[Prev][Next][Index][Thread]

Re: Fluke 27 (don't do it)

At 08:24 PM 12/24/1999 +0000, you wrote:
>I'm sure all the pro's will now scream in horror about what I am about
>to say but... what about replacing that certain fuse with a piece of
>coathanger. An NST won't ever produce a damaging current will it ?
>(unless you try to measure the current when the NST is connected in the
>tank circuit)
>

Yyyyeiiiiooooowwww (horrific scream ;-))

Be sure to keep the meter and leads on plastic insulation so there is no
way an arc can go from the meter guts to ground.  If the NST's windings are
not equal, the whole meter will have to float as much a 1kV off true
ground.  NST's may have output capacitance and turn on transients too that
could kill the meter if you just switch it on to full voltage (I have
always slowly turned up the variac carefully watching for trouble).

There is another cheap alternative.  Many hardware stores sell super cheap
little multimeters.  Those little $9.95 jobs that can measure ac voltages.
They don't do AC current but if you measure the voltage across a 100 ohm 1
watt resistor (60mA gives 6 VAC) you can do the measurement for about $10.
I have one of these cheap ($7.99 on sale) meters and they really are darn
nice for the small amount you pay.  No fancy electronics to fry and you
just toss them if they get cooked.

Also, half the cost of the meter on my web page
(http://www.peakpeak-dot-com/~terryf/tesla/misc/meter.jpg) is in that nice case
aluminum box and binding posts.  A luxury that could be left out if long
term durability is not needed.

It sounds like the original poster is borrowing this meter.  I would be
super careful with the borrowed meter in hopes I could borrow a capacitance
meter, scope, etc. in the future.  Returning the Fluke 27 with the case all
burnt and PC boards all black explaining how you hooked it across a 15kV
transformer output, may not recommend you well for borrowing more stuff. ;-))


I have to give credit to Gary Lau for his other post:

"I tried metering the NST secondary current on a running coil with my 
Fluke #27 (slap me now). The display wigged out and I had to power it off 
and on, and I think it was just luck that it worked afterwards."

That one even raised my eyebrows ;-))  It proves that the fluke 27 is one
tough meter!!!  I wonder if that was before or after the protection filter?
 Raw multi-kV and multi-GHz transients from the gap must have given those
big CMOS chips something to think about :-)))

I should mention that I have used my Tektronix B210 digital scope very
close the my coil before.  I have drawn good static arcs (about 1/2 inch,
from the HV fields and not from direct TC arcs) from my finger to the
electronics behind the front panel (ouch!).  The Tek scope did not seem to
notice in the least.  So some of these fancy electronic gizmos are not
totally worthless for HV and RF work.  Apparently, the bigger the name on
the front, the better your chances...

Cheers,

	Terry



>Tesla List wrote:
>> 
>> Original Poster: "Ross Overstreet" <ross-o-at-mindspring-dot-com>
>> 
>> Sure, you can easily measure the output current of a NST with the fluke
>> meter.  Life is good until for some reason the fuse in the meter blows.
>> Then the Fluke becomes a sealed spark gap and the arc dances all over the
>> board in its attempt to find the lowest impedance path between opposite 
snip...........
References: