Re: My opinion of the Dalton unit.

[rick]

thanks to respond too jimi...


more thoughts the better....


presently use sheet acrylic to make bobins for


permanamet form----


example--take single strength sheet and cut out


3 "donut" shapes--say 2)5"od x 4"id and


1)4.25"od x 4"id////sand smooth edge etc.


now use acrylic cement to make sandwich assembly


(of coarse there are certain technics to follow


such as clamp 2x4 in vice with hole in it for jig


saw blade to keep plastic flat--no bounce cut slow


at slow speed else plastic melt tablesaw surface


flat reference when cement together sandwich ultra


clean less dust make surface not touching---)you do


correct and smile---now in this case bobbin


round (can be ellipse or any shape) 5"od x 4.25id


hence a channel 3/8"deep x ~1/8"wide (use 1/4" or


??? for center ) you smile----line with al. foil


for channel---leave space less 1 turn winding


shunt field........cut 2 plastic face --to make mount


shaft etc....

[rick]

thanks to respond too jimi...


more thoughts the better....


presently use sheet acrylic to make bobins for


permanamet form----


example--take single strength sheet and cut out


3 "donut" shapes--say 2)5"od x 4"id and


1)4.25"od x 4"id////sand smooth edge etc.


now use acrylic cement to make sandwich assembly


(of coarse there are certain technics to follow


such as clamp 2x4 in vice with hole in it for jig


saw blade to keep plastic flat--no bounce cut slow


at slow speed else plastic melt tablesaw surface


flat reference when cement together sandwich ultra


clean less dust make surface not touching---)you do


correct and smile---now in this case bobbin


round (can be ellipse or any shape) 5"od x 4.25id


hence a channel 3/8"deep x ~1/8"wide (use 1/4" or


??? for center ) you smile----line with al. foil


for channel---leave space less 1 turn winding


shunt field........cut 2 plastic face --to make mount


shaft etc....

[Patrick Duff]

I just wanted to comment a little further on Jim's post. If anyone


is considering Dalton's unit for marine use you will no doubt need a


chart recorder. Dalton sells one for around $500 for his system.


As Jim mentioned, you will have difficulty hearing it with boat


motors running. In addition, it will be very difficult to remember


where/when the sound was loudest.


The chart recorder provides a history that your mind will quickly


forget. Especially if you are operating the boat with limited help.


Phil, do you know if anyone has hooked a chart recorder up to your


unit?


Patrick


Jim Koehler wrote:


The Proton Mag ForumHi guys,


The Dalton mag is a gradiometer - that is, it is sensitive to the


difference between the two sensors.The Geometrics unit Patrick is


referring to is, I believe, a single magnetometer only. The big


advantage of a gradiometer is that it is not affected by general


changes in the earth's magnetic field due to ionospheric currents.


At low magnetic latitudes, the local magnetic field varies fairly


slowly and not very much. At high magnetic latitudes, you can get


very rapid and very large changes in the magnetic field on the


ground. Up at Churchill, Manitoba, at the rocket range, I have


seen changes in the magnetic field (on the ground) of more than


1000 nT over a time period of about 5 minutes. Using a single head


mag. like the Geometrics (or any other single sensor mag.), you


can't tell if the change you are seeing is caused by something


you're going past or by the ionospheric currents overhead.


I have seen a Dalton mag. owned by one of my neighbours down here


in Arizona and, in my opinion, it is not worth the money. It is


essentially identical to the gradiometer that Phil Barnes


describes with one small difference. Dalton passes a small DC


current through one of his sensors during the 'readout' phase so


that you get a slow beat even if there is no magnetic material in


the vicinity. Changes in the local magnetic gradient due to nearby


magnetic materials then cause a change in the period of the beat.


He calls this method the "delta-squared' method because he


observes this 'change in the difference' - the difference being


due to this small DC current. This helps but, in my opinion, only


slightly. Unless you are going to invest in a portable chart


recorder, it is very difficult to hear, through earphones, any


meaningful change due to small gradients in the field. I must add


the caveat that I've never taken the Dalton unit apart or looked


at the insides. I've just seen the unit, seen it operating and


read the literature he provides. The unit I saw was built more


than three years ago and I have no idea how much, if any, he has


improved it since then.


All things considered, I'd just buy Phil Barnes excellent


construction CD (http://members.aol.com/phil770/index.htm)and


build the Phil Barnes unit. It works, has readily available


components (most of these can be bought at a local Radio Shack


outlet), is simple and inexpensive, and is essentially the same


thing as the Dalton unit. The sensitivity is, as I've described in


my overall document, about 25 nT, give or take. For a gradiometer


of this type where you are listening to the beat, you want the


signal to decay very slowly and hence probably want to use


distilled water as the liquid since it has a decay time constant


of ~3 seconds. Kerosene has a decay time of ~0.5 seconds so


wouldn't be usable in this type of mag. - the signal just fades


out too rapidly - you need to measure the frequency electronically


over this short a period.


The 'stand-alone' unit I've described in my most recent addition


to my Web pages can use any liquid and gives a digital readout and


has a resolution of about 0.1 nT. However, it is a single sensor


unit, like the Geometrics, and has the failings of a single sensor


unit. For prospecting on the ground, you probably will want a


gradiometer and that requires two single magnetometer units. I've


finished my gradiometer but am making minor changes in it and am


not ready to release the plans till I'm sure all the i's have been


dotted and the t's crossed.


My 'stand-alone' mag. can probably be built for approx. $100 -


that's the cost of the parts and assuming that the labour,


provided by the builder, is free. The gradiometer requires two of


these units plus an additional few parts. I'd estimate a total


cost of about $300.


JimJ.A. Koehler


3290 N. Koehler Rd.


Florence, AZ, 85232


Ph: (520) 868-1156