Measuring small capacitance with KS34465A & TH2830

[The Electrician]

i am so sad, my brand new Tonghui TH2830 LRC meter is not working

https://youtu.be/dMFn2-613Q4

please tell me how to reset this ?

Do the measurement at 100Hz, 1kHz and 10 kHz as well as the 100 kHz you show.  Also show the phase angle at those frequencies..

[mawyatt]

i am so sad, my brand new Tonghui TH2830 LRC meter is not working

https://youtu.be/dMFn2-613Q4

please tell me how to reset this ?

We just ran a couple resistors, 1K and 10K to check out the TH2830, results were as expected on DCR, R+jX and Rs_Q and Rp_Q modes.

You may recall we had an issue with a scale on the TH2830 not reading correctly and reported to Tonghui, which they informed us that they had no authorized resellers on AliExpress where we purchased the TH2830. We contacted the reseller and they made contact with Tonghui and we were allowed to receive an updated firmware which corrected the problem. Recall we had a issue with the 1K range and got correct readings using DCR but not the other modes, worked OK below the 1K and above the 1K range, but not at 1K. You could try different ranges to see if this is a similar effect as we had.

Since you purchased from an authorized reseller have them contact Tonghui for the updated firmware. Hopefully this may correct your issue.

Best,

[oz2cpu]

thanks a lot mike, i allready wrote to them both :-)
resistors seems to to work in DCR mode, all caps and inductors, dont work

[mawyatt]

Try other manual ranges, go to setup and select ranges other than "Auto". I just did a quick test and got inaccurate readings on 3K & 10K ranges with 1K resistor, however got accurate readings with 1K, 300, 100, 30 ranges but not 10 ohm range, so it seems the instrument likes actual values below the next range up but not so far as the 10 ohm range for a 1K resistor!!

BTW, if you turn on the Vm and Im measurement values you can see the applied voltage and measured current.

Edit: Also found it strange that the detailed extensive supplied calibration sheet included measurements in the 1K range that showed it correctly preformed??

Best,

[oz2cpu]

anyone still monitoring this thread ??
is there a better TH2830 support ? tech ? mods thread ?

my question TH2830
how to use the bias feature ?
nothing happens, no matter what i push,
i like to test some cheramic caps with different DC added, any ideas how ?

[mawyatt]

On our TH2830 the DC Bias feature is not enabled.

Best,

[oz2cpu]

darn it.. mine must be like that too,
so how to fix this ?
or a workarround ?

[2N3055]

anyone still monitoring this thread ??
is there a better TH2830 support ? tech ? mods thread ?

my question TH2830
how to use the bias feature ?
nothing happens, no matter what i push,
i like to test some cheramic caps with different DC added, any ideas how ?

I believe TH2832 is the one that supports DC bias..

[jonpaul]

Bonjour nether the Keysight DVM nor a Chinese meter are optimized for very low C 1..10pf.

In decades of developing very low capacité transformers, we used the various HP bridges and LCR meters before settling on

1/ HP vintage LCR and impedance
https://www.hpmemoryproject.org/collection/lcr.htm#mark1
HP 4332A analog mettre has a 0..3 pF lower scale

2/ 1960 Tektronix LC meters 130 valves, analog, very high range of residual capacité
https://w140.com/tekwiki/wiki/130

3/ HP 4195A with impedance test fixtures and SMD adapters
Capable of 100 kHz..500 MHz

We made our own test adapters, a stable mechanical system and guard are much more important than 4 lead Kelvin for such work.

Bon courage

Jon

[oz2cpu]

thanks 3055 the manual see page 17, attached..
this means no bias on my  model TH2830, darn it

[oz2cpu]

the BIAS test workaround , see attached picture.
only concern : lets imagine it is 100V caps,
and i like to test all the way to max voltage,
then one cap get leaky, now broken instrument ?!?!?

i like to have the resistors as high as possible, i tested with 10k to gnd, and it did not affect my capacity range much
the caps i need to test are 10uF

[Kleinstein]

A test with 100 V and 10 µF is definitely nothing for an delicate instrument.  That would more lime something for a separate, more specific test-setup with lower sensitivity and more protection.


