Why Are Top-performing Dry Land Pulse Induction Detectors So Frickin' Heavy?

[GB_Amateur]

29 minutes ago, phrunt said:

Keep in mind the GPX 5000 battery isn't included in these comparisons as it's not on the detector....

I didn't realize that.  There must be some heavy electronics in that under-the-elbow control box.  Did all of the GP's and GPX's prior to the 6000 work that way?

[jasong]

I dont know enough about detector electronics design to know what exactly is required for design specs. But from a pure physics perspective there is another way to achieve a lighter coil and higher db/dt, and that is to use less windings (larger gauge) and a higher voltage, low internal resistance power source that is capable of supplying large currents. The larger the current the larger the B, and the less windings the faster B can change (dB), meaning dB/dt increases. 

Low inductance coils should be lighter since less windings, even with larger gauge wire, if one keeps the B field the same as before though. Plus they decay quicker. 

When I was researching coilguns, the way to do this was to pulse discharge high voltage capacitors through a coil with relatively few windings. One coil I wound only had 5 windings, but many thousands of amps of current. 

I'm sure there is some reason they don't do this on a smaller and safer scale with pulse detectors. But I'd be curious why since it seems like you could get lighter coil, higher sensitivity, and faster rise and decay times versus the low current, high inductance coils we use. Voltages/currents too high to be considered safe? Or some detector specific engineering reasons? FCC regs on radiation from the coil? Oversaturstion of the soil? I'm curious if a detector engineer could explain, as there has to be a good reason. 

[GB_Amateur]

27 minutes ago, jasong said:

...From a pure physics perspective there is another way to achieve a lighter coil and higher db/dt, and that is to use less windings (larger gauge) and a higher voltage, low internal resistance power source that is capable of supplying large currents. The larger the current the larger the B, and the less windings the faster B can change (dB), meaning dB/dt increases. 

Low inductance coils should be lighter since less windings, even with larger gauge wire, if one keeps the B field the same as before though. Plus they decay quicker. 

But I'd be curious why (that method isn't used) since it seems like you could get lighter coil, higher sensitivity, and faster rise and decay times versus the low current, high inductance coils we use. Voltages/currents too high to be considered safe? Or some detector specific engineering reasons? FCC regs on radiation from the coil? Oversaturstion of the soil? I'm curious if a detector engineer could explain, as there has to be a good reason. 

I have a feeling @Geotech can answer that, and more....

[phrunt]

I guess why weight matters so much more on gold prospecting machines is the people that use them tend to go on prospecting trips, detecting all day everyday, most people other than those lucky to live right in the heart of it all have to travel to do prospecting so they try and make the most of their time in the field.

People using detectors for coin or jewellery hunting in many cases can do it quite close to home, a quick trip to the beach or park isn't too difficult for many so they can just spend an afternoon or even an hour detecting, this is usually not the case with prospecting.  It often involves large hikes and long driving trips so you really want to make the most of your detecting time.

Some people use metal detectors looking for gold for a living, they need to get as many hours behind the coil as they can detecting almost every day for weeks or months on end.

It is therefore a shame the prospecting detectors tend to be the heaviest of all the detectors.

You hear a coin hunter complain their Equinox is too heavy for their afternoon beach hunt and saying they get sore after a hour swinging it with the 15x12" coil, well, think about the prospectors swinging their detector that weighs more than three times as much with a big coil looking for gold in the deadly heat of the Australian outback after a two hour long hike to even get to the spot to start swinging 🙂  That's why gadgets like the swing arm, various bungee systems and a myriad of hip stick type contraptions exist and  to try lighten the load a bit.  The GPZ with Minelab 19" Coil seriously needs little plastic and rubber 4x4 offroad wheels on the coil to be viable to swing for any length of time.

I find any VLF a pleasure to swing after spending most of my detecting time using a GPX and GPZ, even my CTX feels quite light by comparison and it's the heavy tank of VLF type detectors even though it's only slightly less heavy than the GPX 5000, it feels nice on my arm.

[BrokeInBendigo]

I figured out how to make my GPX light as a feather the other day. Used a heavy 1.6m crowbar to dig for about an hour. GPX and my pick felt like nothing. 
 

I don’t think the GPX is too heavy unless I put a 25” coil on it. Even with a 19” it’s manageable without a bungie - and I’m not a large or very strong person. But I do use it almost daily for a few to several hours, and I’ve built up the muscles. Also I switch arms (right swings for 80% then takes a break with left for 20% of time). 
 

I suspect the main issue for people detecting for long periods of time is RSI - we can work up the muscle to swing but you can’t really do anything about RSI besides switching arms. After a day swinging a large coil I feel some non-muscular aching in my shoulder - I’ll have to be careful about that in the future. 
 

No comment on the GPZ though. Never swung one. Feels stupidly heavy, and a big coil must really screw up the weight distribution. 

[jasong]

The raw inertia of the coil is a bigger problem for me than weight of the detector. A bungee, hipstick, etc do nothing for that. It's the back and forth motion, stop start stop start that kills my elbow.

The GPZ gave me permanent tennis elbow, I have to get steroid injections this year to try to fix it. 

RSI is real and no laughing matter for sure! I hope the 7000 is the last of the heavy detectors.

[MSC]

I am going to continue using my 7000 but because of the weight, only on flat ground and take more breaks than I normally do. The 6000 will be my most go-to detector from now on for a lot of good reasons. My 5000 will be my back-up gold machine. I have found most of my gold with the 5K, so I am still very fond of that detector. 

[BrokeInBendigo]

I've had my GPX 5000 for just about 1 year but I'm really into prospecting now and would like to have the best technology available for my efforts. Hopefully the next ZVT detector is closer to the 6000 in terms of ergonomics than the 7000. I'm holding off upgrading until that time I think.

[geof_junk]

The answer is not weighing one detector against another. The main concern is the effect on the user. Balance is a factor. When using a heavy "Garrets coil" on the "Deepseeker" back in 1980 I and some of my mates put a counter weight at the back of the detector box. The detector was heavier but less fatiguing. Lighter batteries help and as far from the coil as possible helps. Lighter coils is one of the main improvement. It also reduces inertia and so does speed of the swing. Another thing that stops the leverage on the user is to keep the coil swing closer to the body with a straighter arm and shorter swing length. Only small adjustment of the above factors are needed to reduce discomfort from a long hard day. 

[PhaseTech]

Correct. CTX3030 is heavier than a lot of coin machines, but the balance is excellent. But balance only factors in when walking/swinging. Regardless of balance, it's the full weight of the machine you feel when pulling it out of the car, carrying it to your spot, and every time you pick it up after you've recovered your target. So for these times, a lighter detector sure is felt and appreciated. But as I've mentioned in the past, I don't want manufacturers to start making things so light, that build robustness starts to suffer. 

I remember back in my Minelab days, the boys from service called me over to look at a SD2100 they received. I can't recall the exact story, but I think the owner left it on the ground at the back of the ute, forgot about it and reversed over it! The box was a little mangled as you'd image, but the thing still worked!!