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Cheap SMD LCR Fixture, the Good, Bad and Ugly
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mawyatt:
Unless the plunger assembly is different than what we have those bolt insulators should not be used. The plunger assembly has the center "shaft" insulated from the plunger casing with the white plastic coaxial pieces in each plunger assembly. The conductive plunger shaft sits inside the coaxial plastic surroundings, so the plungers are isolated from the plunger casing and aluminum box.

You want everything at ground potential inside and outside the box as best you can, this also means the plunger case and  box "lid" where the attachment screws create a ground connection to the box. The box is at ground due to the 4 BNC connectors. Make sure the 4 leads (2 pairs) that go thru the box to the plunger are tight, these were loose on one fixture version we had and caused measurement repeatability issues. The leads are soldered to a single long threaded brass insert that screws into each plunger shaft, this was loose and needed tighting.

Also make sure everything is mechanically stable including BNC connectors. Having a stable electrical and mechanical environment as "seen" by the DUT is important for accurate and repeatable measurements.

Once you have reworked these inexpensive fixtures, they preform well we've found :-+

Best,
ExaLab:
Thanks a lot for your prompt reply.
As you suggest I'll remove the two insulating washers and I will check that everything is tightened properly...

I'll use this tool with my Fluke PM6304 (and may be with the ET432 too). To do this, I'm going to make a pair of interface adapters.

I measured the distance between the BNC connectors of this tool and it seems to be exactly 22.0mm (66.0mm exactly between the central pins of the two outermost connectors).
The doubt I have is the following: is this the standard in use (i.e. a pitch of 22.0mm) or rather the most used standard is the 7/8" (i.e. 22.225mm)?
When making interface adapters, to increase their compatibility with possible further tools, I would like to be sure to use the most commonly used pitch!

On your branded LCR analyzer could you please measure with a caliper the distance between the two outermost connectors and tell me if it is closer to 66.0mm or 66.7mm? I don't have analyzers that use this type of BNC interface (My LCR meter PM6304 uses a proprietary interface based on a Lemo connector...).
ExaLab:
I finished reworking the test fixture and the result is very satisfying.
Here are some of the upgrades made (some of them absolutely necessary!!):

1) The right nylon insulating cylinder was reworked (it had an anomalous hole in correspondence with the tightening knob which caused the short circuit between the measurement contact and the case...)
2) To avoid excessive mechanical play, I replaced the M3 screw of the lever with a more suitable M4 one
3) Replaced the rigid PVC internal cables with extra-flexible silicone sheathed cables
4) Replaced the four support rubbers with more suitable and professional products
5) Repainted the entire unit with two-component polyacrylic varnish (RAL 7035). I did this last operation at the same time as painting the containers used for the two interface cables.

For the pair of interface cables I used Hammond die-cast aluminum enclosures (1590G2) and Amphenol BNC connectors.

Now I have really stable and repeatable measurements with both LCR analyzers at my disposal.
Thanks to those who presented this low cost test fixture (with many defects but... all fixable).
mawyatt:
Very nice work!! Like the cables and the box approach with the handheld.

Must apologize for not responded to your question, completely missed it :-[

We also measure 66mm, and 22mm between BNC centers.

An area we've had some difficulty in making quick but repeatable measurements is with some SMD devices where the connection pads are on the bottom, common to some surface mount Polymer Caps, Tantalum and Inductors we use. These required some fiddling to get just right in the SMD fixture "V" groove, the "V" we 3D printed works better for these devices but still isn't as good as we would like.

Been thinking about this for awhile now, and liked the way the plungers Lever Arm worked with our custom Tek577 fixture shown below.

https://www.eevblog.com/forum/projects/smd-test-fixture-for-the-tektronix-576-curve-tracer/msg4553639/#msg4553639

So we came up with a similar type fixture to use with these SMD devices and bench type LCR meters. PCB should be heading to fab house this week along with some other projects. This allows the plunger Lever Arm to be on either side and the PCB can be flipped over for another set of surface contacts for larger devices. For first try we'll just go with standard plating, and if it works well may consider gold plating for the contact area.

Best,
ExaLab:
Cables inside the sheath and box approach are absolutely necessary for repeatability of ac measurements (especially when measuring low impedances where the "weight" of the cables inductance is more evident...).

Thanks for your kind reply. For the two boxes I used the pitch measured on the test tool at my disposal, i.e. 22.0 mm. (I've been lucky!!)
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