Measuring small capacitance with KS34465A & TH2830

[mawyatt]

Thanks Kean

The measurements & fixture look really good. The Tonghui tweezers we have are the TH26009B and claim good to 15MHz, they work well and produce repeatable results, but not like the TH26008A fixture you have. Those results are excellent!!

Didn't know about the CKT5000 or CKT in general. How do you like the instrument and how is the build quality/design?

Thanks again for the measurements and images.

Best,

[Kean]

I believe CKT may be related to, or copied from Tonghui.  There are a lot of similarities.  Just look at the attached screen shot and compare to yours.  It is so similar with pretty much the exact same text, menu options, etc - just rearranged and more spread out for the larger screen.  In fact that screen shot doesn't show the lighter blue band behind the readings but there is one just like on the Tonghui screen.

Regarding CKT, I hadn't heard of them before buying this unit a couple of years back.  I was buying some Tonhgui gear (a TH3321 AC Power Meter and a TH6412 PSU) from an AliExpress seller I often deal with, and was thinking of also buying either the TH2830 like you have, a TH2827C, or the Applent AT3818 [1].  The bundle was starting to get too expensive with shipping, so the seller then suggested the CKT1000 LCR Meter as a cheaper option.  I looked at them and found out they could supply a CKT5000 with good specs for my needs and cheaper than a TH2827C.

The CKT LCR came with fixtures just like the Tonghui ones including the tweezers (an extra $100) which look just like the TH28009B ones in your photo from the first post.  I had to buy the Tonghui SMT fixture though ($150) as there wasn't a CKT equivalent available.  The CKT5000 is bigger and boxier that then Tonghui units (bigger even than some PCs), but that doesn't bother me.  It has a nice big screen, and wasn't too difficult to operate without reading the manual.  The manual isn't too bad, it is in readable English and gives some useful detail, but it is not as good as Tonghui manuals.

Now, would I buy CKT gear again... probably not if I could afford a Tonghui, Keysight, or Keithley alternative.  Maybe if I'm on a budget and willing to live with some rough edges.  It seems to work fine, saved me money, and I've not had any specific issues with it.  I just feel less trusting of it than any of my other gear, but that could probably be fixed by doing a detailed side-by-side comparison with another brand.  It certainly seems better than my handheld LCR meters.

The companies themselves are apparently just a few blocks (1.1km) apart in Xinbei District, Changzhou.  Not uncommon, and it means they probably shared some staff.  Tonghui have been around longer though.  CKT seem to do more in the temperature measuring/calibration market.

TH = Changzhou Tonghui Electronic Co.,Ltd
CKT = Changzhou Chuangkai Electronic Co. Ltd

Oh, and CKT website lists a bunch of Tonghui and Applent/Anbai products including the TH2830 and AT3818.  So that is very confusing...
www.cz-ckt.com/pd.jsp?id=239
www.cz-ckt.com/pd.jsp?id=273

If you have a contact at Tonghui you've been dealing with then maybe you could ask about CKT?

[1] Side note:  I have some Applent AT8612 DC Loads which I'm quite happy with.  Applent (aka Anbai for Chinese market) are yet another lesser known test equipment manufacturer.  Their temperature data loggers seem pretty good, and they seem to have gone to some effort to design their own trade dress and UI although commonalities are still seen like e.g. brackets around titles like "<SETUP>".

[Kean]

Didn't know about the CKT5000 or CKT in general. How do you like the instrument and how is the build quality/design?

And you just reminded me that I bought the CKT5000 over two years ago and still haven't looked inside.  That is a task for another time...

[oz2cpu]

wow fixture TH26008A looks nice
thanks a lot for the detailed pictures.

but how can it be 216 euro + 25% tax = 270 euro
that is a bit intense ?

they could be nice to make a bundte prise, if purchased together with the instrument

[mawyatt]

There's a similar device, but not sure how good this "copy" is. For ~$70, maybe worth a try???

https://www.aliexpress.com/item/1005002561014252.html?spm=a2g0o.cart.0.0.40203c000eoQtn&mp=1

Best,

[oz2cpu]

wow mike, it looks identical to me :-)
from same factory ?

[Kean]

There wouldn't be a lot of demand for these to cover the original design costs, but the design work has been paid for so not surprising there are cheaper copies.
The plastic parts look like they might not be PTFE.  Apart from labour costs there is a good chance they've reduced parts costs.

