LCR meter tests - Page 1
Forum section: electronics / general

author: chilternview
author_rank: Frequent Contributor
timestamp: June 14, 2025, 03:03:34 pm
content: So I wanted to see how the various LCR meters I have access to performed. Tests were carried out on polystyrene or film capacitors with 1V AC signal amplitude, slow integration (in the case of the 4275A, 'high resolution mode', for the DE5000 there is only normal mode), and 4 averages (for E4980A and TH2827C). All instruments were open/short compensated.The results are in the attached Excel sheet, including the % difference from the E4980A, which was considered the standard as it was Keysight calibrated.No surprises really; the differences were largest on the 10pF capacitor, especially on the lowest frequency - the DE5000 could only read the capacitance to 2 significant digits so the large discrpancy is still within the expected result.Of course it would be nice to compare to a set of standard 4 terminal capacitors but a used Agilent 16380A, if you can find one, is a crazy price.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: June 15, 2025, 02:47:54 pm
content: We have three 4980s at work. Nice machines but stupidly expensive, impossible to repair and can't be properly calibrated by anybody other than Keysight. Cal ain't cheap either. Way better for the hobbyist, if capacitance is your main interest, is a used General Radio 1615A. Even a 716C is quite capable if you have the gen and detector. The problem with the classic bridge stuff is it stops at 1.1 uF without a range extending cap and doesn't automatically give you all the various forms- you have to calculate them manually if you need them.Similar to the 4980 is the Quadtech 1920 or similar. The odds of finding a used one are probably higher. I've also been curious about those cheap LCR "tweezers" that seem fairly capable.As for 4-terminal caps, that's easy. Get some NP0/C0G caps, probably MLCC, and put them in a small metal box with 4 BNC connectors. Measure on the 4980 and there's your standard. You probably don't really need a 4-wire standard, just a shielded 2-wire box, IOW, two BNCs. If you want very low values, it's not hard to make up a cap consisting of two plates in their own chambers, separated by a drilled aperture plate.What's much more interesting to me is how low you can go on dissipation factor. Can you tell the difference between polystyrene and polypropylene? Or Teflon? A good meter should at least be able to tell polyester (Mylar) from the better choices. IMHO, any meter worth having will measure dissipation factor.Anyway, it's really nice to see a comparison between instruments, as we have a lot to choose from these days.

author: TimFox
author_rank: Super Contributor
timestamp: June 15, 2025, 03:04:32 pm
content: Dissipation:In my experience, it’s very difficult to measureQ> 1000 (as opposed to knowingQ> 1000), so it is hard to distinguish the “good” dielectrics (polystyrene, polypropylene, NP0, etc.) from each other, but straightforward to distinguish polyester/Mylar, X7R, etc. from the good ones.

author: chilternview
author_rank: Frequent Contributor
timestamp: June 15, 2025, 03:40:41 pm
content: I was quite surprised at how close all the results were to the E4980A. The 4275A probably hasn't been calibrated in at least 10 years but was still right in there.For 4 terminal caps, I found these:https://www.ebay.co.uk/itm/235992705678?var=536467954771They claim to be 0.5% mica caps, I've ordered one to see if they are any good - if not the internal capacitor could be easily replaced.

author: Kosmic
author_rank: Super Contributor
timestamp: June 16, 2025, 04:39:17 pm
content: Quote from: TimFox on June 15, 2025, 03:04:32 pmWith a SR720 it's possible to measure Q (with averaging since the measurement is a bit bumpy with high Q) and differentiate polystyrene from polypropylene.Ex:Polyester:Polypropylene:Corning Glass Capacitor:Polystyrene:

author: EC8010
author_rank: Frequent Contributor
timestamp: June 17, 2025, 08:23:59 am
content: Quote from: TimFox on June 15, 2025, 03:04:32 pmI'm wondering why you are expressing dielectric loss by Q rather than the (more usual) D?

author: kam
author_rank: Newbie
timestamp: June 17, 2025, 02:02:33 pm
content: Using 3 point calibration on your e4989A if you have a known reference. That would do it. The polystyrene capacitor has a stable capacitance over wide frequency but the film capacitor has a lowest loss.I used the q standard on three point calibration, even the machine has no fresh calibration, the three point will adjust it if the machine is not far off. If you don’t have a w standard, use a 0402 50 or 100ohm resistorthat would work well. Good luck 🍀

author: TimFox
author_rank: Super Contributor
timestamp: June 17, 2025, 02:16:29 pm
content: Quote from: EC8010 on June 17, 2025, 08:23:59 amQ= 1 /D.I prefer to evaluate numbers > 1, especially whenQ> 100.I was giving a rule of thumb about where special care is needed for measurement.

author: mawyatt
author_rank: Super Contributor
timestamp: June 17, 2025, 03:59:10 pm
content: Quote from: chilternview on June 15, 2025, 03:40:41 pmThat looks interesting, like the enclosure idea with the Extruded Al Case and PCB Endplates. Should produce a mechanically rigid fixture, now only if a quality precision internal cap is includedBest

author: EC8010
author_rank: Frequent Contributor
timestamp: June 17, 2025, 05:20:19 pm
content: Quote from: TimFox on June 17, 2025, 02:16:29 pmFair enough - I just wondered if there was a special reason. Agreed, when D < 0.001 (or Q > 1000), you start fretting about how accurate that number really is. Nevertheless, my Hameg 8118 could distinguish between polypropylene, polystyrene, and PTFE.

author: TimFox
author_rank: Super Contributor
timestamp: June 17, 2025, 05:28:46 pm
content: As an example, Kosmic's careful measurements posted above, from an (expensive) SR720, gave the followingQvalues:231.04, 1938.1, 1981.8, and 5938.5,For the last one, that would equate toD= 0.000168I also fret about the accuracy of that last value, but it certainly indicates a very high quality (low loss) capacitor.

author: chilternview
author_rank: Frequent Contributor
timestamp: June 27, 2025, 06:42:34 pm
content: So I found a source on eBay for a 'Standard Capacitor Calibration Kit' which is a 4 terminal (HPOT/HCUR/LPOT/LCUR) capacitor in a rather limited range of values i.e. 1nF, 10nF, 100nF and 1uF.Bought the 1nF one to see what they are like, thinking it would be worth is just for the case if the capacitor was not good. It arrived ten days later and I was somewhat surprised to see a rather good anodized aluminium box with calibration values on it, claiming 0.1%.In fact measuring it on my TH2827C and a E4980A indicated it was indeed very close, see the photos. Have yet to measure with bias etc. but its better than I expected.

author: EC8010
author_rank: Frequent Contributor
timestamp: June 28, 2025, 01:25:53 pm
content: I recently made a new test box to hang off the front of my Hioki IM3536. To do that, I needed to buy four chassis-mounting BNCs of the appropriate gender, that came out at >£40 just for the BNCs. And I had to (very carefully) cut the knurled bit off the two centre BNCs. So I'd say one of those boxes is a bargain. What kind of capacitor is inside?

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 28, 2025, 01:39:14 pm
content: Quote from: chilternview on June 27, 2025, 06:42:34 pmDo you mind taking some photos of the insides?Quote from: EC8010 on June 28, 2025, 01:25:53 pmHow did you spend so much on BNC's? It's not high frequency work, even Chinese BNC connectors are more than enough for this application....

author: chilternview
author_rank: Frequent Contributor
timestamp: June 28, 2025, 01:53:41 pm
content: I'll see if I can get a photo later. It's a rather nondescript capacitor, probably a cheap film cap, in parallel with an air dielectric trimmer. Still, it can be easily replaced - I was more interested in the case and the relatively hard to get BNC's with the levers.

author: EC8010
author_rank: Frequent Contributor
timestamp: June 28, 2025, 03:41:17 pm
content: Quote from: TERRA Operative on June 28, 2025, 01:39:14 pmWell, the four BNCs need to be quite accurately positioned so as not to stress the tester's (probably PCB-mounted) BNCs. And the only chassis-mounting BNCs I could find of the right sex were the square type secured by four small screws, made by Amphenol. Hence, the cost. But they're quite easy to position accurately. The Hioki was expensive, and I don't want to introduce noise from poor contacts, so I wasn't too worried about the BNC price. All up, my screened test fixture with Kelvin clips came in at about £80. That's still way less than any commercially made test fixture. I've come to the conclusion that LCR testers are a bit like SLR cameras. The camera body doesn't seem too painful, but what really sets the quality is the lens on the front. Similarly, a poor test fixture throws away the accuracy you paid a lot for in the LCR tester. And that seems to be true for a lot of T&M equipment; you only get good results if you take care over your measurement connections. I now have a collection of die-cast boxes etc with BNCs on them for various tests.@chilternview: Which of the (many) standard capacitors on Fleabay did you go for? Ah, I've just discovered your link in earlier post.Those plastic levers on the BNCs invariably loosen with time, so I've never bothered.

