On 15/09/17 10:37, tabbypurr@gmail.com wrote:> On Friday, 15 September 2017 01:32:45 UTC+1, John Larkin wrote: >> On Thu, 14 Sep 2017 14:02:56 -0700 (PDT), eaglesondouglas@gmail.com >> wrote: >> >>> >>>>> >>>>> Here I would increase the ac frequency to make a coil Q of the required >>>>> number, 1 to 10. >>>> >>>> Are you trying to sense the metal by having it spoil the Q, >>>> or shift the frequency? In both case I might want a higher Q. >>>>> >>>> >>> Yes, I am not a engineer kind of guy. But my inclination is to >>> hope that steel or iron would alter L the coil inductance. Does >>> this mean technically altering Q? >> >> Mostly inductance. Iron will make it go up, brass down. >> >>> >> >From what I read this type of bridge works best at a Q of one >>> to ten. Is ramping it up to 100 allowed? >> >> Likely not possible at audio-type frequencies. >> >>> >>> I have an audio oscillator and wonder if I can just add an audio >>> amplifier for the power source. >> >> You can make an AC bridge, drive it with a good sine wave, listen to >> the null with amplified headphones, tweak the bridge or the frequency >> for a deep null. >> >> I guess you could use a resonated loop in an AC bridge, too. Might be >> more sensitive. >> >>> >>> thanks doug >> >> What would you do next if you found a cannon? > > What would you do after your 99th find of random bits of iron junk?Sell the SCUBA gear and go skiing instead.
Naval Cannon Search Magnetometer/Induction Coil Circuit
Started by ●September 14, 2017
Reply by ●September 14, 20172017-09-14
Reply by ●September 14, 20172017-09-14
On Thursday, September 14, 2017 at 10:51:06 AM UTC-4, millssc...@gmail.com wrote:> Hello: > > I am trying to make a homemade circuit to do underwater detection > of old War 1812 US Navy ship cannons. Magnetometers can be > bought, but they are expensive. So, I am looking at a metal detection > type circuit. I came across the Maxwell Bridge circuit. > > See: > https://en.wikipedia.org/wiki/Maxwell_bridge > > > Here I would increase the ac frequency to make a coil Q of the required > number, 1 to 10. > > My question is can I use the coil L3 in the bridge to scan the floor of > a river for cannon signal? Moving the coil at a certain velocity also. > The cannon would be about 3 foot deep in the river bottom I guess. I have > a Keithley electrometer for the galvanometer. > > The final coil will be 16 foot in diameter and 2 inches long and 20 turns maybe. The plane of the coil would be run parallel to the bottom surface. > > Here is my blogspot on the affair. > > http://douglaseagleson.blogspot.com > > Any other suggestions are very welcome. > thanks doug > > Also how would a low pass filter be added to the electrometer?These sites have a wealth of information about metal detectors (ferrous and non-ferrous), treasure-hunting, magnetometers, etc. Recommended. http://www.geotech1.com/cgi-bin/pages/common/index.pl?page=main&file=main.dat http://www.hobby-hour.com/electronics/metal_detectors.php Cheers, James Arthur
Reply by ●September 14, 20172017-09-14
On Thursday, September 14, 2017 at 5:03:03 PM UTC-4, eagleso...@gmail.com wrote:> > > > > > Here I would increase the ac frequency to make a coil Q of the required > > > number, 1 to 10. > > > > Are you trying to sense the metal by having it spoil the Q, > > or shift the frequency? In both case I might want a higher Q. > > > > > > Yes, I am not a engineer kind of guy. But my inclination is to > hope that steel or iron would alter L the coil inductance. Does > this mean technically altering Q?Huh, well then hire one, spend the money, or spend your time learning. Changing just the inductance of the coil would change the freq. Changing the (energy) loss, changes the Q. A hunk of steel probably does both, not sure which is bigger/easier to detect. George H.> > From what I read this type of bridge works best at a Q of one > to ten. Is ramping it up to 100 allowed? > > I have an audio oscillator and wonder if I can just add an audio > amplifier for the power source. > > thanks doug
Reply by ●September 14, 20172017-09-14
