Re: Experimental Help - Terry?

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

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
 
> very carefully <grin>
 
> If what you want to do is measure RF current, (rather than power),
>then, a bolometric scheme in the base of the secondary might be a
>practical scheme.

> I'd use the brightness of a filament lamp, calibrated with DC.

	Concur.  Since i have recommended it in the pat, I'd better.

	Tricky, as light bulbs are highly nonlinear.  Photocell
	for sensing, fiber optic to couple back to the meter.

	(The nonlinear effect, both of the lamp and the rest
	of the sensor chain would be taken care of by the
	calibration...)

	But.
	The original question was to determine POWER.  And current
	at the base may or may not (i expect does not) match
	current at the top.  (eg:  just as there is a voltage
	peak at the top, there is a current peak at the base.)

	best
	dwp
==============================================================	
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Sunday, February 24, 2002 9:31 PM
> Subject: Re: Experimental Help - Terry?
> 
> > Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <evp-at-pacbell-dot-net>
> >
> > > I'd say that a thermal detector is THE way that RF power is measured
> > > (accurately)... Whether a bolometer or thermistor... The fancy detectors
> use
> > > balanced circuits that hold the detector at constant temperature with a
> DC
> > > current. The amount the DC current decreases (and the resistance..)
> tells
> > > you how much power is being dumped into with the RF.  Uncertainties in
> this
> > > sort of sensor are:
> > >
> > > 1) How accurately you measure the DC current
> > > 2) How accurately you hold temperature (this one's easy, because it's
> > > basically a nulling to hold it at a zero, rather than actually measuring
> > > something...)
> > > 3) RF mismatch.. The RF power has to really get into the load, and not
> >>get reflected back.  The connectors are a problem here..

> > > But, in any case, all those HP power meters use thermistor heads...
> > How would you go about matching the HP 50 ohm thermistor head to the
> > output of the Tesla Coil, so that the correct power could be measured?

> > Ed