Author Topic: LCR test fixture  (Read 428 times)

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Offline Wallace Gasiewicz

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LCR test fixture
« on: October 21, 2021, 12:15:44 pm »
I picked up an old HP 4271B (digitl readout one MHz LCR) for $20 at a Hamfest. After a week of putzing around I think it is fixed. It reads reasonable values on all ranges.
Problems were mostly the relays.
I was wondering if anyone has any suggestions for a Test Fixture. I wonder if one could be easily fabricated?
I believe the normally grounded side of the in/out BNCs is isolated at the 4271 chassis, so I thought I would use a plastic box and mount four male bulkhead BNCs to that.

Or would it matter if the BNCs were all common at this point? (metal box)
I was thinking of using a big Zif socket for the wired components, one side being in and the other out, component could go into any in and out combo..
Was also thinking of using a little SMD pad, like the ones on cheap component testers for SMD parts. Maybe fabricating a little lexan lid on a hinge to hold the components down.
A setup with both could be easily made. Or is this too much surface area and make readings difficult?
About the wiring, should I try to use coax in the fixture box or is this overkill?

I was thinking of using a big Zif socket for the wired components, one side being in and the other out, component could go into any in and out combo..
Was also thinking of using a little SMD pad, like the ones on cheap component testers for SMD parts. Maybe fabricating a little lexan lid on a hinge to hold the components down.
A setup with both could be easily made. Or is this too much surface area and make readings difficult?
About the wiring, should I try to use coax in the fixture box or is this overkill?


Any comments would be welcome

Wally KC9INK
 

Online Kean

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Re: LCR test fixture
« Reply #1 on: October 21, 2021, 12:26:44 pm »
I posted some photos of inside my Tonghui LCR SMD test fixture in another thread.  It may give you some ideas.
https://www.eevblog.com/forum/testgear/measuring-small-capacitance-with-ks34465a-th2830/msg3755315/#msg3755315

I can take photos of the THT test fixture too if you like.  Pretty sure it will common the shields at the BNC entry to the box.
The tweezers would extend the shields as far as possible.  I am pretty sure the shields are all commoned at the LCR meter - they measure as such on my CKT5000 LCR.
 

Offline Wallace Gasiewicz

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Re: LCR test fixture
« Reply #2 on: October 22, 2021, 11:15:55 am »
Kean:
Thanks very much for the info and the pic.The only outer conductor that is grounded on the HP4271 B is the H Pot. The L Pot center conductor can be grounded or floating; controlled with an internal switch.
I measured them and did consult the schematic also.
So I imagine the closer to the DUT the various outer conductors are joined together, the better the reading.
Although I don' know what the last 2 cm would mean.
« Last Edit: October 22, 2021, 12:55:56 pm by Wallace Gasiewicz »
 


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