Minipulse Plus Rev My time has come!

[mushaba]

To excercise yesterdays lesson about coils and Rdump calculations i wrapped a new coil




Measured SRF with oscope and probe loop precedure,counts 2.38MHz

Rd=pi*L*SRF --> Rd=3.14 * 0.00032 * 2380000 --> Rd=2391.4 Ohms

Rd*Rd= L / 4*C --> C= L / Rd*Rd*4 --> C= 0.00032 / 2391.4 * 2391.4 *4 --> C = 0.00032/5718794 --> C = 5.59 e-11 --> 55pF

Conclusion:As SRF goes higher the Rd goes higher therefor capacitance goes higher.So we supose to lower the SRF but how???

And my embarassing moment of the day,what do you mean by "lead" ??

... Possible with a short lead.

... Lead can exceed 1pf/inch

..so measuring coil resonance with leads should be close

... Total parallel coil capacitance including lead capacitance

[dbanner]

So with this procedure we can calculate a coils srf and capacitance..But should have in mind capacitance from cable and from diode..

How can I use this coil to it's max capabilities?I mean what tx pulse width delays etc..and if it is a fast coil why can't I sample below 10us?
Tommorow I will wrap a spiderweb just to practice with the thinks I've learned today and finalise my build.

Searching the web for a decent LF357 for my DP Legend but eBay is full of Chinese rubbish..Equivalents are hard because bom says 50V/us slew rate and above grrrrrrrr0

If you are unsure of genuine LF357AN (I even got fake chips from genuine local dealer, seems they were also fooled), You can use NTE937M.(NTE Electronics) This is genuine direct equivalent replacement for LF357. I use this in my delta pulse. It has slew rate of 50V/uS.
You know it is genuine because it comes in official sealed plastic bag direct from NTE Electronics. You can check out their website for an address of closest dealer to your location.
They have a huge catalog of parts and an on line cross reference database. They specialize in manufacture of direct replacement parts and they are always 100% genuine.

[mushaba]

The main issue is the NE5532 op-amps can not recover from over load (over Voltage) any faster.
This recover time has been discussed much with a few newer op-amps suggested but not much real data on how well they work.

Im open for suggestion and willing to experiment in my board,my knoledge is building step by step but im far away from the point to choose an opamp suitable for this md...

10us is a great short delay for any mono coil and simple front end.
This is fast enough for all but the smaller gold nuggets.

You say its not fast enough to detect gold nuggets?Then i have to make a faster coil since the MPP has the ability to detect them with a fast coil..

I know that coils discussions and posts are a lot but with short guidance from all of you i will try to make a faster one

[mushaba]

Looked at Rev=E schematic. Rin connected to op amp -input. If op amp was fast enough, shouldn't need Rd(Rin should damp).

Hello green,are you reffering to R1 (1K) as Rin?

Wondering what TP3 looks like if a 4148 diode were connected across R8(cathode to amp out) and Rd was adjusted for best decay.

A diode parallel to R8 (cathode on opamp out)..Will do that and take measurement to see what will happen.


In general speaking what is the main feature that a coil named "fast"...Is it its low capacitance and/or its inductance to resistivity ratio?

[6666]

Searching the web for a decent LF357 for my DP Legend but eBay is full of Chinese rubbish..Equivalents are hard because bom says 50V/us slew rate and above grrrrrrrr0

While I have not tried it, I think it was on the TI site they suggested a CA3130, but check the pins

[waltr]

How can I use this coil to it's max capabilities?I mean what tx pulse width delays etc..and if it is a fast coil why can't I sample below 10us?

The main issue is the NE5532 op-amps can not recover from over load (over Voltage) any faster.
This recover time has been discussed much with a few newer op-amps suggested but not much real data on how well they work.

10us is a great short delay for any mono coil and simple front end.
This is fast enough for all but the smaller gold nuggets.

[green]

So with this procedure we can calculate a coils srf and capacitance..But should have in mind capacitance from cable and from diode..

How can I use this coil to it's max capabilities?I mean what tx pulse width delays etc..and if it is a fast coil why can't I sample below 10us?
Tommorow I will wrap a spiderweb just to practice with the thinks I've learned today and finalise my build.

Searching the web for a decent LF357 for my DP Legend but eBay is full of Chinese rubbish..Equivalents are hard because bom says 50V/us slew rate and above grrrrrrrr0

Looked at Rev=E schematic. Rin connected to op amp -input. If op amp was fast enough, shouldn't need Rd(Rin should damp). Wondering what TP3 looks like if a 4148 diode were connected across R8(cathode to amp out) and Rd was adjusted for best decay.

[mushaba]

1335ohms should be close if the mosfet capacitance is isolated from the coil during discharge with the MUR460 diode. Lot lower resistance without the diode. Don't know if scope reads frequency better if display shows 5 or 25 cycles, I usually adjust time base for 5 to 10 cycles. Maybe someone knows if should be different.

I use a different formula for calculating C if I know SRF and inductance. C=1/(2pi*2pi*L*SRF*SRF). Calculates the same 47.7pf you got. Total parallel coil capacitance including lead capacitance. Fast coil, one reason easy to get mosfet avalanche. Parallel capacitance stores little energy at Tx off so 1A peak at Tx off would cause about 570V with Rin=1k and Rd=1335

So with this procedure we can calculate a coils srf and capacitance..But should have in mind capacitance from cable and from diode..

