In order to make a more critical test, I have done the following.
I fixed a rotating branch , on the top of a tripod ,and the PD was fixed on the end of the branch. The branch was rotating by a12V DC motor with controled turns.
After too much tests to find the corect turns, I made the final test.
I started to rotate the branch with none gold coin in sight,
(How far was the coin of the device
and there was no signal from the PD.
Then I put a gold coin in 10 m distance and I noticed that after 3-4 minutes the PD started to give signal. Then I took the coin away,
(The device detects gold over 100 meters; How far hid the coin and after 1 minute the PD stoped to give signal.Then I placed the coin in the same distance but in 90 degrees angle from the first place. The same result, after 3-4 minutes the PD started to give signal from the new position.
Then I put another coin in the starting position and the PD gave signal to both positions.
During the test the controls and the motor turns , were steady.
I also noticed that with the coins on the ground for enough time, and the PD turned of, when I turned it on, it gave signal again after 3-4 minutes.