[mawyatt]

These are not the same as the Tonghui OEM version. If you carefully examine the images from AliExpress you can see the differences. Also the center piece is a yellowish and thicker plastic than the OEM, and as Kean indicates likely not Teflon. Suspect the BNCs are not the quality ones I would expect from Tonghui, and the OEM is rated to 120MHz, but there's no mention for the frequency range for the copy.

Does this mean the copy isn't any good?? Don't know, but might be perfectly fine for use with the TH2830 which only goes to 100KHz, but doubt it's made as well as what I've seen from Tonghui which is first class.

Best,

[The Electrician]

Five or six years ago I bought a fixture on eBay for my LCR meter:



It's made by Meiruike Electronics: http://www.szmeiruike.com/en/product.asp?page=4&lv1=578&=

You can see this fixture (they spell it "fixtue") in that image.  Note the model number: RK26001.

Compare to this fixture: https://www.tonghui.com.cn/en/product_131.html with model number TH26001

A year or so later I bought an SMD fixture also made by Meiruike:



The model number is: RK26008.  It's not silk-screened on the metal but it's a stick on label.  It must be an early unit.
Compare to this fixture: https://www.tonghui.com.cn/en/product_143.html with model number TH26008.

Here's a picture of the insides of my RK26008:



It looks to me like Tonghui may re-badging fixtures made by Meiruike.

The TH26008/RK26008 is not usable at 120 MHz with the kind of wiring they used to connect to the gold plated contact pins.  I found a more detailed list of specs that said the maximum usable frequency is 200 kHz; I can believe that.

There are a large number of SMD fixtures for sale here: https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1312&_nkw=smd+test+fixture&_sacat=181939

A close examination of the construction details persuades me that they are all the same as the Meiruike/Tonghui unit.

On my unit the plastic wedge that holds the DUT doesn't appear to be PTFE; I think it's Delrin which would be more abrasion resistant.

[mawyatt]

Five or six years ago I bought a fixture on eBay for my LCR meter:



It's made by Meiruike Electronics: http://www.szmeiruike.com/en/product.asp?page=4&lv1=578&=

You can see this fixture (they spell it "fixtue") in that image.  Note the model number: RK26001.

Compare to this fixture: https://www.tonghui.com.cn/en/product_131.html with model number TH26001

A year or so later I bought an SMD fixture also made by Meiruike:



The model number is: RK26008.  It's not silk-screened on the metal but it's a stick on label.  It must be an early unit.
Compare to this fixture: https://www.tonghui.com.cn/en/product_143.html with model number TH26008.

Here's a picture of the insides of my RK26008:



It looks to me like Tonghui may re-badging fixtures made by Meiruike.

The TH26008/RK26008 is not usable at 120 MHz with the kind of wiring they used to connect to the gold plated contact pins.  I found a more detailed list of specs that said the maximum usable frequency is 200 kHz; I can believe that.

There are a large number of SMD fixtures for sale here: https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1312&_nkw=smd+test+fixture&_sacat=181939

A close examination of the construction details persuades me that they are all the same as the Meiruike/Tonghui unit.

On my unit the plastic wedge that holds the DUT doesn't appear to be PTFE; I think it's Delrin which would be more abrasion resistant.

This doesn't appear to be exactly like the OEM TH26008 images Kean posted. Note the two center BNC connectors don't have the outside shell and plastic "arms", also note that the OEM using some insulation over the red wires to BNC contacts and the end brackets are not the same (OEM uses swedged threaded inserts).

What type LCR meter are you using, and how is the repeatability with this fixture?

Agree 120MHz seems like a stretch as claimed by the OEM version, maybe the fixture calibration removes the fixture effects sufficient to allow operation at 120MHz?

Anyway, thanks for the information and images.

Best,

[rf-messkopf]

There's a similar device, but not sure how good this "copy" is. For ~$70, maybe worth a try???

https://www.aliexpress.com/item/1005002561014252.html?spm=a2g0o.cart.0.0.40203c000eoQtn&mp=1

Interesting. Rohde & Schwarz sells similar looking test fixtures for use with the Hameg/R&S HM8118 LCR bridge. I opened mine up and it looks exactly identical on the inside. I wonder what the OEM is, maybe Tonghui. Of course a name brand manufacturer will rip you off when it comes to accessories, R&S charge almost 500 Euros for one when ordered separately: https://www.distrelec.de/en/smd-component-test-fixture-hm8118-series-lcr-bridge-rohde-schwarz-hz188/p/11085068.