author: chilternview
author_rank: Frequent Contributor
timestamp: June 28, 2025, 04:30:47 pm
content: Quote from: EC8010 on June 28, 2025, 03:41:17 pmI ordered a 1nF one from a seller called 'valuequalitystore', but there are many sellers with what looks like the same set of capacitors for sale. It took them 10 days to hand it over to the courier, but then only 3 days to arrive in the post.I'd have made my own, but I've not found a source for the BNCs with levers. Yes I know they are not really necessary but I find they help.

author: mawyatt
author_rank: Super Contributor
timestamp: June 28, 2025, 04:48:38 pm
content: We did something similar awhile back, as we couldn't find the proper BNCs with the arms. Repurposed a cheap LCR Meter Kelvin Clip Fixture by removing the Kelvin Clip cable and mounting our custom PCB with a Lever Arm plunger for use with SMD components.Best

author: chilternview
author_rank: Frequent Contributor
timestamp: June 28, 2025, 05:02:28 pm
content: Here's a couple of photos of the insides. As I expected, it's not a capacitor that stands out as 'quality'

author: EC8010
author_rank: Frequent Contributor
timestamp: June 28, 2025, 05:34:41 pm
content: That's a very poor implementation of a four-wire connection. Alright, it uses the four wires coming from the tester, but its connection to the capacitor is dreadful. If you really want to measure a capacitor properly, you need to make your connections within 2mm of the capacitor body. That calls for utmost cleanliness in order that you can make the joint quickly and without damage. To make the joint easier, use wirewrap wire for the sensing connection and the capacitor's own wires for the force connection.It does look like a mica capacitor, though. If so, it should have a value of D of about 0.00025 at 1kHz.

author: mawyatt
author_rank: Super Contributor
timestamp: June 28, 2025, 05:59:52 pm
content: Agree, that cap looks like a molded mica, likely removed from something else and why the short leads. With full length leads it could be attached across the Sense Terminals with leads extending to Force Terminals and appears the cap would just fit across the Sense Terminals getting them very close to the cap body.If one really wants quality measurements then another pair of these fixtures are required, one with an Open (nothing inside except a solid wire from Force to Sense on each side to represent the DUT leads) and another with a good short (wide Cu plate shorting all 4 terminals).We've thought about making something similar where the fixture could support leaded components or SMD components or both, but haven't pursued such as there doesn't seem to be much interest locally here in the states to justify the effort and cost involved.Maybe we should rethinkBest

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 06:11:17 pm
content: General Radio sold standard capacitors with either mica, polystyrene, or air dielectric.Their catalog pointed out that the measured capacitance of mica rises at low frequencies.Polystyrene had higher parasitic inductance and worse tempco, but did not have the low frequency problem.IIRC, the low-frequency effect in mica is somehow related to its water of crystallization.

author: mawyatt
author_rank: Super Contributor
timestamp: June 28, 2025, 06:42:05 pm
content: Recall there were two basic types of leaded mica caps, one dipped and the other molded.Not sure if anyone makes mica in quantity now, there are some surplus houses that still have a stash which should be well aged!! We have a few from surplus that we've periodically measured and they seem stable.Best

author: chilternview
author_rank: Frequent Contributor
timestamp: June 28, 2025, 06:57:08 pm
content: Quote from: mawyatt on June 28, 2025, 05:59:52 pmI was wondering about how to do open/short correction with a fixture like this. On the unit it's marked as for the TH2830, I imagine what they have done is specifically adjusted it to get a good result for that instrument, which it does. Of course with a 1000pF capacitor, strays are going to be fairly small in comparison. Perhaps that's why that's the lowest capacitance value they offer?

author: mzzj
author_rank: Super Contributor
timestamp: June 28, 2025, 07:56:18 pm
content: Cornell-dubilier Knowles seem to make variety of mica caps in leaded, smd and doorknob styleshttps://www.digikey.com/en/products/filter/mica-and-ptfe-capacitors/64?s=N4IgjCBcoJwAwyqAxlAZgQwDYGcCmANCAPZQDaIAzAOwCsATAByIC6RADgC5QgDKnAJwCWAOwDmIAL5EAtPSQhUkQQFdCJciFogWkvUAQuote from: mawyatt on June 28, 2025, 06:42:05 pm

author: mawyatt
author_rank: Super Contributor
timestamp: June 28, 2025, 08:09:13 pm
content: Quote from: chilternview on June 28, 2025, 06:57:08 pmSince there's no way the Test Cap fixture can know the LCR Instrument Open/Short Cal, and the user can't perform such without proper Open/Short fixtures, then the result is just a good guess based upon the typical LCR meter parasitics, which with a specific LCR meter then all then better as the internal meter parasitics should be very similar for the same model LCR Meter.However, this raises the question without these Open/Short references does this Capacitor Fixture provide any significant benefit over the standard leaded LCR Meter fixture where one can easily do an Open/Short calibration??Would think this lack of a Open/Short reference limits the lower value of capacitance range and likely why the lowest value offered is 1nF.The more we think about this the more we are considered rolling our own. This would certainly be a nice set of caps (maybe resistors and inductors also) with the same mechanical case fixture Open and Short fixture. Would think this should give excellent repeatability on quality LCR Meters, even with capacitance values as low as 10pF.Anyway, just what we need another enticing projectBest

author: chilternview
author_rank: Frequent Contributor
timestamp: June 28, 2025, 08:29:32 pm
content: Sounds like a good project. Need to find a source of the enclosure, then make up a pcb for the BNC's.Must work out cheaper than this:https://www.ebay.com/p/1700580452!!!

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 08:49:12 pm
content: Wouldn't a duplicate of the box with BNC connectors, with or without a short across the four terminals, work for the calibration / fixture correction?I have used analogous boxes for my DE-5000 with a small switch between the binding posts to do the short without disconnection.At those frequencies, max 100 kHz, I used four-pole miniature toggles with the sections paralleled for low series ON resistance for SHORT calibration.The Off capacitance of the switch is included in the box + binding posts for OPEN calibration.(This was for use as a test fixture, not a calibration standard, with binding posts on the box.)

author: EC8010
author_rank: Frequent Contributor
timestamp: June 28, 2025, 09:29:53 pm
content: Once upon a time, a standard capacitor could be measured on a bridge and compared with the bridge's standard capacitor. The bridge's resistances could be verified at low frequency or DC, so checking the bridge's standard capacitor effectively verified all L and C measurements. But modern LCR testers don't work like a bridge, and you can't confirm everything so easily. I think the real value of a pluggable four-wire capacitor is that you can quickly test it and check that the LCR tester is probably correct. And because it can be done quickly, you can ensure that itisdone.I've been giving some thought to how you would measure a capacitance accurately using equipment commonly available. Making a CR filter using a known accurate resistance seems like a good starting point. Perhaps one might start by comparing a metal foil resistor to a standard resistor to establish its value, then make and measure the filter to establish the capacitance. Measuring frequency accurately is no longer difficult, so it's now down to whether it is better to measure phase or amplitude.

author: TimFox
author_rank: Super Contributor
timestamp: June 28, 2025, 09:32:01 pm
content: Finding the -3 dB or -45ofrequency of a single-pole filteraccuratelyis difficult, although the frequency you are applying can be measured to any sensible accuracy.Ed: fixed error for 45o.

author: mawyatt
author_rank: Super Contributor
timestamp: June 28, 2025, 09:41:32 pm
content: Some of the LCR meters under discussion can go to 1MHz or even 8MHz (IM3536). If the capacitance is small (like 10pF) then any variation in internal position or fields can corrupt measurements. If you look at the effort EC8010 has gone to with his custom fixture for the IM3536, this becomes apparent.If the cost of the fixtures can be kept low enough, then having separate Open and Short fixtures seems reasonable. Our approach we are considering would have a short extruded aluminum tube with end plates on each end. One would host the 4 BNCs and the other provide a closed Faraday type shield. The extrusions only need to be 30~40mm deep, so shouldn't be too expensive, and the ends would be custom PCBs.For the Short Cal Fixture a strip of Cu, 10mm wide soldered to each of the 4 BNCs should provide a good short reference, here the internal E-Fields aren't critical as the impedance is very low. For the Open, this will require a careful placement of the Force and Sense wire connections on each High and Low terminal sides. Here you want to duplicate the surrounding wire connections as close as reasonable to the actual leaded capacitor version to make the internal E-Fields as similar as possible. This will be important for small capacitors <100pF, for larger capacitors the fields aren't as critical. This also hints that for small DUT capacitors, an Open version of the custom PCB will be necessary for small capacitance SMDs DUTs.Our experience indicates (we've already done such with SMDs) <10pF measurements can be duplicated with excellent repeatability by careful attention to details (like EC8010 has performed).If anyone is interested, ping us by PM, and if we can achieve "critical mass" then may proceed with the project.Best

