Patent of the day: US 5,576,624 Candy

[Anonymous]

Dave E., Eric, and other denizens of the PI tech forum,
I've been away from PI for nearly 10 years since discovering an opportunity for entertainment on this forum three weeks ago. So, I haven't tried to keep up on PI patents.
BEWARE THE SEARCH ENGINE ON THE US PATENT OFFICE'S WEBSITE! It misses huge amounts of stuff that it should be finding. One day just to test it, I tried to find my own patents and came up empty-handed. It also missed '624 Candy although it found a couple other Candy patents. It'll usually find patents if you tell it the number, but on other types of searches it's terrible.
PATENT OF THE DAY
When you read a Candy patent, prepare to be enveloped in an obliterative miasma of obfuscational murk, an overage of garbage verbiage, leading to a condition of brain paralysis before you can get halfway down the page. Darn, that attorney is good.
I haven't digested the whole thing yet-- that'd take years, and you still wouldn't know for sure what you'd eaten. But, I found some interesting stuff in there. Some of I rather like, actually.
Unfortunately my business interests preclude me from disclosing at this time what I found there. But, if someone else finds the same thing or something better, and publishes it here, I will certainly applaud them.
--Dave J.

 

[Anonymous]

Are you refering to the ferrite signal decay time being depenent on the transmit pulse width? That was the most important thing I got from reading it except for a headache!
I really doubt that the patent attorney wrote this patent. Sure, he or she would modify a few things but most patent attorneys will make you do most of your own write up.
This is ESPECIALLY true when the inventor insists on explaining things using math as Candy does. Most people don't realize that the patent examiner's do not even read the write up.
All they are interested in are the claims being made. If they cannot find the same claims made elswhere then they will be allowed. The main job that the patent attorney has is to write the claims.
Check out patents issued to the US Navy etc. Most are only half a dozen pages long and are EASY to read. The claims however are VERY well made.

 

[Anonymous]

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[Anonymous]

Hi Dave,
If I am not mistaken, Candy also mentioned using the flyback for energy recovery to reduce battery drain.
Reg

 

[Anonymous]

An idea borrowed from the Fisher patent.
Which brings me to the issue of borrowing or copying (some people erroneously call it stealing or swiping) ideas.
Knowing what to copy and what not to copy is a proper exercise of human intelligence; and, in an engineer, a sign that he or she is not stuck in the "not invented here" syndrome. All human intellectual progress occurs by copying and modification. Without it, no evolution occurs, and the road is a dead end.
I myself have "copied", arguably not nearly as much as I should have. If you study Bruce Candy's patents carefully in relation to prior art, it becomes evident that Bruce Candy is very good at copying.
Is successful copying a shortcut? No. In order to copy successfully, first you have to know what ought to be copied, and what ought not to be, because there's a whole lot more of the former available than there is of the latter.
--Dave J.

 

[Anonymous]

[No message]

 

[Anonymous]

Hi Dave et. al.
So does what the patent say make sense? Short pulse and long pulses, first order decay. Of course we have discovered on this forum that the subject of eddy current decay has at least three stages of decay, and maybe the last stage for some objects is first order, but only if it is a ring or little cylinder in the right position, or such.
This means the math in the patent is not complex enough. <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="">
The SD 2200 according to ML addvertising (picture of area of discrimination) only discriminates in the first few (4-6) inches or so anyway, which may or may not even be useful, unless one is surface searching.
One apparently needs multipule (plurality) of short pulses to pull this off. This means fewer long (main?) pulses per second (thats no fun). Is this because the short pulses are weaker? Is the new dual voltage stuff having high voltage short pulses (or fewer of them {like one})to make up for this? Does the GP discriminate further than the 2200? ML doesn't seem to be making this point any more.
It seems to me, to be effective, the discrimination needs to be the same as the detection range, or its usefulness in the field is questionable.
JC

 

[Anonymous]

JC:
I haven't tried to translate the entire patent into plain English yet, for reasons I've already stated in a prior post. So, some of what I say here may be off-base, but I'll take a shot at it.
"Math in the patent is not complex enough". If what was disclosed was adequate to interpret the claims, then the math was complex enough. (I'll e-mail you an additional comment on this which I don't want to make public.)
"The SD2200". There is not necessarily any correspondence between what is patented and what is manufactured.
"One apparently needs". As a general rule, one would use more short pulses than long ones, but the patent probably isn't based on that assumption.
"It seems to me". Discrimination is never as deep as the detection range, unless the detection range has been sandbagged. One could get mathematical here, something I'm not very good at. But in plain English, if you can't even see it, you can't tell what it is. .....In most soil, VLF discriminators won't discriminate targets anywhere nearly as deep as they'll find them, but that hasn't stopped VLF's from being the workhorses of the industry.
--Dave J.