I tried an 1.2 pF 0805 capacitor at various frequencies between 100 Hz and 200 kHz, and the test fixture gives me nice and stable capacitance readings across that frequency range. The LCR bridge was set to 1 V measuring voltage, open and short compensation (at each frequency) was used, and it was set to guard drive mode (BNC outer conductors are driven with a copy of the test signal). However, the dissipation factor reading (parallel mode) is garbage for such a small capacity.

[TimFox]

The 1.2 pF is obviously C0G/NP0 with a very high Q, so the loss at 1 kHz is not measurable (as you said), compared to the low susceptance.  At higher frequencies, where the parallel susceptance of the capacitor is higher, it might be measurable.
As a general rule-of-thumb, I have found that Q > 1000 (or D < 0.001) requires very careful measurement on reasonable equipment.

[mawyatt]

There's a similar device, but not sure how good this "copy" is. For ~$70, maybe worth a try???

https://www.aliexpress.com/item/1005002561014252.html?spm=a2g0o.cart.0.0.40203c000eoQtn&mp=1

Interesting. Rohde & Schwarz sells similar looking test fixtures for use with the Hameg/R&S HM8118 LCR bridge. I opened mine up and it looks exactly identical on the inside. I wonder what the OEM is, maybe Tonghui. Of course a name brand manufacturer will rip you off when it comes to accessories, R&S charge almost 500 Euros for one when ordered separately: https://www.distrelec.de/en/smd-component-test-fixture-hm8118-series-lcr-bridge-rohde-schwarz-hz188/p/11085068.

I tried an 1.2 pF 0805 capacitor at various frequencies between 100 Hz and 200 kHz, and the test fixture gives me nice and stable capacitance readings across that frequency range. The LCR bridge was set to 1 V measuring voltage, open and short compensation (at each frequency) was used, and it was set to guard drive mode (BNC outer conductors are driven with a copy of the test signal). However, the dissipation factor reading (parallel mode) is garbage for such a small capacity.

This does look like the Tonghui except for the middle 2 BNCs without the shell. Would not be surprised if this is an OEM Tonghui rebranded as R&S, the construction details look the same. Also showing excellent repeatability as did Kean's measurements.

Edit: Just noticed that the measurements were at different frequencies, did you evaluate the repeatability by making the same measurement on the same DUT at different times?

Thanks for the response and images.

Best,

[mawyatt]

The LCR bridge was set to 1 V measuring voltage, open and short compensation (at each frequency) was used, and it was set to guard drive mode (BNC outer conductors are driven with a copy of the test signal).

How was the implemented WRT the guard drive? It seems the BNC outer areas are all tied together and common with the fixture case?

Best,

[rf-messkopf]

How was the implemented WRT the guard drive? It seems the BNC outer areas are all tied together and common with the fixture case?

You are right, with this fixture, guard drive is ineffective because the outer connectors are shorted together. I wasn't thinking. But it works with Kelvin clamps.

[rf-messkopf]

Edit: Just noticed that the measurements were at different frequencies, did you evaluate the repeatability by making the same measurement on the same DUT at different times?

You mean by re-inserting the same DUT into the fixture? Give me a minute, I will try that.

Edit: Here you go, all measured at 1 kHz, the same C0G cap as above was re-inserted into the fixture ten times, then one measurement (with trigger set to man) was taken:

1.3251 pF
1.3261 pF
1.3258 pF
1.3268 pF
1.3266 pF
1.3277 pF
1.3269 pF
1.3258 pF
1.3265 pF
1.3267 pF

[The Electrician]

Five or six years ago I bought a fixture on eBay for my LCR meter:



It's made by Meiruike Electronics: http://www.szmeiruike.com/en/product.asp?page=4&lv1=578&=

You can see this fixture (they spell it "fixtue") in that image.  Note the model number: RK26001.

