Surfmaster discriminates or what?

[maikl]

Maikl, I'm more angry
At the time when a professional designer begins a project, it must first examine what has been done in this area in the world so far. Even amateur designers are searching WEB and reading patents in order to improve a project.
I'm sure that when started to design the Surfmaster, its designers have not even read the patents issued so far at that moment. The principle of Surfmaster corresponds to knowledge for PI before half century.

mikebg do not be angry I'm joking. I do not force the Surfmaster but I think it is a good (Barracuda better) project for amateurs. For little money we get plenty of.

[mikebg]

mikebg do not be angry I'm joking. I do not force the Surfmaster but I think it is a good (Barracuda better) project for amateurs. For little money we get plenty of.

Maikl, the improvements for Surfmaster are not expensive. As first step try with an induction balanced search head. Then put a trim pot for delay of second sample.

[Tepco]

OK, what is so badly misdesigned in Surf PI by William Lahr (and by others in many similar machines, HHd, Barracuda, seahunters etc), considering it's purpose? He probably read all "previous art" and got US5414411 for this one. What can be achieved by using balanced coils in this design except getting all VLF sort of GB crap in same package? Then go to ML style design to avoid it and make" hybrid" ending up whit excellent machine for completely different purpose, not "generic" monocoil PI. And varying intersample time, for what this is good?(better solutions are already out there)

Improvement of Surf is not expensive, this one for example

http://www.geotech1.com/forums/showpost.php?p=127795&postcount=9

and you wont recognize your detector any more, interestingly, no one tried this or commented so far.

(like 10" coil performance whit 8" coil, and 8" is faster, less issues whit fast decay targets)

[DIRCEU]

Maikl, the improvements for Surfmaster are not expensive. As first step try with an induction balanced search head. Then put a trim pot for delay of second sample.

Hi! Mikebg

What is " induction balanced search head".
Would you like to explain please.

¨Thanks in advance

Dirceu.

[mikebg]

Hi! Mikebg
What is " induction balanced search head".
Would you like to explain please.
¨Thanks in advance
Dirceu.

Sr Dirceu,
Each search head should contain separate TX and RX windings because they have different important parameters:

The TX winding should have enough low resistance, because the efficiency of TX is expressed with magnetic field measured with "Ampere-turns".

The RX winding should have maximal number of turns, because sensitivity depends on EMV induced in it.

For maximal sensitivity, the TX and RX windings should be oriented in induction balance (minimal mutual inductance M or minimal magnetic coupling k). At this loop situation, the AIR signal induced in RX winding is minimal and GND signal is suppressed. That's why the TGT (target) signal appears as high modulation index of AIR and GND signal.
Self-inductance is specific case of mutual inductance when coefficient of coupling is maximal (k=1). That's why the AIR and GND signals are maximal at monocoil sensing head. Monocoil is the worst sensing head for metal detectors because we should reduce the gain of RX amplifier to avoid its saturation by large AIR signal. In addition, the TGT signal appears as very small modulation index of the large AIR & GND signal.
The induction balanced search head is preferable not only for CW metal detectors. The members of former (R)EMI group reinvented that IB coil configuration is also more suitable:

For PI metal detectors, because reduces flyback voltage induced in RX coil. We can call flyback also AIR voltage. This allows early sampling and increased gain of preamp.

For BFO metal detectors, because increases frequency shift. See for example the HOUNDOG project and several designs made by Rev. Thomas Scarborough. The IB sensing head allows to increase gain of amplifier used in oscillating network.

[maikl]

Maikl, the improvements for Surfmaster are not expensive. As first step try with an induction balanced search head. Then put a trim pot for delay of second sample.

Hi mikebg. Show directly on the scheme Surfmaster for what you thought.

[DIRCEU]

To Mikebg

Many thanks.

Dirceu.

[mikebg]

Hi mikebg. Show directly on the scheme Surfmaster for what you thought.

