Questions for Eric F. about Superscan

[jackdetect]

Hi Eric,



I was get one of your Superscan on service.

First, I was found that monoflops gives more then one impulse, and replace it.

But after that, I was have lot of problems with instability of unit, and any adjust wasn’t help.

Finally, I was find that somebody (before my), probably in some copy process, was replace wires for 0V to other place, and provoke wild oscillations. So, I was formed central point of 0V on coil jacks, and oscillations was stopped, but still exist on low level. After adjust, units start works, and I can say that it is very good and sensitive detector. Of course, hi must be with about 10W of power consumption!

I still haven’t much experience with Pi detectors, and can you please help my with some questions?

After repairing, I was try that unit on my polygon, with his 50cm coil. In air tests, hi was fantastic, he fill iron plate 15cm x 15cm more then 1m.

In ground, also was good with brass, but big copper pan 35cm diameter 90cm deep in ground was fill unsatisfactory with lot of ground noise. Generally, with coil nearly to ground I always get strong positive response, and it is produce very questionable results. So, maybe I was miss something in adjust, or things are the same with all Pi units, which dictate work with coil about 20cm above ground?

What a function of 0ohm resistors?

Reducing of power is important with such power consumption, but it is waste of energy with serial transistor. Are you try reduction of power with PWM regulation?

Are you ever try to return energy from negative impulse, like in Minelab GP serie?

Thanks,

Jackdetect.

[Unregistered]

First, I was found that monoflops gives more then one impulse, and replace it.

... i don't understand, the flyback signal have some kind of "ripple" around it's nulling point?

After repairing, I was try that unit on my polygon, with his 50cm coil. In air tests, hi was fantastic, he fill iron plate 15cm x 15cm more then 1m.

In ground, also was good with brass, but big copper pan 35cm diameter 90cm deep in ground was fill unsatisfactory with lot of ground noise. Generally, with coil nearly to ground I always get strong positive response, and it is produce very questionable results. So, maybe I was miss something in adjust, or things are the same with all Pi units, which dictate work with coil about 20cm above ground?

this is normal for a PI unit, the copper 99% have a respons "shape" similat to silver and is very difficlult to detect. For some metals the respons time is very close to the TX-OFF time. This detector is realized for very-very long sample time, it use a long TX transmission pulse (this is the reasons for 10W power usage) to detect very deep but... it loose gold-silver-copper-small objects.

If you detect a ground effect try to check is the coil is shielded with an open loop connected to ground rail. The ground effect is growing with wet soil and mineralized soil. If the cirquit can't detect the ground with some ground-tracking compensation you must accept this.

I have no schematics for this unit but if ther's some double-sample on the integrator OP probably there is some kind of ground-tracking. Verify if the "second" ON-OFF sampler cirquit is working or if is always OPEN.

What a function of 0ohm resistors?

where is used? series with coil?
If yes this is an adaptive resistor for adjust the time constant for different coils.

Reducing of power is important with such power consumption, but it is waste of energy with serial transistor. Are you try reduction of power with PWM regulation?

it's impossible to generate a ripple-free power supply with a PWM, 10mV are to much! I prefeer a linear reg. and a dual battery system.

[Unregistered]

>First, I was found that monoflops gives more then one impulse, and replace it.
... i don't understand, the flyback signal have some kind of "ripple" around it's nulling point?

>After repairing, I was try that unit on my polygon, with his 50cm coil. In air tests, hi was fantastic, he fill iron plate 15cm x 15cm more then 1m.

>In ground, also was good with brass, but big copper pan 35cm diameter 90cm deep in ground was fill unsatisfactory with lot of ground noise. Generally, with coil nearly to ground I always get strong positive response, and it is produce very questionable results. So, maybe I was miss something in adjust, or things are the same with all Pi units, which dictate work with coil about 20cm above ground?[/font][/size][/color]

this is normal for a PI unit, the copper 99% have a respons "shape" similat to silver and is very difficlult to detect. For some metals the respons time is very close to the TX-OFF time. This detector is realized for very-very long sample time, it use a long TX transmission pulse (this is the reasons for 10W power usage) to detect very deep but... it loose gold-silver-copper-small objects.

If you detect a ground effect try to check is the coil is shielded with an open loop connected to ground rail. The ground effect is growing with wet soil and mineralized soil. If the cirquit can't detect the ground with some ground-tracking compensation you must accept this.

I have no schematics for this unit but if ther's some double-sample on the integrator OP probably there is some kind of ground-tracking. Verify if the "second" ON-OFF sampler cirquit is working or if is always OPEN.

>What a function of 0ohm resistors?

where is used? series with coil?
If yes this is an adaptive resistor for adjust the time constant for different coils.

>Reducing of power is important with such power consumption, but it is waste of energy with serial transistor. Are you try reduction of power with PWM regulation?

it's impossible to generate a ripple-free power supply with a PWM, 10mV are to much! I prefeer a linear reg. and a dual battery system.

[Unregistered]

Cossaro

.... by Cossaro Fernando

Hi Jackdetect, have some problems to format my reply!!!!

[Unregistered]

Superscan

Hi Jackdetect,

The settings for the Superscan are as follows -

TX pulse width 500uS

TX pulse frequency 86 pulses per second.

Sample pulse delay 60 - 150uS, adjusted by reject control.

Delay for second sample pulse 1100uS

Sample pulse widths 45uS.

The coil inductance should be 500uH for TX and RX, with a TX resistance of 1.5 ohms, including the cable.

Because of the low pulse rate and wide spacing between 1st and 2nd sample pulses, the unit can be affected by low frequency rf signals and power line noise. The MK2 version has a TX frequency control that can often counteract this. Also the integrator TC is adjustable (response speed) - slower smooths out the noise more.

For best signal on any object, the TX pulse width should be about the same as the decay time of the object signal. A large copper pan could have a decay time considerably longer than 500uS and not give as good a range as a similar size object of less conductive metal.

Ground signals from iron mineralised ground will be strong with a single TX/RX coil, but the Superscan was also designed to use separate TX and RX coils. An outer TX with and inner RX of half the diameter will give much less ground response. Also you can lay a big 10m x 10m TX coil on the ground, and search within it with a 0.5 or 1m RX.

Eric.