Compare to this fixture: https://www.tonghui.com.cn/en/product_131.html with model number TH26001

A year or so later I bought an SMD fixture also made by Meiruike:



The model number is: RK26008.  It's not silk-screened on the metal but it's a stick on label.  It must be an early unit.
Compare to this fixture: https://www.tonghui.com.cn/en/product_143.html with model number TH26008.

Here's a picture of the insides of my RK26008:



It looks to me like Tonghui may re-badging fixtures made by Meiruike.

The TH26008/RK26008 is not usable at 120 MHz with the kind of wiring they used to connect to the gold plated contact pins.  I found a more detailed list of specs that said the maximum usable frequency is 200 kHz; I can believe that.

There are a large number of SMD fixtures for sale here: https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1312&_nkw=smd+test+fixture&_sacat=181939

A close examination of the construction details persuades me that they are all the same as the Meiruike/Tonghui unit.

On my unit the plastic wedge that holds the DUT doesn't appear to be PTFE; I think it's Delrin which would be more abrasion resistant.

This doesn't appear to be exactly like the OEM TH26008 images Kean posted. Note the two center BNC connectors don't have the outside shell and plastic "arms", also note that the OEM using some insulation over the red wires to BNC contacts and the end brackets are not the same (OEM uses swedged threaded inserts).

I think these are the sort of minor manufacturing changes one might expect after 6 years.  Tonghui offers 3 versions of this fixture:
https://www.tonghui.com.cn/en/index.php?module=Product&action=ListView&search=th26008
Note that two of them have the middle two arms and one doesn't.  This insulation over the red wires is different in my earlier unit but it is there.  Only one of the end brackets is swaged in Kean's picture (the one on the right; why only one?); the other uses machine screws and nuts.  Etc.

These differences are trivial and I am persuaded by all the similarities that Meiruike is making at least two of Tonghui's fixtures.

What type LCR meter are you using, and how is the repeatability with this fixture?

Agree 120MHz seems like a stretch as claimed by the OEM version, maybe the fixture calibration removes the fixture effects sufficient to allow operation at 120MHz?

Anyway, thanks for the information and images.

Best,

My favorite meter is the Hioki IM3570: https://hiokiusa.com/product/impedance-analyzer-im3570/

It is a high performing instrument, both an LCR meter and impedance analyzer.  It can show 7 digit measurements which are far beyond the accuracy spec (.08%), but all those extra digits can be used to match components beyond the accuracy spec.

Fixture calibration can't fix those relatively long and arbitrarily oriented red wires for 120 MHz operation.  For high frequency measurement of SMD devices one needs something like this: https://hiokiusa.com/?s=IM9201

Using the Meiruike fixture (not the SMD fixture), I can get 4 digit repeatability with a 390 pF NPO, but with a 5 pF NPO I can only get 2 stable digits since this is at the limits of the instruments capability.  Those two stable digits are, however, repeatable. 

Edit: The foregoing measurements were made at 1 kHz.  At 100 kHz, I get 3 stable digits for the 5 pF, and at 1 MHz I get 4 stable digits.  At 1 kHz the measurements of Rs, D, and Q consist of bouncing digits--they are at the noise floor of the instrument.


I, (like you, I think) am retired, and some of my instruments and components are in storage and not readily accessible.  I found a kit of leaded disc ceramics which is where the 4 pF and 390 pF came from.  In a few days I can access a bunch of SMD ceramics.

[The Electrician]

Edit: Just noticed that the measurements were at different frequencies, did you evaluate the repeatability by making the same measurement on the same DUT at different times?

You mean by re-inserting the same DUT into the fixture? Give me a minute, I will try that.

Edit: Here you go, all measured at 1 kHz, the same C0G cap as above was re-inserted into the fixture ten times, then one measurement (with trigger set to man) was taken:

1.3251 pF
1.3261 pF
1.3258 pF
1.3268 pF
1.3266 pF
1.3277 pF
1.3269 pF
1.3258 pF
1.3265 pF
1.3267 pF

If you insert the capacitor into the fixture and watch the measurement, are the last two digits bouncing around?  Does the instrument have an averaging mode?  A measurement of a 1 pF capacitor at 1 kHz is near the limit of what a modern instrument can do.

