Basics: Recovery Speed, Reactivity

[holyuser]

I think you mean this. I am right now.

I mean this:

[eduardo1979]

I mean this:

True, but I have done differently in the end is the same.

[ivconic]

Sorry Ivconic, it was work time for me. Now it's fun time!

Recovery speed isthe time it takes a detector to recover from identifying any target and signal the presence of another target.

Demod design and filter speed usually dictates this. The reason a 4053-based circuit seems to perform better is that it is usually a full-wave demod, whereas a 4066-based circuit is usually a half-wave demod.

- Carl

That's what i wanted to hear here!
So it is design of synchronous demodulator and filter speed which defines recovery speed.

[Davor]

... or not. It is the time constant of the filters that do the delaying ... thing, and it can be set this way or another.
Say IGSL - it has 20k in series with the bilateral switch that is 50% time open (thus behaving as a 40k resistor) and a 220n capacitor, giving a -3dB point at 18Hz. Using 4053 and two resistors of 20k each would require 440n to keep the same time constant, but the only real big deal is in the way double switch suppresses the carrier. Filter time constant is something you pick for your purpose, and it is as good as you calculate it.

Everything else falls into tsyntsulator, blaybinger, doodah, and doohickey categories. Shortly - marketing.

[ivconic]

I am asking these questions because i would like to clear up those facts on recovery speed.
For me it is the one of most important features at metal detector.
Ok, that's mostly because of the nature of searching i do affect and of course because of the character of my local soils here.
Usually when i pick a model to buy; first i want to be sure about it's recovery speed capabilities.
That's why Deus was my most logical choice (also because of many other nice features too).
Later Cscope CS6MX appeared and i am very satisfied with what i saw on those few youtube clips with it.
TGSL is nice home project. But i always wanted to improve recovery speed at it.
Maybe that's why i later made IGSL??? (couldn't solve recovery speed at TGSL so than decided to overcome problem with different approach! )
Classic III is also splendid home project! Yet it's recovery speed sucks!
etc..etc...
That's why i started this thread to hear others opinions and experiences.
Thanks for inputs!

[Tepco]

I am asking these questions because i would like to clear up those facts on recovery speed.
For me it is the one of most important features at metal detector.
Ok, that's mostly because of the nature of searching i do affect and of course because of the character of my local soils here.
Usually when i pick a model to buy; first i want to be sure about it's recovery speed capabilities.
That's why Deus was my most logical choice (also because of many other nice features too).
Later Cscope CS6MX appeared and i am very satisfied with what i saw on those few youtube clips with it.
TGSL is nice home project. But i always wanted to improve recovery speed at it.
Maybe that's why i later made IGSL??? (couldn't solve recovery speed at TGSL so than decided to overcome problem with different approach! )
Classic III is also splendid home project! Yet it's recovery speed sucks!
etc..etc...
That's why i started this thread to hear others opinions and experiences.
Thanks for inputs!

Interesting issues for discuss, I want to make few comments about all this, from beginning of this post.

Operating frequency is absolutely non-related with recovery speed directly (but can affect it to some degree, depending on detector design, indirectly, some lower freq. machines are actually slower, but not all).Neither switch type used in demodulators can affect it directly in any way, but indirectly can.

Most important parameter defining recovery speed is design of post-detector filter stages. Just simple differentiator type circuit in some designs (diode limited and with reduced dynamic range), more complex bandpass filtering in others, usually DSP in anything recently built. Time domain response of this stage is crucial, but not only factor. As a rule, all faster detectors are built using some more sofisticated filter stages, all simple diferentiator types are slower.

Another thing to consider is demodulator type (not components used in it), single ended, like TGSL, or balanced. First type will “leak” DC\LF component in next stage, never mind, there is no DC or LF at this point. Well almost. LF component coming from GND is sufficiently attenuated in RX preamp and AC coupling after it, but higher freq. components generated during sweep over multiple targets may not always be. Especially if following filter is simple derivative stage, with relatively larger bandwidth and not so sharp roll off, this LF will fall into its passband. Balanced detector will perform better in general, or more aggressive band or high pass filtering at RX input can help with single ended design

(yes, 4053 is usually in balanced detector design, SMW or whatever version of it…)

Change filters (use some existing design), change demod, wach BW and gain distribution, you can get nice speed. Changing just time constants of existing filter is not recomanded, filter performance is limited and will affect motion response time too.

[ivconic]

Interesting issues for discuss, I want to make few comments about all this, from beginning of this post.

Operating frequency is absolutely non-related with recovery speed directly (but can affect it to some degree, depending on detector design, indirectly, some lower freq. machines are actually slower, but not all).Neither switch type used in demodulators can affect it directly in any way, but indirectly can.

Most important parameter defining recovery speed is design of post-detector filter stages. Just simple differentiator type circuit in some designs (diode limited and with reduced dynamic range), more complex bandpass filtering in others, usually DSP in anything recently built. Time domain response of this stage is crucial, but not only factor. As a rule, all faster detectors are built using some more sofisticated filter stages, all simple diferentiator types are slower.

Another thing to consider is demodulator type (not components used in it), single ended, like TGSL, or balanced. First type will “leak” DC\LF component in next stage, never mind, there is no DC or LF at this point. Well almost. LF component coming from GND is sufficiently attenuated in RX preamp and AC coupling after it, but higher freq. components generated during sweep over multiple targets may not always be. Especially if following filter is simple derivative stage, with relatively larger bandwidth and not so sharp roll off, this LF will fall into its passband. Balanced detector will perform better in general, or more aggressive band or high pass filtering at RX input can help with single ended design

(yes, 4053 is usually in balanced detector design, SMW or whatever version of it…)

Change filters (use some existing design), change demod, wach BW and gain distribution, you can get nice speed. Changing just time constants of existing filter is not recomanded, filter performance is limited and will affect motion response time too.

That's nice and educational post Tepco!
Many thanks!