Meter system vs audio

[Anonymous]

I posted this question on another forum without an answer so hopefully this forum can help.
Has anyone tested the difference in signal response for the first indication of a target between a Needle Meter System and Audio System?
Thus would a needle flick first before a audible sound.
Gary.

 

[Anonymous]

Hi Gary,
from my point of view the real problem is 'how the metal detector is designed (?)', I mean that there are 3 ways a target audio/meter signals could be produced by a generic machine (of any kind):
- both , sync. meter ind. and audio tone
- meter indication first, then audio tone
- audio tone first, then meter indication
The way this kind of behaviour appears to us is strictly related to the internal design of the circuits and display/meter/transducers used as output devices.
Some meters and transducers have a 'start-up' time of few ms before they could indicate something. So also if the circuit is designed for a perfect syncro in display operations that thing can't happen.
Anyway, for a human being , in general and if the design isn't too 'naive' the difference in time between audio and meter should be so small (as few milliseconds) that anyone can't determine what's first rings or indicates, if any.
If the difference is in the 1/10 of second then , probably, there are a difference in the display units driving, as in some mds with different schemes for the meter and audio triggering (e.g. an integrator that drives the meter and a logic gate that trigger the audio tone generator, or again phase-pll-circuitry for the discriminative meter indication and clock division for the audio tone amp.) , but it'll be the exception not the rule.
Hope this can help you,
Massimo

 

[Anonymous]

Hi Gary,
I prefer audio as the prime output, with sometimes a meter to give additional information. Meters vary a lot in their response time and a quick fast signal could come and go before the meter was able to respond. Fast response meters are OK, but personally I think it is easier to pick out a weak repeatable signal on audio. Another reason for prefering audio is that you are less likely to trip over a rock or fall down a hole, than if your eyes are glued to a meter. Where a meter is useful is if, once having got an audio signal,it can give you additional information. e.g. on the PPD1 the centre zero meter would indicate left for ferrous and right for non-ferrous. On the Goldscan, I found it easier to ground balance using the meter to find the null, than do it on audio.
Eric.

 

[Anonymous]

As you tried on another forum then your question might not be P.I. related. If you get hold of an old Whites 6000 (pre D.I.model) it had a depth reading meter. On large rubbish (tinplate/alloy etc) the meter would deflect before the audio. So on a large signal all that was needed was to swing off target and slowly back. Deflection before audio no need to dig. Quite handy.