On Thursday, September 14, 2017 at 5:21:08 PM UTC-4, John Larkin wrote:> On Thu, 14 Sep 2017 14:07:39 -0700 (PDT), eaglesondouglas@gmail.com > wrote: > > >On Thursday, September 14, 2017 at 11:33:03 AM UTC-4, John Larkin wrote: > >> On Thu, 14 Sep 2017 07:50:56 -0700 (PDT), millsscientific@gmail.com > >> wrote: > >> > >> >Hello: > >> > > >> >I am trying to make a homemade circuit to do underwater detection > >> >of old War 1812 US Navy ship cannons. Magnetometers can be > >> >bought, but they are expensive. So, I am looking at a metal detection > >> >type circuit. I came across the Maxwell Bridge circuit. > >> > > >> >See: > >> >https://en.wikipedia.org/wiki/Maxwell_bridge > >> > > >> > > >> >Here I would increase the ac frequency to make a coil Q of the required > >> >number, 1 to 10. > >> > > >> >My question is can I use the coil L3 in the bridge to scan the floor of > >> >a river for cannon signal? Moving the coil at a certain velocity also. > >> >The cannon would be about 3 foot deep in the river bottom I guess. I have > >> >a Keithley electrometer for the galvanometer. > >> > > >> >The final coil will be 16 foot in diameter and 2 inches long and 20 turns maybe. The plane of the coil would be run parallel to the bottom surface. > >> > > >> >Here is my blogspot on the affair. > >> > > >> >http://douglaseagleson.blogspot.com > >> > > >> >Any other suggestions are very welcome. > >> >thanks doug > >> > > >> >Also how would a low pass filter be added to the electrometer? > >> > >> > >> Are the cannons iron or brass? Iron would distort the earth's mag > >> field. > >> > >> Cheap fluxgate magnetometers (as in the $20 range) have nanotesla > >> field sensitivity. TI now has a fluxgate IC. > >> > >> A coil+bridge can detect nonferrous stuff. An AC bridge, or an > >> oscillator are the usual metal detector techniques. There are > >> dual-coil detectors, but that wouldn't be practical for big coils. > >> > > > >I hope they are iron. > > > >I will look and likely by a TI fluxgate ic then. > > > >I am also going to make a test bridge system and see how it runs maybe. > > > >thankyou doug > > Speake, a British company, sells a fluxgate board for something like > $25. Stefan Mayer Instruments has something similar. It's apparently > not real hard to do. > > (I know all this from a failed NMR mag field compensation project.) > > A few fluxgates in an array could make a differential field sensor, > that could sense the gradient from a big hunk of iron.Oh, I would really like a good (cheap) B-field gradiometer. I've got drawings of swinging/moving magnetometers... Here's a fun idea. Can you do Earth's field NMR with a coil in a body of water? You need a big field to polarize the spins perpendicular to the Earth's field... that's a big problem. It'd have to be a smaller coil. George H.> > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●September 14, 20172017-09-14
Steve Wilson <no@spam.com> wrote:> The 24-pounders were used in the 1700's and made of cast iron:> https://en.wikipedia.org/wiki/24-pounder_long_gun> Here's a view of hundreds of 1819 24-pounders stockpiled at Fortress > Monroe in Virginia:> http://moultrie.battlefieldsinmotion.com/Artillery-24-pounder.html> They were iron:> "The bore-diameter for all these iron 24-pounders was established at > exactly 5.82 inches, and they were to weigh roughly 5,800 pounds > apiece."> http://moultrie.battlefieldsinmotion.com/Artillery-24-pounder.html> "The Chinese also mounted over 3,000 bronze and iron cast cannon on the > Great Wall of China, to defend themselves from the Mongols."> https://en.wikipedia.org/wiki/History_of_cannon> Doesn't say when. Maybe the 1500'sThey probably made other things from iron: bridges, tools, machines, etc. With all this iron around, how did they keep it from rusting? Even today, rust is a major problem. I moved back to Ontario after living in the US for 30 years. I was astonished to find how quickly everything rusted, often to the point of unusability. Cars, tools, you name it. If this is such a problem today, how did the oldtimers cope?