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 29, 2025, 04:49:27 am
content: Quote from: EC8010 on June 28, 2025, 03:41:17 pmI usually use normal bulkhead BNC's, but with a PCB cover panel with the cutouts placed in the exact locations, like in the capacitor standard that chilternview has here. Also see photos below.I used the type with 4 screws on some other thing I made once or twice, but found them to be too much of a fiddle to install.Quote from: chilternview on June 28, 2025, 05:02:28 pmThat's pretty much exactly how I thought it would look inside. Not great, not terrible.They could be constructed better, but if they are measured as they are built then not touched, they should remain pretty accurate.Here's some 4-wire resistance standards I made a while back (click on them to enlarge). IthinkI maintained 50ohm impedance more or less right to the resistor.I want to make some capacitance ones, but the trick is I'm in a catch-22. I need to measure my standards to be able to calibrate my gear, but my gear isn't calibrated so I need measured standards....The short and open have a bit of copper and nothing at all, respectively.For the levers, I just got them 3D printed when I ordered the PCB'sI also made some binding post to BNC adapters too (not shown), so I could measure these on my 3458A and 34461A.I have a plan to get a bunch of thin aluminium plates cut to build my own air-core capacitors to end up looking like the real HPAK ones, but I'm still at the point of needing access to a calibrated LCR meter to measure them....

author: EC8010
author_rank: Frequent Contributor
timestamp: June 29, 2025, 08:29:52 am
content: Quote from: TERRA Operative on June 29, 2025, 04:49:27 amI found an easy way to fit them on boxes; the key requirement is 22mm between centres, so if you mark out and drill holes the same size as the rear central pin, you can locate a BNC in the hole and use it as a template to mark where its fixing holes should be. I then drilled and tapped M3 and it worked nicely. I'll freely admit that making asetof standards like yours would take time...You are absolutely right about the Catch22 of needing calibrated capacitors to calibrate your test gear. Years ago, I was horrified to discover that the calibration "standard" at work was the HPAK4980. A nice piece of kit, yes, but hardly a standard. Hence my wonderings about going back to fundamentals to measure a capacitance. As TimFox points out, although it's easy to measure frequency accurately, finding the 45 degree phase or -3dB point isn't so easy. Nevertheless, I think that's the way to go. Would I mind needing an entire day to obtain a capacitance measurement that was accurate to 0.01%? Probably not, so I think it warrants further investigation.Essentially, we need to be able to measure an accurate voltage across the DUT whilst accurately measuring the current through it. Fortunately, it's an alternating signal, so we don't have to worry about DC offsets. But we do have to worry about stray capacitances and that probably means we need to keep frequency quite low. Probably <20kHz. 10nF is 796 ohm at 20kHz, and assuming we apply 1V, that would mean a current of 1mA, which is within the range of normal op-amps. That probably sets an upper limit of the capacitance that can be measured.I tinkered a little in spreadsheet with a 10nF capacitor and 1k resistor, giving a frequency of 15.9kHz. The frequency is easily measured, but phase needs to be measured to 0.007 degree to obtain a reactance accuracy of 0.02%. That's not going to be trivial. But a decent function generator will provide a Sync pulse for accurate comparison. Any phase measurement will be limited by noise. We will need a pair of low noise op-amps that don't misbehave when overloaded, followed by a fast XOR gate. The output of the XOR is a pulse whose width indicates phase. We can measure that accurately on an oscilloscope. The pulse width is easily calibrated for 0 degrees and 180 degrees, making 45 degrees easy to find. This may be practical.

author: chilternview
author_rank: Frequent Contributor
timestamp: June 29, 2025, 09:14:47 am
content: Quote from: TERRA Operative on June 29, 2025, 04:49:27 amThose look impressive. Do you have some details as to where you got those made up, drawings/files etc? It would be good to get some made up, and maybe a few people here would be interested.

author: mawyatt
author_rank: Super Contributor
timestamp: June 29, 2025, 12:35:54 pm
content: Quote from: TERRA Operative on June 29, 2025, 04:49:27 amThose look really nice for resistance use (DCR measurements).However for use with capacitance and ACR measurements would think that a vertical conductive shield plate between the High and Low terminal sides should improve the measurement uncertainty. We added a shield in our SMD fixture mentioned above for this purpose.Best

author: mawyatt
author_rank: Super Contributor
timestamp: June 29, 2025, 01:19:37 pm
content: Quote from: EC8010 on June 29, 2025, 08:29:52 amDirect time might be easier to measure than phase, or inferred phase.If you go the pulse route where the DUT cap is charged from a precision resistor from a pulse source of fixed amplitude and measure the time to reach 1/2 the pulse amplitude. The time measurement "t" would be from a fast comparator where the 1/2 pulse voltage is just a precision resistive divider of 2 of the pulse voltage. Here the capacitance is simply R*t/ln2.Guess of all the possible methods to measure capacitance a detailed error/uncertainty analysis needs to be performed. Probably the simplest method is just buy a new Hioki IM3536 LCR Meter and measure a bunch of quality caps using good Open/Short Calibration methods/fixtures. This is what we did way back, and our customer at the time accepted the new Hioki IM3536 as a valid reference instrument (they were picky but had common engineering sense too!). Our experience is Hioki instruments are as well designed and stable as anything from Keysight or R&S, and why this is our "go to" LCR meter for quality reference measurements.BTW if anyone wants us to measure a reference cap (or other RLC component), we'll be happy to do so. Just provide a Self Addressed Return Envelope/Box, and we'll make the measurements with both our TH2830 and IM3536 which are available for rent, 1 brew per reference deviceOur limited experience has shown that C0G/NP0 0805, 1206 and 2512 SMD caps from quality sources are quite stable, inexpensive and readily available.Anyway, YMMV as alwaysBest

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 29, 2025, 03:49:02 pm
content: Quote from: EC8010 on June 29, 2025, 08:29:52 amI have been thinking of ways to accurately measure capacitance too.I have a 3458A, Advantest R6161, Yokogawa AC and DC standards, GPS referenced Siglent SDG2042X AWG andAgilent 53132A Frequency counter, Siglent SDS2104X HD (unlocked to 500MHz) so I'm mostly set up for some half decent measurements etc, it's just a matter of putting the pieces together correctly with my tongue at the right angle to get a reliable result...I was thinking of making a bridge, but that still needs an accurate capacitor, so I'm still stuck there. I have a box of mixed Arco precision capacitor standards, but they are really old and some read out of spec according to my 4263B, chicken and egg once again...A way to hook my gear up to measure capacitance without requiring an LCR meter or a reference capacitor would be perfect, I just haven't had time to think about it yet.Quote from: chilternview on June 29, 2025, 09:14:47 amGerbers and Diptrace files are attached below, I also included the STEP file for the BNC levers.The front panel PCB is specific to the Takachi enclosure I used, but you can resize it to suit what you have available.Quote from: mawyatt on June 29, 2025, 12:35:54 pmYep, that's the plan, a bit of thin copper, or maybe a thin bit of PCB completely covered with a ground plane on one side, so I can get it made to a specific shape without having to do it myself.

author: Kean
author_rank: Unknown
timestamp: June 29, 2025, 04:23:22 pm
content: Quote from: chilternview on June 28, 2025, 06:57:08 pmThis listing has options for 6 decade values from 10pF to 1uF, although the text only mentions 4 decades from 1nFhttps://vi.aliexpress.com/item/1005009324551761.htmlAnother seller offers 5 decades of caps from 100pF, and 6 decades of precision resistors, although their pricing is much higherhttps://vi.aliexpress.com/item/1005009101889469.htmlI've not ordered any yet, but will likely try one from the first seller as a test.

author: TimFox
author_rank: Super Contributor
timestamp: June 29, 2025, 04:33:11 pm
content: I have used a PAR two-phase lock-in amplifier to measure complex impedance, with a standard resistor (Vishay RNC90 metal foil) in series and the LIA’s high impedance differential input.Of course, I need a good measurement of the fixture impedance (without the impedance under test) to correct the reading.This relies on an accurate quadrature phase generated in the LIA and a close-tolerance resistance, similar to the approach in many LCR meters (since the G-R Digibridge).

author: EC8010
author_rank: Frequent Contributor
timestamp: June 29, 2025, 05:11:00 pm
content: Yes, lock-in allows very low noise bandwidth. And, as you point out, that is how most LCR meters work. I've been wondering about configuring a CR network as an op-amp differentiator and looking for 45 degrees of phase. An oscilloscope should be able to zoom in directly on the phase change, but it will have noise, so I suspect comparators are required. Ultimately, we want to be able to compare the reactance of a capacitor with the resistance of a resistor because we can measure resistance more accurately.