How can I use this coil to it's max capabilities?I mean what tx pulse width delays etc..and if it is a fast coil why can't I sample below 10us?
Tommorow I will wrap a spiderweb just to practice with the thinks I've learned today and finalise my build.

Searching the web for a decent LF357 for my DP Legend but eBay is full of Chinese rubbish..Equivalents are hard because bom says 50V/us slew rate and above grrrrrrrr0

[green]

Here it is

[ATTACH]46192[/ATTACH]

So Rd=pi*L*SRF --> Rd=3.14*0.00034*1250000=1334.5 Ohms.

So this coil when it will be attached to a PI detector should damp at 1.33 Kilo Ohms ????

I noticed that distance between testing and working coil had to do with signal amplitude not frequency..



Yes my oscope measures lots of stuff,trully value for money...I cant understand what is the trigger freq in the upper right of the photo..

Now Rd*Rd= L / 4*C --> C= L / Rd*Rd*4 --> C= 0.00034 / 1334.5*1334.5*4 -->C= 0.00034/7123561 --> C= 4.77 e-11 ...what is that now





That would be my South African nickname or my name in a next life as a lion (or an elephant because in this life im near 110 kgs..)

Up The Irons !!!!!!!!

1335ohms should be close if the mosfet capacitance is isolated from the coil during discharge with the MUR460 diode. Lot lower resistance without the diode. Don't know if scope reads frequency better if display shows 5 or 25 cycles, I usually adjust time base for 5 to 10 cycles. Maybe someone knows if should be different.

I use a different formula for calculating C if I know SRF and inductance. C=1/(2pi*2pi*L*SRF*SRF). Calculates the same 47.7pf you got. Total parallel coil capacitance including lead capacitance. Fast coil, one reason easy to get mosfet avalanche. Parallel capacitance stores little energy at Tx off so 1A peak at Tx off would cause about 570V with Rin=1k and Rd=1335

[godigit1]

And the Amador nail recently found on a expidition to recover hot rock samples.
Incased in a conglomerate surly it must be thousands of years old

Ok A little side track got to go to work

[mushaba]

Nice decaying oscillation-perfect.
Decrease the scope's time base, maybe 2usec/div, to see and measure the time between oscillations (period of oscillation). divide into 1 (1/t) to get the SRF in Hz.

Here it is



So Rd=pi*L*SRF --> Rd=3.14*0.00034*1250000=1334.5 Ohms.

So this coil when it will be attached to a PI detector should damp at 1.33 Kilo Ohms ????

I noticed that distance between testing and working coil had to do with signal amplitude not frequency..

Looks like your scope can display frequency. Set scope to display frequency and do what waltr suggested, change time base until you get a good reading.

Yes my oscope measures lots of stuff,trully value for money...I cant understand what is the trigger freq in the upper right of the photo..

Now Rd*Rd= L / 4*C --> C= L / Rd*Rd*4 --> C= 0.00034 / 1334.5*1334.5*4 -->C= 0.00034/7123561 --> C= 4.77 e-11 ...what is that now

Mashuba Thanks for starting your thread Im sorry ive piggybacked on to asking questions but the information here is the missing link for me.
Best Regards

That would be my South African nickname or my name in a next life as a lion (or an elephant because in this life im near 110 kgs..)

Ps like the eddie avatar.

Up The Irons !!!!!!!!

[godigit1]

Thank you guys and thank you Mushaba. That I can understand.
Ps like the eddie avatar.

[green]

Looks like your scope can display frequency. Set scope to display frequency and do what waltr suggested, change time base until you get a good reading. Adding a scope picture I posted awhile back.

Ok,these formulas are to calculate Rd ONLY or can be used to calculate C and SRF via various Rd values?? Can i use it like C = L / (Rd*Rd*4) or SRF = Rd / (pi*L) ?? YES

[waltr]

Oscope Output.jpg

What did i measure in this precedure??

Nice decaying oscillation-perfect.
Decrease the scope's time base, maybe 2usec/div, to see and measure the time between oscillations (period of oscillation). divide into 1 (1/t) to get the SRF in Hz.

[mushaba]

Hello green thanks a lot for one more valuable lesson!!!!Please be patient until theese things comes clear to my damaged brain


In some posts ago you wrote..

Wondering what the coil specs are. A 300uH coil would need 23pf total capacitance to critical damp with a 1.8k resistor. Possible with a short lead.

1)As i understand from the formulas you gave is impossible my circuit (coil - RG58 - MUR) to have only 23pf capacitance,ok,can you think what else could it be?I've never measure capacitance,added 5ohms to limit the spikes and then via pot i adjusted the waveform of amp out not to have ringing,were did i go wrong??

2)What do you mean by short lead???

Rd*Rd=L/4C and Rd=pi*L*SRF

Ok,these formulas are to calculate Rd ONLY or can be used to calculate C and SRF via various Rd values?? Can i use it like C = L / (Rd*Rd*4) or SRF = Rd / (pi*L) ??

Clip the scope lead to it's ground lead making a loop. Lay the loop on the test coil and position the test coil near a operating PI coil to get a good scope reading of resonant decay(scope 5mV or 10mV/div). Record SRF.

The test coil leads are open right? I have another 3dss waiting (340uH 1.9 Ohms made from PTFE 24AWG silver plated)



I will lay on it the loop i made from oscope + and gnd and how close should i put it near the working coil of my MPP...Put the oscope dc coupling and 10mV/div...





What did i measure in this precedure??