G'day,
There was a recent post by Eric relating to the GS5 that seems to have disappeared following the hacking of this forum a day or so ago. It occurred to me that Eric or Mr Bill may not have retained a copy of the post so it could be reposted ... so I've taken the liberty of reposting it myself (My suggestion is it could be copyed -- as below -- and reposted by Eric and this post deleted. At the very least it will save someone some time retyping it).
Regards,
Rob(RKC)
In response to some recent questions, here is a summary of how the GS5 compares to ealier Goldscans in this respect, and how it make the IDing of some "difficult" ferrous targets easier.
Earlier Goldscans i.e GS2, 3 and 4 had a very different audio system to the GS5. Also the GB circuitry in the GS5 has been considerably refined, so as to overcome the shortcomings of the previous models. The earlier Goldscan had a pulse type audio, and when using the GB mode, signal decays that were either faster or slower than the ground signal decay, came out as the same polarity. i.e. both slow decays and fast decays sounded the same. There was a switched facility to eliminate the response from slow decays, so that ferrous targets did not sound at all; but neither did non-ferrous targets with a long decay. Some ferrous targets that were thin, flat and fairly small, still sounded, as the decay was predominantly fast due to the objects geometry.
One of the main features of the GS5 is the totally new audio system that enables target identification to a considerably greater degree. Taking the ground decay as a reference, we still have target signals that decay either faster or slower than the ground. However, the receiver output is now positive for fast decays and negative for slow decays. This signal is then fed into a sensitive voltage controlled oscillator, arranged so that the audio tone goes higher for fast decays, and lower for slow ones. This tone generator, in turn, controls an audio chopper circuit, so that as the signal strength increases, the loudness also rises, whether it is a rising or a falling tone.
These features give additional information to the GS5 user, to evaluate the nature of the target, in particular, to determine ferrous junk, so as not to waste time digging it. It takes a little practice to be able to do this efficiently, and it does also depend on the hearing of the operator. Thin flat and rusted steel / iron / tin plated steel is a problem. Because it is thin, there is little magnetic response when the coil is right over it. What you get quite strongly, is the eddy current response of a poor conductor, and the tone will go high, just like a nickel. However, if the coil is off to one side, so that the pulsed TX field has a good horizontal component, then you get a strong magnetic response which generates a low tone. You have to listen carefully as you scan the target for a low - high - low response, as the eddy current response (high tone) is often the strongest. This type of signal usually means flat steel. Another way to enhance this, is to tip the coil on its edge, and draw it over the target. Assuming the steel is lying horizontal, the field will then also be horizontal, thereby maximising the magnetic (low tone) response. I can easily identify our modern 2p coins by this method, as they are copper plated steel, and sound very different to the full copper originals.
For deep targets, that little dip in tone, before it goes high, may only just be discernible, as is the dip just after the signal has passed. That is why practice is needed to develop this ability. The closer the object is, then the two opposite responses become clearer.
Eric.
There was a recent post by Eric relating to the GS5 that seems to have disappeared following the hacking of this forum a day or so ago. It occurred to me that Eric or Mr Bill may not have retained a copy of the post so it could be reposted ... so I've taken the liberty of reposting it myself (My suggestion is it could be copyed -- as below -- and reposted by Eric and this post deleted. At the very least it will save someone some time retyping it).
Regards,
Rob(RKC)
In response to some recent questions, here is a summary of how the GS5 compares to ealier Goldscans in this respect, and how it make the IDing of some "difficult" ferrous targets easier.
Earlier Goldscans i.e GS2, 3 and 4 had a very different audio system to the GS5. Also the GB circuitry in the GS5 has been considerably refined, so as to overcome the shortcomings of the previous models. The earlier Goldscan had a pulse type audio, and when using the GB mode, signal decays that were either faster or slower than the ground signal decay, came out as the same polarity. i.e. both slow decays and fast decays sounded the same. There was a switched facility to eliminate the response from slow decays, so that ferrous targets did not sound at all; but neither did non-ferrous targets with a long decay. Some ferrous targets that were thin, flat and fairly small, still sounded, as the decay was predominantly fast due to the objects geometry.
One of the main features of the GS5 is the totally new audio system that enables target identification to a considerably greater degree. Taking the ground decay as a reference, we still have target signals that decay either faster or slower than the ground. However, the receiver output is now positive for fast decays and negative for slow decays. This signal is then fed into a sensitive voltage controlled oscillator, arranged so that the audio tone goes higher for fast decays, and lower for slow ones. This tone generator, in turn, controls an audio chopper circuit, so that as the signal strength increases, the loudness also rises, whether it is a rising or a falling tone.
These features give additional information to the GS5 user, to evaluate the nature of the target, in particular, to determine ferrous junk, so as not to waste time digging it. It takes a little practice to be able to do this efficiently, and it does also depend on the hearing of the operator. Thin flat and rusted steel / iron / tin plated steel is a problem. Because it is thin, there is little magnetic response when the coil is right over it. What you get quite strongly, is the eddy current response of a poor conductor, and the tone will go high, just like a nickel. However, if the coil is off to one side, so that the pulsed TX field has a good horizontal component, then you get a strong magnetic response which generates a low tone. You have to listen carefully as you scan the target for a low - high - low response, as the eddy current response (high tone) is often the strongest. This type of signal usually means flat steel. Another way to enhance this, is to tip the coil on its edge, and draw it over the target. Assuming the steel is lying horizontal, the field will then also be horizontal, thereby maximising the magnetic (low tone) response. I can easily identify our modern 2p coins by this method, as they are copper plated steel, and sound very different to the full copper originals.
For deep targets, that little dip in tone, before it goes high, may only just be discernible, as is the dip just after the signal has passed. That is why practice is needed to develop this ability. The closer the object is, then the two opposite responses become clearer.
Eric.