Ground Balance

[Carl-NC]

What is your timing without GB, and what is it with GB?

[revmaster]

Hi Carl,
My timing is as under;
Tx=150us
Delay Period=16us (Have a fairly fast coil)
Target Sample=20us
Delay=10us (Did try to adjust this delay)
GB Sample=(variable)
After long delay=EMI sample (GB sample width-target sample width)

GB Sample width = Target sample width + EMI sample width.

[Carl-NC]

To simplify, I would turn off the EMI sample and work with just Target & GB sample. Try reducing the Target sample to 10us. Also try increasing the GB delay.

[revmaster]

Have tried this earlier, but with smaller target sample the S/N ratio is reduced a lot...

[6666]

No worries I'll go find a few different magnets and do some more testing and report back shortly.

Hi Mick do you remember what types of magnets you used for testing the EF? where they ceramic ?

[6666]

Hi Carl
do I understand your GB description correctly , that when you use a single ended integrator
the first pulse on switch 2 has variable width and that is the GB control ?
Would you mind suggesting some timings please ?
Thanks

[Carl-NC]

Yes, that's correct. The exact timing requirements depend on a lot of things, like coil inductance, damping, and preamp compensation, but here is a rough example:

Target sample: turn on at 15us, turn off at 20us
Ground sample: turn on at 25us, turn off at 40-50us

[6666]

Thanks Carl for reply, will give it a try.

[6666]

Hi Carl
is this something like what should be happening with sw1 and sw2 ? for the single int
you will see the 100uS tx pulse at the top and sw1 and sw2 at bottom
the width of the first long pulse on sw2 is being altered with a pot the rest are fixed ?
The long pulse is going from 100uS to about ~180us.
dont take any notice of the distortion of the bottom of the wave form
this is caused by combining the sw1 and sw2 waveforms with diodes and resistor for cro.
The camera is not square onto the cro screen.

https://www.youtube.com/watch?v=NvmH...ature=youtu.be

[Davor]

This seem to be correct, provided EF pulse duration is balancing the previous pulses. This variation is easier to implement in a micro than my analogue solution with initial delay variation.

[6666]

Thanks Davor

[Carl-NC]

I assume the sequence is SW1-SW2-SW2-SW1. As Davor said, the 2nd SW1 width needs to track the first SW2 width. Also, I would move the EF samples as far away from the main samples as possible, to minimize depth loss.

[6666]

Thanks Carl
yes the sequence is sw1-sw2-sw2-sw1, and I now have second sw1 tracking the first sw2 WIDTH, and moved the EF pulses out further.
The video shows the two long pulses tracking in width. Does this look a bit better.
https://youtu.be/J8MGv5RZg6U

[Carl-NC]

Yep, that's it.

[6666]

Hi Carl
another question please, with your 4 sample duel integrator GB circuit (attached) does it matter if the variable gain amplifier after the integrator is inverting or non inverting ? thanks.