Replies to Minipulse Plus

[green]

http://www.geotech1.com/forums/showt...ircuits-for-PI From mickstv reply #456

With spice I get a gain of about three, same as calculation from reply #459 by King. The (track/hold differential integrator)from above post #1 has a pot in series with output opamp feedback resistor labeled Integration TC. Changing the pot value or sample time changes integrator TC Changing the pot value has a small effect on gain. Still haven't figured the circuit formulas, maybe my spice model isn't correct, but that's what I'm getting.

[Davor]

...Changing the pot value or sample time changes integrator TC Changing the pot value has a small effect on gain...

It sets slew rate.

[green]

http://www.geotech1.com/forums/showt...ircuits-for-PI From mickstv reply #456

With spice I get a gain of about three, same as calculation from reply #459 by King. The (track/hold differential integrator)from above post #1 has a pot in series with output opamp feedback resistor labeled Integration TC. Changing the pot value or sample time changes integrator TC Changing the pot value has a small effect on gain. Still haven't figured the circuit formulas, maybe my spice model isn't correct, but that's what I'm getting.

Scope pictures from spice. Target = 1volt, EF = 0 volts, signal DC coupled to input with a 100 ohm resistor. Fc approximate from scope screen. 1khz sample rate

[6666]

I love the dd... it gives me the added advantage of ferrous metal discrimination.

KingJL in what way does your DD discriminate ferrous , thanks.

How did you screen it ?

[KingJL]

KingJL in what way does your DD discriminate ferrous , thanks.

How did you screen it ?

DD coils are made with a slight overlap of the 2 D sections. The detection zone of the dd is in the overlap area. Ferrous targets provide a negative response in the detection zone and a positive response on either side of the dectection zone. All other targets provide a provide a positive response in the detection zone and a negative response on either side of the zone. So as you are swinging the coil, non-ferrous targets provide an audio beep as the coil crosses the target. A ferrous target provides a beep as you approach the target, goes silent as you cross the target, and provides a beep as you leave the target. I love DD's!

[johnandles]

DD coils are made with a slight overlap of the 2 D sections...... I love DD's!

Are the loops wired in phase or out of phase, does it make a difference?
Thanks

[6666]

KingJL thanks for your reply, what did you use for shielding ? and did you induction balance the coils ?

[KingJL]

KingJL thanks for your reply, what did you use for shielding ? and did you induction balance the coils ?

I used Scotch copper mesh for shielding,on each of the 2 coils following bbsailor's advice. The coils were balanced by observing the preamp output signal and adjusting the overlap until the tx signal was completely cancelled. Fine tuning of the balance after the overlap had been carefully set was accomplished by a small length of the rx coil lead (usually refered to as an adjustment loop) that I left exposed when building the coil. There is an old geotech thread/post by Reg where he discusses building the dd, which I used as a guide when constructing mine. The instructions were well written and easy to follow.

[KingJL]

Are the loops wired in phase or out of phase, does it make a difference?
Thanks

I don't know which phase is correct... but It does make a difference... before you button up the coil, test it... If you do not get a positive response with a nickel passed over the overlap zone, reverse your rx leads.

[green]

DD coils are made with a slight overlap of the 2 D sections. The detection zone of the dd is in the overlap area. Ferrous targets provide a negative response in the detection zone and a positive response on either side of the dectection zone. All other targets provide a provide a positive response in the detection zone and a negative response on either side of the zone. So as you are swinging the coil, non-ferrous targets provide an audio beep as the coil crosses the target. A ferrous target provides a beep as you approach the target, goes silent as you cross the target, and provides a beep as you leave the target. I love DD's!

Been trying to discriminate with a PI. For me target direction or ferrous, non ferrous effects the signal during the coil off decay. Including some scope pictures of integrator out for the first sample after delay of coil off. I've been trying to discriminate during coil on time. Integrate a sample near the start and integrate an inverted sample near the end of coil on time (5usec samples, 100usec on time). Sum the two outputs, monitor the sum and adjust the gain on sample 2 for no change for a ferrite core target. Compare the change of sample 1 and corrected sample 2. If sample 1 change is higher the target is non ferrous, if change is lower its ferrous. Could use the sum output for target sensing. Probably need EF samples. Seems to work on the bench. Maybe not on the ground.

[green]

Been trying to discriminate with a PI. For me target direction or ferrous, non ferrous effects the signal during the coil off decay. Including some scope pictures of integrator out for the first sample after delay of coil off. I've been trying to discriminate during coil on time. Integrate a sample near the start and integrate an inverted sample near the end of coil on time (5usec samples, 100usec on time). Sum the two outputs, monitor the sum and adjust the gain on sample 2 for no change for a ferrite core target. Compare the change of sample 1 and corrected sample 2. If sample 1 change is higher the target is non ferrous, if change is lower its ferrous. Could use the sum output for target sensing. Probably need EF samples. Seems to work on the bench. Maybe not on the ground.

some scope pictures. Same as above except 80usec 0n time

[KingJL]

Been trying to discriminate with a PI. For me target direction or ferrous, non ferrous effects the signal during the coil off decay. Including some scope pictures of integrator out for the first sample after delay of coil off. I've been trying to discriminate during coil on time. Integrate a sample near the start and integrate an inverted sample near the end of coil on time (5usec samples, 100usec on time). Sum the two outputs, monitor the sum and adjust the gain on sample 2 for no change for a ferrite core target. Compare the change of sample 1 and corrected sample 2. If sample 1 change is higher the target is non ferrous, if change is lower its ferrous. Could use the sum output for target sensing. Probably need EF samples. Seems to work on the bench. Maybe not on the ground.

I believe that Tinkerer did some experiments along these lines... you might want to touch base with him and compare notes... He is a great guy to work with.

[green]

Back to the integrator. Still trying to come up with formulas. Got some that work with the spice model. Not sure if they are correct, but I think they are close. Some scope pictures and a chart for R 22 value for Fc = 10 Hz.

[Davor]

You may seek formulas for switching capacitors, but estimation is not that complicated - you simply divide input resistance by the portion of time a switch is closed. It is much easier to figure it out by measurements or simulation though. This integrator is a little bit different from the lot.

[maikl]

Did someone do ground balance?