Hi Ed:
You might surf the Accessories Catalog for Impedance Measurements.
https://www.keysight.com/us/en/assets/7018-06727/brochures/5965-4792.pdf
They have a number of SMD fixtures for 4-terminal pair LCR meters.
https://prc68.com/I/Z.shtml#KeyDocs
--
Have Fun,
Brooke Clarke
https://www.PRC68.com
axioms:
1. The extent to which you can fix or improve something will be limited by how
well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
On 5/25/22 3:16 PM, ed breya via time-nuts wrote:
Thanks Mike, for info on LCR alternatives. It's good to know of others out there, if needed. I have an HP4276A and
HP4271A. The 4276A is the main workhorse for all part checking, since it has a wide range of LCZ, although limited
frequency coverage (100 Hz - 20 kHz). The 4271A is 1 MHz only, and good for smaller and RF parts, but very limited
upper LCR ranges. I think it works, so I can use it if needed, but would have to check it out and build an official
lead set for it. I recall working on it a few years ago to fix some flakiness in the controls, so not 100% sure of
its present condition.
The main difficulty I've found in measuring small chokes is more of probing/connection problem rather than instrument
limitation. For most things, I use a ground reference converter that I built for the 4276A many years ago. It allows
ground-referenced measurements, so the DUT doesn't have to float inside the measuring bridge. The four-wire
arrangement is extended (in modified form) all the way to a small alligator clip ground, and a probe tip, for DUT
connection, so there is some residual L in the clip and the probe tip, which causes some variable error, especially
in attaching to very small parts and leads. When you add in the variable contact resistance too, it gets worse.
Imagine holding a small RF can (about a 1/2 inch cube) between your fingers, with a little clip sort of hanging from
one lead, and pressing the end of the probe tip against the other lead. All the while, there's the variable contact
forces, and effects from the relative positions of all the pieces and fingers, and the stray C from the coil to the
can to the fingers. I have pretty good dexterity, and have managed to make these measurements holding all this stuff
in one hand, while tweaking the tuning slug with the other.
I had planned on making other accessories like another clip lead to go in place of the probe tip, but not yet built.
I also have the official Kelvin-style lead set that came with the unit, so that's an option that would provide much
better accuracy and consistency, but the clips are fairly large and hard to fit in tight situations, and the DUT must
float. Anyway, I can make all sorts of improvements in holding parts and hookup, but usually I just clip and poke and
try to get close enough - especially when I have to check a lot of parts, quickly.
The other problem is that the 4276A is near its limit for getting measurements below 1 uH, with only two digits left
for nH. The 4271A would be much better for this, with 1 nH vs 10 nH resolution.
If I get in a situation where I need to do a lot of this (if I should get filter madness, for instance), then I'll
have to improve the tools and methods, but I'm OK for now, having slogged through it this time.
You might check out the NanoVNA - people have made a variety of novel fixtures
for measuring small parts (i.e. 0604 SMTs)
It certainly has the measurement frequency range you need. The trick is figuring out whether you want to do a series
or shunt measurement, and that sort of depends on the reactance of your device at the frequency of interest.
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