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SURF PI PROBLEMS

D

daverave

New member
ive just taken my surf pi apart to do some measurements and can anyone tell me the ideal sample pulse (width setting) it was set to 45 uS and now ive changed it to about 10 uS........is this about right for low conductive items ???? my normal pulse delay is set at 15 uS...have i got both settings correct ?? i also have a problem with noise on the back emf waveform which is causing jitter on the audio signal causing instability !!! im going to try a better op amp and see what happens !!!!!!!!!!!! i wonder sometimes if the 7660 negative supply ic may cause jitter as its not in sync with the oscillator also my damping resistor is only a 1/4 watt metal film which gets hot and maybe cause noise ??? any thoughts on these problems would be appreciated.
 
Hello Dave.

Questions....What is your reason for reducing the sampling gate time, to 10 micro-seconds?

Also, please can you determine the PRF ? (pulse repetition rate) and TX pulse width?

Any idea what the search-coil inductance is, and it's damping resistor value?


Dave, what are the main group/type of targets you hopefully search for with this unit?

If we can get the rational right, then maybe we can help......Matt

p.s. Do you have an oscilloscope?
 
since i asked these questions i did some experimenting and i much improved the depth on low conductive items using a narrow sample pulse width and increasing the tx frequency to around 3 khz.....my main problem had been noise from the 1st amp causing some threshold instability so im experimenting now with filters...im now getting good depth but its taken a lot of trial and error.
 
daverave
Your pi is it a white surf pi or a TDI
What did you change or replaced to lower uS to 10
Frank-s
 
my detector is a surf pi and i had to decrease tx pulse width and critically damped the coil and increased coil voltage.
 
ITMD.
http://www.amazon.com/Inside-Metal-Detector-George-Overton/dp/0985834218/ref=pd_rhf_ee_p_img_2?ie=UTF8&refRID=1CMM3XDDMSEQ5SG7TWCJ
 
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