Epe pic magnetometer

[olsteffe]

I believe you kind of misunderstand eachother. There is a significant difference between the epe magnetometer and the speake gradiometer. The speake gradiometer (Carl) is doing a proper calibration of the sensors storing max min values of both sensors and adjusting for sensor offsets. The epe gradiometer is just doing a nulling of the sensors in the present field without taking into account the difference sensitivity of the two sensors.
A perfectly aligned gradiometer should give a close to zero reading in a homegenous field meaning no external disturbances (anamolies).
Commercial Fluxgate magnetometers as used in archeology are capable of at least a .01 nT sensitivity.
stephane is finding 10 nt variation useless for his purpose and I do not think You can argue him on that. Diurnal variation as You mention is of no regard in a gradiometer setup as this will be seen by both sensors simultasionly and nulled. This is the whole point of the gradiometer setup.

Regards
olsteffe

[ivconic]

To get more clear picture of what's really going on; you should try horizontal sensor setup , instead vertical (like on some OKM's).
Use horizontal setup and place sensors vertical on horizontal pipe or holder. Space between those to be 1m or so. Turn sensors each separately to get close values. Than compare that with previous setup.
Another thing;
if (like i stated in previous post) sensors not supposed to read constantly same values, than how to achieve accurate measurements? Simply - relative difference between two sensors will stay relative in same range all the time.
At some minor percentage - that relative. So..that relative difference is taken as default all the time without worrying to much. You may try to decrease relative difference by more proper calibrating. Never mind, just like Don stated; sensors actually not need to be calibrated at all (in pipe). No matter how hard you will calibrate those - always will be some relative difference taken as default value - not a big deal.
So.. my advice to you is to reconsider all this, because i am almost sure that you misunderstood the whole concept here.
Best regards!

[ivconic]

No, I'm still not satisfied for a serious use. Even setted, you still have some variations on the measures when you move the sensor (from e/w to n/s for example), also it's pretty unstable, the variations are 10-20 nt.
It's a good device to learn how it works, but I dont think you will be able to find interesting archeological "treasures"

For this, and for an accessible price, you have the PPM mark2 made by willy Bayot, I own one (that I sell) and it's a excellent device, very sensitive and without this boring n/s e/w sensitivity problem.

Some people on this thread managed to use the EPE to find some buried pipes, but it's really constraining, read above how they managed to do such a thing.

sorry for my poor English, I'm French !

Hopefully you don't expect both sensors to give you same and stable values all the time!? It is not possible. There are constant natural variations in earth magnetic field. It is normal, sensors to read different values constantly. Also it is not normal both sensor at the same time to read same value (exactly the same). Simply because of their setup; top sensor is higher 50cm (more or less) than bottom sensor. There are different variations 50cm above, so it is normal to expect small differences between sensors. Small - meaning some 1-5% not more. Exactly what i got with both of my mags. Those are good and sensitive sensors and therefore are capable to read smallest variations in magnetic field.
If you get very same values with another type of mag (you mentioned it) than it is not sensitive enough - it is deaf, that's why you get same values.
I think that you misunderstood whole concept here. Sorry, but that's what i am thinking.
W-E and N-S orientation dependence is quite normal at this type of sensors due their internal morphology. Coils inside sensors are wounded directionally and PURPOSELY dependable of orientation in space. Initial purpose of these sensors is use in compass electronic devices. That's why those are orientation dependable.
Normal and pretty right.
Sensors are accurate and pretty sensitive.
EPE mag is excellent project and it is a way over simple experiment.
I already have some splendid results on real field with it.
So... i simply need to write all this to stop and debunk terrible confuse you made here with your non adequate remarks.
Don't guess me wrong, i have not bad intentions. Just want to justify that EPE project is not waste - it is splendid, workable and already proven in real life.
Regards!

[damiafix]

Hi Stephane,
many thanks for your reply! I'm building a Fluxgate Magnetometer (Carl Moreland project) so your experience for me is much important. You write "I dont think you will be able to find interesting archeological "treasures"" This tool is really so unstable? Pratically useless? I would to use it for militaria, and other, but I'm worried from your words; maybe I'm losing my time?
There's someone in this forum that have used this tool with success?

All the best, and again thanks for your help, D.

P.S. Don't worry for your english; I've the same problem, my english is very bad (I'm from Italy)

[stephane.mg]

No, I'm still not satisfied for a serious use. Even setted, you still have some variations on the measures when you move the sensor (from e/w to n/s for example), also it's pretty unstable, the variations are 10-20 nt.
It's a good device to learn how it works, but I dont think you will be able to find interesting archeological "treasures"

For this, and for an accessible price, you have the PPM mark2 made by willy Bayot, I own one (that I sell) and it's a excellent device, very sensitive and without this boring n/s e/w sensitivity problem.

