Something odd..

-when surface hunting for modern coinage I have experienced some rather odd vdi readings....
-just to show you I will use a common norwegian small coin as the test object..
50 ore ,- produced from 1996 onwards..
metal content: 100% copper
weight: 3.60 grams
dia.: 18.50 mm
thickness: 1.5 mm
and here are some resulting vdi.readings from four different detectors.....

Minelab Xplorer XS : 28
Whites MXT: 79-80
Fisher CZ6a: Top segment ,always
Fisher F75-F70: 69-83 !
I know my tectors fairly well ,but i have a certain feeling that something is wrong in the F- departement...
--need your comments on this one..
trond



Edited 1 time(s). Last edit at 08/01/2010 05:40AM by trond.

.....Check the tightness of your coil connector first. Try a different coil also.........if you have one. Fortunately......this is a common coin in your country................so....................if possible...................try to find another F75 and/or person of whom has one..........and see how their detector responds/ID's. ((( Are you having identical results with F75 AND F70??? Two different detectors???...........Swap the F75 for F70 coil....and see if you encounter any difference/change ))).

Tom
I know this seems strange-and just to explain things a little bit more....
The results for the F-brothers are seemingly equal,-when surface hunting there is little diffeference in the vdi.numbers
I have tried the 5"DD with much the same results..
The 50 ore or half-crown is really the troublemaker,-the higher values are locking normally with only small variations in the the vdi.numbers.
The F70 seems to work nicely,-everything is tight and fine (the battery springs are ok. on this machine)..I am able to throttle
up into the nineties when conditions allow.
The problem with the small copper coin still puzzles me though,-maybe small variations in the copper alloy can explain the vdi.
variations .
Well thanks for looking in,and thanks for your comment Tom
trond



Edited 1 time(s). Last edit at 08/04/2010 03:49AM by trond.

Hmmmmmm..........Yes, I do wonder if it's something about that coin. The F75/70 should lock on to it with only a few numbers variation. Wonder if there is any bit of iron for an alloy.

----having checked with Norges Bank the central bank of Norway, I have come to the conclusion that some of
the trouble with the varying id.numbers lies within the coin itself.
The nominal weight is allowed to vary around a middlepoint of 3.6 grams...
This fact triggered me to a little test....
From a batch of twenty coins ,I picked two,-- one weighing apr.3.55 and one with a weight of 3.65
-when air-testing these two ,there were clear repeatable variations
3.55 gives 74-75
3.65 gives 75-76

-the metal content of the coin is an alloy mix of 97%cu, 2.5%zn and 0.5%sn......
cross testing with the MXT gave no variations in numbers..
here is the adress [www.norges-bank.no]
for checing details of coins and notes you have to use norvegian language ...
trond

And that makes much more sense. Looks like the F75/70 is locking on to a good VDI with both of those coins. That's better.

Sorry for the time gap -- well Tom I partly agree with you ,but remember that this last test was stricly an in-house air test
to check if weight had any influence on the VDI.results.
--I feel there is still something strange or odd about the low- 69-73,and the high section 77-83 (in surface conditions)
The fact that the F- brethren are both high speed analysing units that are tuned to be "on the edge"all the time,can
maybe explain their tendency towards multiple VDI.hit numbers,-versus the more calmer analysing abilities of the MXT.
Thanks for your comments and good luck on future hunts....
trond



Edited 2 time(s). Last edit at 08/13/2010 04:21AM by trond.