xr-71 sniffer powerscan coil

[Sulyman27]

Hi, I'm begginer in Electronic,
I'm on my way to build xr-71sniffer powerscan detector , i bought the pcb from Bulgarian site, i 've just finished the 28cm coil , It 's 32 turns as they mentioned in work paper, the coil values is 2.7Ohm 0.86 uH, is that Ok?!!
Do i need damping resistors?

[dbanner]

No! That should be 2.7 ohms, 0.86mH. This is 860uH. This is OK, and yes you need damping resistor. It should be on circuit board(PCB)

[dbanner]

Look schematic. The coil you built measures 2.7 ohms, 860uH. You can build different coils according to your needs. But they have to be properly damped with appropriate value of damping resistor depending on coil.

[dbanner]

In the schematic, 2.2K resistor is used for damping. But this is for coil about 2mH. Your coil is 0.86mH, so your damping resistor will be different value(less). Ideally, you should use an oscilloscope.

[Sulyman27]

Thank you dbannet,
The damping resistor is the one that connects directly across the coil right? ( see my pcb attached pic) if yes, so this is 1.957k resistor after testing,
my question is if i want to use my 28cm coil I have to replace it with another (less) value? How can i know the proper value without oscilloscope?and also what is best coil value for this 1.957k resistor?.
Finally i need to learn about damping resistance's funtion could you pls post me some links about that?
Thank you again.

[waltr]

Within the other threads on PI detectors and articles is info about How to Adjust the Damping Resistor for critical damping.
This is also covered in the book ITMD.

Best is to use a Pot/resistor combination to adjust then remove and measure the pot/reisitor value and solder in a fixed value (or combination).

[kt315]

DP/sniffer XR71 is working with relatively big SAMPLE DELAY and thats means it does not need
in the tuning of the overdamping resistor.
min delay value for DP is 40us, but really i set 100-120us for cut-off of small metal garbage.

[Tibuck19]

Hi, I'm begginer in Electronic,
I'm on my way to build xr-71sniffer powerscan detector , i bought the pcb from Bulgarian site, i 've just finished the 28cm coil , It 's 32 turns as they mentioned in work paper, the coil values is 2.7Ohm 0.86 uH, is that Ok?!!
Do i need damping resistors?

Greetings would you happen to be Jason that has posted videos on Youtube about your build ? Would it be possible for you to post a lint to the website you bought this kit from ?

[dbanner]

Thank you dbannet,
The damping resistor is the one that connects directly across the coil right? ( see my pcb attached pic) if yes, so this is 1.957k resistor after testing,
my question is if i want to use my 28cm coil I have to replace it with another (less) value? How can i know the proper value without oscilloscope?and also what is best coil value for this 1.957k resistor?.
Finally i need to learn about damping resistance's funtion could you pls post me some links about that?
Thank you again.

your pcb shows a damping resistor red/black/red this is 2Kohm(2000 ohm)resistor. Where did you get the coil specs from? Did it come with the Kit? If so then the 2K resistor should be fine. Read here for a method to compute damping resistor value http://www.geotech1.com/forums/showt...hlight=damping

[dbanner]

Did you get any instructions with the kit? Where did you get kit from?

[Sulyman27]

Thank you Walter & Kt315 for your help.

[Sulyman27]

Tibuck19,
I'm not Jason.
I bought this pcb populated with all its components and tested from this site :http://www.powerscan.eu/open/upload/...r_id=11&page=2

But, this site does not exist anymore

[Sulyman27]

Dbanner,
Yes i got it from this site:
http://www.powerscan.eu/open/upload/...r_id=11&page=2
Shipped from Bulgaria , it Comes with schematic and instructions paper . he said that this pcb works with different coils 28cm ,38cm, 40×40cm,1×1m....
But he did not talk about damping resistance adjustment.

[Toros]

Delta pulse will work with all the coils you point to, but with none of them you will not get maximum results. The meaning of setting this damping resistor is when you work with just one particular coil. With another coil the value of the resistor will be different.

[eclipse]

KT315 described it very well. This schematic doesn't aim for early sampling so it samples 30-40us or whatever where the ringing is gone no matter the damping resistor.
Just set 680R damping resistor (2 - 3 Watts) and start hunting. You can try 1K - 2K values if you're not happy with the low value and see on the field if it's better or worse.
Good luck.