Reply by ●September 14, 20172017-09-14
On Thursday, September 14, 2017 at 8:32:45 PM UTC-4, John Larkin wrote:> On Thu, 14 Sep 2017 14:02:56 -0700 (PDT), eaglesondouglas@gmail.com > wrote: > > > > >> > > >> > Here I would increase the ac frequency to make a coil Q of the required > >> > number, 1 to 10. > >> > >> Are you trying to sense the metal by having it spoil the Q, > >> or shift the frequency? In both case I might want a higher Q. > >> > > >> > >Yes, I am not a engineer kind of guy. But my inclination is to > >hope that steel or iron would alter L the coil inductance. Does > >this mean technically altering Q? > > Mostly inductance. Iron will make it go up, brass down.Won't brass mostly change the Q.. or should I think of it as shielding the field from some volume of space? George H.> > > > >From what I read this type of bridge works best at a Q of one > >to ten. Is ramping it up to 100 allowed? > > Likely not possible at audio-type frequencies. > > > > >I have an audio oscillator and wonder if I can just add an audio > >amplifier for the power source. > > You can make an AC bridge, drive it with a good sine wave, listen to > the null with amplified headphones, tweak the bridge or the frequency > for a deep null. > > I guess you could use a resonated loop in an AC bridge, too. Might be > more sensitive. > > > > >thanks doug > > What would you do next if you found a cannon? > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●September 14, 20172017-09-14
On Thursday, September 14, 2017 at 8:46:36 PM UTC-4, Steve Wilson wrote:> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > > > Did anybody make iron cannons in that era? AFAIK it was Alfred Krupp in > > the mid-19th century who figured out how to found steel cannons that > > didn't explode randomly. > > > Cheers > > > Phil Hobbs > > Apparently, the USS Revenge sank in 1811. The US Navy just recovered an > iron cannon believed to be from the ship: > > http://www.businessinsider.com/the-navy-just-found-cannon-that-they-think- > was-war-of-1812-ship-2017-6?op=1 > > The 24-pounders were used in the 1700's and made of cast iron: > > https://en.wikipedia.org/wiki/24-pounder_long_gun > > Here's a view of hundreds of 1819 24-pounders stockpiled at Fortress Monroe > in Virginia: > > http://moultrie.battlefieldsinmotion.com/Artillery-24-pounder.html > > They were iron: > > "The bore-diameter for all these iron 24-pounders was established at > exactly 5.82 inches, and they were to weigh roughly 5,800 pounds apiece." > > http://moultrie.battlefieldsinmotion.com/Artillery-24-pounder.html > > "The Chinese also mounted over 3,000 bronze and iron cast cannon on the > Great Wall of China, to defend themselves from the Mongols." > > https://en.wikipedia.org/wiki/History_of_cannon > > Doesn't say when. Maybe the 1500'sNice info / links. Cheers, James Arthur
Reply by ●September 15, 20172017-09-15
On 2017-09-15, George Herold <gherold@teachspin.com> wrote:> On Thursday, September 14, 2017 at 8:32:45 PM UTC-4, John Larkin wrote: >> On Thu, 14 Sep 2017 14:02:56 -0700 (PDT), eaglesondouglas@gmail.com >> wrote: >> >> > >> >> > >> >> > Here I would increase the ac frequency to make a coil Q of the required >> >> > number, 1 to 10. >> >> >> >> Are you trying to sense the metal by having it spoil the Q, >> >> or shift the frequency? In both case I might want a higher Q. >> >> > >> >> >> >Yes, I am not a engineer kind of guy. But my inclination is to >> >hope that steel or iron would alter L the coil inductance. Does >> >this mean technically altering Q? >> >> Mostly inductance. Iron will make it go up, brass down. > Won't brass mostly change the Q.. or should I think of it > as shielding the field from some volume of space?it changes the inductance by acting as a poorly coupled shorted turn>> >From what I read this type of bridge works best at a Q of one >> >to ten. Is ramping it up to 100 allowed? >> >> Likely not possible at audio-type frequencies.high Q means poor coupling to the universe. using litz to wind the coil and special materials for the former will help performance a bit. but oodles of Q indicates a short-sighted sense coil.>> >I have an audio oscillator and wonder if I can just add an audio >> >amplifier for the power source.>> You can make an AC bridge, drive it with a good sine wave, listen to >> the null with amplified headphones, tweak the bridge or the frequency >> for a deep null. >> >> I guess you could use a resonated loop in an AC bridge, too. Might be >> more sensitive.A cheap kitset metal detector beats two oscillators against each other and presents the beat frequency to the user. user adjusts one oscillator go reduce the beat frequency OTOH perhaps do TDR on the sense coil. that gets you a kind of ground penetrating radar. -- This email has not been checked by half-arsed antivirus software
