Decay Curve

[1843]

Hi everybody,

Sometimes when I adjust the dmping resistor, I get a such waveform at the op amp output:

I want to know what problems it causes?
The curve point, where the sample occurs is decent?!
Also, after that point the waveform looks good for later samples?!

Best regards

[Ray-NM]

You need to check your input to the op amp looks like it is ringing to me.
Also your coil is not damped critically if this is the signal you get.
Someone else correct me if I am wrong.
RayNM

[Reg]

Hi 1843,

Ray is correct, the signal indicates some oscillation has occurred prior to the sampling time. Now, will that oscillation cause a problem if it occurs before the sampling time, and the signal is stable at the time of sampling? The answer is no. As long as the signal is stable at the time of sampling and stable after then things should be ok.


The ideal response is to not have the oscillation, but that may not be possible when trying to match a large variety of coil sizes to a detector.

Also, when you look at your pic, you have the sampling starting before the signal has reached 0V. Ideally, once again, you would want to move your minimum sampling to a little later time, but it will still work this way. If the sampling is done too soon, and most of the sampling is done before the curve has leveled out, the signal strength may be great enough that the output of the differential integrator is saturated. If this happens, then all signals will be muted to the point one would think something is seriously wrong with the detector. Moving the sampling to a little later time will correct this problem. Also, if most of the sampling occurs before the decay curve has leveled out and the coil seems to work, then the coil may seem hypersensitive.

Reg

[JC1]

You are correct

Ray you are correct.

It is ring a dinging.

[Max]

Hi everybody,

Sometimes when I adjust the dmping resistor, I get a such waveform at the op amp output:
[ATTACH]2251[/ATTACH]
I want to know what problems it causes?
The curve point, where the sample occurs is decent?!
Also, after that point the waveform looks good for later samples?!

Best regards

Hi,
Ray and Reg are correct. It's ringing...1843 try to adjust your dumping resistor with a lower value...and if not works try make another coil. Less capacitive, less inductance...and less energy storage means faster operation...thus could avoid too much ringing and you can sample earlier.

Best regards,
Max