity through this coil of wire, what happens besides 0:07:23.000 --> 0:07:26.120 the fact that electrons are moving through because of the 0:07:26.200 --> 0:07:32.120 nature of electricity and magnetism, Well, when you run electricity 0:07:32.120 --> 0:07:35.160 around a coil like that, it generates a magnetic field. 0:07:35.200 --> 0:07:38.400 That's right. It does generate a magnetic field, and it 0:07:38.440 --> 0:07:42.440 generates a magnetic field perpendicular to the direction of the electricity. 0:07:42.640 --> 0:07:46.160 It's just the nature of electromagnetism. It's amazing, it's awesome. 0:07:46.240 --> 0:07:50.160 That's what how electro magnets work. And uh dynamo's work 0:07:50.200 --> 0:07:53.800 in uh and sort of using this in reverse. Um. 0:07:53.920 --> 0:07:57.440 So you've got electricity flowing through these coils and that 0:07:57.520 --> 0:08:01.240 generates the magnetic field. Well, it doesn't just the electricity. 0:08:01.280 --> 0:08:04.320 Actricity doesn't just flow in one direction, no, it it 0:08:04.600 --> 0:08:08.040 goes back and forth. It alternates very very very fast, 0:08:08.640 --> 0:08:10.760 almost as fast as I waffle back and forth on 0:08:10.760 --> 0:08:13.160 what I want to eat for lunch. And that means 0:08:13.240 --> 0:08:18.560 that the magnetic field also alternates. The direction of the 0:08:18.600 --> 0:08:22.120 magnetic field changes. Uh. And if you think of it 0:08:22.160 --> 0:08:26.880 in terms of the disc, the coil disc being towards 0:08:26.920 --> 0:08:29.040 the ground, you can think of it as the magnetic 0:08:29.080 --> 0:08:33.840 field occasionally is pushing against or pulling the ground in general. 0:08:33.920 --> 0:08:35.679 That just think of it that way. That's the direction 0:08:35.679 --> 0:08:37.880 of the magnetic field while the electricity is going around 0:08:37.880 --> 0:08:40.080 and around in a circle, back and forth and in 0:08:40.200 --> 0:08:45.320 the various directions, and that alternation is happening hundreds of 0:08:45.320 --> 0:08:49.480 times per second. So you've got this magnetic field that's 0:08:49.600 --> 0:08:54.000 that's just oscillating essentially right there against the ground. When 0:08:54.000 --> 0:08:56.959 it comes to contact with something that is metal, well, 0:08:57.000 --> 0:09:00.199 the metal will start to that magnetic field will as 0:09:00.440 --> 0:09:05.320 a a weaker magnetic field to generate around the metal object. Yeah. 0:09:05.400 --> 0:09:09.679 Basically induces a magnetic field in a metal object in 0:09:09.720 --> 0:09:13.040 the ground. So let's say, uh, um, you drop a 0:09:13.120 --> 0:09:17.920 screw and when you're trying to build something outside and 0:09:17.960 --> 0:09:19.800 you're trying to find it with your metal detector so 0:09:19.840 --> 0:09:21.439 that you don't step on it with a bare foot 0:09:21.440 --> 0:09:23.600 and you know need a trip to the hospital and 0:09:23.640 --> 0:09:27.280 a technis shot. Um. So as soon as you run 0:09:27.440 --> 0:09:29.640 the coil of the field and you're not trying to 0:09:29.640 --> 0:09:31.560 touch the ground with it, you really just need it 0:09:31.760 --> 0:09:35.320 close to the ground. Um, it will find the screw. 0:09:35.600 --> 0:09:39.200 The screw will basically start inducing a it will end 0:09:39.960 --> 0:09:43.320 metal detected detector will generate a field, and that will 0:09:43.480 --> 0:09:47.400 cause the screw to generate its own a weaker magnetic 0:09:47.480 --> 0:09:51.160 Oh yeah, yeah, considerably weaker, but it will the metal detector, Uh, 0:09:51.200 --> 0:09:55.000 the antenna coil inside the transmitter coil will say, oh, 0:09:55.080 --> 0:09:58.120 look there's something right there that is generating a magnetic field. 