author: FiveFiveFive
author_rank: Contributor
timestamp: June 29, 2025, 11:12:16 pm
content: You could use a dual channel signal gen to generate sine and cos signals. Apply the sine output to your series RC network and apply the capacitor voltage to a pair of phase-switchers (e.g. DG403 (or better) swapping over the inputs to instrumentation amps in response to a logic signal). Drive one phase-switch logic input from the sig gen sine output, one from the cos output, probably via comparators. This gives you synchronously demodulated quadrature outputs whose DC content is poroprtional to the quadrature components of the capacitor voltage (plus some excitation frequency harmonics!). These should be equal at the 45° point. Low pass filter the two outputs to ditch the excitation frequency and measure the voltage difference between the two channels. Set the sig gen frequency to roughly what you expect the -3dB point to be (1/(2*pi*R*C)) then tweak it to get a null between the two outputs. Calculate C given R and the frequency. If you want to be really fancy-pants, integrate the difference and apply it back to the sig gen for frequency modulation to 'seek' the frequency of the equilibrium point.The trouble with this will be small gain differences between sin and cos demodulator channels will cause errors, as will the ability to change frequency by small enough amounts to really home in on the 45° point, and switching times of the phase-switches could be significant, but then if you're looking to resolve down to 0.02% with home-brew kit, most of the methods discussed so far will come unstuck because it's a very small change to measure!It's quite late here and I've been rattling my brains listening to The Prodigy at Glastonbury, so that lot might not make complete sense.

author: EC8010
author_rank: Frequent Contributor
timestamp: June 30, 2025, 08:29:39 am
content: That makes sense. Damning admission; I don't have a dual channel signal generator. I've used (analogue) state variable oscillators before now to generate sine and cosine at 60Hz, but not to the degree of precision required. I suspect a digitally synthesised source is required, and even then the accuracy will be questionable.

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 30, 2025, 10:06:45 am
content: I wonder if a Siglent SDG2000X is good enough? I have one of those looking for a job to do.. It has 2 channels and I unlocked mine to 120MHz (not that capacitance measurement needs to go that high) but it is GPS referenced so the absolute accuracy is pretty spot on.I'll have to do some research on these methods proposed, unless someone can draw me a diagram with colourful crayons so I can easily understand it?

author: Hydron
author_rank: Super Contributor
timestamp: June 30, 2025, 10:26:03 am
content: I've got a SDG2042X arriving tomorrow (see above for what the BW will be shortly after it arrives) and also would love to have a good way to transfer a resistance standard to a capacitor.I picked up a 10nF GenRad 1409 recently but have no way to tell if it has drifted (only LCR meter I have is a DER5000). Not in the US either so can't take up mawyatt on his kind offer (well I do end up there for work sometimes but probably tricky to turn it around in a week!). Is there anyone in the UK that could offer something similar (paid or unpaid) for a hobbyist?One of the end goals is to use the 10nF (or a smaller polystyrene) cap to calibrate low current ranges on my electrometer and SMUs via I = C dv/dt. Would also be useful to know capacitance change at low frequencies for this use, so a method that allows for testing at a few different frequencies would be handy (have seen some genrad notes that mica can increase in capacitance at very low frequencies).

author: EC8010
author_rank: Frequent Contributor
timestamp: June 30, 2025, 12:00:20 pm
content: Yes, that's what this thread is about isn't it? Transferring a resistance standard to a capacitor. Thank you for defining it.At the risk of derailing the thread, one way to calibrate an electrometer is via a current divider that can operate over a large range. I've found a useful way of doing that is to put two 1980s LEDs (HLMP3401) face to face in a light-tight box and drive one from a controllable CCS. The other LED will produce a much smaller current, but with a constant ratio. Starting at the top range of the electrometer, that can be calibrated reasonably easily and the LEDs allow range switching steps to be identified and calibrated out, eventually leading to lower electrometer ranges being calibrated.The light-tight box is much harder to achieve than you might think. Self-adhesive copper tape is needed to stop light - not black insulating tape! And insulated BNCs or insulating kits leak light too. Only metal stops light.

author: mawyatt
author_rank: Super Contributor
timestamp: June 30, 2025, 12:34:58 pm
content: Quote from: TERRA Operative on June 30, 2025, 10:06:45 amGPS locking only effects the AWG frequency. You'll need the two AWG channels to be phase quadrature with very high precision. What might work is to use your DSO with both channels skew calibrated out, then check the AWG for the quadrature time between zero crossings. Think the SDG2042X has a feature to "adjust" the time skew between channels, altho we've never needed to use this feature (yet).Best

author: mawyatt
author_rank: Super Contributor
timestamp: June 30, 2025, 12:40:59 pm
content: Quote from: EC8010 on June 30, 2025, 08:29:39 amNow you have areasonexcuserequirementfor a new dual channel AWG to augment your IM3536Best

author: EC8010
author_rank: Frequent Contributor
timestamp: June 30, 2025, 03:32:59 pm
content: Quote from: mawyatt on June 30, 2025, 12:40:59 pmSadly, I thought that too. I have already thought of another use for a dual channel AWG. It all depends on how finely phase can be tweaked between channels - either I wasn't looking in the right place, but I couldn't seem to see a specification for that on the Siglent.

author: TimFox
author_rank: Super Contributor
timestamp: June 30, 2025, 03:49:02 pm
content: I haven’t done the math explicitly, but I was thinking about the requirements on quadrature phase accuracy for capacitance measurement.The error in capacitance should depend on the cosine of the phase error, but the error in dissipation should depend on the sine. Cosine errors are much slower than sine errors (for small angles). An exercise for the interested reader.

author: EC8010
author_rank: Frequent Contributor
timestamp: June 30, 2025, 06:58:00 pm
content: But I think we'd be measuring at the frequency where Xc = R and phase would be 45 degrees, so I don't see your argument holds. But please correct me if you can argue differently - it would be a useful advantage.I've been wondering about the FFT on an oscilloscope for this problem. The FFT can be considered to be an array of lock-in amplifiers each followed by a filter that defines noise bandwidth. Of course, the dynamic range of an oscilloscope is only around 42dB (ENOB of 7 bits), whereas a genuine lock-in amplifier is likely to be 80dB. But the oscilloscope is readily available...I feel sure the tools are there if only we have the wit to work out how to use them and don't care much about measurement time.

author: TimFox
author_rank: Super Contributor
timestamp: June 30, 2025, 07:16:39 pm
content: Quote from: EC8010 on June 30, 2025, 06:58:00 pmTo clarify: I'm referring to measuring "I" (in-phase) and "Q" (quadrature-phase) components of the voltage and current, where the lock-in or LCR meter uses two phases (90ophase difference) to do phase-sensitive detection of the components. The error is between reality and the ideal 90ophase difference in those reference signals from the same frequency source. This is the scheme I have used with my PAR lock-in amp, but I have not pushed the accuracy.

author: mawyatt
author_rank: Super Contributor
timestamp: July 01, 2025, 11:41:31 pm
content: Here's something we've been thinking about for a couple days.If the DUT Cap is ideal with no loss, then using an AC signal source with a precise source impedance (series precision resistor, call Rgg, plus generator Rg) and another precision resistor, call R, where the AC source is connected to the shunt R. Set the Signal source to some value and measure the AC voltage (good DMM) across the shunt R, then move the source to the DUT Cap and adjust only the AC source frequency so the same AC voltage magnitude is across the Cap.A little analysis shows when these are equal in magnitude (DMM can’t measure phase) and you equate the magnitudes of both and solve for the Cap the result is:C^2 = [(2*Rgx/R + (Rgx/R)^2]/[2*pi*F*Rgx]^2, where Rgx is Rg +Rgg, F is the frequency where the voltage magnitude across the precision resistor R equals the voltage across the DUT Cap.Did a quick experiment with a couple 1K 1% Resistors, measured with KS34465A, and a couple film Caps with AC signal from SDS2042X AWG. Using the KS34465A as the AC Voltage measurement instrument the results were close to that measured by our TH2830 LCR Meter.Disclaimer didn’t let the DMM, AWG, or LCR Meter properly warm up, and used a protoboard with dangling leads, so far from any "controlled" experiment.The results were Calculated (LCR Measured). All caps were large low ESR polypropylene types.T = 26.4C 42% RHAC Source SDG2042XDMM KS34465ALCR Meter TH2830Rg ~ 50Ω, Rgg = 995.833Ω, R = 997.090Ω1uF 1.011678uF (1.01889uF)2uF 1.970749uF (1.97126uF)1.8uF 1.796541uF (1.79710uF)4.8uF 4.839765uF (4.84051uF)Anyway, sure there are lots of holes in this and certainly not good enough to evaluate a Reference Cap, but initially seems to give reasonable results with the uncontrolled experiment, curious to what others thinkBest

