Whites PI3000 timing

[Anonymous]

Hello,
I'm probably talking of the obvious and Eric will smile <img src="/metal/html/biggrin.gif" border=0 width=15 height=15 alt=""> reading me, anyway I hooked my oscilloscope to my PI3000.
I tested pin TP2 (R12) of the clock generator.
Clock speed is 30Khz (32 in my machine) .
As obvious from the schematic, clock is fed in to Clk pin of CD4017 that acts as a Clock divider (by ten).
A TX pulse is generated by the CD4017 at Q1 pin 2. TX pulse length is 30uS.
Ater TX shutoff, sampling is started by CD4017 after a delay of 30uS (!).
Final sampling of background noise is taken 210uS after Tx shutoff.
So my conclusion is that this is a 30uS samplig detector and this well explains why it does't easily (or at all) detect small gold....
HH

 

[Anonymous]

Luca, 4069 is IC that will lower time delay. I modified my 1000,its not safe to tell you to make a change,with out compairing your print with my print to see if they are the same or close.Did you have any problem getting 13000 apart.make sure to use new O-rings and put water proof lub on them.
4069 IC mod; increased dept about 4".it was more sensitive to smaller non-ferrous metal and smaller gold rings.(Dont make the same mistake that I maked)I wonted a PI that would detect small nuggets.(my mistake)I lowered resastance to fast to get where I wonted to go.End results a transister got hot,detector off line now.can not get the trans;
If you lower R by putting another resister across it.Start off with a very high value resister, slowly come down to what you think it chould be.Good Luck.

 

[Anonymous]

Hi Luca,
Are you sure the TX pulse is only 30uS? This seems a bit short for that type of detector. Normally two or three of the 4017 outputs are OR'd together to give a TX pulse that is either 60 or 90uS wide. However, if this were done, it would not leave enough outputs to give the 210uS second delay.
If you wanted to improve the sensitivity to gold, I would double the clock frequency to give 15uS pulses out of the 4017. Then OR pins 2,4 and 7 with diodes into the transmitter drive to give a 45uS TX pulse. Take pin 1 as the signal sample pulse and pin 3 as the noise subtraction pulse. You are left with 60uS between the end of the signal sample and the start of the noise sample, which is adequate for most gold objects.
I'm not familiar with the circuitry of the PI3000 so there are bound to be other things that are not optimum, but the above is a good start on improving the sensitivity.
Eric.

 

[Anonymous]

Thanks for the suggestions!
I'm sure (as far as my understanding of the schematic is good)that TX pulse is 30uS.
The TX transistors are bound only to pin 2 (Q1) of CD4017 .
Signal pulse is bound only to pin 11 (Q3) of CD4017 and ground pulse to pin 7 (Q9).
So if I made it right, given a clock of 30Khz (I measured it) e.g. 30uS cycle , the cd4017 will pulse each gate for as long as 30uS.
So at Q1 we transmit (30uS), at Q3 we sample signal (after 30US of Q2) and at Q9 we measure ground signal , 7 cycles after TX pulse, so 210uS later.
My schematic of the PI3000 is very similar to the PI1000; they did't change much...
I hope I did not bother too much since this is a hold detector and , maybe, I should get a better one.
HH

 

[Anonymous]

Hello,
well removing the board worries me . Probably I can get it out without having to loose the front cables because it looks like there is enought free cable inside the case to let the board out.
If I undrestood your suggestion you mean I can double the clock speed working on the CD4069 and achieve a 15uS speed as Eric also suggested.
What I did not understand is how you "fried" the ZTX750 TX transistor.
My idea of a possible modification is to make a small board with a PIC16F84 processor to replace the CD4017 and program a diferent timing. This would leave the TX pulse width unchanged and not arm the TX transistor, but will the 4Mhz clock of the PIC influence the LM5534 RX first stage amplifier? Shielding required? Mmmmmhhhhhhh <img src="/metal/html/confused.gif" border=0 width=15 height=22 alt=":?">

 

[Anonymous]

http://www.donberg.ie/descript/z/ztx750.htm

 

[Anonymous]

Hi Luca
I follow your posts and have one more suggestion to adjust your timing circuit. I'm sure it works. Change/replace either R11 or R12 with a poti. One of them will work. By replacing the resistor with a poti you can adjust the clock circuit frequency.
The Clock circuit (CD4069) triggers your IC U4. With adjusting the poti you can "speed up" or "slow down" your clock circuit frequency. The clock "speed" adjustment works than like a discrimination and it gives you the opportunity to adjust your sample delay.
Chris

 

[Anonymous]

Hello Chris,
I know it will work, but a problem I see is that, in this way, I also shorten TX pulse lenght and this is undesiderable since , as Eric stated, the TX pulse lenght appears to be already too short (30uS); bringing it down to 15uS would limit detection depth in my opinion.
While it is a very easy modification( R12 can be replaced without disassembly of the whole detector) I still think that replacing the CD4017 would be better. I'm looking forward to see if a piggiback board for a PIC16F84 would fit.
<img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=""> HH

 

[Anonymous]

I fried 750 by lowering R12 or R11 to fast.Not sure witch one, will check and let you know later.R11 AND R12 is same as R5-R6 on a 555 timmer.R12, start off with 470K then go lower.first thing you wont to do is lower a cap at 4069.if it has a 150 pf go to 130pf no lower.4069 is main timer.I HAD asked to see the print to compair.if the 1300 has been changed from 1000.you might frie something.I am at libary what I just said is from memery.(Large cap next to 4069 what size is it).
4017 I could be wrong,Eric siad to make a change to pin () () TO SPEAD up clock. dest-a durd-a
Frank-S

 

[Anonymous]

Hi Frank and Luca,
Changing the clock speed by half, up or down, should not fry anything. Whether you speed up, or slow down the clock, the transmitter current should remain within reasonable limits. That is because the pulse width and pulse rate change proportionally. In practice you will find that the TX current falls somewhat as the clock speed is raised. This is because the current is limited by the coil inductance. Assuming a coil inductance of two or three hundred uH, a 30us pulse is too short for the current to reach its maximum value, which would be limited by the circuit resistance with a much wider pulse. A 200uH coil with a total of 2 ohms series resistance, has a time constant of 100uS. To reach 95% of its final value, the TX pulse would need to be 300uS wide. A 30uS pulse will only reach about 25% of the final value current before it switches off. At this point it is still rising steeply and inducing eddy currents in the target which are in opposition to those which you want at switch off. Result; loss in detection range.
I suspect that in Frank

 

[Anonymous]

Hi Luca,
you can try to remove R13 from U4 PIN2 and connect the resistor to U4 PIN4 + the clock circuit mods. This mod will trigger your TX pulse later at a later stage.
Chris