Carl's fluxgate Gradiometer ckt.

[damiafix]

Hi again,
from the Speake site,
these are the application notes, for the SCL007 about the high sensitivity mode, as you can see:

Pin 1 is an input giving two different sensitivities when set either high or low. The two sensitivities,
controlled by pin 1 differ by a factor of eight to provide a range for larger field anomalies.

this is the SCL007 schematic about the connections:


All the best, D.

[Krzysztof]

Hi Damiafix.

for now I'm in a impasse (dead point)

Maybe a problem of calibration. You must strive to achieve close to "0" at the beginning of the test track as suggestions FOT9.
On this forum people have been disappointed recently indicated MAG.
This could be it.
Best regards Chris.

[damiafix]

Thanks Chris,
I'll try again, I don't have much options in this moment! The doub about the high sensitivity mode of the SCL007 is born after the reading of the 3d that I've mentioned!
I could to insert a swith for high and low sensitivity mode.

Thanks, Dam.

[Krzysztof]

Hi Damiafix.
At the end of the chocolate cream.
I do not know the algorithm SCL007 nor I own, from now on are my ideas:
1. Apparently autocalibration needed to obtain the signal at min activation of 0 to D0-D7.
Also, get the max signal level H on D0-D7.
Then the scale of the instrument is always up and always stretched fully used.
It will show 0 on the line W / E and max on the line N / S for 57deg.
In the working position (V) will show 75% of which is not any benefit for us
2. To achieve high sensitivity in the workplace on the ground vertically and MAG hold the power supply (not move).
Then try a little metal around the sensor.
The signal should go from 0 up quickly.
I do not know what would then be an option for higher sensitivity switch PIN1?
may be even greater tilt - strengthening nT/mV equivalent to nT/Hz.
3. I walked around the room I measure drive the 50-75% level but 0 when the horizontal line W / E.
In the field, always upright, and often do reset once the ground has changed in nature.
For me it is reset button and save to memory the current value of the field, the next field values are always deducted from that stored in memory.
The speaker on the LCD and then I remembered only the difference of level.
Then get a high sensitivity to changing conditions.
I recommend you also carry out calibration quite frequently by the switching power supply and not to move too MAG (no rotation).
Are you sure you do the calibration test area!
Good luck!
Best regards Chris.

[damiafix]

Dear Chris,
many thanks for your reply, for now I'm in a impasse (dead point) the circuit is ok, the sensors are ok, but when I test it in pratical use, something don't go fine, but I still don't know
I'll repeat the test on the field, I hope to understand what is the problem, where I'm in error!
Renewing the call to share a video of some mate that use this gradiometer without problems, maybe my problem is only a misunderstanding about the use.

All the best, Dam.

[Krzysztof]

Hi Damiafix.
1. First rotation.
As Speake says, the system expects to max and min.
These values occur after a course of 180deg, and 360deg gets traded twice, that's the whole philosophy.
Because certainly recorded maximum and minimum should be rotated in a vertical plane in the direction of N/S.
2. The suggestion of FOT5 serves only to regulate.
The suggestion of FOT8 to normal operation.
It is entirely natural that indicate the vertical MAG are larger than the level in the NS direction, with your max is the angle of 57deg.
3. In the beginning, when you use to force a piece of metal, use a low sensitivity mode.
High sensitivity when needed.
Resistor value of non-critical, it serves as collateral for rhytidectomy to Vss (2-10Kom).
Best regards Chris.

[damiafix]

I'm back from another test, I went in a land close my house far from interferences!

R6:0Ω and 2.2kΩ resistor inserted between DAC Pin14/15 and GND, both sensor FGM3 connected to the PCB and placed on a aluminium "V" (I know that the fluxgate sensors are not sensibles at the aluminium, right? In every case in one of the first test I was used a pvc tube with the same results), the central unit was placed in the middle of the "V".
The gradiometer was oriented in N/S direction, with a angle of 57° (I'm in the center Italy) like this picture:




I've powered on the gradiometer and during the first 16 seconds I've rotated of 360° (in another test I was rotated the probe, of 180° with the same results) the "V" probe in clockwise (like the propeller of a aeroplane) and after this phase, I've oriented the "V" probe along the axis W/E and I'm started with the sensor adjustments for find the combination wich the gradiometer reproduce a sound at most low frequency respect the default sound (like FOT5 of the Chris suggestions). With the 2 sensors perfectly aligned I should to hear no sound, but this is a ideal condition, I know!
After this phase, I tryed to use the gradiometer in vertical (like the FOT8 of the Chris suggestions) but when I moved it, (rotated is in the vertical axis), the gradiometer was much instable. I got the same result moving it is in air; I don't understood if it was working correctly! What do you think?