author: mawyatt
author_rank: Super Contributor
timestamp: July 02, 2025, 01:45:00 pm
content: If the DUT Capacitor has a significant ESR (wrt Rgg) the analysis gets much more complicated and one needs to know the ESR to accurately evaluate the DUT Capacitance.Here's what this looks like, a quadratic in C^2 with a bunch of terms, will leave that for others to tackleBest

author: Kleinstein
author_rank: Super Contributor
timestamp: July 02, 2025, 02:59:59 pm
content: The difficulty with the I/Q measurement is not so much the phase shift in the actual measurement. With digital systems the delay can be very accurate.The real limitation is from having a reference part (resistor or capacitor) with a exact phase shift of 0 or 90 degree. A good air capacitor and coaxial resistor may come close, but is for a limited range (relatively small capacitors or low resistance). So the issue in measuring the phase between a current and a voltage and not 2 voltages.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 02, 2025, 03:19:20 pm
content: Quote from: mawyatt on July 02, 2025, 01:45:00 pmI don't think that's a practical problem. I've modelled quite a few film capacitors and ESR is generally in the low milliohm. I think that for the R/C swapping technique, Xc needs to be >1k anyway, making ESR negligible. However, even if it should turn out that ESR needs to be known, it's no great problem to measure it. Bear in mind that the ESR would be a second-order effect, so there would be no problem in measuring it using the LCR tester you're eventually intending to verify.

author: mawyatt
author_rank: Super Contributor
timestamp: July 02, 2025, 03:39:21 pm
content: It's interesting in the concept we mentioned in #51 and #52 above apparently the AC signal source and AC measuring device don't need to be accurate in amplitude, the signal source needs to be accurate in frequency tho. The actual value of the precision reference resistor R matters, which reflects in the voltage measurement magnitude ratio. As long as the signal source is stable during the measurements the amplitude doesn't matter, same for the AC measurement instrument, it doesn't need to be accurate at the measurement frequency just stable between the Resistor and Capacitor measurement since they both are "hand servoed" to be equal. When equal the magnitude the Reference resistor R voltage is equal to the DUT Capacitor voltage, one can assure this within limits after adjusting the source frequency to equalize the voltages, by returning to the Reference resistor at frequency, then back to the DUT capacitor for a final frequency tweak to equalize the AC magnitude voltage readings.Intuition suggests; no we are not going to solve that equation above, that's for grad studentsthat a solution including ESR should yield less uncertainty for a better estimate of the DUT Capacitance, but will leave for others to discover.Best

author: mawyatt
author_rank: Super Contributor
timestamp: July 02, 2025, 03:48:53 pm
content: Quote from: EC8010 on July 02, 2025, 03:19:20 pmPractical or not, agree keeping the ESR many orders-of-magnitude below the Reference Resistor and effective source impedance should make it insignificant. However, if one is attempting to resolve the DUT Capacitance to reference levels previously indicated, it would be beneficial to have a relationship that reveals how ESR affects the final result, we'll leave that for others to solve and discover tho!!Also, it does seem higher impedances should be beneficial, altho the effects of AC Measurement device load and parasitic capacitances become more problematic at higher overall impedances. So expect some "sweet spot" impedance levels which would depend on DUT are desirable.Best

author: mawyatt
author_rank: Super Contributor
timestamp: July 02, 2025, 06:04:25 pm
content: We let instruments warm up and did a few more measurements with same setup above except terminated the AWG with 50Ω, so effective Rg is ~25Ω (measured 25.33Ω). Also used IM3536 after calibrated Open/Short for LCR measurements.Here's the results with cheap Mylar/Polyester caps with high ESR, calculated value (measured with ESR at frequency).10uF 9.894837uF (9.8670uF, 113mΩ)1uF 1.001296uF (1.00208uF, 88mΩ)220nF 221.0192nF (220.552nF, 2.32Ω)100nF 99.63127nF (99.3289nF, 3.44Ω)10nF 10.24981nF (10.1400nF, 6.1Ω)Considered the high ESR, these results were better than expected!!Best

author: EC8010
author_rank: Frequent Contributor
timestamp: July 02, 2025, 06:42:15 pm
content: I suspect those results indicate the validity of the method. To prove it, full uncertainty calculations will be required. We'd need to know the value of the resistance used for transfer, and its uncertainty. Also, its parasitic inductance and capacitance. And test frequency. We'd also need to know details of how the experiment was conducted. Make no mistake, I'm by no means belittling the results - I think they're very encouraging. It's just that a bit more work will be needed. I'm busy on a couple of other projects at the moment, but I will certainly repeat the experiment, and with quite similar equipment.Oh, and the test needs to be done with polypropylene or polystyrene capacitors as polyester capacitors have a variation in capacitance with frequency of about 3% from 20Hz to 20kHz.

author: mawyatt
author_rank: Super Contributor
timestamp: July 02, 2025, 07:11:37 pm
content: Quote from: EC8010 on July 02, 2025, 06:42:15 pmYeah, our efforts are very crude and limited, hopefully just an encouragement for others. Frankly these results were better than we expected.Agree Polystyrene and Polypropylene are better and why we initially used the Polypropylene types (don't have any larger Polystyrene types), however curiosity got the best of us and we decided to try the cheap Mylar/Polyester types.Anyway, hopefully those more knowledgable like yourself will look into this method and wring out the details. It's interesting that a DMM and AWG can produce these results with just a single Reference ResistorBest

author: TERRA Operative
author_rank: Super Contributor
timestamp: July 02, 2025, 10:31:01 pm
content: Once the setup is more nailed down, I have a few Yokogawa 2792 resistance standards (0.1R, 1R and 10K so far) that I can use. I plan to add more to the decade set as they come available on the second hand market.They will provide me with a known characterised reference.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 02, 2025, 10:32:16 pm
content: Quote from: mawyatt on July 02, 2025, 07:11:37 pmWe should always remember the subtle experiments done a century ago despite the equipment available at the time. As a friend commented to me recently, "It's not so much the equipment as the person in front of it." The T&M manufacturers are always keen to sell new products, but often you can get just as good a result with older equipment. It just takes longer and requires more knowledge...On the topic of reference resistors, I fully expect to need a transfer there as well. I have some standard resistors, but they have horrible parasitics, so a resistor having fewer parasitics will need to be compared to a reference and calibrated before comparison with the capacitor. Not a problem, but an expected extra step. And the resistor compared with the capacitor will need its parasitics quantified. Again, not a problem, but an extra step.

author: TimFox
author_rank: Super Contributor
timestamp: July 02, 2025, 10:44:19 pm
content: Metal-foil (“bulk metal”) resistors are “non-inductive” and have low internal capacitance.Typically < 100 nH and < 1 pF (I believe that spec is for 1000\$\Omega\$).The inductance is mainly in the leads.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 03, 2025, 12:05:46 pm
content: As it happens, I measured a couple of 1k metal foil resistors some time ago. I should be able to make a better measurement now. Nevertheless, it looks as though a metal foil resistor is near-perfect at audio frequencies. Even better, one could set a up a spreadsheet that includes the resistor and capacitor's parasitic components to calculate their impedance, then match impedances at a measured frequency and work backwards to determine true capacitance. That should work. I'll give it a go later.Edit: Yes, I can do much better now. The IM3536 can go to 8MHz, allowing inductance to be seen properly. Inductance is surprisingly high. Also, it's lossy, necessitating a six-component model. Given that the resistive material is nichrome and nickel is weakly magnetic, perhaps that's not so surprising. The IM3536 was short and open circuit calibrated before measurement and had been warmed up for several hours beforehand. The significance of the discrepancy graph is that it shows that the six-component model fits to within 0.01% up to 1MHz, so model values could be used in a capacitance calculation up to a frequency of 1MHz.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 03, 2025, 05:35:59 pm
content: Having looked at the resistor, I looked at a few 100n capacitors to see what their inductance and ESR was like. Inductance was typically between 35nH and 20nH, and ESR varied between 8mohm (Vernitron silvered mica) to 92mohm (Ashcroft polycarbonate). But the real problem is that they all have capacitance that changes with frequency. This was visible in the residual graphs that plotted discrepancy between model and measurement.