 

[Anonymous]

I agree, patents aren't normally what is manufactured. I don't have a 2200, but from long time ago posts, some people saw that it puts out 3 or four (don't remember) short pulses and one long pulse. Past that it is a great leap of assumption to assume that the short pulse long pulse ML patents are tied to this detector, but that is what I did.
Discrimination is never as deep as detection range, is usually true (always), but since the detector is not as sensitive in discrimanate modes (often), at least in the now short range detector, the area of discrination is equal to the area of detection. This would seem to me to be most useful, in keeping from being fooled so often by the rusted can.
Of course having said this means that the detection range of the objects of interest, and the range of the objects of discrimination, will set the range of the detector to the shortest range of all these objects.
JC

 

[Anonymous]

Hi guys, Seems that there is a bit of confusion as to the different Minelab SD's and the GP. The SD2000 used one long pulse and one short pulse. Many of the guys on the finders forum claim that the 2000 beats the new GP and that it is still the best detector available today.
All the other SD series machines as well as the GP use a long pulse followed by three short pulses. The GP differs by transmitting a bipolar signal. The long pulses are 250uS and the short are 62.5uS.
None of the SD's discriminate against iron. The GP discriminates against shallow iron. Most GP users report the discrimination ability of the GP to be very poor.
Unlike the forerunner to the SD which is of course the non Minelab Goldscan, the entire series of SD's as well as the GP become totaly inoperable near any kind of electrical interference! Don't even think of using one of these detectors anywhere inside town limits.
For those who do not know the basic SD principle of operation, I will add a brief description. The SD generates two different length transmit pulses. More on this later. The receive signal is sampled by a series of sample and hold circuits after each pulse.
A sample taken immediately after a transmit pulse will contain components of high, medium, and low, frequency if they are present due to a target or ground signal. A sample taken a little later will not have the high frequency signal component as it will have died away. The receive sample will contain only medium and low frequency components.
A sample taken later still, will not contain either high or medium frequency components. It will however consist of low frequency components.
As is evident, the frequency components of the receive signal have now been effectively seperated by time. OK, so for three time seperated samples of the receive waveform, we have a first signal containing high, medium, and low frequency information, or "HML". The second sample contains medium and low frequency information, or "ML" and the third sample contains only low frequency information, or "L".
If you take the HML sample and subtract ML from it in the correct proportion, you have "H". You have now seperated the high frequency component from the signal.
If you now take the ML signal and subtract L from it in the correct proportion then you have M. You have now seperated the medium frequency component from the signal.
The low frequency, or L component is already seperated from the rest of the signal.
The Minelab SD's seperate a medium frequency or "M" component from the long pulse and a high frequency or "H" component from the short pulse/s. The M and H signals are processed as seperate channels. A low frequency "L" signal is also seperated from the receive signal.
The L signal contains the ground signal as well as a signal from the earths magnetic field when the coil is in motion. It also contains signals from some hot rocks etc.
The L signal is subtracted in the correct proportion to both the H and the M signal channels to balance the ground signal. This was done on the early SD's by adjusting a ground balance control for both the H and the M channel.
OK, so why use two different transmit pulse widths. If you think about it, the subtraction of a portion of L from say M will cause a notch response equal to the ground signals timing. Unfortunately, there will be some targets which will have similar timing. These targets will be lost.
To his credit (I think?) Bruce Candy discovered that the decay time of a ferrite ground signal was proportional to the transmit pulse period. A long transmit pulse provides a longer decay time for ferrite than does a short pulse.
What this means is that a ground balanced receive signal from a long pulse and a short pulse will have different notch timing! OK, so a small gold nugget with timing similar to the M channels notch will NOT be notched in the H channel or vice versa.
The rest of the circuitry is simple. As you can imagine, some targets will provide a positive voltage and others a negative voltage depending on their timing and the timing of the ground signal. Both channels are provided to op-amp full wave rectifier circuits so that all targets have the same polarity.
It is obvious that the signal for a specific target will have a higher amplitude in one channel than the other. A voltage comparator controls an analog switch to select the highest amplitude signal for application to the audio modulator.
Hopefuly, this description is a little easier to understand than the one provided in US patent number 5,576,624. Dave. * * *

 

[Anonymous]

