On Mon, 15 Mar 2004 19:01:01 -0500, Active8
wrote:

So why beat yourself to death building a sweep gen to test filters
when you got that there sig gen?

Because it has to be small and light enough to be mounted on our robot
for field checks. Try doing that with a 120lb Marconi. :-)

--

The BBC: Licensed at public expense to spread lies.

On Tue, 16 Mar 2004 13:02:44 +0000, Paul Burridge wrote:

On Mon, 15 Mar 2004 19:01:01 -0500, Active8
wrote:

So why beat yourself to death building a sweep gen to test filters
when you got that there sig gen?

Because it has to be small and light enough to be mounted on our robot
for field checks. Try doing that with a 120lb Marconi. :-)

That's more macaroni than even *this* eyetalian can eat.

You're confusing me again. If you have a filter on a bot in the
field, it's the same filter that was on the bot before you got there
and should do the same thing.

If you change a filter in the field, you'd want to sweep it before
it's installed in der bot.

--
Best Regards,
Mike

On Tue, 16 Mar 2004 13:02:44 +0000, Paul Burridge wrote:

On Mon, 15 Mar 2004 19:01:01 -0500, Active8
wrote:

So why beat yourself to death building a sweep gen to test filters
when you got that there sig gen?

Because it has to be small and light enough to be mounted on our robot
for field checks. Try doing that with a 120lb Marconi. :-)

That's more macaroni than even *this* eyetalian can eat.

You're confusing me again. If you have a filter on a bot in the
field, it's the same filter that was on the bot before you got there
and should do the same thing.

If you change a filter in the field, you'd want to sweep it before
it's installed in der bot.

--
Best Regards,
Mike

On Tue, 16 Mar 2004 10:40:27 -0500, Active8
wrote:


If you change a filter in the field, you'd want to sweep it before
it's installed in der bot.

Sigh.. Yes, I know this has been raised (and answered at considerable
length before). Raised so often, in fact, that I wrote a full
explanation and stuck it on our website. Sadly, that's not up and
running at the moment so I can't refer you to it. Take it from me,
however, that there *is* method in my madness. :-)

--

The BBC: Licensed at public expense to spread lies.

On Tue, 16 Mar 2004 10:40:27 -0500, Active8
wrote:


If you change a filter in the field, you'd want to sweep it before
it's installed in der bot.

Sigh.. Yes, I know this has been raised (and answered at considerable
length before). Raised so often, in fact, that I wrote a full
explanation and stuck it on our website. Sadly, that's not up and
running at the moment so I can't refer you to it. Take it from me,
however, that there *is* method in my madness. :-)

--

The BBC: Licensed at public expense to spread lies.

On Tue, 16 Mar 2004 20:26:17 +0000, Paul Burridge wrote:

On Tue, 16 Mar 2004 10:40:27 -0500, Active8
wrote:


If you change a filter in the field, you'd want to sweep it before
it's installed in der bot.

Sigh.. Yes, I know this has been raised (and answered at considerable
length before). Raised so often, in fact, that I wrote a full
explanation and stuck it on our website. Sadly, that's not up and
running at the moment so I can't refer you to it. Take it from me,
however, that there *is* method in my madness. :-)

I'll make a mental note to visit yer site once in a while. same
domain as the gifs you've been posting?
--
Best Regards,
Mike

On Tue, 16 Mar 2004 20:26:17 +0000, Paul Burridge wrote:

On Tue, 16 Mar 2004 10:40:27 -0500, Active8
wrote:


If you change a filter in the field, you'd want to sweep it before
it's installed in der bot.

Sigh.. Yes, I know this has been raised (and answered at considerable
length before). Raised so often, in fact, that I wrote a full
explanation and stuck it on our website. Sadly, that's not up and
running at the moment so I can't refer you to it. Take it from me,
however, that there *is* method in my madness. :-)

I'll make a mental note to visit yer site once in a while. same
domain as the gifs you've been posting?
--
Best Regards,
Mike

On Tue, 16 Mar 2004 16:18:30 -0500, Active8
wrote:

I'll make a mental note to visit yer site once in a while. same
domain as the gifs you've been posting?

(Answered by e-mail)

--

The BBC: Licensed at public expense to spread lies.

On Tue, 16 Mar 2004 16:18:30 -0500, Active8
wrote:

I'll make a mental note to visit yer site once in a while. same
domain as the gifs you've been posting?

(Answered by e-mail)

--

The BBC: Licensed at public expense to spread lies.

"Paul Burridge" wrote in message
...
Hi all,

I've got quite a huge stash of inductors in my parts bin. The colour
codes don't always seem to relate to the values I've been able to
measure, with my multi-function DVM, however, and I can't accurately
measure any inductor about 10uH. Is there a circuit anywhere that
would enable me to get a reasonably accurate idea of the values I've
got down to say 100nH or thereabouts?


"splat" test

V=L*dI/dt

charge up a large cap to some voltage V

short the cap thru the inductor, and measure the current with a scope
(digital is great, as long as the single-shot sample rate is high enough - I
did this once with an HP 56000 series scope, and got 1 data point - very
easy to fit a line to, very hard to fit the right line to!)

knowing dI/dt and V, calculate L

then, you can see saturation from where dI/dt increases rapidly (invaluable
for power electronics)

also, ensure that 0.5CV^2 0.5LI^2 at the current of interest - this
ensures that V is approximately constant

I have a couple of 33mF 35V caps in parallel, with 10 x 1R MRS25 resistors
paralleled as a current sensor. It takes about 45s to set up for a
measurement. I often use the shaft of a screwdriver to make the "splat" - a
nice hard material is good.

I have used this technique successfully to measure inductors ranging from
the tiny ( 500nH) to huge (3mH 2,000A chokes). Actually, big chokes tend
not to read true on LCR meters, as the magnetic material permeability is
often much higher at very low currents - especially true of iron powder.

if you dont have a digital scope, make a tiny, LF oscillator with a 555.
Drive a grunty FET, with a small (I use 0.1R - 10R) source resistor. Then,
you'll get a repetitive waveform, which works nicely on any analogue scope.
If Rsense is nice and low, use a 50R BNC cable to connect to scope, with a
50R terminator at the scope - lovely clean waveforms.

I built a little tester like this to test air gaps in planar cores for a 55W
smps that lives inside an LED video screen (actually, thousands of them live
inside). works a treat, and cost $5.

One of my techs once built a splat tester for big chokes - he had several
1200V 600A IGBT's in parallel running as a series pass regulator, with about
100mF of capacitance (charged to 700Vdc thru several lightbulbs) to control
V, even at currents on the order of 5,000A. A honking great LEM DCCT
measured the current, and the "switch" was purely mechanical - he used the
pole faces from an HV contactor, as the material is astonishingly arc
resistant, so no pitting/welding