It depends on how good the instruments are protected. The problem is that protection can interfere with sensitivity with small capacitors.

[oz2cpu]

good point, maybe i should perform the DC test, using one of my old handheld LCR meters, I cry much less if this blows up

[gamalot]

the BIAS test workaround , see attached picture.
only concern : lets imagine it is 100V caps,
and i like to test all the way to max voltage,
then one cap get leaky, now broken instrument ?!?!?

i like to have the resistors as high as possible, i tested with 10k to gnd, and it did not affect my capacity range much
the caps i need to test are 10uF

https://www.keysight.com/au/en/assets/9018-01469/user-manuals/9018-01469.pdf

[mawyatt]

I would not consider subjecting the TH2830 to any external applied voltage without a proper fixture that is verified to be instrument safe, but that's just my personal viewpoint considering this particular instrument. If you study the link provided by gamalot, this shows the extent HP goes to to protect the HP instruments.

Think a reasonable less risky approach would be to get a cheap LCR meter like being reviewed by Martin52 and make a special fixture similar to the one HP uses for evaluation of capacitance vs DC bias behavior.

If/when we decide to do some tests like these, getting a cheap "expendable" LCR meter and adding a special DC bias fixture will be the approach. Since the measurement under consideration is C vs DC bias, the measured values are relative to no DC bias, and these values can be "inferred" to the more accurate no bias measurement from the TH2830. So plot the C vs DC value then shift the zero bias voltage reading to the value acquired from the better instrument, this should yield a reasonable result that can be believed.

Anyway, YMMY.

Best,

[The Electrician]

i am so sad, my brand new Tonghui TH2830 LRC meter is not working

https://youtu.be/dMFn2-613Q4

please tell me how to reset this ?

Did you ever determine why you were getting this odd result?

[oz2cpu]

>Did you ever determine why you were getting this odd result?

not really, I think it is possible to either create bad settings, or wrong combinations,
a factory reset did recover all to perfect working conditions,
i tried to play with all possible combinations, i am not able to recreate the issue.

[mawyatt]

Here's the link I was referring too above regarding the cheap LCR meter. Maybe Martin72 can look into the possibility of external DC bias on this LCR meter?

https://www.eevblog.com/forum/testgear/east-tester-et4410-desktop-lcr-meter/msg3989009/#msg3989009

Best,

[oz2cpu]

did the test, using old crappy lrc meter :-)
two 10uF caps in series,

[mawyatt]

did the test, using old crappy lrc meter :-)
two 10uF caps in series,

 

If one of these two caps was very large, then the measurement should converge to the other smaller DUT actual cap value. For polarized (Electrolytics & Tantalum) caps this large cap could be a quality low leakage low ESR cap placing in the proper polarity direction for the applied DC bias.

Edit: Also reminds me of the use of polarized capacitors where the AC voltage under test is allowed to become significantly negative WRT the DUT polarity. Think of a common low voltage aluminum electrolytic, where tantalums are known to be less sensitive under modest reverse bias. Long ago many used special tantalums that allowed reverse voltage under normal operation, we did so ~50 years ago in a very low noise & frequency amplifier. These were wet-slug types tantalums and specially selected and specified from a select vendor at the time, we did numerous tests and verification on these caps before factoring into the design.

Best,

[mawyatt]

This shows the importance of understanding how capacitors behave, especially ones that employ high dielectric constant ceramic materials like XR7 and such! Your data shows a decrease in effective capacitance value of 5X over the 90V DC bias span! Also this points to the well known behavior amongst older "seasoned" folks, if you need a minimum value capacitance under DC bias, then either use a much greater capacitance value, or much higher breakdown voltage, or a much less voltage dependent dielectric like COG or NPO ceramic, or all of the above, or a film type dielectric!!