author: Hydron
author_rank: Super Contributor
timestamp: July 03, 2025, 07:47:12 pm
content: EC8010 - is your IM3536 recently calibrated? I've certainly seen notes from Genrad about silver mica going up in capacitance as frequency got close to DC, didn't know polypropylene did the same, but I'm assuming the meter is right given what I've read. Might try and run some of my own swept frequency tests with a resistor as reference.Also, how close are you to London? Got a few capacitors that I'd be very interested in a trustworthy measurement of (especially my Genrad 1409 10nF Standard capacitor) if you'd be willing to run a few tests.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 03, 2025, 09:32:10 pm
content: I sincerely hope so! It only arrived from Japan about six weeks ago. As far as I'm aware, they all have capacitance that falls with frequency. Years ago, a chap who knew far more about capacitors than me explained that it all comes from the Debye theory of permittivity. I'll PM you.

author: mawyatt
author_rank: Super Contributor
timestamp: July 04, 2025, 02:25:33 pm
content: Believe all capacitors with a dielectric other than air have this characteristic due to the permittivity being a complex function rather than a simple scalar, same for permeability.BTW that's really good agreement with your resistor modelSuspect that an equivalent capacitor model covering this frequency range will be quite involved.Best

author: mawyatt
author_rank: Super Contributor
timestamp: July 04, 2025, 02:34:05 pm
content: Quote from: EC8010 on July 03, 2025, 12:05:46 pmWas this a leaded or SMD resistor, and what type fixture did you use?Best

author: Kleinstein
author_rank: Super Contributor
timestamp: July 04, 2025, 03:09:22 pm
content: The capacity going down with frequency is at least valid for relatively low frequencies (below resonance in the dielectric materia). The frequency and loss are related with the Kramers Kronig relations.So higher loss capacitors, like mica show more frequency dependence than low loss ones (e.g. polypropylene).

author: EC8010
author_rank: Frequent Contributor
timestamp: July 04, 2025, 03:17:54 pm
content: Yes, as you say, it all comes from permittivity being complex.Resistor was leaded and tested in my latest jig. I was surprised by the inductance, but when I thought about it, it made sense. Its nichrome foil is much thicker than the nichrome condensed onto a thin film resistor, so it needs a much longer track, and although it's not a helix, it must suffer higher inductance.I'm getting increasingly annoyed with those Mueller Kelvin clips. They often don't make a good connection because they just press flats to the lead, rather than edges. I can see I'm going to have to make my own. I also discover that I need a light inside the box so I can see what I'm doing - my hands block the light from my fingers! It would probably also help if I polished the DUT's leads with metal polish beforehand.Plotted on a log-log scale, a simple LCR model looks quite reasonable from 100Hz to 10MHz. It's when you plot the discrepancy between model and measurement that you see that the LCR model is flawed. Looks like I need to modify C in the spreadsheet to have a frequency dependence.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 04, 2025, 03:20:15 pm
content: Quote from: Kleinstein on July 04, 2025, 03:09:22 pmAre they now? Would you care to expand on that?

author: mawyatt
author_rank: Super Contributor
timestamp: July 04, 2025, 03:54:03 pm
content: Quote from: EC8010 on July 04, 2025, 03:17:54 pmMaybe try those cheap Kelvin Clips, they have "ridged teeth" to make the connections, but are bulky. The Kelvin Clips that come with the Tonghui LCR fixture are smaller and also have contact ridges.Wouldn't say the simple LCR model is "flawed", more "limited" tho. Getting good model agreement over this frequency range isn't trivial as many think, and you well know, takes some effort to create and fit the model.Your resistor model as shown by the deviation, shows quite good results. If a capacitor model can achieve similar results this will be very beneficial. However, solving the equality magnitude equations between the resistor and capacitors models we mentioned earlier will be a good PhD dissertation for some young grad student interested in network theoryBest

author: Jacques
author_rank: Contributor
timestamp: July 04, 2025, 04:46:42 pm
content: Quote from: EC8010 on July 03, 2025, 12:05:46 pmUsing BMF resistors at audio frequencies can be a bit tricky. To quote from an article by Bruce Hofer (of Audio Precision fame): "My recent experiments (which are also corroborated by another individual) show that some metal foil resistors with exceptionally low TCR behave as if |Z(ω)| >> θR, thus contributing higher modulation distortion than a thin film resistor with a larger TCR under identical conditions."High-quality thin-film SMT resistors can contribute less than -140 dB to THD at audio frequencies (measured some years ago using custom fixed-frequency sinewave generators and notch filters). Do watch out for thermal modulation effects with the smaller footprint ones.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 04, 2025, 05:16:55 pm
content: @mawyatt: That very small standard error is a bit misleading. It was calculated over the entire tested frequency range as part of the least squares fit. But because the resistor is resistive over much of the range, you get a very small standard error. I'll tweak it to calculate standard error over the curved bit of the range to give a better representation of how well the inductive bit has been fitted. Have you a photograph of better Kelvin clips?@Jacques: Yes, I haven't even got to the thermal bits yet, but am keenly aware that the low mass of metal foil resistors makes them vulnerable to changes in self-heating. And most SMD resistors are thick film - I notice you were careful to specify thin film SMD. It's probably worth remembering that metal foil resistors achieve their TCR by treating the foil and ceramic substrate as a system and using the ceramic's thermal coefficient of expansion as a means of controlling foil resistance. But whilst that can work when the system has reached equilibrium, I can easily imagine it not working during changes, simply because the thermal masses are mismatched.

author: mawyatt
author_rank: Super Contributor
timestamp: July 04, 2025, 05:44:11 pm
content: Quote from: EC8010 on July 04, 2025, 05:16:55 pmCheap AliX Kelvin Clip tip (Red) and Tonghui Kelvin Clip. Don't know if they are "better" tho.Best

author: EC8010
author_rank: Frequent Contributor
timestamp: July 04, 2025, 09:15:29 pm
content: A pair of those came with the Hameg; I was hoping you might have found something the same size (or smaller) than the Mueller clips.

author: mawyatt
author_rank: Super Contributor
timestamp: July 04, 2025, 11:20:55 pm
content: The Tonghui clips are a little smaller than the AliX types.Best

author: Hydron
author_rank: Super Contributor
timestamp: July 05, 2025, 09:44:18 am
content: There are some other AliExpress options that are between the tonghui and the very common but kinda long ones. Similar size to the tonghui but slightly different construction.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 15, 2025, 09:54:13 am
content: I ordered one of those 10nF "standard" capacitors. It arrived about a week ago, but it's only today that the temperature has fallen to 23C, so I measured it on in-calibration Hioki IM3536. The Hioki says 9.97978nF whereas the Tonghui 2830 said 10.0013nF, so today's value is 0.22% low. But my RH (as measured by cheapo Maplin meter) is 38%, whereas the RH stated for the Tonghui measurement was 57%. I looked inside my capacitor box and found three very ordinary looking silvered mica capacitors in moulded brown plastic. Most plastics absorb water, so I figure the difference in capacitance is down to the casing applying stress to the internals. My measured value of D was 0.00038 compared to the Tonghui value of 0.00068. Again, that could be down to reduced water load in the capacitor casings.Where does this leave us? I think it means that a standard capacitor needs to be hermetically sealed before measurement to ensure that it has unchanging humidity. It probably also needs to be left for a little while to settle after sealing. There's no reason why a tin plate box could not be soldered up with soldered feed through connectors to keep a capacitance more stable, but those open boxes aren't good enough.At some point, I will put my thinking cap on and tackle the equations needed to transfer a known resistance into an accurate capacitance measurement.

author: chilternview
author_rank: Frequent Contributor
timestamp: July 15, 2025, 11:09:56 am
content: Your silvered mica caps in brown plastic sound the same as mine. They don't look the part of a 'standard' somehow.The Keysight capacitor standards are air dielectric. Not sure how they are constructed e.g. are they sealed in an inert atmosphere. I doubt if I'll ever get to see one as they cost something like £10k for four 1pf-1000pf caps.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 15, 2025, 12:06:28 pm
content: But looks can be deceptive. They're silvered mica and that's the most stable (plastics can creep). Admittedly, the moulded plastic outer isn't the finest and would probably measure poorly in isolation, but I suspect that the real issue is the changing humidity. I see no reason why those capacitors hermetically sealed shouldn't be nice and stable. All that is necessary is to fold up some tin plate into a box and solder it closed. 0.1mm tin plate can be cut with tin snips or even ordinary scissors (doesn't do them much good, mind). Needle file to take off the burrs. Anyone on this forum can solder. The tricky bit is finding the (preferably ceramic) air-tight feed through insulators; fortunately, I bought a bag of five on Sunday at a radio rally...As for air dielectric, one could salvage an air dielectric tuning capacitor from an old radio, set the vanes fully closed, anchor that position, and hermetically seal it. That would certainly be practical for 100pF. Most of the large twin gang are 365pF per gang, but some are 500pF per gang, so 1nF should be possible.

