FGM-3 Alignment and Calibration

[damiafix]

Many thanks again, Olsteffe!

All the best, D.

[olsteffe]

Hello
No mystery just something written in Carl`s document FMX1. It is under the first section in the VCO chapter. Added a word doc with som arrows.
You still have to follow the alignment description, but at least you do not have to be confused by the threshold and sensitivity settings. Note that this can not drive any low impedance circuitry it will then have to be buffered by an op amp.
My project is still in the design phase, I have been looking at a lot of material (web sites and forum postings) and done quite a bit of thinking. Have purchased som fiberglas tubing and some fiberglassreinforced putty so that I can cast me some sensor fixtures. so fore now I am just sharing my ideas. Free of charge

Happy building
olsteffe

[panzerfaust]

FGM-3 Alignment and Calibration

Hello again D
You could try and use a digital voltmeter directly at the pin 14 and 15 and to ground of the DAC. Then 0 V = perfect alignment.
Then adjust the treshold of the VCO so you get a comfortable put put frequency when there are no anomalies.

Regard olsteffe

Hello Olsteffe,

Can you explain us your FGM-3 alignment methode using digital voltmeter.
This methode seems to be very accurate.
Where do I have to connect voltmeter (I'm a beginer , so don't hesitate to make a quick shem!).
What is detailled protocole when using this methode?

Thanks a lot for your help.

[damiafix]

Hi Olsteffe,
many thanks again for your reply! I will search a solution with nylon screws; about your probe,
do you have used this design or other? Can you take some photo from your probe? I'm much curious to see your project!

All the best, D.

[olsteffe]

Welcome back

You could check out this supplier;
http://www.fittings.it/private/index.html

Representing

https://secure.microplastics.com/default.aspx

look for the glassfiber reinforced type of nylon screws

Sincerely
olsteffe

[damiafix]

Hi Olsteffe,
I'm sorry for the delay but I was away...many thanks for your reply and the new suggestions! About the differential screw I understand perfectly, the only doubt concerns its manufacture, since the screws must be non-metallic (aluminum or plastic). Where I could find it?
Meanwhile, I will buy a right-angle (aluminium section) for a best sensor alignment; let you know the results in the next days.

Best Regards, D.

[olsteffe]

adjustment explanation, I hope

In Italian it is called, if I translate it directly "differenziale vite" used in micrometro, strumenti di misura. The functioning is so that when the blue skrew is rotated it will advanced according to its given pitch so will the yellow skrew which is mounted solid in the hinge green bolt, but this yellow skrew will at the same time retract into the center of the blue so the effective pitch is increased.

Regards

olsteffe

[olsteffe]

Now for your next question about the best distance. A helmet as you have will under good condition result in a 2 nT field at 2meters. Considering that the speake gradiometer is able to respond to a 10 nT anamalie you will see that there is no reason for the 1,3 m lenght you are not able to sense the disturbance.

If you are satisfied to find the object at 1,5 meters depth your are looking at a 20 nT field difference and 1,3 meter would be the best choice.


Regards
olsteffe

[damiafix]

Hi Olsteffe,
many thanks for your reply! I'm sorry but I don't understand what do you use for the green ball, and the link with the internal screw.

Best regards, D.

[olsteffe]

Hello
Hope this new sketch give you an idea of the sensor mount.
I`ll try and give an explanation on the distance relation but I have to get back to you on that.

[damiafix]

Hi Olsteffe,
Many thanks for your help! I don't understand precisely, the junction from the screws and the green ball! Please, can you draw this particular, or take a photography of this, from your probe?
For the deep, also 1.5 m is ok for me! Can you confirm me that the distance between each sensor is 0.5m? What is the best distance?

Best Regards, D.

[olsteffe]

I think you are pushing the limits if that is a german steel helmet 6 feet under. Based on experience with a fôerster gradiometer. if there is a bunch of them in the same spot you might see it.

By the way, is there anyone who has comments or question on the sensor mount I have suggested. Please comment. I will try and find the time to draw it up in 3D and post it here.

Sincerely
olsteffe

[damiafix]

Hi Olsteffe,
I'm using PVC tubes, please look the follow picture, for the detailed measures:

the structure seem to be stable, never flexions. I've used a electrical tape, between the first and the second external tube (34mm to 32mm).
For the deep and the size of the objects, I would be happy to see, ojects as this:


at least 2 mt.

Do you think that's possible?

All the best, D.

[olsteffe]

Damiafix
I think your biggest problem would be mechanical stability, if you are not using carbonfiber tubing, the flexing of the tubing would give false readings.
Secondly, what size does the objects have and at what depths are they?

olsteffe

[olsteffe]

Sensormount II

Hello
I realised that the ball and socket is to complicated. New design suggestion is given.

Best regards
olsteffe