Products > Test Equipment

East Tester ET3502 LCR-Bridge

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Martin72:
We will find out whether that plays any role.

Martin72:

--- Quote from: mawyatt on August 05, 2024, 01:50:48 am ---Think you have a TH2830 available, this could be a good reference to use.
--- End quote ---
Yes, at work.
If you want to know "exactly", either the ST2830 has to go to me or my ET35 has to go to work, because of the same ambient temperature/humidity.
However, this should only be of an academic nature, although with 0.05% basic accuracy with an LCR measuring bridge, we are already close to the academic question.


--- Quote ---For reference components consider quality leaded Polystyrene, Polypropylene, Mica Capacitors, with some C0G SMD types. For DC or very low frequency using the Kelvin Clips for leaded precision resistors should be acceptable, and you can also use your precision DMM to verify results.
--- End quote ---

That is clear, or I hope it is clear to everyone.


--- Quote ---Inductors are another story tho, and we don't place much faith in any typical inductors we have where precision is considered. Precision reference inductors may be available tho, but likely expensive.
--- End quote ---

Inductors are the "bitches" among complex components.
If they have a core, things get quite adventurous.
The core causes them to saturate (well, you won't usually achieve this with an LCR bridge).
The core has its own inductance, Al, which plays a role.
A core has a large tolerance range, easily around 30%.
If Q is negligible, and this is the case with a pure measurement, the tolerance values can be considerably reduced by adjusting the air gap.
Nevertheless, I don't really "like" coil measurements. ;)


--- Quote ---If you consider the actual LCR measurement taking place with an inductor, it's the same as for a capacitor. The DUT Complex Voltage and Current are measured, then the Complex Impedance is computed. The only difference is the Impedance Angle is + for Inductance and - for Capacitance, then the test frequency is taken into account to display the Inductance/Capacitance Value. So unless the LCR is misbehaving the impedance levels measured, computed and displayed should be similar in magnitude but opposite in phase for Inductors and Capacitors. Sometimes meters display negative Capacitance for Inductance and visa-versa as the component goes thru resonance, or the wrong parameter is selected.
--- End quote ---

If you have ever done arithmetic with complex values, you should be familiar with this.
In principle, we can cover the majority of inductance measurements with a measuring bridge such as the ST2830/TH2830.
The situation is different when calibrating power chokes, as the measuring voltages and currents of a standard measuring bridge are not even close to being sufficient.
Or to put it the other way round, you are scratching at the "beginning" of an inductance.
For such cases, there is then the voltage-time area measurement, with real voltages and currents.

mawyatt:

--- Quote from: Martin72 on August 05, 2024, 10:09:12 pm ---We will find out whether that plays any role.

--- End quote ---

Answer is, It does make a slight difference where the moving Plunger section is active with the H or L terminals, favoring the latter just as we suspected   ;)

Curiosity got the best of us, so we used our SDM fixture with the TH2830 at 100KHz.

First we did an Open Cal with the spacing ~ 0805 spacing, then measured an "Open" at same spacing with average of 64 and saw a variation of ~3fF total.

Then we flipped over the SMD fixture so the H terminal is driving the SMD Movable Plunger, here we saw a Open variation of ~7fF. We returned to upright position and mounted a 0805 C0G 0.3pF capacitor and witnessed a ~6fF variation, then flipped over the SMD fixture upside down and had ~13fF variation, all with 64 averages at 100KHz.

Next first we did an Open Cal upside down,  and repeated the above with 0805 C0G 0.3pF results showing ~7fF variation upside down and ~5fF normal.

These tests were done as quick tests just to "see" if terminal orientation had any effect on High Z Small Capacitance measurements.

Very subtle effect but favoring the normal terminal orientation for our LCR Meters when using our modded SMD fixture as we suspected.

BTW agree that Inductors are more of a measurement issue than capacitors, since we all can get quality, stable, somewhat precision capacitors in reasonable values, for reasonable prices. Not so to the best of our knowledge with inductors.

We can send you a quality 10, 100, or 1000pF 0805 C0G chip cap from US to Germany and expect you'll get a result comparable to what we measure. Not sure what values would appropriate for the inductor tho, and what the results would be??

Anyway, you can do the same tests we did with your ET35 by flipping over the SMD fixture, or do so with your SH2830 at work.

Edit: Another simple test is to vary the plunger spacing between two fixed distances, use a spacer on the "Arm" so as not to disturb the fields around the active plunger and compare the results when flipped over and normal, we found the normal position has ~28% less variation in capacitance readings.

As always, YMMV.

Best,

Martin72:
Hi,


--- Quote ---We used our SDM fixture with the TH2830 at 100KHz.
--- End quote ---


--- Quote ---First we did an Open Cal with the spacing ~ 0805 spacing, then measured an "Open" at same spacing with average of 64 and saw a variation of ~3fF total.

Then we flipped over the SMD fixture so the H terminal is driving the SMD Movable Plunger, here we saw a Open variation of ~7fF. We returned to upright position and mounted a 0805 C0G 0.3pF capacitor and witnessed a ~6fF variation, then flipped over the SMD fixture upside down and had ~13fF variation, all with 64 averages at 100KHz.

Next first we did an Open Cal upside down,  and repeated the above with 0805 C0G 0.3pF results showing ~7fF variation upside down and ~5fF normal.
--- End quote ---

Don't be angry with me, but I very much doubt that a TH2830 can still resolve values in the femto range accurately, I consider that to be "background noise".




mawyatt:

--- Quote from: Martin72 on August 06, 2024, 09:16:12 pm ---Hi,


--- Quote ---We used our SDM fixture with the TH2830 at 100KHz.
--- End quote ---


--- Quote ---First we did an Open Cal with the spacing ~ 0805 spacing, then measured an "Open" at same spacing with average of 64 and saw a variation of ~3fF total.

Then we flipped over the SMD fixture so the H terminal is driving the SMD Movable Plunger, here we saw a Open variation of ~7fF. We returned to upright position and mounted a 0805 C0G 0.3pF capacitor and witnessed a ~6fF variation, then flipped over the SMD fixture upside down and had ~13fF variation, all with 64 averages at 100KHz.

Next first we did an Open Cal upside down,  and repeated the above with 0805 C0G 0.3pF results showing ~7fF variation upside down and ~5fF normal.
--- End quote ---

Don't be angry with me, but I very much doubt that a TH2830 can still resolve values in the femto range accurately, I consider that to be "background noise".

--- End quote ---

Agree, it can't!!

However it can resolve with good repeatability to 10~20fF with carefully setup.

For this level one must have an extremely stable mechanically and electrically setup. We prefer the modified LCR Meter SMD Fixture with the 4 cover attachment bolts. This has proven more stable due to the superior mechanical construction over the 2 bolt types. Also for the "Open Calibration" use a Plunger Spacing similar to the expected DUT spacing, the best way we've found is to wedge the Fixture Lever Arm so the Plunger Spacing is appropriate.

Here's a measurement of a quality 0603 C0G "Ref Cap" we use. Measured 4.68440pF with TH2830 & SMD Fixture @ 100KHz on 12/23/22 and just now 4.68808pF shown. Over the years we made similar measurements with similar results, with the IM3536 even better :-+

Anyway, hope this shows what we've been talking about and the better of the two cheap SMD Fixtures we have, expect the quality Tonghui types should be even better. If anyone wants to ship us one we'll be happy to evaluate such ;)

Edit: Added images of SMD Fixture Interior, and lastly what we got putting the fixture back together and remounting on TH2830 with no recalibration (using previous Cals)!!!

Best, 

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