field test unit no 001 "model T"

[mickstv]

Drawing a long bow here ....I predict you wont need the gb sample ...gb will be done by adjusting the damping control ...manual in this code but future code will track automatically.

Moodz

I see what you talking about. Once those last parts turn up and have it build the front end I'll have a better understanding of what's going on.



Mick

[moodz]

Maybe not just depends on how it works out in the field, I guess if it was needed we could use the main TX pulse to trigger a 3rd sample using maybe a 4538 and feed the signal back in before the ADC. But this is purely speculation till I have a working prototype and are testing out in the field.



Mick

Drawing a long bow here ....I predict you wont need the gb sample ...gb will be done by adjusting the damping control ...manual in this code but future code will track automatically.

Moodz

[mickstv]

That would mean I will have to move to the 4011 chip with 4 sample pulses available.....not enough free ports on 4012.



moodz.

Maybe not just depends on how it works out in the field, I guess if it was needed we could use the main TX pulse to trigger a 3rd sample using maybe a 4538 and feed the signal back in before the ADC. But this is purely speculation till I have a working prototype and are testing out in the field.



Mick

[moodz]

Hi Paul, Do you think we will need a third sample for ground balance with the new front end ? the ground I'm talking about is Central Vic goldfields.



Looks like no building this week, I suspect the mosfet np's wont be come till Monday or Tues.



Mick

That would mean I will have to move to the 4011 chip with 4 sample pulses available.....not enough free ports on 4012.



moodz.

[mickstv]

I have several kilos of different ferrites and minerals here but I cant get any of them to produce a response ... the differential coil only seems to respond to conductive items like metal. ( ie induced currents ) Anything that is not conductive is invisible. I have previously done some experiments with DD coils and these targets do respond so I know they are good test rocks. Wet clay / damp salty ground may be a different story though.

Paul.

EDIT: I should say that the hotrock testing has been done on the previous version of the circuit with resistor / diode "crowbar" amplifier protection ..... the results may be different for this version with blocking FETs fitted as the voltage is not clamped off at 0.6 volts as it was with the diode / resistor arrangement.

Hi Paul, Do you think we will need a third sample for ground balance with the new front end ? the ground I'm talking about is Central Vic goldfields.



Looks like no building this week, I suspect the mosfet np's wont be come till Monday or Tues.



Mick

[moodz]

D'oh

Actually I was thinking about using maybe the OP37 as a second stage. Guess i'll find out if that's the way to go when the parts turn up. Could we do a similar circuit to the ZPI ver1.0 circuit from last year ?

http://www.geotech1.com/forums/showpost.php?p=100688&postcount=192

Mick

That should be fine to try out ... I am going to modify the UNIPI code to move the damping control to the primary adjustment followed by sample pulse 1 position ... the damping level and the sample time for pulse 1 are the two most critical controls on for setting up and using the detector .... or they seem to be. The voltage "gap" or differential between the two flybacks at the settling point can be minimised by adjusting the damping. This point is also where the descrimination occurs.



moodz.

[mickstv]

We don't have the channel samplers and amplifiers either

D'oh

Actually I was thinking about using maybe the OP37 as a second stage. Guess i'll find out if that's the way to go when the parts turn up. Could we do a similar circuit to the ZPI ver1.0 circuit from last year ?

http://www.geotech1.com/forums/showpost.php?p=100688&postcount=192

Mick

[moodz]

What else needs fixing ?



Mick

We don't have the channel samplers and amplifiers either

[mickstv]

...there are some things that need fixing ..for instance the damping circuit is conducting power during the tx on time .
This a waste of power.

Moodz.

What else needs fixing ?



Mick

[WM6]

...there are some things that need fixing ..for instance the damping circuit is conducting power during the tx on time .
This a waste of power.

Moodz.

Yes! From my point of view very important.

We need to reach as much low power consumption as possible.

With an old Fisher Impulse we get with one battery set 10 day of use.
Why nowaday this have to be worsten to 10 hours?

[moodz]

...there are some things that need fixing ..for instance the damping circuit is conducting power during the tx on time .
This a waste of power.

Moodz.

[moodz]

Just ordered the parts needed hopefully they will all turn up by Friday. But in the mean time I don't seen any reason why I couldn't at least get the damping circuit installed and tested on the existing setup.

Back on your previous version, did you ever get a chance to test the diff setup over heavily mineralised ground and hot rocks. Just wondering how it may have performed.


Mick

I have several kilos of different ferrites and minerals here but I cant get any of them to produce a response ... the differential coil only seems to respond to conductive items like metal. ( ie induced currents ) Anything that is not conductive is invisible. I have previously done some experiments with DD coils and these targets do respond so I know they are good test rocks. Wet clay / damp salty ground may be a different story though.

Paul.

EDIT: I should say that the hotrock testing has been done on the previous version of the circuit with resistor / diode "crowbar" amplifier protection ..... the results may be different for this version with blocking FETs fitted as the voltage is not clamped off at 0.6 volts as it was with the diode / resistor arrangement.

[mickstv]

The unbalanced damping improves the fly back time and the descrimination signal. ....arranging for variable damping on both sides of the coil is more difficult. You will see hopefully when you build one that damping only one side provides near perfect damping for both sides of the coil providing the coils are made as specified in my coil posts. I guess there is plenty of room for investigation here though.
Paul.

Just ordered the parts needed hopefully they will all turn up by Friday. But in the mean time I don't seen any reason why I couldn't at least get the damping circuit installed and tested on the existing setup.

Back on your previous version, did you ever get a chance to test the diff setup over heavily mineralised ground and hot rocks. Just wondering how it may have performed.


Mick

[moodz]

Yeah for the price i'll order 10 because knowing my luck lately i'll blow the first few up.


EDIT i've noticed the damping circuit is only across one of the two coils whereas the previous version using a damping resistor was across the two ends of the diff coil. Wouldn't the other half of the diff coil have undampened coil pulse on it or am I looking at it the wrong way.



Mick

The unbalanced damping improves the fly back time and the descrimination signal. ....arranging for variable damping on both sides of the coil is more difficult. You will see hopefully when you build one that damping only one side provides near perfect damping for both sides of the coil providing the coils are made as specified in my coil posts. I guess there is plenty of room for investigation here though.
Paul.

[mickstv]

I am going to get some also for testing. They have a lower gate threshold of 2 volts which means the blocking threshold can be made lower also

Yeah for the price i'll order 10 because knowing my luck lately i'll blow the first few up.


EDIT i've noticed the damping circuit is only across one of the two coils whereas the previous version using a damping resistor was across the two ends of the diff coil. Wouldn't the other half of the diff coil have undampened coil pulse on it or am I looking at it the wrong way.



Mick