0:09:58.360 --> 0:10:00.959 It's right here. And the way that the the that 0:10:01.520 --> 0:10:04.600 antenna works is the way I was talking about with 0:10:04.640 --> 0:10:07.560 a dynamo. So if you have a coil of wire 0:10:08.080 --> 0:10:11.440 and you introduce it into a fluctuating magnetic field, that 0:10:11.480 --> 0:10:15.200 will induce the flow of electricity within the wire. Just 0:10:15.400 --> 0:10:18.520 as electricity and the wire will create generate a magnetic field, 0:10:18.800 --> 0:10:22.640 a magnetic field will induce electricity to run through wire 0:10:23.440 --> 0:10:26.560 fluctuating magnetic field. It can't just be just a magnetic field. 0:10:27.160 --> 0:10:31.960 So when the weak magnetic field from the mental object 0:10:32.120 --> 0:10:36.559 hits that that the wire in the the the the 0:10:36.600 --> 0:10:42.439 receiver coil that generates the electricity, which then alerts the 0:10:42.440 --> 0:10:45.760 control box that that's what When the control box gets 0:10:45.960 --> 0:10:50.160 an electric signal from the receiver coil that says beep, 0:10:50.559 --> 0:10:55.800 something is here stuff? What beeps? Yeah? Stuff what beeps. So, yeah, 0:10:55.960 --> 0:11:01.600 that's the basic uh way that a VLF metal detector works. 0:11:01.640 --> 0:11:05.640 It shoots out this magnetic field. The polar polarization is 0:11:05.640 --> 0:11:09.920 alternating the same as the the flow of electricity around 0:11:10.000 --> 0:11:14.080 the the the transmitter coil and then the receiver coil 0:11:14.120 --> 0:11:17.559 picks up any magnetic fields generated by metal objects that 0:11:17.600 --> 0:11:20.720 are under the surface of the ground. It's pretty cool 0:11:20.960 --> 0:11:25.320 and generally it will go more or less about a foot. Yeah, 0:11:25.520 --> 0:11:28.080 you're not going to find you know, the Earth's core 0:11:30.840 --> 0:11:34.720 and the depth of what the depth of the The 0:11:34.760 --> 0:11:37.360 effectiveness of this metal detector is also going to be 0:11:37.440 --> 0:11:41.400 dependent on other factors, like the nature of the metal 0:11:41.440 --> 0:11:44.800 object itself, because some some metal objects are going to 0:11:44.840 --> 0:11:49.240 generate a stronger magnetic field than others, like iron. Uh. 0:11:49.240 --> 0:11:52.760 It will also depend on the composition of the soil. 0:11:53.400 --> 0:11:56.080 So the soil has a lot of elements in it 0:11:56.240 --> 0:11:59.000 that would create a magnetic field, you're gonna get a 0:11:59.040 --> 0:12:03.959 lot of interference, yeah, or or an environment where uh 0:12:04.000 --> 0:12:07.800 that that would conduct electricity more readily. Like if you're 0:12:07.840 --> 0:12:11.600 trying to look for something and say saltwater, you might 0:12:11.679 --> 0:12:14.200 have more difficulty than if you were looking you know, 0:12:14.360 --> 0:12:18.200 on on a different type of soil. UM. Now there 0:12:18.240 --> 0:12:22.480 is something to uh called phase shifting, and that's how 0:12:22.480 --> 0:12:25.400 it's able to tell what sort of metal, what sort 0:12:25.400 --> 0:12:28.560 of metal it is UM, And it really has to 0:12:28.600 --> 0:12:32.160 do with the the inductance and the resistance of the 0:12:32.160 --> 0:12:35.479 object that you're looking for. Now, the inductance is UM 0:12:35.559 --> 0:12:40.559 the objects ability to conduct electricity UM. And if it's inductive, 0:12:40.679 --> 0:12:43.440 it would be able to to conduct electricity easily, but 0:12:43.600 --> 0:12:49.160 it's slow to react to changes in the electrical current. UM. 0:12:49.200 --> 0:12:52.040 If it's resistive, it doesn't conduct electricity is easily, but 0:12:52.120 --> 0:12:54.959 it is quick to react to those those changes. And 0:12:55.200 --> 0:12:58.760 a sophisticated metal detector will be able to tell you, well, 0:12:58.800 --> 0:13:03.560 that's I think that's gold or based upon that phase shift. 