IB Rx coil at Tx off

[green]

I would start out on the high side. You can remove turns easily and take data as you do it.

Thanks, Entered 20 turn Rx coils for the DD and figure8 into spice. Coils are different so maybe amplitude should be different. Response similar for both coils unless the simulation isn't correct. Looks like a good place to start.

[green]

Finished the templates for winding the spiral coils. Hope I have enough wire. Any thoughts before I make them?

[green]

Any thoughts which coil, DD or figure8 will give the greatest detection distance for a quarter or nickel? I'm guessing figure8 because of less noise.

[eclipse]

Figure8 should have less sensitivity in the center right? If thats the case it is a huge drawback.

[green]

Figure8 should have less sensitivity in the center right? If thats the case it is a huge drawback.

Zero response in center of Tx coil. Max response over center of each Rx coil.

[Carl-NC]

As I mentioned before, the Figure-8 lobes tend to cancel more for distant targets. So it is not a good choice if you want raw depth.

[green]

As I mentioned before, the Figure-8 lobes tend to cancel more for distant targets. So it is not a good choice if you want raw depth.

I chart I posted quite awhile back. 8 inch oOo is the figure8 coil I've been using. Probably didn't use enough care when doing the measurements, think offset signal should be similar for both sides. Peak signal with target at 12inches(1.5*coil diameter)is about .01 * signal with target at 4inches for all the coils. DD is lower overall, think mostly because Rx circumference isn't the same. Wondering if 24inch figure8 will be similar with target out to 36inches and if going to 30inch diameter with the DD will cause the signal amplitudes to be closer. Also wondering what happens with target(maybe a coke can) at 48inches(2*diameter)with the figure8 and DD. Mono coil would be best if no noise.

[Carl-NC]

This really doesn't compare apples-to-apples, your oOo coil is significantly larger. Yes, look at a big target out to 24-36", the Figure-8 eventually starts to cancel the signal. That's whys it's so good for EMI.

[green]

This really doesn't compare apples-to-apples, your oOo coil is significantly larger. Yes, look at a big target out to 24-36", the Figure-8 eventually starts to cancel the signal. That's whys it's so good for EMI.

- What are the elements that determine the performance of MD?

TX: Current, size of coil, number of turns.
RX: Size of coil, number of turns, SNR of the circuitry.
Very simplified, there are many other elements. Your reply https://www.geotech1.com/forums/show...837#post269837

Goal is to detect a US quarter at 24inches. Need to select size and number of turns for Tx coil . Need to select size and number of turns for Rx coil. Need to set Tx current, try to do it with 4A peak. What's left is SNR of the circuitry.

What would be the best coil type, size and turns to accomplish the goal?

The O(Tx)coil is larger but the o(Rx) coils are 8inch same as mono coil. Not saying it has to be practical for detecting, would just like to know if I could make a PI detector to detect a US quarter at 24inches.

[green]

I'm posting my attempt at detecting a quarter at 24inches for a couple reasons. Thinking the coil is important if not the most important part. Posting what I plan on doing forces me think what might be best way to succed. And hope if I'm doing something stupid someone will correct me. Not betting I can do it with 4A peak, maybe 8A peak.

[Carl-NC]

I've never seen a detector of any kind that could hit a quarter at 24" so you're blazing new territory here. The best advice I can offer is 'keep going' and put a lot of hooks in the design for trying out alternative methods.

[green]

Wanting to start winding the coils. Thinking spiral. Circumferece of smallest over 6 feet, largest over 10 feet. Have wound smaller spiral coils using double sided tape or super glue to keep windings together when winding. Slow process for me, has anyone found a good way to wind a spiral coil?

[Carl-NC]

I think it's gonna be difficult to wind such large spiral coils. Start with scramble-wound, see what that gives you. Spiral will only be very slightly better at that size.

[Altra]

Wanting to start winding the coils. Thinking spiral. Circumferece of smallest over 6 feet, largest over 10 feet. Have wound smaller spiral coils using double sided tape or super glue to keep windings together when winding. Slow process for me, has anyone found a good way to wind a spiral coil?

An old trick for making large pi coils is to use multi-conductor control type cable. Say you have 4 conductor cable, you wrap 3 or 4 turns on a 48" frame. Then you solder the individual wires to give you 12 turns total, or what ever number of turns you desire. Start red, finish red soldered to start white, white finish to start black etc. PVC pipe makes a good material for a frame. Once you get your inductance use tape or tie wraps to secure the bundle.


https://www.automationdirect.com/adc...waAlW0EALw_wcB

[green]

Thanks for the replies. I'm stuck with AWG19 magnet wire for Tx and AWG28 magnet wire for Rx, only wire I have enough of. Think spiral wind might be better, maybe not. Going to attempt it, have the templates for spiral. Would have to make something to wind bundle.