About the rotation, another little doubt: in the Carl's document about the FMX-1 I read that it should be of 360°:

Switch on the
power and slowly rotate the tube, head over heels, through 360° during the first 10 seconds. That’s all there is to it; this procedure
should be done every time the mag is turned on for use.


but in the documents that I've received from the Speake about the SCL007, I read that:

The system performs an auto calibration during the first ten to twenty (dependent on crystal frequency) seconds after switch on, during which it expects to see the maximum and minimum value of the earth's field. The best way to do this, is to hold the gradiometer in a north-south orientation pointing upwards at about the angle of the field's inclination, (in the UK about 67° to the horizontalin the north/south direction) then swith on and rotate the gradiometer through 180° to directly reverse its direction, during the ten seconds after switch on. It is best not to do this any more hastily than necessary


so, who is the best calibration solution, 360° or 180°?

Another question is about the SCL007, in this forum I've read in a 3D that is better don't use the SCL007 in high sensitivity mode, this mode depending from the tension at the PIN1 (gain) of the SCL007:

Don't use the SCL-007 in the most sensitive mode......several people have tried, and it is nearly impossible to get it balanced.
Erich Kern

...in high-gain mode, I've never had any success in getting the sensors balanced, and every slight movement of the mag makes the output go whacko. It's just too sensitive.
Carl

my question is, in the Carl's gradiometer, the SCL007 work in high or low sensitivity mode? The pin 1 of the SCL007 is directly connected to 5v through a 4.7kΩ resistor, who is the treshold value, for to switch from low to high sensitivity mode?


After so many hours spents to understand the "modus operandi" of this gradiometer, would be wonderfull if someone that have built it (and that work correctly) could show, with a small video, the gradiometer in action. A little video, sometime is better of a lot of words.

I wish to thank again Chirs for his costant help!



Many thanks for your help!

Best regards, Dam.

[damiafix]

ok!

[Krzysztof]

Hi Damiafix.

Leave as is and go into the field!
Fountain takes time.
Best regards Chris.

[damiafix]

Hi Crhis,
many thanks again for your precious help, now I understand, with this settings, the magnetic fields variations are most easy of to hear, that with a low operating frequency; my comments was referring to the document wrote from Carl, absolutely nothing critical about your suggestion, now is all most clear for me!
About the output sound, I was thinking if could be usefull, to insert an adjustable noise gate, that reduce the sound or cut it at the start operating frequency range, but play or increment the sound when there are also small frequency variatons, what do you think? Like the classic md volume threshold!
In every case, I'll continue adding the second fgm3 sensor, the most critical phase for me, is still the alignement of both the sensors!

All the best, Dam.

[Krzysztof]

Hi Damiafix.

Nowhere is not mistaken. Already work in the past suggested a lower value R6.
For Test3j.... of Information was to verify the operation of V / f totally alone!
Now you do not measure the voltage at Pin16 longer because I will never = 0.
You can measure the voltage at Pin14/15 but there is no such need.
You should be guided by the value of the measured signal indicated on your Analyzer logical, there is more transparent because of the exponential scale.
When the signal = 0, D0 = 0, R6 = 0 I hear the sound of about 50 Hz plus harmonics, but no clatter, clicks that interfere with listening.
With your last test you can hear that with the increase in the frequency of the sound signal increases up to several kHz. The signal is clear and constant! Super!
Compared with R6 = 5Kom, call all the time clicks, at the beginning of the scale there are only cracks and the maximum rated output is only a few hundred kHz, is unpleasant, difficult to distinguish the increase of frequency.
It does not matter that this is a very low frequency, it is useless with a signal from 0 to 25%.
And it is a signal of low value should be well distinguished because it testifies to its sensitivity.

Why would you smash your head when the sensitivity of the treasure chest, you have to dig it!

It probably is a bad translation into English, but you do not need a MAG when you stand next to a large treasure chest, or looking smashes his head against the tank, because then you hear it!
You need high sensitivity to small signals when something is deeply buried. Then count the frequency of large-scale extension in the beginning, that you can quickly locate anything! So a large slope (value) Hz / mV.
Note that the two FGM-3 differential and signal work should be small under normal conditions (specificity gradiometer work).
You can leave your R6 1Kom value for regulation in the field of exploration, I'd left the resistor to GND 2.2 Kom. Will provide an initial higher frequency, then adjust R6 to taste!
Note that the MD type of BFO are essentially analog outputs (at least all the old), so that their sound is pleasant, without a large amount of harmonics, and can be adjusted to the frequency of several Hz.
We are happy to accept criticism, but spubuj my ideas.
Best regards Chris.

