IDX Pro VDI issues

[maxfly]

Hi all,

have been using my silverdog idx vdi for some time now with good success. One problem that has always been present is when a target detected then moved closer to the coil, the vdi number would usually creep up by up to 15 numbers depending on the target type. The same target but using pin point (all metal) made the VDI stable regardless of distance from coil. I had gotten used to this but recently things have changed and the VDI number now starts out high and gets lower as the target reaches the coil, stabilizing at a believable number. Again when in PP the number is perfect no matter where the target is.
Would this be a faulty U3?

Any help would be appreciated,

Max

[dfbowers]

Hi all,

have been using my silverdog idx vdi for some time now with good success. One problem that has always been present is when a target detected then moved closer to the coil, the vdi number would usually creep up by up to 15 numbers depending on the target type. The same target but using pin point (all metal) made the VDI stable regardless of distance from coil. I had gotten used to this but recently things have changed and the VDI number now starts out high and gets lower as the target reaches the coil, stabilizing at a believable number. Again when in PP the number is perfect no matter where the target is.
Would this be a faulty U3?

Any help would be appreciated,

Max

[ATTACH]23949[/ATTACH]

I have observed similar things with my Arduino based VDI, but It's not the Arduino. If I were to connect two channels of my scope to the X and Y outputs and observe the Lissajouse pattern, I could tell that the pattern changes somewhat according to the target distance from the coil. Now, I just back the coil off a little to improve accuracy. Other than that, I have no idea how to compensate.

I do not know what the PP has to do with anything either, unless your batteries are getting weak or have a regulator problem as the PP tone may cause a higher current draw on the whole system with a continuous tone. I noticed the higher current draw because I have an LED installed to remind me if the unit is left on. It gets slightly dimmer when the speaker sounds.

Don

[golfnut]

Hi I took a look at the x,y on scope on my IDX one time.

What I saw is if a medium size target the the diagonal result line on the screen was just that, a diagonal line.

If you used a bigger target closer to coil the line folds over on the highest traversals.


I think this is related to compression of the Filter/Amp stages. Large signal swings are limited by the supply rail.

If you had a higher pos and neg rails e.g. +/-15v then Id guess this effect may go away somewhat.


The other way is to have active gain control - with a large signal coming thru you switch th gain down appropriately. -

Another option is to leave the Rx alone and turn the Tx power down in line to keep Rx sigs from crashing the rail and going non linear.

All commercial Rx's employ gain control in this way to maximise sensitivity by landing all signals at the right amplitude into the A/D's - using all of the dynamic range available - (keeping the S/N as good as poss)


S

[eduardo1979]

I'm not sure that's the problem of the instability of VDI numbers. I have an original and IDX-PRO brings the factory screen does not have any kind of changes. I tested with Arduino, the program has posted DON and I've noticed that the numbers vary depending on the distance of the target. I have inserted a module with an operational amplifier between the detector and the Arduino, but the results are not very good. By adding this module, you get some more stability in the numbers, but it is an extraordinary result. Would have to research the topic a little more in depth. My opinion is that the program should improve. Greetings. Eduardo.

[dfbowers]

Well the Arduino was a fun experiment anyway. I would surely like to know how to improve things a bit. I just can't see how it could get any better since slope changes slightly with target distance. If anyone has any suggestions I can continue the experiment.

Another odd thing I noticed, at least with the Arduino is that higher VDI numbers become more accurate with more samples and lower VDI numbers become more accurate with less sampling..

[maxfly]

Thanks for the replies all,

I will keep playing around to try and restore the idx to the way it used to be and will post again if any joy!

max