Minipulse Plus Rev My time has come!

[mushaba]

Thanks waltr thanks a lot you gave me a lot to study.Day by day I understand more why Pi's constructed this way!

[waltr]

Forgot about this paper that covers GB in detail. It starts with VLF but then goes into PI detectors.

https://www.minelab.com/__files/f/11043/KBA_METAL_DETECTOR_BASICS_&_THEORY.pdf

[waltr]

As George stated: "The EFE sample is usually taken a few hundred microseconds later" than the main sample ", when the target signal has substantially died away".

Think of the EF as causing an OFFSET to the entire time of TX off. This offset is caused ob moving the coil through the Earth's Magnetic field which induces a current to flow in the coil wires.
Since the sampling cycles (pps rate) is quite quick and your swinging the coil is much slower then this EF current is close to a steady DC offset. So a late sample (EFE) subtracted removes the offset and leave the signal from a target's eddy current decay.
The other reason to do and EF sample is that the current flow in the coil is in one direction when you sweep the coil to the left and the opposite direction when sweeping the coil to the right. Without subtracting the EF sample there can be a 'target detection' at the ends of each coil sweep.

GEB sampling is typically done at a different time and when there is still a response from minerals in the ground. However, the EF & GB samples can be combined and taken and various times.

Check the three sample GEB method in my HH2 thread (following the links on the theory) for a discussion.

https://www.geotech1.com/forums/showthread.php?24251-My-take-on-the-HH2

Then study the TDI timing and circuits on when the samples are taken and how these are processed. TDI schematic attached.
The TDI does do two EFE samples (D,B) and then combined with two GEB samples(A,B). The "main" samples are C with A detecting longer TC targets.
Also the SD2000 timing and circuits. Also attached.

TDI PRO PROTO.pdf
Full SD2000 schematic Part one.pdf
Full SD2000 schematic Part two.pdf

[mushaba]

Thanks guys for spending your time trying to spread your knowledge!!As i said before please be as patient as possible for each one...

Another question,what is the difference between Earth Field Elimination and Ground Balance??

A few posts back:

Question of the day,how does the EFE work?I imagine it takes a sample of the field,then invert it and substract it from original sample?To achieve that it should drive three op-amps one with sample another to produce the inverted sample and a third to substract them?

The main sample will contain a signal from the target plus a contribution from the Earth field. The EFE sample is usually taken a few hundred microseconds later, when the target signal has substantially died away, whereas the EF signal will remain the same. By subtracting the EFE sample from the main sample you are then left with the target signal.

The thing i cant get sometime now and i need help is how the EFE signal is the same during first sample and EFE sample,isnt it an ac signal??How it can stay exactly the same a few hundred microseconds later??There must be something left of the EFE after the substaction..There goes GB??

[6666]

C24 is not needed

[godigit1]

Wire your 5534s in this manner then you can use them as a double amp. but maybe you figured it out allready. Use your pin 4 and 8 for power and wire the amps dead bug style should fit right on your board.

[Qiaozhi]

OK!

Time for the stupid question (please excuse me but just a week ago i started studying about opamps):Our goal is to achieve specific gain or specific voltage at the output of the preamp??For example why did you stop at 1000 gain and you didnt go for 2000??I know that besides signal amplification we also amplify noise..

There are some simple designs that use a higher gain (such as 2000), but these are micro-based units with a 10-bit ADC. In this case, the higher gain is used to partially compensate for the lack of resolution. Depending on the opamp, you may be limited by the gain-bandwidth product. Also, the higher gain will force the opamp into saturation for longer, which means you need to sample later. As usual in any type of engineering, it's always about compromise.

[godigit1]

. This is a add on board plugs in right where your 5534 goes and you can use a 5532 or max 412 or other dual amps with the same pinout.
My bad when I said it was not for a 534 its for a dual amp to replace a 5534. Will work on the CB.

[mushaba]

OK!

Time for the stupid question (please excuse me but just a week ago i started studying about opamps):Our goal is to achieve specific gain or specific voltage at the output of the preamp??For example why did you stop at 1000 gain and you didnt go for 2000??I know that besides signal amplification we also amplify noise..

[Qiaozhi]

At the MPP there is one NE5532 ic that contains 2 seperate amps.As i understand they are in connected as inverting amp the first stage and non inverting the second :
First stage (U2a) has a gain of: Gain=Rfeedback/Rinput --> Gain=R1/R8 --> Gain is 33.
Second stage (U2b) has a gain of: Gain=1+Rfeedback/Rinput --> Gain=1+R27/R26 --> Gain is 34.

Correct.

What is the total gain of the 5532 on the MPP??

The gain is 33 * 34 = 1122

At the CB Gain=Rfeedback/Rinput --> Gain=R32/R8 --> Gain is 1000????

Yes, the gain is 1000, but it will work fine with 1122.

[mushaba]

You can use two 5532s in place of a single 5534, but each stage needs to have a gain of 33k. Look at the schematic for the MPP and copy that.

Ok,lets break it down and please show mercy

At the MPP there is one NE5532 ic that contains 2 seperate amps.As i understand they are in connected as inverting amp the first stage and non inverting the second :
First stage (U2a) has a gain of: Gain=Rfeedback/Rinput --> Gain=R1/R8 --> Gain is 33.
Second stage (U2b) has a gain of: Gain=1+Rfeedback/Rinput --> Gain=1+R27/R26 --> Gain is 34.
What is the total gain of the 5532 on the MPP??


At the CB Gain=Rfeedback/Rinput --> Gain=R32/R8 --> Gain is 1000????

I have a two stage plug in that was for the Hammerhead it will plug in pin for pin into the old socket but it is not for the 34.
its under plug in dual front end in the HH 1 thread.
Current gain is that of the HH 2.
Ive pluged it into a Surf pi and Barracuda It worked pretty good, The attachment cable I made could be better It could just be hard pinned into the socket .

You say that you have a card like that for the HH but will not work for the 5534?For sure because they are different ic's.32 has 2 opamps inside and 34 has one,totally different pinout.

I asked George if i could implement this stage with the 5534 because i have 12 original TI ic's,i have trouble to source (from europe) 5532 in THT package.

Just dont know how much gain we need at the output

[godigit1]

I have a two stage plug in that was for the Hammerhead it will plug in pin for pin into the old socket but it is not for the 34.
its under plug in dual front end in the HH 1 thread.
Current gain is that of the HH 2.
Ive pluged it into a Surf pi and Barracuda It worked pretty good, The attachment cable I made could be better It could just be hard pinned into the socket .

[Qiaozhi]

George here is a thought:IS it possible to modify the CB with 2 stage pre amp using NE5534 (i have a lot originals from TI and having trouble to order 5532 THT version) ??

Im thinking a small addon "card" ,the I/O of this card will be placed on the U5 (i hane installed an ic socket so i can change the opamp if needed) according to this schematic i made only based on how it is connected on the MPP.Dont know what values of R1 and R2 of this card and if i should change the values of R31-C13 and R25-V47 possibly...It should need 1 extra 0V from pcb.

[ATTACH]46423[/ATTACH]

You can use two 5532s in place of a single 5534, but each stage needs to have a gain of 33k. Look at the schematic for the MPP and copy that.

[mushaba]

NE5534/32 has protection diodes on inputs and you have to know that good before to use.
thats specific feature we discuss much times.

The first 2 diodes for first 5534 are on the CB pcb..Should I add 2 more?As I see from MPP preamp there are diodes only on first opamp input..

[kt315]

NE5534/32 has protection diodes on inputs and you have to know that good before to use.
thats specific feature we discuss much times.