[damiafix]

Hi Chris,
I'm back from another test, but I'm still a little confused...for AD557 PIN16=0v (DAC PIN1 to PIN 8 "Low" GND) when the sensors are perfectly aligned no sound should to be hear:

The minimum output voltage of the DAC is 0v (when the sensors are
balanced) which should result in a silent VCO

so with only one sensor used (SCL007 pin 17/18 wired) when I power on the gradiometer, for R6=0Ω I should to hear a very low frequency sound:


It is actually desirable to have the VCO idle at a very low frequency. The reason for this is partly why the old BFOs were tuned up to run at a slow putt-putt frequency: the human ear is very sensitive to frequency changes. By running at a very low rate we can discern very minute changes; if we run it too low we risk getting a rate change that is actually too low to distinguish. A nominal rate of 5-10 Hz is a good operating point. Obviously this is below the frequency range of average human hearing (about 20Hz on a good day) but remember that the speaker waveform (E) is a square wave, not a single tone, so what we hear are “clicks.”



and not a high frequency sound; in my case, for R6=0Ω and a resistor of 2.2kΩ inserted between the DAC PIN14/15 and GND, I get a high frequency sound, while for R6=5kΩ I get a most low frequency sound, but for my personal opinion , still much high for a good pratical use, but maybe I'm in error about this impression!?!
Please hear yourself the results directly from the media player below, this is a easy test:
after that I've powered on the FMX-1, you can hear the different output frequency result for the two settings of R6 (0Ω and 5kΩ) and after the 10 cal seconds, I put a steel object close the FGM3 sensor, the gradiometer seem to work, but my doubt is the operative frequency work, becouse I think that the gradiometer should to work with a start low frequency sound, and not a constant high frequency sound (it's like a hammer on my mind) :


One sensor Test, R6:0Ω; R6:5kΩ

With all the components on the PCB and one sensor inserted I don't get the results of the previous test (DAC Pin16 close the 0v) when I could to hear the single low frequency "click" why?



Best regards, Dam.

[damiafix]

Hi Damiafix.
I heard the sound you should get the (highest) are already close to 0V! 100% agreement with Carl translation. As even at 0.5 V, still hear the tapping is to say that you lost 20% of the sensitivity of 0; because nothing but tell a knock. Why would you smash your head when the sensitivity of the treasure chest, you have to dig it!
Best regards Chris.

Dear Chris, I'm sorry, I don't understood perfectly, so you think that my results are ok, right? Nothing of strange?
But with R6=0ohm when I power on the FMX-1, It start with a constant high frequency sound....it's ok?

Many thanks, Dam.

[Krzysztof]

Hi Damiafix.
I heard the sound you should get the (highest) are already close to 0V! 100% agreement with Carl translation. As even at 0.5 V, still hear the tapping is to say that you lost 20% of the sensitivity of 0; because nothing but tell a knock. Why would you smash your head when the sensitivity of the treasure chest, you have to dig it!
Best regards Chris.

[damiafix]

Hi Damiafix.
Power supply decoupling is typically always use. There must be the same. There may be several nH or a dozen om. It may be a few beads ferite. FGM-3 is resistant to changes in power to a limited extent but you can always go further to protect.
Moreover, the same as the generator produces a low distortion power line in moments of change in H / L and L / H output (jumping power change).
FGM-3 is much more sensitive to temperature changes. It is good to put it in a Styrofoam.
For the trials on the table, the lack of security does nothing!
Best regards Chris.
P.S.
Subject of the film. Discard R6 and add 2.2 Kom and you will have glitches at the beginning of the measuring scale.

Hi Chris,
I'm back from another test, I've removed R6 (AD557 PIN14/15 direct connected to the transistor Q1) and inserted a resistor of 2.2kohm between AD557 PIN 14/15 to GND, but the default output frequency is high, not at the beginning of the measuring scale, maybe R6 should to be replaced with a resistor of 5k, infact if i use this resistor the output frequency is most low, like the test 3j for R6=4.5kohm.

From the original Carl document about the FMX-1 I read:

The minimum output voltage of the DAC is 0v (when the sensors are
balanced) which should result in a silent VCO. In reality, the sensors are
never perfectly balanced so the VCO is always running at some low
frequency. It is actually desirable to have the VCO idle at a very low frequency. The reason for this is partly why the old BFOs were tuned up to run at a slow putt-putt frequency: the human ear is very sensitive to frequency changes. By running at a very low rate we can discern very minute changes; if we run it too low we risk getting a rate change that is actually too low to distinguish. A nominal rate of 5-10 Hz is a good operating point. Obviously this is below the frequency range of average human hearing (about 20Hz on a good day) but remember that the speaker waveform (E) is a square wave, not a single tone, so what we hear are “clicks.”
Because the square wave is rich in harmonic energy slight variations in the fundamental mean larger variations in the harmonics which gives us an even more effective frequency change.

but with only a sensor and SCL007 PIN17/18 wired I should to hear nothing, or some "clicks" like this ideal test for R6:5k and AD557 PIN 16: 02v, pratically, I hear a most high output frequency, like the video test that I've showed, why? It's normal?

All the best, Dam.

P.S. I've replaced the FGM3 flying connections with a most solid pcb: