CTX giving false depth readings

[Lensman]

I've consistently been getting depth readings that are far too deep. For example, the other day I got a Merc that the display said was 7-8 inches, but it was only two inches. Any experts out there have an idea what's going on?

 

[GateKeeper]

Yes, you are not getting the coil over the sweet spot of the coil. The sweet spot is the Minelab sticker. If you are not over that sticker, then the target will show deeper..

 

[Lensman]

Wow! I did NOT know that! I thought it was the exact center of the coil where the shaft meets. Thanks!

 

[McClod]

Good info to know, thanks! I've had similar experience, figured it was similar to my AT Pro in that the depth reading often was deeper than the target while scanning but when I pinpointed then I would see the most accurate depth. Thanks for posting your question and the answers!

 

[Stever0812]

I have had alot of coins say 4-5 inches, multiple directions, pinpoint on and off, and the coin comes out only 2-3 inches. seems to only happen on shallow coins though. Can't seem to figure out why depth readings are so inaccurate.

 

[Dirtbag Kevin]

Is it only in trash areas or everywhere? Same thing happens to me.. I just thought it was pinpointing on a target that was close but a little deeper.

 

[Bayoubug]

Yes, you are not getting the coil over the sweet spot of the coil. The sweet spot is the Minelab sticker. If you are not over that sticker, then the target will show deeper..

So.. The center of the coil will not give the strongest signal on the CTX? This seems odd that the sweep spot for pinpoint and depth would be at the front of the coil instead of the center. I've noticed the same problem with the depth for me too, but I've also been having some issues with being able to zero in of a good pinpoint too. It seems the shallow targets are the worse. I've chalked this up to newbie error with the CTX. Every other machine I've used had a sweet spot in the center of the coil. I guess this is good to know now. I will have to try this out.

Thanks

 

[Johnnyanglo]

Remember that the depth is based on the best amplitude signal from the coin - parallel to coil and free of mineralization. Lower the returned signal amplitude with mineralization or coin on edge (or damaged coins / corroded) and the depth will be off. Usually, the coin signal has been attenuated (weakened) by iron contamination and is appears deeper on the meter than it actually is.

In your case, you are finding the opposite, the coin is shallower than the meter. Another cause can be swinging high (over grass) and the reading is accurate (meter says 7") but when you find the coin it is at 4" deep (that's 3" of gap over the ground). The meter was correct.

If it reads more shallow, the other cause can be because of non-standard coils and/or sweeping off-center. Sweeping off-center would normally give a weaker return signal (which implies a deeper target), but it can also just give an inaccurate depth reading because of insufficient information.

Try and focus the sweep right over the top of your suspected target (2-3" movement back-n-forth) and watch the meter from there. Wide sweeps that are too fast may average too much volume of dirt and not have sufficient processing time to get a good return signal from the coin. So, the rule for accurate depth reading is go slow, narrow the sweep, turn from different angles, keep the coil parallel to the ground and near to the ground.

Johnnyanglo

 

[Relic digger]

Thanks Johnny. That's good advice. I'll give it a shot tomorrow.