Re: Variation of secondary Q

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Paul,

At 06:27 PM 3/16/2002 +0000, Paul wrote:
....
>
>> Colorado State University's little weather station is only a few
>> hundred yards away.  I wonder if its data is on the Internet
>> somewhere?...
>
>Drop them a line and tell them you're correlating the performance
>of a delicate piece of electronics with temp and humidity - ask if
>they can supply data, say hourly records?

No problem there.  They pump all the station's data to the net every ten
minutes in real time and they keep full historical records on-line ;-))

http://ccc.atmos.colostate.edu/cgi-bin/wx_form.pl

I am a bit surprised they have the "actual" air pressure instead of the
"corrected" barometric pressure (~30 inches "corrected") that used to vex
me so much...  (Terry is at ~5400 feet).  Gasp! for air ;-))

>
>>  The ring down current is tiny.  With 10V P-P in, I only get
>> about a 200uA base current signal:
>
>Malcolm wrote:
>>  Any reason why you can't use the E-field to measure Q? 
>
>Terry wrote:
>> I could directly connect my 2.5pF 10Meg ohm probe (Tek5100)
>> directly to the top of the coil
>
>which might raise doubts about the stability of the probe Z, which
>could potentially affect Q.  Better to use the E field pickup -
>remember, the amplitude and phase is not important and can vary
>from shot to shot.  No need to average several shots, the accuracy
>can be achieved even with a single fairly noisy shot.
>

Ok, If the equation "Vin x Q = Vtop" is adequate, I can do a lot of things
;-)  I need to replace the capacitors in the antenna with poly types
instead of XR7 so the caps remain stable over temperature but that is easy
and I have the caps here.  Of course, I can calibrate the antenna with the
scope probed coil ;-)

>> The scope could then save a data file like this:
>
>http://hot-streamer-dot-com/temp/TEK00000.CSV
>
>The data is perfect - will cope with a noisier signal than this if
>need be.  The size is a problem: you'll only get half dozen or so
>of these onto a floppy, so if you record 1 shot/hour, you'd have to
>change floppy 3 or 4 times a day!  Does the scope offer a more
>compact binary format?  Maybe it can compress the files?
>
>The other problem is to figure out how to time stamp each file.
>
>Pity you don't have that RS232 option, would solve all these probs
>and the PC could also alert you when something goes wrong with the
>setup.

The scope (all scopes) have a problem with "high vertical accuracy".  As
the temperature varies, so does the front end electronics.  Scopes simply
are not usable for long term -+1% despite the fancy numbers they give.
They can self calibrate it all out, but that is unworkable on a test like
this.  The front end and digitizers are made for super speed instead of
super accuracy.

I have been experimenting with it and the amplitude response of the scope
is obviously affected by ambient temperature too much.  However, I have a
way to take the scope out of the test. (next post...)

Don't worry with the program, I am thinking of using added electronic
circuits to eliminate the scope.  I can then coax cable all the signals
inside to the test equipment and free up the test equipment for other
testing too ;-)).  The HP 6-digit multimeter is RS-232 and I have the nice
software to pull data from it periodically.  I also have the old 486
laptop.  Have to plug it into the server's UPS to run for weeks at a time
since the old laptop's battery is gone...  Thinking......

>
>> If you can figure out the computer "A, theta, w, and r which give
>> the closest (least squares) match to the waveform" part, I can
>> supply the raw scope data files.
>
>No problem, I can supply the code to convert those CSV files into
>F and Q numbers. 

If "Vin x Q = Vtop" is adequate, there is no need.  I can rig it up to read
off Q directly.

>
>> So if I put the big coil's SonoTube secondary out there ...
>
>Ah, your trusty 30" coil that has already proved so useful - yes!
>Must count as one of the most useful TCs ever built!

Still goes strong at making streamers too ;-))

>
>> ...take a bunch of data files at various times and note the
>> conditions the best I can... would that be ok?
>
>Ideally it needs to be fully automated so that you can forget about
>it for a couple of weeks at a time. At worst you should have to
>visit the setup once every few days to swap floppy disks.
>
>> How much of a ground plane is needed?  I am thinking of putting
>> it on top of a shelf about 5 by 3 feet with very near by walls
>> and roof.  I could do the split aluminum foil thing.
>
>In order to establish which part of the coil/ground/environment is
>affecting Q, it will likely be necessary to perform runs with
>various configurations:  With/without groundplane to determine
>sensitivity to ground losses;  With/without faraday cage to 
>determine sensitivity to environment;  With/without coil in a 
>sealed bag to determine involvment of coil former;  A week or two
>in each configuration perhaps?
>
>> I wonder if the Q variation is not so much the coil changing but
>> the surroundings changing with weather?  The coil is far more
>> stable for temperature and humidity than the ground, walls,
>> ceiling, etc. 
>
>Yes, hence the need to apply a process of elimination, runs in
>different configs to isolate each possible factor.  Repeat with
>the PVC coil former.
>
>As you can see, potentially a long series of tests, hence best to
>automate so that the results are standardised as much as possible.
>
>> So I think we got the of the stuff here 
>
>Definately.  You have the kit and the expertise, and this would
>generate a valuable dataset of unequivocal measurements.
>
>The only potential stumbling block is if the weather there doesn't
>cooperate by being reasonably variable in both temp and humidity.

Don't worry about that 0 to 70 F  5 to 100% humidity is typical over a few
days here.  Wind may be a factor as those 80 MPH gusts might blow the
experiment over...

>
>BTW, this would make an nice accurate Q detector for those current 
>profile measurements.

Yep!  Is it ok if the secondary is slightly cone shaped for that test?  If
so I have a form for it.  The local Sonotube was in bad shape since no one
wants it in winter and it just sits on the shelves getting banged up.  In a
few months, the stock will turn over to nice fresh tubes.

Cheers,

	Terry


>--
>Paul Nicholson
>--
>