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I am going to build a Minipulse plus just for fun and experimental purposes, but I am interested to know the performance differences between the 2. Has anyone compared them side by side?
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Minipulse just went onsale reciently I'm not sure anyone has performance data yet.
They sure look similar from a quick view of the schematics. I just ordered from Silverdog
1 or 2 days before the board was there so missed buying one or I'd compare them... -
Looks like the Mini might be working a little bit better;
HammerHead
1 eurocent copper coin (11mm diameter) is detected clearly from 17cm
50 cent Australian coin (32mm, white metal) is detected from 25cm
$1 Australian coin from 20cm, $2 Australian coin from 17cm
EUR1 from 18cm.
Minipulse
I plan to run some tests before posting my results within the next few days but so far it appears to be working ok about 30cm to a coin..!Comment
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Hi Silver dollars,Originally posted by Silver Dollar View Post
Do you know from what year that euro cents is?
Because if the euro cent is younger than the year 2000 is made from iron with a very thin layer of copper. It's magnetic.Comment
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No I found that quote in the HammerHead area. I don't know who did the measurement...Comment
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Thanks for finding those results, very usefull.Originally posted by Silver Dollar View PostComment
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Thanks for that. I am looking forward to building mine and having a play with it. No point in just using all my test gear for work. May as well use it for fun stuff!Comment
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Here are the results of my own tests:Originally posted by Silver Dollar View Post
HH with 10" diameter coil ... 1 euro at 11"
MPP with original 8" diameter coil ... 1 euro at 8".
However, you have to be careful with these type of comparisons.
Firstly, the HH is designed as a learning tool for PI technology. It has a lot of options and adjustments, and is probably the most complex PI design on Geotech to construct. It certainly shouldn't be your first choice of a DIY detector if you've never built one before. The pre-amp is single-stage, which limits its use to a coin and relic detector. The HH is a really good detector, and early sampling is limited mainly by the pre-amp. The HH for this test has a 1000pps TX rate and a TX width of 120us.
The MPP is intended as an alternative to the Surf-PI and Barracuda designs, which (like the HH) both have a single-stage pre-amp. The MPP splits the pre-amp into two separate stages to allow the use of a faster coil and earlier sampling. The TX rate in this case is set to 1000pps with a TX pulse width of 58us. Also, the test shown above on the MPP was using the original MP coil, which is 500uH and quite slow. There are many tweaks you could do to the MPP to increase depth, such as increasing the TX pulse width, so you need to consider all these factors when making comparisons.
Unless you set up both detectors with the same settings and use the same coil, it will be difficult to get a direct comparison. With the current setup, the MPP is not about depth, but more about detecting smaller low conductivity items. The other USP (unique selling point) of the MPP is its ease of construction and calibration.
By the way, the earlier claim by Dean Sarelius of 30cm depth on a coin was incorrect. Apparently he should have posted that it was 15cm. Again, we don't know anything about the size of the coil or the coin. I will be posting DS's photos in a new thread later today.Comment
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Thanks for your detailed reply Qiaozhi. The ease of construction was never an issue for me as was depth. I want to experiment with a machine to try to get sensitivity as high as possible with very low noise.
Can i just ask one more question.. When you say a faster coil, I understand the electronics theory behind it all but how does that translate into the physical... Different construction methods? Layout of coil?Comment
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The answer to your question can be found here ->Originally posted by CAS View Post
http://www.geotech1.com/cgi-bin/page...oils/index.datComment
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I had read that article but as it was written in 2006 I thought maybe there were different materials used now. For eg the Teflon coated wire, spiral wrap etc. New materials having a lower dielectric etc. Have improvements been made with experimentation over these materials or are they basically as good as anyone has got?Originally posted by Qiaozhi View PostComment
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It's possible that different [newer] materials could produce a slightly faster coil, but the law of diminishing returns will be in action. Once you get the coil fast enough to sample at sub-10us, you start to detect the ground matrix itself, and then you have other problems to worry about.Originally posted by CAS View PostComment
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_____________________________________Originally posted by CAS View Post
I made extensive use of BB Sailors paper in building/testing my coils.
The best coils I have built are in the CHANCE PI COIL thread of the COILS forum. While they are more work to build, they pay off in exceptional speed (8"/335uh/6us) and the fact that they 'self shield' by virtue of the coil geometry. The self shielding removes a major task from the coil construction and improves speed and eliminates additional shielding losses. Take a look at Page 2, post numbers 30, 31, 35, 36, 47 and you will see pictures and description of the coil construction. This coil will not see your hand completely gripping around it with the detector set to 8us sample delay (evidence of effective shielding) as long as the outermost end of the windings are at system ground. I would use 600volt Teflon/PTFE insulated #26 awg silver plated stranded wire (EBAY) to wind this coil and .091" thick LEXAN (from Home Depot) to create the form. I would cut the slots no wider than 1/8" wide in the form. I use a continuation of the coil wire twisted with a cordless drill at a rate of 3 turns per inch to eliminate solder in the coil which can be detected at short sample delays, and to eliminate much of the capacitance inherent in the use of coax cable. As there is no additional shield the coil can just be profiled out with polyethylene foam, over wrapped with self adhesive cloth hospital tape, and then directly fiberglassed.
Best of luck,
DanComment
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Dan
Thanks for sharing all your hard work. I have access to a few different gauges of the Teflon coated wire so while I will build he first one using your instructions, I will invariably try other sizes to see how they go. Thankfully I have most of the materials laying round the workshop so if they don't work, it's only time I have lost.Comment
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I'm glad to help. The reason I suggested 26 gauge wire with the thick 600 volt insulation is that coil speed is much better with smaller wire gauge and thicker PTFE/Teflon insulation. Thinner wire and thicker insulation means less capacitance and that is what we want to keep low in a coil and feed line. However too thin of wire has more resistance than we want so there is a limit on small wire size.
Regards,
DanComment
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