Some people on this thread managed to use the EPE to find some buried pipes, but it's really constraining, read above how they managed to do such a thing.

sorry for my poor English, I'm French !

[damiafix]

Hi Stephane,
with the new fgm-3 sensors, the Gradiometer work correctly?

All the best, D.

[msolc]

Thanks, I am constructing similar PPM device for maritime usage, differential, and having a lot of trouble with it, but now it seems to work, will be tested on the sea next month, signal analyse and logging is done with laptop, and boat is towing two fishes containing sensors.

[stephane.mg]

I dont own a production unit, but a prototype, but it's identical in electronics, the package is a little more basic but effective.
The magnetometer is very sensitive, the sensor must be kept horizontal for me (living in France), and it's accuracy is really precise. When you use it, you feel that the measurements are real, and stable. The first maps I've done of some places are efficient, real and precise. I made some tests on some objets detected, and my etrac confirmed the locations of two ferrous objects 20cm long and 2 cm thick, buried at 30 cm each, it was a dot in the map, easy to locate.
This device seems to be able to locate ferrous objects, and the sensor is small so you can go to places where a 1m 2m frame cannot, but the limitation is by design, only ferrous objects.
This detector can be very useful for archeologists, and also a precious complement for PI detector for deep object it will confirm that the object is ferrous / not ferrous for example.

[msolc]

Can you tell us first opinions about Willy's magnetpmeter, please

[stephane.mg]

Hi,
finally, bill was kind enough to send me two new sensors, and again, same problem.
So I wanted to try them with an independant power +5v, and guess what, I've finally noticed that there is a terrible mistake on page 474 of epe magazines, the gnd and sig out are inverted on fgm-3 pin map !!! Thats just why my epe wasn't working, not it works like a charm.
Btw, I've bough the magnetometer from Willy Bayot, and it is sincerely a great device. So if someone is interested, I'm now selling my epe, I can send photographs for whoever is interested.

Thanks for the help everybody provided here.

Regards,

steph

[stephane.mg]

To be correct with him, I would not post his mail without his approbation.
he just sent me two new fgm-3, he told me that the sensors normally resists up to 12v, reversed wires and maybe the problem I had could be due to a shock. I'll sent him back the defective sensors when I'll receive the new ones.
I'll remove the hex inverter I've put to correct the defective signal I had. And also test again them aligned to see if there's a difference of resolution between them.
There's another method of aligning them on car's fluxgate manual, I will use his method, it seems more logical to me (read the pdf on the magnetometers project part of geotech's forum)
So again, I will make some further tests with my epe and report here when I'll receive the new sensors.

[olsteffe]

Speake respons

Hello stephane.mg
Could you tell us how Speake is going to resolve your problems. Maybe you could post the mail here on the forum.

Sincerely
olsteffe

[stephane.mg]

just to correct one thing :
bill speake just mailed me, and will help to resolve the two issues I had.
thanks to him !

[stephane.mg]

yes you're right, surely a reversed diode. but when I've read in the fgm-3 specs that there were sensitivy differences between devices, I decided to give up everything.
for example , one sensor rotated at the max sensitivity, orientated e/w gives 50000 hz, put to n/s gives 54000
the other, same conditions : 48000 and rotated to n/s gives 49000 hz !!!
even if I modify the microcontroler program, it will be not precise to make some serious detection. the fgm-3 sensor is not well tested, and they dont have serious building tolerances, so it's not a serious product.
what I would do if I didn't bought the ppm from willy is to replace them with the honeywell hmc1001 which seems pretty sensitive and surely built better than the fgm3. I would have to put a voltage to frequency converter to feed the epe with frequence. But I will not do, I dont need anymore the epe, and I'm really disappointed by Bill Speake who didn't even responds to my emails.

[olsteffe]

overshoot in FGM

Hello
Stephane.mg
Not that it helps regarding the sensitivity of the gradiometer. There seems to be a reversed diode in your FGM-sensors, based on the circuit of the sensor this will result in a overshoot, and negative spikes due to the back emf not countered by the diode similar to the ones you experienced on your scope. Maybe you could file a complaint and get a refund. Good luck with your upcoming purchase of the PPM. Remember that as for the sampling you will have to sample with the PPM as for the FGM type, descibed by Ivconic to get the resolution you want (surface search for small anomalies?). Sampling is limited around 1 HZ as the PPM precession rate is in this area.

Sincerely
olsteffe