IDX-PRO+VDI

[jlsilicon]

Question for the Gurus here ...

I am trying to calibrate my coils using a Sensitive Dual Band Datascope.
But, I can not reduce the idle (no coins) Frequency below about 10mV Sign.

How can I reduce this noise even more ?
What else do I need to adjust besides aligning the Coils ?
What could be causing this - caps, resistors, or ?

[Davor]

There is always some capacitive linkage that is out of phase and it may be balanced with a small piece of foil that you need to move around coils on spots that you may stick permanently. Cut a small 1cmx1cm piece of milk carton and play with it while observing your balance. You'll see that Rx signal changes a little, so aim for a minimum.

[golfnut]

Is this at the preamp output?

If it is then 10mV is as good as it gets.


These machines can tolerate 300mV with ease.

Getting the phase correct so it rejects ferrite and accepts non ferrous is more important

[Koala]

The shape of the coils affect it.

Tweaking the RX capacitor can give you more distance. I find to the detriment of stability and discrimination


I do the same as Davor but use a small piece of graphite.



I aim at the minimum as it always alters a bit even using epoxy resin and might alter a lot with polyester resin.

[jlsilicon]

Would replacing the PreAmp ne5534 with OPA129 help increase the Resolution by removing any Noise and Distortion ?

[jlsilicon]

- Or how about THS4032 ?
- Or Ad797 ?

[Koala]

Don't think there is much to be gained. The original project was refined over several months and just about every combination tried. What was found was some variation in the ICs and you were best to order a few and test in sockets for best performance. If you try any Other combinations that work better post your results.

The MD is mighty fine in the field. People have tried to up the gains and get good results on the bench but becomes unstable in the field. Much better to build a bigger coil.

[jlsilicon]

Actually, I am using the Computer to analyze the Data.
So, improvement in reducing Noise would be useful.
I am already Amplifying the Lf347 second stage outputs.
So the PreAmp is important.

(maybe ad8620 ?)

Problem is that I can not find direct comparisons of Gain, Noise, etc - between ne5534 and opa129 and op275 and Ad797 and Opa2132 and Ths4132 ...
Do you have this info ?

- Thanks in advance !

[Koala]

Actually, I am using the Computer to analyze the Data.
So, improvement in reducing Noise would be useful.
I am already Amplifying the Lf347 second stage outputs.
So the PreAmp is important.

(maybe ad8620 ?)

Problem is that I can not find direct comparisons of Gain, Noise, etc - between ne5534 and opa129 and op275 and Ad797 and Opa2132 and Ths4132 ...
Do you have this info ?

- Thanks in advance !

I bought the best ones I could find using the data from Farnell.

Even OPA129 have different slew rates by different manufactures.

You can down load manufacturs data direct of the site just click on the PDF icon

[jlsilicon]

Ok, different question ...

How about using ne5532 to replace the Lf347 OpAmps in the dual sequences ?
- or multiple ne5534's ... ?

- The Lf347 have a Noise level of 20nV.
While the 5532/5534 have a Noise level of 4nV.
- Both have a Gain of 100V/mV.

[scrungy_doolittle]

I am really sorry, but will not publish the source code of VDI, to prevent unacceptable commercial use of it, sorry...

I'd be happy to port it to C for you. I'd like to have it running on a different platform. Either a PCI24 or an Silabs8051F040 which I work on all the time.
I also have a number of tweaks I'd like to see. Rather than the battery, I'd like to see a real time clock in the upper corner, and even better a settable timer that counts down. That way I could
set it for the amount of time I have over my lunch hour, and go detect until it timed out and make it back to work on time. That would be a huge feature especially for me.
I bought the original VDI kit, built it, but it just makes the regulator get really hot, and it does not work. i'm sure it is pilot error)

[holyuser]

I'd be happy to port it to C for you.

No, thanks, I don't like C.

[Davor]

Ok, different question ...

How about using ne5532 to replace the Lf347 OpAmps in the dual sequences ?
- or multiple ne5534's ... ?

- The Lf347 have a Noise level of 20nV.
While the 5532/5534 have a Noise level of 4nV.
- Both have a Gain of 100V/mV.

You can't directly replace LF347 (quad opamp) with NE5532 (dual opamp). You can replace a fet opamp with bipolar if care is taken to equalise bias, and you can see that in schematics where both inputs have roughly the same resistance on input. You don't need to do that with fet inputs, but there you can't simply replace the opamb because bias would be off.

20nV/sqrt/Hz) if fine for a 2nd stage preamp stages providing enough gain.

[seadoggy]

how connect light on vdi?,to have controls on new hex code.
Regards

[holyuser]

1. Keep pressed "less" button before turn power on.
2. Turn power on.
3. Wait a while until "CONTRAST SETUP" message appears.
4. Release button.