Amplifier frequency response

[Chet]

Hi Chet, how deep can the 5000 detect 5x5mm side wall target using the 14x9 ?

Thanks
Mick

Hi Mick
Both coils detect the ¼” sidepiece at 1.5” to 2” this would probably be better in the field.
Have a good day,
Chet

[mickstv]

Mickstv, Thanks for the follow up on taking a close look at the 6mm X 6mm target in the video. It confirms that the target is not square and is most probably larger than 6mm X 6mm.

Regards,

Dan

Hi Dan, thats ok.

Hi Mick
Both coils detect the ¼” sidepiece at 1.5” to 2” this would probably be better in the field.
Have a good day,
Chet

Hi Chet, thanks for the reply. Your right in town EMI will effect the depth, my test had alot of noise so I would expect the 5x5 to go deeper out in the field as well.

[green]

Target amplitude vs distance for the four targets. RC feedback_.2usec

Calculated amplitude. Integrator out/total gain. Amplifier gain=300, integrator gain=R fdbk/R in * sample rate * sample time (300k/3k*1000*10usec=1). For short TC targets the amplitude at 4usec is a lot higher than the 10usec average. Made a chart to show effect. Adjusted start amplitude to give a value of 100 at 4usec. The amplitude at 4usec is 9 times higher than the 10usec average for the 5x5mm can side. Included 5 and 10usec TC decays and ground slopes of -1 and-1.49 for reference. Trying to determine the best delay and sample times to ground balance and get the best target signal. Hope the chart is correct.

[Old cart]

Calculated amplitude. Integrator out/total gain. Amplifier gain=300, integrator gain=R fdbk/R in * sample rate * sample time (300k/3k*1000*10usec=1). For short TC targets the amplitude at 4usec is a lot higher than the 10usec average. Made a chart to show effect. Adjusted start amplitude to give a value of 100 at 4usec. The amplitude at 4usec is 9 times higher than the 10usec average for the 5x5mm can side. Included 5 and 10usec TC decays and ground slopes of -1 and-1.49 for reference. Trying to determine the best delay and sample times to ground balance and get the best target signal. Hope the chart is correct.

Green very good work. Thank you for doing this. Wouldn't the response from any specific target be the area under the curve (integral) rather than the average? This can be easily calculated using a Riemann sum I think. It is not obvious to me how set up the graphs to optimize this but perhaps a 3D plot of initial delay, sample pulse width, and signal amplitude would be appropriate. Perhaps use only a single target per graph to avoid visual conflict.
You are so good generating these decay curves and graphing them that I think this may prove very useful.
Thanks again for all your work.

[Old cart]

Green could you be so kind as to explain how you gather these decay curves. I know you explained it before but I can not find it now.

[Chet]

Hi Green
Great charts! If I understand your work correctly, it sounds like as an example; that increasing the transmit pulse rate to 5000 pulses per second. And reducing the sample window to 2 us wide starting 4 us after the transmit pulse will provide a much higher target amplitude. And will also provide a high signal to noise ratio.
Thank you and have a good day,
Chet

[green]

Green could you be so kind as to explain how you gather these decay curves. I know you explained it before but I can not find it now.

Record amplifier out with an oscilloscope. Record a no target recording and a target recording. Dump the data in Excel and chart linear log. Insert a line in the chart thru the decay curve. Move line so it crosses 2 at zero time. Divide time at the .1 crossing by 3 for the TC. Smaller targets might need a smaller coil for enough signal. The chart in reply #33 is calculated, not measured but based on measured targets. I have found ground to decay with a slope between -1 and -1.5, closer to -1.5 than -1. Tx time and shape is one of the things that has effected the slope. Chart log log for ground and other targets that decay with a straight line on a log log chart.

[green]

Hi Green
Great charts! If I understand your work correctly, it sounds like as an example; that increasing the transmit pulse rate to 5000 pulses per second. And reducing the sample window to 2 us wide starting 4 us after the transmit pulse will provide a much higher target amplitude. And will also provide a high signal to noise ratio.
Thank you and have a good day,
Chet

Hi Chet

Integrator gain for the one I've been using, R fdbk/R in*sample rate*sample time. The example you give should have the same gain(5 times the sample rate, 1/5 sample time). The increase should be from averaging the signal earlier in the decay. Including a chart comparing signal increase,(4usec delay, 2usec sample). Don't know why increasing sample rate would change amplitude if the gain didn't change. My thoughts, maybe I'm missing something.