author: mawyatt
author_rank: Super Contributor
timestamp: July 15, 2025, 12:29:54 pm
content: Quote from: EC8010 on July 15, 2025, 09:54:13 amThat's a significant change, wonder if a C0G/NP0 Ceramic Chip SMD Capacitor might be better wrt humidity?Best

author: mawyatt
author_rank: Super Contributor
timestamp: July 15, 2025, 01:03:34 pm
content: Here's some things we are playing around with.3D printed end plates and enclosures for direct connect to the LCR BNC connectors. End plates and center "tube" are covered with Cu tape, and size is same as an extruded Al split enclosure so we can use either. Need to cut the Al extruded in half as they are 70mm long, and we are going to use 25 or 35mm lengths for the enclosures where the Reference Component will be directly soldered to the BNC center contacts and "suspended" mechanically by the leads.An "Open" and "Short" enclosure is for Open/Short LCR Reference Calibration. Our present thought is to have 10pF, 100pF, 1000pF, 1nF, 10nF, 100nF and 1uF versions using Mica for the smaller values to 10nF and Polypropylene for the 100nF and 1uF.Will likely do some comparisons with the full 3D printed and Al Extruded enclosure versions.Certainly not close to "Standards" but may suffice for our meager needs!!Anyway, this is where we are heading as time permits.Best

author: EC8010
author_rank: Frequent Contributor
timestamp: July 15, 2025, 01:09:41 pm
content: A capacitor needs to be sealed to prevent water getting into its internals. I would expect the coating on an SMD capacitor to be pretty thin in order to minimise the increase in component size. If the coating is thin, it shouldn't be able to exert much force on the internals. On the other hand, how permeable is it?I didn't think 0.2% discrepancy was very much. I suspect the Tonghui and Hioki are very similar accuracy, so one tester only needed to be out by 0.1% one way and the other by 0.1% in the opposite direction to account for the entire 0.2%. As impecunious researchers say, "Further research is needed"...Those 3D printed boxes look hopeful. Bear in mind that although the foil is nice and conductive touching another foil the day it was done, that contact will degrade. But it's easy to run a fillet of solder along joints. Self-adhesive copper tape is fiddly stuff, isn't it?Noting your later comments, I'll email you.

author: mawyatt
author_rank: Super Contributor
timestamp: July 15, 2025, 01:31:55 pm
content: The 3D boxes will certainly warp with time, temp, humidity and everything else, and the Cu foil is far from ideal.....but this may prove to be satisfactory for cheap in-house capacitive references.The Cu foil is thin and just for E-Field suppression, mainly so local things around don't effect measurements (like hands near DUT), so having a very low contact resistance isn't critical.Anyway the "Open" seems the be working well, can move my hands around the box with no effect. Now on to finishing the "Short", then a Ref Cap.Best

author: EC8010
author_rank: Frequent Contributor
timestamp: July 15, 2025, 01:38:01 pm
content: Although it might look crude, copper foil works just fine. I'm a great fan of self-adhesive copper tape ever since a piece about 1/2" x 3/4" got me through radiated susceptibilty tests. I learned there that a 0.1mm gap is enough to let 600MHz crawl through...

author: Kleinstein
author_rank: Super Contributor
timestamp: July 15, 2025, 04:24:33 pm
content: Quote from: mawyatt on July 15, 2025, 12:29:54 pmWith 2 different meters the difference can be more than just the humidity. With the plastic case the humidity effect can be indirectly by swelling in the plastic case and mechanical stress to the capacitor. This could also effect air capacitors.Not all COG ceramic capacitors are the same. C0G only specifies a low temperature effect, not directly the dielectric. Ideally the ceramic would be no sensitive to humidity and only residual porosity would be an issue. It may be worth testing a few of the C0G brands / types.I have seen quite some difference in the losses at low frequency (10 Hz range). Quite some where comparable to PP and PS types and one (TDK brand) was about a factor of 5 better.

author: mawyatt
author_rank: Super Contributor
timestamp: July 15, 2025, 05:03:48 pm
content: Short completed and tested, not too bad at 8MHz!!!Now on to the test DUT Capacitor fixture!!BestLater edit: After a longer warmup, this is what the TH2830 returned after an Open/Short Cal with these fixtures, no shenanigansBest

author: EC8010
author_rank: Frequent Contributor
timestamp: July 15, 2025, 06:30:14 pm
content: Quote from: Kleinstein on July 15, 2025, 04:24:33 pmI suspect that it is humidity in the casing causing swelling and pressure on the capacitor.I had a nasty feeling C0G referred only to temperature and not the dielectric itself. Low frequency losses sound like differences in imaginary capacitance, which I have measured between plastic dielectrics.In the end, I suspect that useful test capacitors range from 10uF to 10pF, and that the most important are 1uF to 100pF.I have yet to fit a model to the changes in capacitance with frequency; I believe you mentioned a model?@mawyatt: That short looks good. I assume you did full frequency compensation on both.

author: TimFox
author_rank: Super Contributor
timestamp: July 15, 2025, 07:23:37 pm
content: Although the dielectric material itself has some variation with C0G capacitors, I imagine that with the inherently very low dielectric loss, theQof the manufactured capacitor is very sensitive to construction details that affect the parasitic series resistance.In my previous employment, when doing postmortem investigations into circuit failures due to MLCCs, we found that, for a given capacitance, voltage, type, and package, there were different numbers of layers from different manufacturers.

author: mawyatt
author_rank: Super Contributor
timestamp: July 15, 2025, 07:27:48 pm
content: I know the better DMMs use these C0G/NP0 Ceramic SMD types, so what they (brand ?) are using must be good!!I have some C0G/NP0 and they are very stable within our home lab environment here. Don't think there is any type "coating" on these, just the ceramic. Might be worth an experiment as they aren't expensive.Just finished the 1st Ref Cap Fixture and used a old 10nF dipped 1% dipped Mica. A couple years ago it measured 10.0365nF @ 100KHz (that's what's on the plastic bag), within fixture showing 10.0353nF so this is encouraging.(Edit: We just turned on the TH2830 and used the Open Short Fixtures for Cal without warmup, then attached the DUT Cap, it measured 10.0342nF!!!)Altho we did attach the lever arms of the BNCs backwardsToo much of a PITA to reverse, so they are staying that way for nowBest

author: Kleinstein
author_rank: Super Contributor
timestamp: July 15, 2025, 08:55:35 pm
content: I found very low dielectric absorbtion (test with some 1 ms discharge and 50 ms charge / waiting - so faster than the standard DA test, but still relatively low effective frequencies) for TDK brand C0G capacitors (2.2 nF in 0805 size).I forgot about the other 3 brands I tested - I stopped after finding a good one. Even the other ones were about on par with PP when it comes to the loss. So they would probably still be OK as integration capacitor in a DMM.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 15, 2025, 09:10:48 pm
content: Yes, significant dielectric absorption tends to be associated with a high D (or low Q), although I've never seen any explicit relationship. As you say, your test was very fast, but should still be indicative. Looks as though TDK 1nF C0G capacitors would be worth investigation.

author: Hydron
author_rank: Super Contributor
timestamp: July 15, 2025, 09:55:13 pm
content: Quote from: EC8010 on July 15, 2025, 12:06:28 pmThe General Radio silver mica caps have quite a bit of effort put into them to keep humidity constant - they have the clamped capacitor stack inside a metal box with a dessicant tube, with tar-like potting compound to seal it all (including passthroughs) from atmosphere. Unfortunately it seems that the compound used can eventually crack and let in air, which is why I removed it all from mine, dried everything with dessicant in a sealed box for a few weeks and then remelted the sealant into the case.Interesting idea RE using radio air capacitors for lower values, sadly the collection of them I had when I was a kid was tossed 20 odd years ago (I don't think by me), along with a lot of other old-school goodies (tubes, switches, nixies) :'(

author: TERRA Operative
author_rank: Super Contributor
timestamp: July 15, 2025, 11:58:36 pm
content: I wonder how hard it would be to get a bunch of metal plates cut at one of the Chinese PCB fab houses that also do all the machining services to construct some fixed air capacitors, with a trimmer capacitor attached to pull it into spec?Would be interesting to come up with some designs for the various values (up to the limit of capacitance of a reasonable value for an workable physical size air capacitor) and design the mounting arrangement of the plates so thermal expansion doesn't have too much of an effect.I've been idly thinking about it for a little while, I think it would be doable to come up with something that can go in some Takachi/Hammond/etc aluminium enclosures. I know Takachi have IP rated enclosures with a rubber seal, I assume Hammond would have something similar.

author: TimFox
author_rank: Super Contributor
timestamp: July 16, 2025, 12:58:08 am
content: The General Radio air-dielectric standard fixed capacitors used special internal hardware to maintain the plate spacing against temperature variations.Specific glass parts and metal (Invar?) pillars, if I remember correctly.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 16, 2025, 08:15:29 am
content: Interesting thoughts; I had not considered the possibility of making an air dielectric capacitor from scratch. I very much doubt one would need to go to the lengths of needing invar, but one might usefully balance the thermal expansion of two materials in the way that gridiron pendulums combined brass and steel to keep their bob at the same position.

