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Originally posted by WM6 View PostIs this lasted under target or free run?
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sample target info
I am using a coil with 32 turns / 22 cm dia. It appears to have a 20 usec decay.
The amp gain in this case is set to 100 not 1000 as there is too much gain at this setting.
The trace below shows a plot for target / no target. The purple trace is the no-target reference trace. The target is an australian $1 coin ( .... this is not a gold coin BTW ) and was placed in the centre of the coil.
There is about 200mV of deflection caused by placing the target coin. IMHO this is quite good.
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Originally posted by WM6 View PostNot bad really.
Interesting to know if ideal balanced (without bump) can give better or worst deflection rate.
moodz.
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variable damping
Substitute this circuit for the main 1K damping resistor. ( ends of 330 ohm resistors )
I used 3 x 1k resitors in parallel.
VPH is the +VE bias voltage input to 78L05 reg on the diff amp supply.
Note this does add some parasitic cap which will add a few usec to flyback.
The pot is 10K however not that critical.
the installation .... neat huh ?
various settings of the pot are obviously changing the damping value.
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Decay
One thing that the waveforms show is that the under-damped RX wants to resonate at ~110kHz. That somewhat explains the slow decay of ~25usec. The 22 cm diameter coil with 34 turns of twisted pair connected as described results in a total RX inductance of ~2.2mH (68 turns). This combined with a combined circuit capacitance of ~650pf-750pf (MOSFET 330pf, C1 220p, 5 41418 diodes total 20pf, coil 80pf (?), cable 50pf(?) calculates to ~120kHz which corresponds with what the waveforms tell us. I think moodz has done some great work and has advanced the PI technology discussion. I do like the concept of the differential front-end and I am excited to explore the possibilities, but I think we need to get a faster decay to be a viable PI design. I have been toying with a negative supply variant that exhibits ~175pf total capacitance and 800uH RX (effective 212uH TX) inductance that results in 12.5us-13us total decay (10mv @ 12us after amplification G=100). As I get the opportunity and time, I am planning to rig this and test it.
Great work, moodz!
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Originally posted by KingJL View Post
One thing that the waveforms show is that the under-damped RX wants to resonate at ~110kHz. That somewhat explains the slow decay of ~25usec. The 22 cm diameter coil with 34 turns of twisted pair connected as described results in a total RX inductance of ~2.2mH (68 turns). This combined with a combined circuit capacitance of ~650pf-750pf (MOSFET 330pf, C1 220p, 5 41418 diodes total 20pf, coil 80pf (?), cable 50pf(?) calculates to ~120kHz which corresponds with what the waveforms tell us.
I am excited to explore the possibilities, but I think we need to get a faster decay to be a viable PI design.
It would be great if you and others from design group join this great moodz development.
With faster decay you mean something like this?:Attached Files
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Originally posted by WM6 View PostThanks for explanation KingJL.
It would be great if you and others from design group join this great moodz development.
With faster decay you mean something like this?:Attached Files
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Originally posted by KingJL View PostNot really. The base that you are indicating (the negative section of moodz display) is actually the value during TX. The decay goes to the proper base, but takes 25-30usec to get there (the 25-30usec positive section of moodz display). Remember you are seeing the decay amplified by G=100. For the 1st 20-25usec it is limited at the positive rail by the amplifier being in saturation (all this is normal), thus appears as a positive pulse. In a faster decay the apparent pulse would be shorter as in the attached waveform (the attached waveform does not show the TX pulse as it is sync'ed to start at TX turn-off and is not of long enough duration to show the next TX pulse).
Evidently I need some term of part signal explanation for my "inglish" English.
Is this correct (regarding by letters marked parts of signal on attached picture)?:
A => rising pulse
B => pulse delay (pulse duration)
C => point of pulse decay (point of decay)
D => pulse decay
F => fly-back pulse duration
G => fly-back nulling
H => waiting time to next pulse (waiting time), waiting Period
I would be very thankful for help in this term clarification.Attached Files
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Originally posted by WM6 View PostThank you KingJL.
Evidently I need some term of part signal explanation for my "inglish" English.
Is this correct (regarding by letters marked parts of signal on attached picture)?:
A => rising pulse
B => pulse delay (pulse duration)
C => point of pulse decay (point of decay)
D => pulse decay
F => fly-back pulse duration
G => fly-back nulling
H => waiting time to next pulse (waiting time), waiting Period
I would be very thankful for help in this term clarification.
A=> start of flyback (end of TX)
B=> saturation during flyback
C=> coming out of saturation during decay
D=> ending of decay
F=> quiesent level (fully decayed)
G=> start of TX pulse
H=> TX pulse duration
Kind regards,
J. L. King
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Originally posted by KingJL View PostThe way I see them :
A=> start of flyback (end of TX)
B=> saturation during flyback
C=> coming out of saturation during decay
D=> ending of decay
F=> quiesent level (fully decayed)
G=> start of TX pulse
H=> TX pulse duration
Kind regards,
J. L. King
regards, moodz.
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