W
Winfield
I will check these out, thanks!!!
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I will check these out, thanks!!!
W
Winfield
John said:
I got mine on eBay for less than 10% of that, IIRC.
Comes with spare resistors - what, do they burn out?
J
John Larkin
Maybe the wires break off the ends?
I got one on ebay, too. Once we figured it out, we bought a bunch of
additional Caddocks for fun. The longer, higher-value parts are handy
for monitoring high voltage pulses.
John
N
none
Joerg a écrit :
RH series are definitly not low inductance.
I just measured one RH25-82R I have at 1.4uH
RH series are definitly not low inductance.
I just measured one RH25-82R I have at 1.4uH
R
redbelly
Look on p. 2 of Joerg's link, under Ordering Information. There is an
option for non-inductive winding.
Mark
T
The Phantom
And what did you find?
F
Fred Bloggs
Winfield said:Now, now, you know exactly what I mean. Low-value power
resistors are well characterized as a resistance in series
with an inductance. They "become" primarily inductive
above f = R / 2pi L, where the inductive reactance exceeds
the resistance.
No. A good LCR meter will show the same value for series
inductance over a wide range of measuring frequencies (to
be sure of the measurements, I do a quick check to verify
that I'm measuring with a high enough frequency to get a
sizable phase shift from the inductance, e.g. 5MHz or more
if needed). --- Sorry, here's a missing datum, the 48nH
measurement was on a 3-ohm 5-watt KoolOhm resistor, so
f = 3 / 2pi*48nH = 13MHz. Oops, where'd 10MH come from?
That was from an earlier 66nH measurement, except after
re-zeroing the meter I got 48nH. There are just too many
numbers floating around.
L = R / 2pi f = 23nH, or 2x better than 48nH (another
measurement yielded 66nH, hence the 2x - 3x estimate).
The carbon is close to a piece of similarly-shaped wire.
The breakpoint frequency. It's convenient to say the part
acts primarily as a resistor until a 3dB point, afterwhich
it acts primarily an an inductor. Plot Z vs. frequency: a
straight line from DC to a breakpoint, then rising with f.
You know the drill, I assume.
I don't know what your fixation on low inductance is about, but it does
not pertain to wirewound resistor design for broadband applications as
practiced in the industry from 1940 onwards. I guess that was a time
when engineering did not shy away from things like transmission line
equations and expansions of their solutions into usable approximations
which today would be described as "math-uh-magical bullshit" by the
zeroids. The wirewounds were modeled as distributed transmission lines
with "shorted return" and uniform R, L, G, C per unit length, configured
in such a way as to make the characteristic impedance the same as the DC
total R. They went with resistance wire to reduce high frequency skin
and proximity effects, and they balanced R,L,C to cancel any reactance
effect out to 100MHz. And even then, they could design in the high
frequency "residual reactance" to be either inductive or capacitive. Any
number of winding techniques were available to them, including the
Chaperon dual winding, loop or hairpin winding, or concentric winding.
Your inductance measurements are meaningless without the R and C, since
to a first approximation, in the general case, L=1/3 x R^2 x C is used
to neutralize quite a bit of the residual reactance.
I scoped out an IRE Proceedings advert from Sprague Specialties Co.
KoolOhm from 1941 and they don't mention anything about special winding
techniques, just their ceramic wire insulation rated to 1000oC. Anyhow,
originally, the L was not minimized but deliberately introduced.
J
Joerg
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^redbelly said:
Don't know what's readily available these days though but I've
successfully used some around 10MHz.
F
Fred Bartoli
Joerg a écrit :
Sorry, I mistook that one with some other vishay series where the first
letter of prefix changes when you want the low inductance winding.
Sorry, I mistook that one with some other vishay series where the first
letter of prefix changes when you want the low inductance winding.
J
Joerg
Fred said:
They must have bought Dale, like so many other companies, and then kept
their part numbering convention.
J
Joerg
Winfield said:
Probe kits are notoriously exposed to "Oh s..t, I shouldn't have touched
that!" situations.
J
JosephKK
john jardine [email protected] posted to
sci.electronics.design:
So are you saying buy stock thin film parts and build up what you
need?
DPA of a few KoolOhms as a kid and sound engineering and physics
allows me to make equivalents onesie-twosie near cost (i eat the
labor) for myself. If you want a very few i can explain the tricks i
remember or can figure out to make your own. For any kind of
production quantities it is a different matter.
sci.electronics.design:
So are you saying buy stock thin film parts and build up what you
need?
DPA of a few KoolOhms as a kid and sound engineering and physics
allows me to make equivalents onesie-twosie near cost (i eat the
labor) for myself. If you want a very few i can explain the tricks i
remember or can figure out to make your own. For any kind of
production quantities it is a different matter.
F
Fred Abse
Only *really* expensive probes. IME.
J
Joerg
Fred said:
And they can be ramarkably tough. I had a Philips probe and accidentally
used it at a place with 230VAC. Didn't want to calibrate, hmm, why? Then
I realized that its wall wart was freaking hot. It was at least 10
minutes. Oops! Switched it to 230VAC, everything worked fine.
R
Rich Grise
That's what that little plastic sleeve in the accessories bag is for. ;-)
Cheers!
Rich
J
Joerg
JosephKK said:
That's what I did as a kid when I needed a 50ohm resistor that could
take a kilowatt for 10 minutes or more. Waited until there was a sale of
some carbon overstock, took an old one-gallon metal bucket with a lid
(honey container, almost like a paint can), cut copper to make a cone
shaped structure, soldered all day long, made a vent hole and filled
that with oil. Worked nicely all the way up to around 100MHz.
Don't know what became of them but
Surplus sales of Nebraska has some in stock.
al
J
JosephKK
Joerg [email protected] posted to
sci.electronics.design:
Now that was a serious act of determination.
sci.electronics.design:
Now that was a serious act of determination.
J
Joerg
JosephKK said:
It was just one method to stretch the allowance
The metal can was free. The oil wasn't and I resisted the temptation to
get some they drained from a tractor but sprung for a can of fresh oil.
The cheapest I could find, of course, some brand I'd never heard of before.
