f75 differant coils, differant numbers

[prospect007]

why is it when I change coils the numbers change? when using the 11" coil a penny will read 61 where it's suppose too, but when I put the medium coil (7") the same penny reads 64. anyone know whats up with that change?

 

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[masterjedi]

Just a ? ... How do you know 61 is where its supposed to be? Not being funny here. I have a new F75 SE coming next Wednesday...

 

[Sandman]

It's called Calibration. When calibrated for one coil it naturally changes for different coils. Also numbers can change due to orientation of item in ground.

 

[prospect007]

masterjedi, the so called instruction book that comes with the machine said a (new) penny reads 61 (old, pre-82) reads 71. I would think that factory coils no matter the size would be calibrated for the machine.

 

[Charlie P. (NY)]

I have three coils for my F-75se (if you consider the Sunray as a 1" coil) and they all read consistently - but I get between 58 and 60 for post '82 and invariably 70 for pre '82 cents . Individual coins can vary from different depths and orientations.

I think Sandman is on with calibration. There must be some factory acceptance range for coils as they can't make them all perfectly consistent. You may just have two that were on opposite ends of the acceptance range. That display number is just relative conductivity to the surrounding soil. It's not like the detector knows what it's over. The manual gives you a statistical average.

I made up a list for targets and it holds up pretty well in use.



And here's one from Garrett that shows the relative targets on a 0-180 scale.

 

[Sandman]

Spot on Charlie. It would be nice it all component's of detectors met the specs exactly, but they don't.