GOLDSCAN 5 SCHEMATIC QUESTION

[dbanner]

Perhaps the user manual can shed light, although I'm skeptical about any manual making reference to "microseconds" when dealing with devices meant for public consumption.

[Qiaozhi]

Hello Qiaozhi....its just all confusing as i asked someone on youtube who was using a fisher AQ about the 7 uS delay setting and they told me they could use the 7 uS setting on wet sand without chatter but they said in the surf if the coil is swept in the waves then the detector will chatter

There's nothing on the front panel that indicates micro-seconds.

[daverave]

Hello Qiaozhi....its just all confusing as i asked someone on youtube who was using a fisher AQ about the 7 uS delay setting and they told me they could use the 7 uS setting on wet sand without chatter but they said in the surf if the coil is swept in the waves then the detector will chatter

[Qiaozhi]

on youtube some claim they can use a delay of say 7 uS on wet sand using the fisher AQ which has a bi polar coil drive from what i see...so im a bit confused

Bipolar pulsing can only ignore signals which have the same polarity during both positive and negative cycles. The signal from wet salty sand changes polarity during each pulse.

I think I've found the youtube video you're referring to. On the front panel of the Fisher AQ there is a control marked "Reject" which is labelled from 1 to 12, and I notice that the default setting is 6. I suspect these numbers do not refer to the actual main sample delay.

[daverave]

on youtube some claim they can use a delay of say 7 uS on wet sand using the fisher AQ which has a bi polar coil drive from what i see...so im a bit confused

[daverave]

someone told me the whites tdi sl has a fake threshold that gives a more stable threshold

[6666]

Hello Qiaozhi....when you say a bi polar coil drive minimizes the problem of magnetizig the ground so does that work the same for wet sand and does that allow the use of lower delays without chatter on the wet sand...also does anyone have a diagram of a bi polar coil drive that can be used for any pulse detector.

There was some work done on this BP design

https://www.geotech1.com/forums/showthread.php?18157-White-s-AF108&highlight=af108

https://www.geotech1.com/forums/showthread.php?25357-A-closer-look-at-the-AF108-bi-polar-drive-circuit&highlight=af108

[Orbit]

orbit do you know how whites got the audio threshold so stable in the TDI sl version even at max sens setting ???

Yes I know but I think it's TDI still a commercial device , although there are some other ways that the threshold of the tone be silky without ipon effect,I do it on my analog detector , moreover it can make even less noise than the original TDI SL..

[Qiaozhi]

i have modified two of my detectors to work down to 8 uS and work fine on the dry sand but on the wet sand too much chatter and thats why i wondered if a bi polar coil drive would eliminate the chatter at low delays...so is it only on inland field sites that the bi polar coil system will eliminate the ferrous ground effect ???

If you're lucky you may be able to set the sample delay between 10us and 15us, but in general (for wet sand) it is normal to use a 15us sample delay.
What you're referring to for inland sites is called viscous remanence magnetization (VRM). Carl should be able to give you a more detailed explanation on this.

[daverave]

orbit do you know how whites got the audio threshold so stable in the TDI sl version even at max sens setting ???

[daverave]

i have modified two of my detectors to work down to 8 uS and work fine on the dry sand but on the wet sand too much chatter and thats why i wondered if a bi polar coil drive would eliminate the chatter at low delays...so is it only on inland field sites that the bi polar coil system will eliminate the ferrous ground effect ???

[Qiaozhi]

Hello Qiaozhi....when you say a bi polar coil drive minimizes the problem of magnetizig the ground so does that work the same for wet sand and does that allow the use of lower delays without chatter on the wet sand...also does anyone have a diagram of a bi polar coil drive that can be used for any pulse detector.

Bipolar drive will not cure chatter from wet sand. The salt in the wet sand looks like a low conductivity target to the detector. Salt is sodium chloride, and sodium is a metal. Increasing the sample delay will allow you to ignore it.

[daverave]

Hello Qiaozhi....when you say a bi polar coil drive minimizes the problem of magnetizig the ground so does that work the same for wet sand and does that allow the use of lower delays without chatter on the wet sand...also does anyone have a diagram of a bi polar coil drive that can be used for any pulse detector.

[Qiaozhi]

whats the advantage of using a bi polar coil drive in a pulse detector ????

1) It automatically removes Earth field effect (EFE) so no need to generate a secondary (late) sample pulse to subtract from the main sample pulse. This is because the polarity of the Earth's field is the same for both positive and negative TX pulses.

2) Since the polarity of the pulse is constantly reversing, it minimizes the problem of magnetizing the ground. This is also important when searching for landmines, as some of these can be triggered when they detect a constant magnetic field.

3) As there's no requirement for the secondary EFE sample pulse, the TX pulse rate can be greatly increased. This is useful when searching for small low conductive targets such as gold nuggets.

[daverave]

whats the advantage of using a bi polar coil drive in a pulse detector ????