Getting ready to build the MPP

[green]

Hi green
How you calculate/conclude on TC?
Par example, as I understand TC of target No. 7 is about 10 not 1.9 as stated.
Can you explain a little more?

One of two ways. Time between amplitude of 3 and 8 for 1 TC or time between 5 and 100/3(3 TC 1/20 or 5%), hope it's right. I usually draw a line on the chart parallel with the target in Excel where I can move it and get a closer reading.

[WM6]

Hi green
How you calculate/conclude on TC?
Par example, as I understand TC of target No. 7 is about 10 not 1.9 as stated.
Can you explain a little more?

[green]

That would be interesting. I'm sure the metal detector manufacturers must have this information, but I cannot find anything in the public domain.

Some pictures from other threads.(gold chain) need to scan down to see ruler for size, exponential decay TC=3.8usec.(coins, al slugs, cu coin ring) US nickel TC=10usec, wire ring TC=24usec exponential decay, the rest not. (steel balls) not exponential decay. (aluminum balls) not exponential decay. (ferrous) most, exponential decay after 10usec. (lead bullets) smaller, exponential decay, larger not. (gold nuggets_2) exponential decay, orientation effects TC. I don't remember having Tx on time or shape effecting TC for targets with exponential decay, maybe it can. Tx on time and shape does effect target decay for targets that don't have an exponential decay. If we are going to make a simple chart, need to define what the chart should look like. I think most larger targets don't have an exponential decay.

[Qiaozhi]

Not yet. Other than a couple thin wire rings I've made a US nickel with a TC of 10usec is the longest exponential decay I've measured. Foil,small nuggets and pieces of aluminum can are usually shorter TC's. I'll look at the data and see if I can put something together.

That would be interesting. I'm sure the metal detector manufacturers must have this information, but I cannot find anything in the public domain.

[green]

Reply #281 I stated total gain 400. True for target sample. Total gain 7200 for GEB sample to eliminate ground signal. Increased integrator gain

[green]

Green - I cannot remember if you've posted this already, but do you have a [simple] table of time constants for different types of target?

Not yet. Other than a couple thin wire rings I've made a US nickel with a TC of 10usec is the longest exponential decay I've measured. Foil,small nuggets and pieces of aluminum can are usually shorter TC's. I'll look at the data and see if I can put something together.

[Qiaozhi]

http://www.geotech1.com/forums/showt...get-simulation

Should be some info for different targets in gold nugget simulation. If you don't see what you want I'll try to add some more.

Green - I cannot remember if you've posted this already, but do you have a [simple] table of time constants for different types of target?

[green]

Good stuff Green! Looks like that 1/4 X 1/4" target is a pretty good/tough target. The gold nugget info is especially good too as it gives real world stats on what nuggets really do. I'd be interested to see how 4, 10, and 18 grain pieces of lead compare to the gold nuggets.

regards,

Dan

http://www.geotech1.com/forums/showt...get-simulation

Should be some info for different targets in gold nugget simulation. If you don't see what you want I'll try to add some more.

[Chet]

Hi Green,
Great charts as usual.
Thank you,
Chet

[baum7154]

Good stuff Green! Looks like that 1/4 X 1/4" target is a pretty good/tough target. The gold nugget info is especially good too as it gives real world stats on what nuggets really do. I'd be interested to see how 4, 10, and 18 grain pieces of lead compare to the gold nuggets.

regards,

Dan

[green]

Reply #274 I charted amplitude vs delay time for a .25x.25 in piece of aluminum can. Added more targets, California clay, US nickel, US quarter, 18 grain nugget and piece of aluminum can. Included a chart of gold nuggets I did awhile back. The TC's varied between 1.9usec and 6.6usec. The piece of aluminum can decays faster than any of the nuggets I tested. The nugget and aluminum can decay faster than clay. Adding GEB reduced the nickel, increased the quarter and did little to the nugget and aluminum signal strength. For the shorter TC targets 5.5usec or 7usec delay would be better.

[Monolith]

Thanks for the calculator. I need to enter twice the distance for the calculated field vs distance slope to match the measured target vs distance slope. Calculate 4 inches for target at 2 inches, calculate 8 inches for target at 4 inches.

That makes sense, as the calculator gives the primary field strength at the calculated distance. The secondary field, the one generated by the eddy currents in the target, then has to travel back to the RX coil.

[green]

Practical calculator

Thanks for the calculator. I need to enter twice the distance for the calculated field vs distance slope to match the measured target vs distance slope. Calculate 4 inches for target at 2 inches, calculate 8 inches for target at 4 inches.

[6666]

I agree. I had charted the .25x.25 aluminum can awhile back. Charted more data to get a feeling what it might take to detect it at 6 inches. Not the same as KR's MPP but should give an idea of the variables. Both charts show a TC of about 1.4usec.

Thats an interesting graph- Delay vs Signal- thanks.

[baum7154]

Yeah.... aluminum can, metallized plastic juice pouches, thin rusty iron, and old tin cans are the bane of a nugget hunters searches. If only we could discriminate Al from Au on a PI machine. I was surprised to see a very thin rusty razor blade discriminate as Al/Au the first time.

Dan