Hi Dave,
Well that sounds like the best description I've read yet as to what is going on inside the SDs and GPs. About all I could do is guess, and not a good one at that. I'll have to print this out and read slowly even though it is alot easier reading than the patent.
JC

 

[Anonymous]

You were going to be breif???
Anyway, the reason a lot of people say the 2000 is still the best is because it runs the quietest on hot ground, hence being able to use larger coils more effectively. Also, it draws the least amps which keeps voltage to a maximum. Also the mods available in australia make the machine extremely sensitive yet it remains stable in comparison to earlier models. Is this because the 2000 with the mods still only uses two pulses? When they said Multi Period Sensing, was Multi only referring to two?? Anyway, I assume the SD 2000 mods only changes the second pulse which makes it more sensitive to smaller targets but will still find the larger targets because the long pulse is unaffected. Is this right??
If this is so, then a modded 2000 would be the best machine available at present.

 

[Anonymous]

Hi Dave!
Your Quote:
"None of the SD's discriminate against iron. The GP discriminates against shallow iron.
Most GP users report the discrimination ability of the GP to be very poor."
The SD2200D(with DD coil) and the GP(with DD coil or Black coil) both discriminate against iron. And yes the iron discrimination ability of the GP and The SD2200D is very poor.
Your quote:
"Unlike the forerunner to the SD which is of course the non Minelab Goldscan, the entire
series of SD's as well as the GP become totaly inoperable near any kind of electrical
interference! Don't even think of using one of these detectors anywhere inside town
limits."
It is true that the SD2100,SD2200D and the GP are affected by electrical interference,
a lot of it can be tuned out.The GP has a cancel mode which when used with the Black
series of coils is Very good at canceling some types of electrical interference but not all.
The SD's and the GP cancel electrical interference one better then the other depending
on the source.This is all based on my experiences with all Three.

 

[Anonymous]

Howdy there from down under. As to my brief explanation of SD - GP theory, Bruce Candy's US patent number 5,575,624 is 19 pages long. The type is also very small!!!
As to the multi period sensing, this refers to the timing of when the receive signal is measured. It is nothing to do with the transmitted pulses. All of the SD's and the GP use one long transmit pulse and three short transmit pulses except for the 2000. The 2000 uses one long and one short pulse.
The SD2200's sample the received long and short pulses 12 times per pulse set. This is what multi period sensing means. Most PI's sample the receive signal twice, so the description is accurate.
I don't know what the mods do for the 2000. I do know that people who own them love them like a baby. Modification of the short pulse width may well be what the mod does. Please let us know if you find out. All the best, Dave. * * *

 

[Anonymous]

Hello guys.
I beleive the 2000 mods are frequency mods, - that is an extra 3 crystals are included with a swith to select between the four. That crystal is responsible for the whole timing of the machine, - and by selecting a higher frequenct, - you get a shorter Tx pulse, - shorter pulse delay and shorter off time, - faster response on the ground. All SDs should have had this user adjustability, - and in some areas the 2000 is a very good machine still. John Kah coiltek

 

[Anonymous]

John,
Thanks for the info on the Minelab 2000 mod's. Changing the crystal frequency obviously changes both the long and the short pulse widths as well as the receiver sample times.
I have read a number of posts on the Finders forum where owners of the old 2000's swear that they will never part with them. A few of these people claim to have run both 2200's and GP's. They claim that the old 2000 beats all else. I cannot comment as I have never used any of the Minelab PI's.
My wife and I own a couple of Soveriegns. I use your big WOT coil. I could not believe difference that this coil made to the Soveriegn. My hat's off to you for a fantastic product, Dave. * * *

 

[Anonymous]

Dave:
Thanks for the complement, - and thanks for the input you have given to the forum of late. Its a pity more dont get involved, - I bet there is a lot watching! John

 

[Anonymous]

<BLOCKQUOTE>I don't know what the mods do for the 2000. I do know that people who own them love them like a baby. Modification of the short pulse width may well be what the mod does. Please let us know if you find out. All the best, Dave. * * * </BLOCKQUOTE>
Hi Dave, back in '96 I developed those Xtal mods for the SD2000.
Beleive me, it was pretty scarey messing with a less than year old SD2000 that cost $3670 at the time. lol <IMG SRC="/forums/images/biggrin.gif" BORDER=0 ALT="">
Those early mods simply increased the freq of both the pulses.
The SD2000 has one long and 4 short pulses. (the SD2200 has one long and 3 short).
The resident Xtals in the SD2000 are 2.0meg and 2.2 Meg.
If you add a simple switching CCT you can add the other two Xtals below, or change the ones on the board.
The Xtals used to increase sensitivity are 2.5meg and 3meg.
Only one Xtal is used at a time.
This dramtically increases the sensitivity to small targets and improves allround sensitivity as well.
This is great for working DD coils.
The possible drawbacks are when using Mono coils in hot ground as it can be extremely noisey.
I have since developed a new system of mods on the SD2000 series using Mono Coils that permits excellent sensitivity in hot ground with fast balancing and minimal "noise" problems, I call it GRM1.
There's only 32 of these mods being "tested" out there, all with no problems, (some of the Aussies here may have come across them)... I may even officially release them one day <IMG SRC="/forums/images/biggrin.gif" BORDER=0 ALT="">

