Battery power

[Anonymous]

G'day to all,
Tony asked an interesting question about how much battery power effects the detection depth on the GQ.
Eric pointed out that "the laws governing metal detection show that even for a 50% reduction in TX
current the detection range will only fall by 10%"
My question is do these laws apply to Minelab SD detectors ?
Here in Australia,fitting a 7.3v regulated power supply is highly recommended by most "after market" companys. They claim that 7.3v will increase depth and sensitivity plus make the detector smoother and quiter than the standard 6v supply.
These claims are also made in regard to the GP and the new 3000.
Can anyone explain that one ??
Regards
Brian

 

[Anonymous]

Hi Brian,
Yes, the converse applies, even to Minelab. If the transmitter current is increased, say doubled, then the detection range will increase by 10%. This is because of the inverse sixth power law that governs metal detection, where you are transmitting to a target, and getting a return signal. To double the transmitter current on a PI, you would need to go from 6V to 12V supply. Going from 6V to 7.3V is only a 21% increase in voltage, which will give only a very small increase in range. I haven't the information here to work it out, as I am still away from the office, but will have a look when I am back. By the way, it is not possible to run the SD's at 12V. They stop functioning properly at 8.5V, so there is a built in safety margin when using the 7.3V regulator that should not be exceeded.
There are benefits though, in having a regulated TX supply. The transmitter current and detection range remains constant throughout the charge life of the battery. The signal from a target will be noticeably stronger when compared at the same range at 6V and 7.3V.
The most effective way of gaining detection range is to use a larger coil. As long as you can detect a given size object at a greater distance than the coil radius, then using a larger coil will give increase in range. You eventually reach a point, though, where the coil is too big and the range starts to fall.
Eric.