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?
Naval Cannon Search Magnetometer/Induction Coil Circuit
Started by ●September 14, 2017
Reply by ●September 14, 20172017-09-14
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. -- John Larkin Highland Technology, Inc lunatic fringe electronics
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.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.> > 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.comHmm not all steel is magnetic, check it before you dump it in the bay. George H.> > Any other suggestions are very welcome. > thanks doug > > Also how would a low pass filter be added to the electrometer?
Reply by ●September 14, 20172017-09-14
> > > > 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? 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 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
Reply by ●September 14, 20172017-09-14
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 dougSpeake, 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. -- 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 09/14/2017 05:07 PM, 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 >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 -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●September 14, 20172017-09-14
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 dougWhat 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 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? NT
Reply by ●September 14, 20172017-09-14
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 HobbsApparently, 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