0:13:03.600 --> 0:13:06.000 Because the face shift for a particular element is going 0:13:06.040 --> 0:13:09.720 to remain constant, you know. That's that's why if it 0:13:09.760 --> 0:13:12.640 didn't remain constant, then this wouldn't matter at all, because 0:13:12.679 --> 0:13:14.880 it wouldn't you know, we wouldn't know, you know, it's 0:13:14.880 --> 0:13:17.000 like we just know something is down there, we wouldn't 0:13:17.040 --> 0:13:19.680 know have any way of guessing what it is. But 0:13:19.840 --> 0:13:24.680 because it's an inherent property of this particular material, and 0:13:24.679 --> 0:13:27.800 it's really dependent upon the molecular composition of whatever that 0:13:27.840 --> 0:13:31.760 material is. UM, then we can make start making guesses 0:13:31.840 --> 0:13:35.120 based on that phase shift UM. And it's yeah, the 0:13:35.120 --> 0:13:37.080 face shift, you know, with it being that difference in 0:13:37.120 --> 0:13:41.839 timing between the transmitters frequency uh and the frequency of 0:13:41.880 --> 0:13:46.520 the magnetic wave that's generated by the object. Um. You know. 0:13:46.640 --> 0:13:51.120 It's these are sort of ranges, right like if it 0:13:51.480 --> 0:13:54.120 if it's a certain range there, then the male detector 0:13:54.160 --> 0:13:57.680 can give a best guess as to what that material maybe. 0:13:58.240 --> 0:14:02.720 So there's no ever necessarily a guarantee that whatever it 0:14:02.760 --> 0:14:06.280 is you've detected is specifically going to be you know, 0:14:06.320 --> 0:14:09.880 aluminum versus goal or whatever. But it's a it's an indicator, 0:14:09.960 --> 0:14:13.360 so that uh, it gives you at least the idea 0:14:13.400 --> 0:14:16.280 of you know, is that you measure risk versus reward, right, 0:14:17.120 --> 0:14:21.400 the risk of exhausting yourself digging up useless junk versus 0:14:21.440 --> 0:14:25.760 the reward of possibly finding something that is of true value. Yes, 0:14:26.120 --> 0:14:29.000 so that's really the whole purpose of this anyway. It's 0:14:29.040 --> 0:14:31.480 just you know, to kind of tune in on that 0:14:31.560 --> 0:14:34.240 beep and make it more meaningful so that you know, 0:14:34.280 --> 0:14:38.320 you don't waste your time digging up uh little poll 0:14:38.400 --> 0:14:43.520 tabs from soda cans. Yeah. Now, yeah, if you have 0:14:43.560 --> 0:14:47.320 a higher inductance, it's going to create a larger phase shift, 0:14:47.360 --> 0:14:51.320 and lower inductance has a smaller phase shift. Now, metal 0:14:51.360 --> 0:14:57.560 detectors use a phase demodulator to read this, and uh, 0:14:57.720 --> 0:15:02.880 what that creates is scrimination. Yeah, yeah, I know it's terrible, 0:15:03.000 --> 0:15:07.440 but within metal detectors, it's okay, yeah, because the thing is, 0:15:08.080 --> 0:15:11.640 a good metal detector will allow you to filter out 0:15:11.960 --> 0:15:15.720 stuff that you don't want because the metal detector, if 0:15:15.720 --> 0:15:17.920 you said it at a certain setting and say, you know, 0:15:17.960 --> 0:15:21.880 I'm really looking for metals that fall within this range, yeah, 0:15:21.920 --> 0:15:27.080 perhaps gold. I've actually seen uh, metal detector booths and 0:15:27.120 --> 0:15:29.920 they'll have like this giant jar of class rings that 0:15:30.000 --> 0:15:32.880 people have lost, which is sort of a you know, 0:15:32.960 --> 0:15:35.760 reminder that you know, hey, you you can find stuff 0:15:35.800 --> 0:15:37.800 if you just take your metal. Of course people look 0:15:37.800 --> 0:15:41.360 at you funny, but yeah, that way. That way. Let's 0:15:41.360 --> 0:15:44.040 say that you're out there looking for something specific, you 0:15:44.080 --> 0:15:47.480 can you know, some meld detectors have settings where you can, uh, 0:15:47.640 --> 0:15:50.920 you can tell the meld detector to ignore anything outside 0:15:51.000 --> 0:15:53.800 of a particular range of frequencies. So in other words, 0:15:53.840 --> 0:15:57.400 you're saying. You might say, I'm only interested in finding silver. 