How can i increase detecting dept?

[Unregistered]

My language very bad ,so sorry . Now , My metal detector can detect about 10 cm. .
I want to adjust for increase dept of detect . How can i do ? please help me
I hope you can understand me

[Reg]

Hi,

I assume you built the Hammerhead and are asking questions about that detector so I will try to give you some ideas.

Now, there are several reasons you could have a lack of depth and I have listed some of them below.

If you have adjusted the delay so it is real long then you could have a lack of depth. Objects made of lead or gold may have a weak signal, while objects made of copper or silver may have a stronger signal if the delay is too long. So, if you have the delay too short, you could have a lack of depth but it shows up more on non ferrous objects.

If you have adjusted the sample width too long, you could have a lack of depth. Too long of a sample width also extends the delay indirectly, so it can affect the sensitivity of lower conductive objects such as lead or gold. If you have this sample width too short, then it may not be sampling correctly or at all some of the time. So, if you have the sample width too short or too long, you could have a lack of depth.

If you have set the pulse width too short, you could have a lack of depth. You should start with a longer pulse width of 75 usec or so to get started. This will help with the depth capabilities.

If you have a coil with very few turns, you could have a lack of depth. You could start with a coil of at least 300 uh to begin with to assure a decent depth of detection.

If you are using too low of a power supply voltage, you could have a lack of depth. A good voltage is 12V but I don't recommend anything less than 10V.

If you have one of the other adjustments such as R 35 or R 41 set at maximum resistance, you could have a lack of depth. Both of these controls sort of act like a sensitivity or depth control. Set them at mid position or less resistance to begin with.

If you have the autune speed, R 34 set to minimum resistance, you could have a lack of depth. Autotune or also called autotrack, determines how fast the circuit will retune itself to the original threshold. Reducing the resistance of R34 will will reduce the sensitivity or depth capability. Set R 34 for maximum resistance to begin with.

If you have a component installed that is incorrect in value, you could have a lack of depth. Double check all values of components to make sure you didn't install something like a 1K instead of a 100K. This can happen easily.

If you have a combination of any of the above conditions, you could have a lack of depth. So, it is important to begin with all controls set to give you a good depth.

Now, if you have a scope, you need to check each stage to see what is happening and set the key or important controls for some start position.

As an example, set the delay for 20 usec, set the pulse width for 75 usec, set the sample width for 20 usec Set R35 and R 41 for mid position, Set R 34 for maximum resistance. Next, check to see if the depth has increased.

Check the voltage at TP 5 and make sure it isn't near or greater than 4 Volts DC. If it is, then the opamp IC 8A may be in saturation. If that happens, you will have a lack of depth. This is usually caused if the delay is too short or the coil is not built properly. If you have a voltage of 4 volts or greater, slowly turn the delay to increase the amount of delay you have and see if this voltage begins to decrease. Once it does, see if you now have much more sensitivity. If this happens, then the coil is not built properly, or you have used some shielding material that simply causes too much of a problem.

What test equipment do you have? How many turns in your coil and what is the diameter of the coil? What are you using for coil shielding?

Measure the +5V and the -5V. Do they measure correctly?

What value resistor do you have for the damping resistor?

I have mentioned several items that need to be checked. Also, we need more information to help you find out why you have a lack of depth which is also the same as a lack of sensitivity.

Hopefully, with more information we can help you solve the problem.

Reg

[rajesh]

hh

My language very bad ,so sorry . Now , My metal detector can detect about 10 cm. .
I want to adjust for increase dept of detect . How can i do ? please help me
I hope you can understand me

hi whats your language ?can you tell me r8 r9 r7/option vco / nonvco/

[rajesh]

t/r locator

I'm interested about to built a t/r locator based hammerhead cuircut and I need to know rx /tx varticaly /horizantlly style if you can share the components too.

[nick_f]

Hi Reg,
You provided plenty of hints about how to increase the detection depth and I agree with most of them. However, I don't think this one is right:
"So, if you have the delay too short, you could have a lack of depth but it shows up more on non ferrous objects."
If one has the adjustments set properly (I am talking mostly about R18, R31, R34) and the coil + final transistor allow the delay to be set very short, then I think the detection depth will increase especially for gold, but also for any other metal. If the adjustments are correct, the user should not be able to set the first delay under the physical possibilities of the coil circuitry without a severe reduction of sensitivity for any metal. If the first delay is short and second delay is set far enough from first delay, the detector should have increase sensitivity for any metal.

Regards,
Nicolae

[rajesh]

hh

Hi Reg,
You provided plenty of hints about how to increase the detection depth and I agree with most of them. However, I don't think this one is right:
"So, if you have the delay too short, you could have a lack of depth but it shows up more on non ferrous objects."
If one has the adjustments set properly (I am talking mostly about R18, R31, R34) and the coil + final transistor allow the delay to be set very short, then I think the detection depth will increase especially for gold, but also for any other metal. If the adjustments are correct, the user should not be able to set the first delay under the physical possibilities of the coil circuitry without a severe reduction of sensitivity for any metal. If the first delay is short and second delay is set far enough from first delay, the detector should have increase sensitivity for any metal.

Regards,
Nicolae

hi nick i think reg is out of city. you have good view i'm used r 45 100k and r42 set to midpoint it give me better sensetivity.