You'll notice in the image of my Hioki's measurement of a 5 pF capacitor that just to the right of the measured quantities, there are two values labeled Vac and Iac.  These are the actual voltage applied to the DUT and the current through the DUT.  The value of Iac shown there (with 1 volt applied) is 31.85 nA (for a 1 pF capacitor this current would be about 7 nA).  That current must measured to calculate the capacitance.  As one can imagine, that small current is nearly buried in the front end noise of the instrument, and it's the difficulty of measuring it that leads to bouncing digits in the display.  Those bouncing digits are just a measurement of the instrument front end noise.

[mawyatt]

Those Hioki instruments are some of the best available I believe, nice!!

Don't know if the Meiruike is the OEM for Tonghui, or a clone of such, and agree it could be an early version and that's why the slight differences.

If the internal fixture wires don't move around and you can get a good fixture cal and null, you might be able to do some useful comparisons/relative measurement at higher frequencies, but not anywhere near 120MHz I suspect.

Yes, I'm retired but also consulting and formed a company earlier this year Wyatt Labs LLC to support such.

Best,

[The Electrician]

As I said earlier my stock of SMD parts are in storage, but the two caps I mentioned came from a kit of the sort vendors give when you are still working as an EE. 



I measured every one of the caps in the upper left hand compartment thinking that I may have put some smaller caps in there, and sure enough I found a 1 pF (leaded of course) cap.   Here's what it looks like in the Meiruike fixture:



Here's what the Hioki says about it:

 

The leading digit "1" really doesn't count as a significant digit (numerical analysis course taught me that), and the last 3 digits are bouncing around, so I'm getting 2 significant digits.  Notice what the measured current in the cap is--7 nA!!

All, that's all, of the digits in the measured Rs, D, and Q are pure noise, bouncing around like crazy.

If I pull the cap out of the fixture about 5 mm, the value increases to 1.03 pF.

But consider the noise problem with a measurement at 1 kHz.  You can't measure to better than 2 digits, so you can't expect better repeatability than that.

If I turn on averaging, and average 100 readings, I can get another stable digit.

Edit: Or, of course, make the measurement at 10 kHz or 100 kHz.

[nctnico]

Interesting that it is branded 'Rek'. Recently I bought a few small switching PSUs with the same 'Rek' logo. Pictures here: https://www.eevblog.com/forum/testgear/rek-kps6003-and-gophert-nps-1602-60v-3a-psu-hack-review/msg3336994/

Hmm, reading my own thread back I noticed I posted a link to Rek / Meiruike: https://en.chinarek.com/index.html

[The Electrician]

Those Hioki instruments are some of the best available I believe, nice!!

Don't know if the Meiruike is the OEM for Tonghui, or a clone of such, and agree it could be an early version and that's why the slight differences.

If the internal fixture wires don't move around and you can get a good fixture cal and null, you might be able to do some useful comparisons/relative measurement at higher frequencies, but not anywhere near 120MHz I suspect.

Yes, I'm retired but also consulting and formed a company earlier this year Wyatt Labs LLC to support such.

Best,

Did you look at all those fixtures at:  https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1312&_nkw=smd+test+fixture&_sacat=181939

Look at the pictures--they are all essentially identical to the Meiruike/Tonghui fixture, and for a little over $100!!  I think they are all posted by the same guy (or a few guys) with access to an Asian source.

[The Electrician]

Interesting that it is branded 'Rek'. Recently I bought a few small switching PSUs with the same 'Rek' logo. Pictures here: https://www.eevblog.com/forum/testgear/rek-kps6003-and-gophert-nps-1602-60v-3a-psu-hack-review/msg3336994/

Hmm, reading my own thread back I noticed I posted a link to Rek / Meiruike: https://en.chinarek.com/index.html

I have persuaded myself that Rek/Meiruike is making those fixtures.

The spacing of the BNC connectors seems to fit almost every bench LCR meter out there.  It even fit the (very expensive) Agilent 4294 analyzer we had in the lab.  And for frequencies up to, say, 200 kHz they work fine.

[gamalot]

It seems that my NF fixture has an unreasonable design. You can even see that the Kelvin 4 wires have been merged into two wires inside the box. 

[The Electrician]

I wonder if the reason the sellers of clones of these fixtures claim 120 MHz performance is because they know that Keysight sells a lot of impedance measuring instruments like this: https://www.keysight.com/us/en/product/E4990A/impedance-analyzer-20-hz-10-20-30-50-120-mhz.html

and claiming 120 MHz performance seems like the thing to do!!