A
Anonymous
Guest
I have read the interpretations of Candy's patent and method of canceling the effects of ferrites in the ground by members here (and at Finders) and would like to comment on some of these.
Firstly Candy states that a target such as gold decays at the same rate independent of the pulse length and that ferrite decays dependant on the pulse length, that is, if ferrite is exposed to a linear non saturating field for one second then it would take one second to decay.
If you were to experiment with this in conventional PI design then your results would be influenced by the coils Q-factor, damping and the non-linear build up of current in the coil.
In other words, if you hit a particular coil with one pulse length and then one 1/4 as long then the results won't make much sense if the above isn't considered. He gets around all this by adjusting circuit gains to fit his equation.
It is interesting to note if the ferrite particles are fully aligned with the field before the pulse ends then the whole thing breaks down, thus, in his design, at no time can his detector be allowed to supply a field strong enough during any one pulse that will saturate ferrites close to the coil as the decay time (within the ferrites) would be an unknown time instead of being directly related to the pulse on time. Arguing, for now at least, whether or not saturation can occur during normal conditions isn't the point but taking it into consideration is.
In his early SD's he stated that one source of problems was the fact that part of the effect of every pulse may be handed down to the next because of his very short off times, ie the ground composite signal could still exist at the beginning of the next pulse and it has been found since that there is ground that can make the SD quite unstable because of this. I assume from this that additional pulses of the same polarity can create adding, leading to saturation as the search head is virtually stationary during the large number of pulse trains per second in his design. He was able to partly get around this in the SD's with a balancing act and, in all fairness, his bi-polar pulse in the GP is more about canceling previous ground sampling history and avoiding saturation than making false claims as some believe, tho it is obviously also a very good way of canceling noise and improving gain at the same time and has always been the prefered method in his patent.
I have only studied the early 2000 with a cro and along with the patent saw that he was using one long pulse followed by 4 short pulses that equaled the times of the long pulse. The long and short pulses are to gain the needed info to cancel ferrite and the equalization of times, in its simplest form, was done so as to cancel noise in line with normal practice.
All pulses have off times equaling the on times except the last short pulse that has a long off period so that field effects etc can be further cancelled. Minelab also used a stack of different xtals pairs for their clocks (SD2000) which I found alarming.
I would also like to say that I have never been lucky when buying one of his PI's new. When testing these I have been alarmed in every case to find that mine were less sensitive than others that I tested them against. I would love to get hold of the tune up procedure as a lot of the problems probably lie in the "adjusting circuit gains to fit" part. It would be nice if Minelab did something about their quality control.
One other thing, I am pretty certain that the Australian CSIRO used the effects that Candy claims as his patent in the late 1970's early 80's, in their stationary geophysical survey equipment tho his patent relies in part that at least one coil is in motion. His understanding and explanation of these effects shows a greater understanding maybe? The magnetic decay effect has been well known by geologists for a lot longer than this. Magnetic rocks that have become magnetized by the earths weak field over millions of years would take the same period for that magnetism to decay if removed from any magnetic influence.
I would also like to see the bit that Dave Emery reckons that Candy pinched from a well known English design?? Candy's patents are a bit of a nightmare to get thru but he has given very usefull explanations and even ideas for PI circuits that use simple novel ground balance and also ones where the coil is continuously switched with bi polar pulses and only sampled during the on times.
Anyway, I only wrote this as I think that some people may be looking at his concept in the wrong light and that this may impede their progress when attempting experiments of their own.
If any one believes that I have any of this wrong I expect a good thumping.
Robby_H.
Newcastle
Australia.
Firstly Candy states that a target such as gold decays at the same rate independent of the pulse length and that ferrite decays dependant on the pulse length, that is, if ferrite is exposed to a linear non saturating field for one second then it would take one second to decay.
If you were to experiment with this in conventional PI design then your results would be influenced by the coils Q-factor, damping and the non-linear build up of current in the coil.
In other words, if you hit a particular coil with one pulse length and then one 1/4 as long then the results won't make much sense if the above isn't considered. He gets around all this by adjusting circuit gains to fit his equation.
It is interesting to note if the ferrite particles are fully aligned with the field before the pulse ends then the whole thing breaks down, thus, in his design, at no time can his detector be allowed to supply a field strong enough during any one pulse that will saturate ferrites close to the coil as the decay time (within the ferrites) would be an unknown time instead of being directly related to the pulse on time. Arguing, for now at least, whether or not saturation can occur during normal conditions isn't the point but taking it into consideration is.
In his early SD's he stated that one source of problems was the fact that part of the effect of every pulse may be handed down to the next because of his very short off times, ie the ground composite signal could still exist at the beginning of the next pulse and it has been found since that there is ground that can make the SD quite unstable because of this. I assume from this that additional pulses of the same polarity can create adding, leading to saturation as the search head is virtually stationary during the large number of pulse trains per second in his design. He was able to partly get around this in the SD's with a balancing act and, in all fairness, his bi-polar pulse in the GP is more about canceling previous ground sampling history and avoiding saturation than making false claims as some believe, tho it is obviously also a very good way of canceling noise and improving gain at the same time and has always been the prefered method in his patent.
I have only studied the early 2000 with a cro and along with the patent saw that he was using one long pulse followed by 4 short pulses that equaled the times of the long pulse. The long and short pulses are to gain the needed info to cancel ferrite and the equalization of times, in its simplest form, was done so as to cancel noise in line with normal practice.
All pulses have off times equaling the on times except the last short pulse that has a long off period so that field effects etc can be further cancelled. Minelab also used a stack of different xtals pairs for their clocks (SD2000) which I found alarming.
I would also like to say that I have never been lucky when buying one of his PI's new. When testing these I have been alarmed in every case to find that mine were less sensitive than others that I tested them against. I would love to get hold of the tune up procedure as a lot of the problems probably lie in the "adjusting circuit gains to fit" part. It would be nice if Minelab did something about their quality control.
One other thing, I am pretty certain that the Australian CSIRO used the effects that Candy claims as his patent in the late 1970's early 80's, in their stationary geophysical survey equipment tho his patent relies in part that at least one coil is in motion. His understanding and explanation of these effects shows a greater understanding maybe? The magnetic decay effect has been well known by geologists for a lot longer than this. Magnetic rocks that have become magnetized by the earths weak field over millions of years would take the same period for that magnetism to decay if removed from any magnetic influence.
I would also like to see the bit that Dave Emery reckons that Candy pinched from a well known English design?? Candy's patents are a bit of a nightmare to get thru but he has given very usefull explanations and even ideas for PI circuits that use simple novel ground balance and also ones where the coil is continuously switched with bi polar pulses and only sampled during the on times.
Anyway, I only wrote this as I think that some people may be looking at his concept in the wrong light and that this may impede their progress when attempting experiments of their own.
If any one believes that I have any of this wrong I expect a good thumping.
Robby_H.
Newcastle
Australia.
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