 

[Anonymous]

Just a addition Gaz, the original xtals are not all the same. I have modded 5 for friends etc and they all had 1.8 & 2.0Mhz xtals as standard. We also go below that (1.6 and 1.2Mhz) 1Mhz doesn't function properly. However the lower freq's are only for large coils (18" etc) Tests we have carried out give the detector at least a 3" extra depth advantage on nuggets around the 1oz size. Obviously the lower frequencies lose sensitivity with smaller coils and smaller nuggets. Overall a good compromise though. I have 1.2, 1.6, 1.8, 2.0, 2.4, 3.0 and 3.2Mhz Xtals in my 2000 plus I changed the Output FET from the IRF710 (some had 720,730 in them)to a IRF740, also used a IRF840 with not much difference. Gives me about a 1" depth advantage. 12V conversion (regulated 7.xxVDC) doesn't appear to give me anything over a decently charged 6VDC battery only longer detecting. Although I do not dispute 7.xx claims. I found that I have to run my detector most of the time at 7 - 7.1 VDC anything above and balancing becomes a problem in normal mod position 4 (3.0Mhz) even with the 10" eliptical. Must admit I haven't tried it with larger coils and at lower freqs maybe better. I will run some test in the coming weeks as I hope to be going out bush again.
Well that's about it for me TOO long winded for a reply :0)
Regards Ismael

 

[Anonymous]

Hiya Ismael,
It's good to see some adventurous Techy's out there <IMG SRC="/forums/images/biggrin.gif" BORDER=0 ALT="">
I have come across what appears to be 5 different models of the SD2000 so far as it appeared pretty experimental in the beginning, so yes the Components changed quite a bit, the later series used the components I mentioned earlier and there's a lot more of 'em. <IMG SRC="/forums/images/wink.gif" BORDER=0 ALT="">
The 2.5(off the shelf Xtal is 2.45) and 3meg mod Xtals I refered to are the summary of what will give a generally good performance in overall ground conditions using the DD and in quieter areas with a Mono.
In my original tests I used any and every Xtal in the book!. lol <IMG SRC="/forums/images/biggrin.gif" BORDER=0 ALT="">
Your results are pretty much the same as mine for the range you posted.
I feel the the real key to utilizing the lower freq is to wind a coil to suit as all the coils available today, no matter what physical size, are set up for a specific window of performance and groundbalance pre-requisites across the SD's performance range.
Be carefull of blowing up the front end RX FETs when you build coils (I've killed about 15 over the last few years lol <IMG SRC="/forums/images/biggrin.gif" BORDER=0 ALT=""> ) , they don't handle back EMF or excess signal spike too well (especially with the DD designs)...it's another reason I believe Minelab use a stronger RX in the 2200.
I have tried the IRF840 with no real benefit at standard voltage, however in those days I grabbed whatever was around, i.e the Makita 7.2V drill battery and it's DC fast charger to get some performance increases that worked ok...I still use a similar setup.
If anyone is interested in a cheaper and lightweight alternative to the available 12V/7.45 system, you can grab a 7.2 Volt Battery from most Aero model suppliers along with a fast charger.
These vehicle powered fast chargers cost around $25(Aus) and the batteries are about the same. (it's a lot cheaper than buying Makita stuff, I'm not even sure if their 7.2V stuff is available anymore), they don't last as long of course (3 hours), but then there are a lot of retiries that don't work 8 hours straight anyway and it makes the battery dept very lightweight or you can parrallel as many 7.2 V battery packs as you want to increase duration times. <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="">
For the non techy's, it's always a good idea to check the Voltage of the battery when it's fresh off the fast charger as it can be quite high (8.2), making up a little 15W light bulb CCT to momentarily load the volts back to the nominal 7.2 before use is a good idea...(or just put a Zener in the lead CCT)
p.s Ismael, I emailed you back but it was returned as unsendable. <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="">