Reply by ●September 15, 20172017-09-15
On Friday, 15 September 2017 02:43:34 UTC+1, dagmarg...@yahoo.com wrote:> On Thursday, September 14, 2017 at 8:46:36 PM UTC-4, Steve Wilson wrote: > > Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > > > > > Did anybody make iron cannons in that era? AFAIK it was Alfred Krupp in > > > the mid-19th century who figured out how to found steel cannons that > > > didn't explode randomly. > > > > > Cheers > > > > > Phil Hobbs > > > > Apparently, the USS Revenge sank in 1811. The US Navy just recovered an > > iron cannon believed to be from the ship: > > > > http://www.businessinsider.com/the-navy-just-found-cannon-that-they-think- > > was-war-of-1812-ship-2017-6?op=1 > > > > The 24-pounders were used in the 1700's and made of cast iron: > > > > https://en.wikipedia.org/wiki/24-pounder_long_gun > > > > Here's a view of hundreds of 1819 24-pounders stockpiled at Fortress Monroe > > in Virginia: > > > > http://moultrie.battlefieldsinmotion.com/Artillery-24-pounder.html > > > > They were iron: > > > > "The bore-diameter for all these iron 24-pounders was established at > > exactly 5.82 inches, and they were to weigh roughly 5,800 pounds apiece." > > > > http://moultrie.battlefieldsinmotion.com/Artillery-24-pounder.html > > > > "The Chinese also mounted over 3,000 bronze and iron cast cannon on the > > Great Wall of China, to defend themselves from the Mongols." > > > > https://en.wikipedia.org/wiki/History_of_cannon > > > > Doesn't say when. Maybe the 1500's > > Nice info / links. > > Cheers, > James ArthurA mixture of iron and bronze cannon was found in the remains of the Mary Rose which sank in 1545 and which was launched in 1511. John
Reply by ●September 15, 20172017-09-15
On Friday, September 15, 2017 at 1:01:14 AM UTC-4, Jasen Betts wrote:> On 2017-09-15, George Herold <gherold@teachspin.com> wrote: > > On Thursday, September 14, 2017 at 8:32:45 PM UTC-4, John Larkin wrote: > >> On Thu, 14 Sep 2017 14:02:56 -0700 (PDT), eaglesondouglas@gmail.com > >> wrote: > >> > >> > > >> >> > > >> >> > Here I would increase the ac frequency to make a coil Q of the required > >> >> > number, 1 to 10. > >> >> > >> >> Are you trying to sense the metal by having it spoil the Q, > >> >> or shift the frequency? In both case I might want a higher Q. > >> >> > > >> >> > >> >Yes, I am not a engineer kind of guy. But my inclination is to > >> >hope that steel or iron would alter L the coil inductance. Does > >> >this mean technically altering Q? > >> > >> Mostly inductance. Iron will make it go up, brass down. > > Won't brass mostly change the Q.. or should I think of it > > as shielding the field from some volume of space? > > it changes the inductance by acting as a poorly coupled shorted turnRight, I was trying to understand how that changed the inductance. I'm using the model that 1/2LI^2 is equal to the integral of B^2 over all space. (B^2/ 2*mu_0) George H.> > >> >From what I read this type of bridge works best at a Q of one > >> >to ten. Is ramping it up to 100 allowed? > >> > >> Likely not possible at audio-type frequencies. > > high Q means poor coupling to the universe. using litz to wind the > coil and special materials for the former will help performance a bit. > but oodles of Q indicates a short-sighted sense coil. > > >> >I have an audio oscillator and wonder if I can just add an audio > >> >amplifier for the power source. > > >> You can make an AC bridge, drive it with a good sine wave, listen to > >> the null with amplified headphones, tweak the bridge or the frequency > >> for a deep null. > >> > >> I guess you could use a resonated loop in an AC bridge, too. Might be > >> more sensitive. > > A cheap kitset metal detector beats two oscillators against each other > and presents the beat frequency to the user. user adjusts one > oscillator go reduce the beat frequency > > > > OTOH perhaps do TDR on the sense coil. that gets you a kind of ground > penetrating radar. > > -- > This email has not been checked by half-arsed antivirus software