0:15:57.760 --> 0:16:00.000 Let's say, So what I'll do is I'll set my 0:16:00.040 --> 0:16:04.200 MELD detector so that it'll it'll only uh activate, it 0:16:04.200 --> 0:16:09.320 will only alert me if something that generates a magnetic 0:16:09.800 --> 0:16:13.280 frequency similar to that of silver is encountered by the 0:16:13.320 --> 0:16:15.560 metal detector. So in other words, what you might you 0:16:15.640 --> 0:16:19.120 might pass over a gold deposit and nothing happens. But 0:16:19.320 --> 0:16:21.720 as soon as you go over that that silver half 0:16:21.720 --> 0:16:24.080 dollar but ink, and then you dig it up and 0:16:24.120 --> 0:16:26.280 you're like, hey, look I'm rich. I Meanwhile, the gold 0:16:26.280 --> 0:16:30.640 guy behind you was like, sucker. Well that's that. That 0:16:30.680 --> 0:16:33.120 can be called notching. Basically, you set it for a 0:16:33.840 --> 0:16:36.920 if you imagine a scale, uh you know, one notch 0:16:36.960 --> 0:16:40.040 on that scale, or some of the more sophisticated metal 0:16:40.080 --> 0:16:43.120 detectors will allow you to set more than one notch r. 0:16:43.240 --> 0:16:44.880 So that way you could look for both silver and 0:16:45.000 --> 0:16:50.320 gold and you'd say, ha ha, Mr smarty gold pants. Um. 0:16:50.360 --> 0:16:55.080 Now that's that's the VLF. The post induction metal detector 0:16:55.440 --> 0:16:57.280 is a little bit different. Yeah, it uses only a 0:16:57.320 --> 0:17:01.000 single coil, or it can use multiple oils working at 0:17:01.040 --> 0:17:03.320 the same time. Yeah, but there these are these are 0:17:03.400 --> 0:17:06.359 coils that haven't that don't have that shielding. It's not 0:17:06.440 --> 0:17:09.639 like you have a transmitter coil and then a receiver coil, 0:17:10.840 --> 0:17:16.480 and all of these coils are generating very quick bursts 0:17:16.560 --> 0:17:20.560 of electricity, which of course creates a very sharp magnetic wave. 0:17:21.800 --> 0:17:24.240 And uh so it's just a really quick spike. And 0:17:24.280 --> 0:17:26.720 then what will happen is that magnetic wave if it 0:17:26.800 --> 0:17:29.399 encounters a metal object. Again, that metal object will have 0:17:29.440 --> 0:17:33.760 to will generate its own magnetic wave, and the metal 0:17:33.800 --> 0:17:36.160 detector will pick up on that, and it's all it's 0:17:36.240 --> 0:17:38.760 kind of like an echo, right, It's kind of like 0:17:38.800 --> 0:17:42.720 an echo, right, thank you. So if you think about 0:17:42.720 --> 0:17:46.159 it that way, it's it's like sending out a signal 0:17:46.200 --> 0:17:48.640 and waiting for something to bounce back. Yeah, but it's 0:17:48.760 --> 0:17:51.040 very fast. I mean the average is about a hundred 0:17:51.040 --> 0:17:55.440 pulses per second, which is yeah, fairly rapid, pretty quick. 0:17:55.720 --> 0:17:59.240 And then you're looking for the reflected pulse, yes, which 0:17:59.280 --> 0:18:02.679 is what the the object that is under the ground 0:18:02.800 --> 0:18:07.639 or wherever. Uh, that's the the the pulse that it 0:18:07.800 --> 0:18:10.480 generates in response to the one that came from the 0:18:10.520 --> 0:18:14.040 mel detector. Yeah, Now it uses a these these types 0:18:14.040 --> 0:18:16.960 of metal detectors use a sampling circuit, basically trying to 0:18:17.000 --> 0:18:21.359 determine whether it's actually metal that you're finding or something else, 0:18:21.440 --> 0:18:23.879 some other type of magnetic field that is interfering with 0:18:23.920 --> 0:18:26.639 this signal, and it's basically judging that based on the 0:18:26.680 --> 0:18:32.960 amount of time it takes UH two to reflect. Um. Yeah, 0:18:33.000 --> 0:18:34.840 that's another thing that we should point out is that 0:18:34.880 --> 0:18:38.520 MEL detectors can and encounter lots of different kinds of interference. 