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Re: [TCML] Measured Q vs. Predicted



Hi,

I rarely drop to my knees with laughter now... But I did a few days back when a person ask me how a 'plastic' caliper can "measure" to 0.001 inch!!

Dude!! They are "precision" calipers!! NOT "accurate" calipers!! :D :D They measure very precisely how far they are from any accuracy measurement standard... Not too bad with a calibrated "standard" really...

The "devil is in the details", about how any measurement is made...

My BK 878 is 120 HZ or 1kHz... 1kHz is the usual... It has the D/Q function at 1kHz function... Better than nothing... But if you are "playing" in that 1% range... You not only need a measurement, but two other very different ones to 'sort of suggest' and confirm you are not all wet there ;) And if your measurement seems all off. Worry a bunch!! It is "you" 99% of the time...

Any data is useful. But finding and calculating the 'errors' is a BIG 'science'!!

ALL data is very welcome!!! But provide any and all of the details about how the data was obtained.... You will be very stunned at how easily others can fish out the errors and "correct" your measurements!! With background information. One bit can turn into kilo bits really fast!!

I deal in airsoft fun problems now. There are many folks that "get it" an provide a "full page" about the machine they have... It makes all the difference in the world!!!

The measurement is the 'point', the details are what makes the 'data'...

Terry


Paul Nicholson wrote:
> 38.99 Ohms = DC Resistance
> 19.487 mH = Ldc-Low Frequency Inductance
> 2.785 = Q

> Is there a reason why my measured Q is so much
> lower than that given by JAVATC?

Depends what frequency the instrument is working at. At low
frequencies, Q is proportional to frequency.

  Q = 2 * pi * frequency * inductance / resistance;

For example, if your meter works at 900Hz, you'll get a reading
of around Q = 2.78.

Whereas, if the measurement takes place at a much higher
frequency, say, the resonant frequency of the coil, you'll
get Q = couple of hundred or so.

Above a few kHz, the resistance increases due to skin effect
so the proportionality tails off.

If you have a scope to hand, see if you can see what frequency
the LCRQ meter is working at.  Compare that with the predicted
resonant frequency of the coil.  That should resolve the
discrepancy.
--
Paul Nicholson
--
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