Maikl, sorry for Ratko Mladich :-(
In the attached mod diagram should be connected a damping resistor in parallel to RX coil.

[nelson]

This is out of my knolegments, but motivate me to learn, so many thanks Mikebg for your contribution.
Has i understand, this will allow susrfmaster to get more sensitivity?
Or it can allow to discriminate?
Regards
Nelson

Sr Dirceu,
Each search head should contain separate TX and RX windings because they have different important parameters:

The TX winding should have enough low resistance, because the efficiency of TX is expressed with magnetic field measured with "Ampere-turns".

The RX winding should have maximal number of turns, because sensitivity depends on EMV induced in it.

For maximal sensitivity, the TX and RX windings should be oriented in induction balance (minimal mutual inductance M or minimal magnetic coupling k). At this loop situation, the AIR signal induced in RX winding is minimal and GND signal is suppressed. That's why the TGT (target) signal appears as high modulation index of AIR and GND signal.
Self-inductance is specific case of mutual inductance when coefficient of coupling is maximal (k=1). That's why the AIR and GND signals are maximal at monocoil sensing head. Monocoil is the worst sensing head for metal detectors because we should reduce the gain of RX amplifier to avoid its saturation by large AIR signal. In addition, the TGT signal appears as very small modulation index of the large AIR & GND signal.
The induction balanced search head is preferable not only for CW metal detectors. The members of former (R)EMI group reinvented that IB coil configuration is also more suitable:

For PI metal detectors, because reduces flyback voltage induced in RX coil. We can call flyback also AIR voltage. This allows early sampling and increased gain of preamp.

For BFO metal detectors, because increases frequency shift. See for example the HOUNDOG project and several designs made by Rev. Thomas Scarborough. The IB sensing head allows to increase gain of amplifier used in oscillating network.

[Jose]

Hi all
Thanks Mikebg by the illustrative diagram.
I believe that in addition to R buffer, should be included R7 1 k, TX. (Perform similar tests on the delta pulse)
What is the advantage of using a potentiometer to vary the display time of the signal.
thanks
Jose

[Jose]

Sorry, I meant: it should include R7, 1 K, in RX.
jose

[maikl]

Maikl, sorry for Ratko Mladich :-(
In the attached mod diagram should be connected a damping resistor in parallel to RX coil.

Hi mikebg. I am very sorry for Ratko Mladić. He is now an old and very sick man...But I have another question which would be the inductance and resistance of the RX coil (TX kept the old values)?

[mikebg]

What is the advantage of using a potentiometer to vary the display time of the signal. Jose

Jose, do you know how operates this circuit?

[mikebg]

Which would be the inductance and resistance of the RX coil (TX kept the old values)?

Maikl, for best results we need new value of TX coil. At PI metal detectors, we can not calculate inductances of TX and RX winding because we do not know the equivalent capacitances connected to it. They are shown below as equivalent circuit diagram.

We need to determine suitable inductances L1 and L2 experimentally connecting coils with more turns than expected, then test operation of circuit, unwind one turn, again test etc.

For the same reason it is necessary to determine experimentally and damping resistances, because they depend on capacitances, inductances and coil resistance (not shown).

[Jose]

Hello Mikebg
Do not really know how this circuit. I know what function to perform.
I have some concepts
U7A and U7B are keys that are activated during a time of 50 usec. Approximately at the inverting input and noninverting of U3B.
U7A trips after the time called delay time, measured from the end of the TX pulse, this time (minimum) depends on the characteristic of the coil and circuit capacitances, etc. While the control variable "disc of 100 K
From this moment, U3B, making the sign of the signal and amplifies it for a time determined by the second shot U7B.
This time last 210 usec. Approximately, taking into account the values of R28 and C11.
The Delta Pulse, this control variable (second sample) and not notice much difference except more profit but also more noise, if the selected time is great.
So my question, if this control has another advantage that I do not know.
Thanks for responding and please correct me or clarify my doubts.
Sorry for my bad English
Jose