0:18:39.320 --> 0:18:41.720 Not just the composition of the soil. But let's say 0:18:41.760 --> 0:18:45.439 that you happen to cross over where an electrical cable 0:18:45.520 --> 0:18:49.480 has been buried. That could cause a problem. Your male 0:18:49.520 --> 0:18:52.240 detector might think that, hey, look there's gold in them 0:18:52.240 --> 0:18:55.959 the Oar hills, and truth, what you've hit is the 0:18:56.000 --> 0:18:58.560 power line, which you don't want to dig that up. No, 0:18:58.960 --> 0:19:03.480 it could result in everything from death, which UH is 0:19:03.520 --> 0:19:06.440 in the metal detection biz we call a bad thing, 0:19:07.720 --> 0:19:11.480 or it could result in or and or it could 0:19:11.520 --> 0:19:16.960 result in an entire region losing electricity. That's also a 0:19:17.000 --> 0:19:20.240 bad thing. That's that's a very good point. I mean, 0:19:20.280 --> 0:19:23.280 these these metal detectures are not only incredibly useful, they 0:19:23.280 --> 0:19:24.920 can be a lot of fun. A lot of hobbyists 0:19:25.040 --> 0:19:29.400 love them, but you do have to be very very careful. Um. 0:19:29.520 --> 0:19:32.359 And it's good to know your the territory to quote 0:19:32.400 --> 0:19:35.240 a certain musical, but yeah, I mean you need to 0:19:35.280 --> 0:19:38.520 know the territory. You gotta know where you're you're digging 0:19:39.000 --> 0:19:42.199 because you you really could get hurt. Honestly, I've got 0:19:42.280 --> 0:19:46.119 Rock Island going through my head. Now, cash for the merchandise, 0:19:47.240 --> 0:19:51.240 al right, sorry, all right. So we have an integrator 0:19:52.000 --> 0:19:56.080 on these, on these pulse induction metal detectives, uh, and 0:19:56.119 --> 0:19:59.360 that's reading the signals from the sampling circuit and converting 0:19:59.359 --> 0:20:03.600 them to D that's current Yeah, not the district of Columbia. Yeah, 0:20:03.680 --> 0:20:07.240 not not a comic book publisher either. And that's feeding 0:20:07.240 --> 0:20:10.160 into it the audio circuit and that is what beats. Yeah, 0:20:10.200 --> 0:20:12.879 that's the stuff what beats for the pulse indicator. The 0:20:13.200 --> 0:20:16.440 thing is, uh, these are very good at detecting metal, 0:20:16.520 --> 0:20:19.240 but they're not very good at discriminating between different types 0:20:19.280 --> 0:20:23.000 of metal. Um, So you're not going to get the 0:20:23.600 --> 0:20:26.440 level of precision that you would get with a VLF 0:20:27.160 --> 0:20:30.639 metal detector. But you know they also you've got to 0:20:30.680 --> 0:20:33.359 remember that these different types of detectors, while some of 0:20:33.359 --> 0:20:36.160 them may work in conditions that others do not. There's 0:20:36.240 --> 0:20:40.840 there's also a price range here as well. Oh yes, yes, now, yeah, 0:20:40.880 --> 0:20:46.360 the beat frequency oscillator metal detectors can be uh fairly affordable. Um. 0:20:46.400 --> 0:20:49.000 They also used two coils, but one is in the 0:20:49.040 --> 0:20:51.080 search head and the other one is actually in the 0:20:51.080 --> 0:20:54.800 control box. UM. They're connected to an oscillator that as 0:20:55.760 --> 0:20:59.920 pulsing UM many many times per second. That was in 0:21:00.040 --> 0:21:03.199 of times per second UM. And and the and the 0:21:03.240 --> 0:21:06.240 frequency of the one that's inside the control box and 0:21:06.280 --> 0:21:10.400 the one that's inside the actual detector are slightly offset. 0:21:10.520 --> 0:21:16.160 They're not in sync or backstreet boys. Oh you got 0:21:16.200 --> 0:21:22.040 the other one I was gonna do U. So yeah, well, 0:21:22.080 --> 0:21:25.400 ironically enough to our our current part of the conversation. 