[Chet]

Hi Green
Thank you for the new chart; it shows a good improvement by using the early narrow sampling. I think there are two reasons to have a 5000 pulse per second or higher transmit pulse rate. One is that sweeping from side the small or weak targets will build up the integrator level quickly even though the coil may be moving relatively fast and be over the target for a very short time. Another is that signal to noise ratio should improve by having more target returns to integrate out bipolar noise returns.
Have a good day,
Chet

[green]

One more chart. Increased time so 10usec TC line and -1.49 ground slope crossed and added more delay time data. TC, US nickel(10usec), 4grain nugget(3.1usec), 10grain nugget(6.7usec), 18grain nugget(5.7usec)

[Monolith]

quarter inch can target

Reading about the quarter inch can tests, I decided to knock up a breadboard circuit to see if it can detect a target of 6.5x6.5mm, cut out of the side of an aluminum beer can.

Here is the signal trace in blue for the target passing over the coil.

The red trace is the static reference signal.

[Old cart]

Reading about the quarter inch can tests, I decided to knock up a breadboard circuit to see if it can detect a target of 6.5x6.5mm, cut out of the side of an aluminum beer can.

Here is the signal trace in blue for the target passing over the coil.

The red trace is the static reference signal.

is this the output of the integrator? I assume the positive going signal is the actual target response. If so looks like you get a good signal to noise ratio at this target distance. How close was the target? Any idea where those very narrow spikes are from?

[Monolith]

is this the output of the integrator? I assume the positive going signal is the actual target response. If so looks like you get a good signal to noise ratio at this target distance. How close was the target? Any idea where those very narrow spikes are from?

The circuit consists of a pre-amp, analog switch, integrator and level shifter at the end, to have a signal ready to be fed into an ADC. Messy on the breadboard. It kind of evolved on its own, but seems to have some merit, so I will draw out the schematic and try to improve on it.

The target distance is 35mm. The target is stuck to the bottom of a glass bottle. The bottle is hanging from the ceiling and swings like a pendulum over the coil, as this is a "motion" circuit. No idea what the sources of noise are at present.

The coil is 24cm diameter.

Do you have any suggestions of how to improve the setup to obtain better results?

[Old cart]

The circuit consists of a pre-amp, analog switch, integrator and level shifter at the end, to have a signal ready to be fed into an ADC. Messy on the breadboard. It kind of evolved on its own, but seems to have some merit, so I will draw out the schematic and try to improve on it.

The target distance is 35mm. The target is stuck to the bottom of a glass bottle. The bottle is hanging from the ceiling and swings like a pendulum over the coil, as this is a "motion" circuit. No idea what the sources of noise are at present.

The coil is 24cm diameter.

Do you have any suggestions of how to improve the setup to obtain better results?

Actually the signal looks pretty good. Is the 1st stage of
If the preamp on a plug in type soldered breadboard you might try a "dead bug" board to get lower noise and a better ground.

[green]

The circuit consists of a pre-amp, analog switch, integrator and level shifter at the end, to have a signal ready to be fed into an ADC. Messy on the breadboard. It kind of evolved on its own, but seems to have some merit, so I will draw out the schematic and try to improve on it.

The target distance is 35mm. The target is stuck to the bottom of a glass bottle. The bottle is hanging from the ceiling and swings like a pendulum over the coil, as this is a "motion" circuit. No idea what the sources of noise are at present.

The coil is 24cm diameter.

Do you have any suggestions of how to improve the setup to obtain better results?

I like your ideas for the tester. I would like to see something anyone could make for the test setup. Been doing some testing with 6x6mm pieces cut from the side and bottom of an aluminum beverage can. Might consider them as targets. Targets glued to a piece of poster board 25x25mm. A picture would allow easy target size check. Was playing in the workshop trying a couple ideas. Maybe a wooden dowel or yard stick with a specified length suspended from a shaft with enough space below to raise and lower the coil to adjust target distance. Start with the dowel at some angle, maybe 90 degrees. Just some thoughts. Looking forward to your schematics and some way to compare the signal to noise I get with someone else. Thanks. Another thought was using the glass or plastic bottle. Some hot ground could be put in the bottle as it swung to check for GEB at the same time. Don't know how to get everyone using the same ground. Coil inductance, diameter, Tx waveform and peak current are a few things that would be nice to know.