Edit: One of the interesting stories behind these capacitors dates back into the 70s, we had put in quite an effort to understand the capacitor materials and capacitors themselves and had the resources on-site to do so. This was to support the requirements for nuclear survivability in which one common requirement was to survive the EMP, the Radiation impulse and long term effects. Some required work-through, others required surviving allowing a equipment "reset" . We had developed considerable knowledge into electrolytic, tantalum, film and ceramic materials/capacitors which was held as proprietary, and knew the amount of energy required from different capacitors types and materials that would destroy a chip under radiation impulse which causes all the PN junctions to become highly conductive.

One program called XM21 (Remote Sensing Chemical Agent Detector) required surviving a point-blank Nuclear Detonation!! This was a battlefield instrument purposed to protect solders by early warning of a chemical attack utilizing a remote very controversial (another story, I'll discuss if folks want) technique. We unsuccessfully argued that nuclear battlefield survivability made no sense, as anyone still around surely wouldn't be concerned about a chemical attacks after a nuclear attack!! So we had to design for survivability and the simultaneous EMP and Radiation pulse from a point blank detonation!! This imposed a limit on the decoupling capacitance and type we could use, and required that all the supply inputs and outputs were swiftly crow-bared not to mention all the other things required to pass, which we did but this drove the instrument cost up by ~4X!!   

Best,

[The Electrician]

I scored an HP16034E on eBay last week.  The outside looks just like the low-cost SMD fixture shown in reply #33 earlier in this thread.  Here's a picture of what's inside.  The terminals are shorted in pairs very close to the BNC connectors.  I could believe this will allow reasonable performance at higher frequencies than the technique used in the low-cost fixture, but it probably doesn't matter at 100 kHz and below.

As one might expect, the sheet metal work and build quality of the HP unit is much better than the eBay copy.

[mawyatt]

That's not how the inside of ours looks, it has separate wires from each BNC to the plunger, no shorting bar!! Suspect the wires terminate at the plunger metal shaft and form a somewhat Kelvin type connection. There's also a ground wire across each BNC which has the solder lug terminal and goes to the center shield.

Edit: Just took a quick picture of the inside, the black wires on each end we added to ground to the brackets which the back lid mounts to. We were just characterizing some COG capacitors and checking some 0805 small caps, these were from Venkel. Recall a 0.5pF that measured 0.51444pF with the fixture, then removed and later remeasured at 0.515pf something (we recorded the initial value but not the remeasured). All the other measured caps were very close to the Venkel specified value.

BTW I did a crude experiment to see if my hand touching around the fixture would influence the reading of the 0.5pF cap, recall it did have an effect before we modified the fixture by cleaning the paint from the various mounting holes and added the two black ground wires. My hand had no influence in the measurement, even at 0.5pF the readings were very stable.

Best,

[oz2cpu]

The Electrician, if you need to measure the last mili ohm of smd parts, maybe an idea to make all wires as close as possible to what  Mawyatt shows ?
specially the red wires are importent for sub mili ohm performance.
i got the same TH fixture and mine dont seems to be affected by hands on the outside,
i also use it to very small pF
and down to sub mili ohms internal resistance on some of the caps i use right now.

[The Electrician]

That's not how the inside of ours looks, it has separate wires from each BNC to the plunger, no shorting bar!! Suspect the wires terminate at the plunger metal shaft and form a somewhat Kelvin type connection. There's also a ground wire across each BNC which has the solder lug terminal and goes to the center shield.

Edit: Just took a quick picture of the inside, the black wires on each end we added to ground to the brackets which the back lid mounts to. We were just characterizing some COG capacitors and checking some 0805 small caps, these were from Venkel. Recall a 0.5pF that measured 0.51444pF with the fixture, then removed and later remeasured at 0.515pf something (we recorded the initial value but not the remeasured). All the other measured caps were very close to the Venkel specified value.

BTW I did a crude experiment to see if my hand touching around the fixture would influence the reading of the 0.5pF cap, recall it did have an effect before we modified the fixture by cleaning the paint from the various mounting holes and added the two black ground wires. My hand had no influence in the measurement, even at 0.5pF the readings were very stable.

Best,

You can see that the HP fixture has the internal paint masked off where the BNC connectors are bolted to the sheet metal.  There is also some paint masked off where the wires penetrate the sheet metal, and where the little brackets at the end are riveted on.