0:21:26.119 --> 0:21:29.240 They create radio waves um, and then the receiver in 0:21:29.280 --> 0:21:33.000 the control box uh picks that up and plays tones 0:21:33.680 --> 0:21:37.000 to let you know when you're you're coming into range 0:21:37.040 --> 0:21:39.879 of metal, right, Because what's happening is that when the 0:21:40.160 --> 0:21:46.280 metal encounters this uh, this this this electromagnetic field that 0:21:46.600 --> 0:21:50.240 is going to alter that radio wave. And so what's 0:21:50.359 --> 0:21:53.720 really listening for our changes in the sound that you're hearing. 0:21:54.240 --> 0:21:56.919 The change in the sound indicates that you have encountered 0:21:57.040 --> 0:22:00.919 something that is generating this man medic field because of 0:22:00.920 --> 0:22:05.639 the one you're generating, they know what they're going through. Um. 0:22:05.840 --> 0:22:09.359 So yeah, I mean detectors killed the radio star. But 0:22:09.440 --> 0:22:12.520 these these uh, Like I said, these are a lot 0:22:12.640 --> 0:22:16.880 cheaper to manufacture. And therefore, if you are uh interested 0:22:16.920 --> 0:22:20.640 in getting your feet wet, uh and the metal detector 0:22:21.200 --> 0:22:23.199 the thing is a hobby, you might consider this, but 0:22:23.240 --> 0:22:26.560 they're they're far less accurate in terms of um being 0:22:26.600 --> 0:22:29.800 able to give you any kind of discrimination or any 0:22:29.840 --> 0:22:34.520 really any real control. Um they actually use these are 0:22:34.520 --> 0:22:37.600 the types of metal detectors that you the handheld detectors 0:22:37.600 --> 0:22:40.359 that they use the airport. Um, you know, if you 0:22:40.400 --> 0:22:43.080 walk through the scanner and and then yeah, that's the 0:22:43.080 --> 0:22:44.880 type they use in the one because they don't really 0:22:44.920 --> 0:22:48.479 need to know whether it's gold or iron. They just 0:22:48.920 --> 0:22:50.720 want to know what it is that you've got now 0:22:50.760 --> 0:22:53.479 once once, once something beeps, then they can say, all right, 0:22:53.480 --> 0:22:55.639 well let's see what that is. They don't, you know, 0:22:55.760 --> 0:22:59.560 necessarily need to know immediately. Yeah. And the metal detectors 0:22:59.640 --> 0:23:03.600 the frames at the airport, they work on essentially the 0:23:03.600 --> 0:23:07.320 same principles we've talked about here. They're generating electromagnetic fields, 0:23:07.320 --> 0:23:10.159 which of course has brought up some concerns with people 0:23:10.200 --> 0:23:14.840 who may have UH devices like medical devices that could 0:23:14.880 --> 0:23:18.199 react to electromagnetic fields. That's why you'll occasionally hear about 0:23:18.840 --> 0:23:22.040 UH folks like that having to go through like a 0:23:22.080 --> 0:23:25.320 pat down security as opposed to a metal detector, just 0:23:25.359 --> 0:23:27.679 because of the concern that it could interfere with a 0:23:27.720 --> 0:23:32.760 medical device. Right right now, with with all of these um, 0:23:32.840 --> 0:23:36.000 what you're gonna find depends on the type of metal detector, 0:23:36.200 --> 0:23:39.840 the type of metal that you're looking for, about how 0:23:39.880 --> 0:23:41.760 big it is, the kind of makeup of the soil, 0:23:42.480 --> 0:23:45.800 um any kind of interference from other objects, and the halo, 0:23:46.320 --> 0:23:49.600 which is basically, you know, if you have a piece 0:23:49.680 --> 0:23:53.119 of metal in the soil, it's going to read a 0:23:53.160 --> 0:23:55.600 little bit differently, it's going to it's going to register 0:23:55.720 --> 0:23:59.720 is larger than it actually is. Yeah, because those interesting things, Yeah, 0:23:59.720 --> 0:24:02.560 they I could see your halo. I was I was waiting. 0:24:02.920 --> 0:24:05.880