Help for negative resistance oscillator

[Robert Baer]

Scott Stephens wrote:

Robert Baer wrote:

As the assemble passes (inside) from one (connected) pipe to the next,
the thicker "collar" which connects the pipes together had a different
permeability.
The movement past this distorts the hyperbolic magnetic field, and so
generates the dV/dT mentioned.

I was thinking that "maybe" one could turn the inductor into an
oscillator and thereby get rid of the expensive magnets.
Now you know my "secret".

You should have said that from the start. I was wondering why anyone
would want to fool around with an inductor of such poor Q, other than
some kind of perverted fetish for obscure junk.

That gadget was probably designed, 'tuned', to the velocity it passes
through pipe permeability transitions.

Now what is your purpose today? Same application, just different mode of
operation by sensing FM rather than amplitude?

I can't see that reluctance sensor in that application functioning
better in an FM mode. Eddy currents will reduce the sensor
effectiveness. It needs to oscillate at a low frequency to be sensitive,
so it would have to move slowly through the pipe.

But just using a current amplifier would allow it to move through the
pipe faster to sense transitions. It wouldn't function well at low speeds.

--
Scott

**********************************

DIY Piezo-Gyro, PCB Drill Bot & More Soon!

http://home.comcast.net/~scottxs/

**********************************

Unfortunately it seems that your assessment is correct.
Oscillation frequency would probably be too low to allow "reasonable"
probe velocity.
The present magnetically biased mode puts out 10-500mV depending on
speed, and the pulse width due to speed and a 4 inch collar appears to
be roughly 0.1-1.0 seconds.

 

[Robert Baer]

Winfield Hill wrote:

Robert Baer wrote...

Nope; swept it from 0.01Hz to 10MHz. Had to get into the 100KHz
and above region before i could see phase shifting. No amplitude
variance, except at the very low end; had to use "Lazy Joe" for
the phase variations..

Swept with what source impedance? 50 ohms? Try feeding the
coil with 10k or 100k (i.e. a current source) and monitoring
its response with a 10M scope probe when you sweep it.

Thanks,
- Win

whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)

Correct; 50 ohms. Will try 10K and 100K.

 

[ddwyer]

In article <4ZudnV3eNfj5PAjdRVn-hQ@giganews.com>, BFoelsch <BFoelsch@com
cast.ditch.this.net> writes

Generally refers to an oscillator with only two terminals to the tuned
element; no tapped L as in Hartley, no tapped C as in Colpitts, no feedback
winding as in Armstrong.
I regularly analyse coulpitts oscillators as negative resistance

oscillators.
The colpitts cam be seen as presenting a single port with one terminal =
ground across an inductance,or for my application a crystal with modes
and overtones , knowing the variation of negative resistance with
frequency enables the maintaining circuit to be designed to only
activate the wanted mode as the magnitude of negative resistance peaks
at a certain resistance and hence preferentially oscillates a required
mode.


--
ddwyer