TGSL Tuning & troubleshooting

[dbanner]

Long story short, as long as you have correct inductances for coils, and they are nulled, then everything else should fall into place, like phases etc.

[dbanner]

Now when your coils are "nulled", this should result in Tx and RX signals being "out of phase" by about 20 degrees or maybe a little more (if I remember correctly). This would result in ground balance and discrimination functioning correctly as designed.

[dbanner]

Your receiver coil is tuned by C6 to around 6.12KHZ(off resonance). It is called "off resonance" because the TX frequency is around 14.5Khz. Therefore the TX and RX are tuned to resonate at different frequencies, hence the term "off resonance". This is required to get proper PHASE relationship between TX and RX for Ground balance and discrimination to work correctly.
The phase relationship between RX and TX can be seen on oscilloscope.

[dbanner]

Well, beyond just nulling, you are able to see shape of waveform, the amplitude, and the phase relationship between RX and TX. This last one would require dual trace scope. I learned that the phase relationship between RX an TX signals are related to ground balance and proper discrimination. Each metal detector might be designed differently with these parameters in mind.

[BKY1337]

Ok, i could not see it because the wave was too big. I need to remove this plastic things first in my enclosure because the coils are too far away from each other.

Btw: Which advantage has the nulling with this DSO to a Multimeter?

[BKY1337]

I didnt saw that something expands. I also cannot measure anything at pin 6. I will give it one more try.
The coil works but only 18cm with a euro and a weak signal.

[dbanner]

When you move the RX coil with respect to the TX coil, you'll notice the RX waveform expanding and contracting in amplitude. The theoretical "null" is when 0V is induced into to RX coil, this state is called inductive null(balance). In practice, you want to get RX and TX as close to perfect inductive null, look for smallest waveform you can get on RX coil and this would be your null point.

[homefire]

The Null Voltage is the Lowest Voltage you can obtain just on the Positive side.

[BKY1337]

Which voltage is the null voltage at my DSO?

[BKY1337]

My whole unit worked before. I had 38cm depht without shield with my old coils.
I think the pots are ok. I can make pictures tomorrow , i really wanna finish this project.

It works way better now but i can not reach more than 20 cm. It took me one week to make this graphite shielded coils.
I applied every day one layer of 2K epoxy glue, it needed to cure 24h.

[ripsdevala]

Check the pot and disc switch connection also, wrong connection=faulty. Dont worry all will be okay, if not just contact blobber from germany

[BKY1337]

Thanks. But my detector clackers all the time , i dont know whats wrong. I could measure 4Volts at pin 6 of the 4024 , now i cant measure anything. Maybe because the Transistor was damaged.

I tried to measure the Testpoints in the pdf and the one at U100 Pin 6 is not working. I get a Signal but way to weak , only a few mV.

When the black probe is at the battery while the detector is on and i touch the red one everything clackers more and beeps.

I will change the BC Transistor to the original one tomorrow because the new ones arrived today.

Maybe its better when i build a new unit.

EDIT: I saw that my shield is connected to the RX coil connector at the board. This is wrong. I will fix it tomorrow.
Maybe it was this what caused the strong clackering.

[ripsdevala]

Use 5v first with 20us, then drag the coil if u using DD until the wave is change into smaller wave, then change the voltage at the lowest dso to fine balance.

[BKY1337]

How do i null the coil with the DSO? I connected the black probe to GND Battery and the red one to Pin 7 LF353. But i dont know which one of the Voltages is the right one. I also can not see that the voltage is changing when i move the coil.

Are my voltages OK for TX?

I used the 0.1V and 50uS Setting for RX Signal Pin7.

[BKY1337]

I have changed the connection to the other hole.

Now i got this voltages:

Vmax = 0,00V
Vmin = -23,73V
Vavr = -16,02
Vpp = 24,13
Vrms = 17,03

It worked for a short while. I had over 20cm and a strong signal for a few seconds , then i tried to null the coil and it wasnt possible to measure the pin 7 voltage.