author: mawyatt
author_rank: Super Contributor
timestamp: July 16, 2025, 03:14:45 pm
content: 3D fixture seems to work well with 10pF Molded Mica. Agreement between IM3536 and TH2830 at 100KHz 10.0213pF and 10.0228pF respectively and we get 9.9993pF with Q of 1110 @ 1MHz.Think we'll order some more BNCs and create a few more 3D Reference Component LCR Meter enclosures.Best

author: Perrold
author_rank: Contributor
timestamp: July 16, 2025, 09:52:58 pm
content: Capacitor second and third order effects are a complex and frustrating rabbit hole. I've mostly dived into the topic from the perspective of what's best for an oscillator or general RF use but the same issues appear. Taming one set of problems tends to reveal the next set. Attached is a GR article on their air dielectric standard capacitors. This is not something I would want to replicate, pursuing it is reserved for the suitably masochistic types. A gridiron type construction is seen with some old variable capacitors where the stator is copper plated steel and the rotor is aluminum or brass. Far cry from invar capacitors and invar variable capacitors, which do exist and can be found on the surplus market relatively easily if one looks out for them.Silver mica caps are nice but watch out for a host of issues with old or surplus caps. Just because a cap shows the right capacitance does not mean it is fully healthy. Excessive loss that is just low enough to not notice immediately, capacitance fluctuations that vary by discrete jumps, and capacitors that are a fraction of the marked value until being soldered in place are just a few examples. Variation from unit to unit in the same batch can be considerable. The situation with C0G dielectrics can be even more frustrating. Easy +/-20% Q variation in the same lot. The Q of C0G caps in the same product family can vary by an order of magnitude depending on the capacitance. This suggests that the actual ceramic used is different. The Q of C0G capacitors of the same value can vary by a factor of a few or more across product families.Humidity effects can be downright evil. The sensitivity to humidity for air dielectric caps is mild, about 2ppm per %RH per that GR document. Great, trivial. Now seal that capacitor in a box. The amount of water is now constant and the %RH varies ~10% per C. Effective tempco is now 20ppm on top of the actual capacitor tempco. Short of a hermetically sealed enclosure that is soldered shut, has feedthroughs, and is bone dry it's an exercise in futility. If the enclosure is not hermetically sealed then the time constant due to a small opening can be on the order of days and with gaskets and such it can be on the order of months.I'd be curious to see how a vacuum capacitor behaves in a metrology application. Only copper and glass or ceramic tempco to deal with. Full immunity against humidity effects, aging, and (sensible) pressure variations. No meaningful voltage coefficient. The loss is effectively nonexistent as well, only minor resistive losses and the minor loss due to the capacitance from the housing dielectric which should be a small overall contribution with an already fairly high Q of the base material to begin with.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 17, 2025, 06:21:53 am
content: Perrold: Thank you for that; I've previously only stuck my hand in the rabbit hole. Yes, I was aware that the RF people have already encountered many of the problems, so I'd been looking at their solutions. I was contemplating a soldered box with feedthroughs, but I had not considered the effect of temperature on trapped humidity. I shall read the GR paper with interest.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 17, 2025, 08:32:16 am
content: With a vaccum capacitor or other capacitor in a sealed box one can still get an effect of air pressure. Air pressure changes deform the enclusure and this can transfer stress to the capacitor. Especially with the vaccum capacitors expect the capacitance to go up with higher air pressure, as the plate woudl come closer. There is a good chance that the glass of the vacuum capacitors is not especially low loss and with the usually small overall capacitance the parasitic part can be quite a bit.For the humidity effect it should be the absolute humidity that matters, not RH. So the simple argument higher temperature reduces RH looks a bit dubious. There is more the opposite of higher temperature reducing the humidity trapped to surfaces and this way increase the absolute humidity in a sealed enclosure. Anyway if one takes the effort if sealing one could as well add dry gas. A nasty point with humidity effects is that they can be delayed. So no easy correction.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 17, 2025, 09:27:27 am
content: Everything has an effect in the end. But Icancut and fold a tin plate box, solder all along its joints to seal it, and solder feed through connectors into it. Not a lot I can do about the dryness or otherwise of the air inside when I seal it, although I could dry a dessicant bag in an oven and pop that in just before sealing. It's really a case of doing everything that is practical.

author: chilternview
author_rank: Frequent Contributor
timestamp: July 17, 2025, 11:26:59 am
content: Maybe Dave could do a teardown of one of the Keysight air capacitors? I guess that'd be unlikely, though...Meanwhile I've been trying out C-t measurements using a HP4280A. Basically pulsing the capacitor to 100v then measuring C at regular intervals. So far with the internal pulse gen there has been no change over time when measuring with 50mS intervals. To get shorter intervals (down to 10uS) I need to rig up an external 8112A pulse generator.

author: Hydron
author_rank: Super Contributor
timestamp: July 17, 2025, 12:33:22 pm
content: I've got a selection (4nF - 100nF) of old soviet SSG Silver Mica caps on the way from Ukraine - these are hermetically sealed so humidity shouldn't be an issue (as with intact GenRad units). See some other eevblog tests on them here:https://www.eevblog.com/forum/metrology/(ask)-standard-capacitor/msg899385/#msg899385I may end up sacrificing one for science to see what the construction is like - they only range from $2-$10 each (I wish I'd gotten an extra of one of the cheaper values now that I think about it!)EC8010 - will be in touch once they arrive, these are much more amenable to risking in the post than the genrad units!

author: mawyatt
author_rank: Super Contributor
timestamp: July 17, 2025, 03:26:39 pm
content: What sort of "Q" do these Soviet Silver Mica caps show?We have a surplus molded Sangamo 1nF Silver Mica that's showing a Q of over 5000 at 100KHz (-89.989 degrees), and ~ 10,000 at 1MHz (-89.994 degrees). We've made this measurement a couple days now with multiple Open/Short Cals (and LCR Meter Power Up/Downs). Shouldn't be measurement result, altho the TH2830 shows only 1100 at 100KHz, but suspect the IM3536 is correct as it has a lower Z ranges, thus capable of correctly interpreting a high "Q" component like this Molded Mica with better resolution.We utilized the fixtures shown above for the Open, Short and DUT measurements.Best

author: mawyatt
author_rank: Super Contributor
timestamp: July 21, 2025, 02:21:21 pm
content: We've created a few of these 3D printed capacitor fixtures hosting the direct to LCR BNCs with Cu foil lined interiors.Values are 10pF, 100pF, 1nF and 10nF Silver Mica types, and 0.1uF and 1uF Polyproplyene types.We need another 0.1uF PP type as the ones we have are slightly unstable and likely not PP (like all these caps they were from surplus). Some are showing exceptionally low Dissipation, for example the 10pF, 100pF and 1nF Silver Mica molded case show 0.00094, 0.00018 and 0.00015 respectively @ 1MHz ,and the large 1uF PP 0.00005 @ 1KHz!!!Anyway, certainly not reference material but initial results are encouraging and will be interesting to see how these hold up in the future!!Best

author: TimFox
author_rank: Super Contributor
timestamp: July 21, 2025, 02:52:20 pm
content: Quote from: mawyatt on July 17, 2025, 03:26:39 pmThose molded mica capacitors were called "postage-stamp" micas.

author: TimFox
author_rank: Super Contributor
timestamp: July 21, 2025, 03:03:13 pm
content: With respect to loss in PP capacitors:About 10 years ago, I attended an IEEE pulse-power meeting in Chicago.(Cool stuff: some of it is designed to generate a single pulse by exploding the wiring.)I had an interesting discussion with an engineer from SBE (formerly Sprague) about their huge pulse-rated PP capacitors.He said that some of them had such low loss that they needed to use calorimetry to measure it.

author: mawyatt
author_rank: Super Contributor
timestamp: July 21, 2025, 04:37:04 pm
content: These were probably the type that was used in the intense Flash X-Ray setup used for testing special hardware that had to survive and some cases work thru a thermo-nuclear event. They stored the energy that was quickly dumped into the X-Ray tube upon trigger, and every PN junction in every semiconductor in the System Under Test gets turned ON by the intense X-Ray Flash unless within very heavy shielding.We used 3 large junction NPN transistors in 3 axis to detect the "Event", these were wired OR to a large Crow Bar SCR which would dump the Power Supply as fast as possible. The individual circuits had limits on the available PS decoupling to help survive the "Event". All this created a nightmare with the System and Circuit Designs!!!We have a few more PP types, largest value being ~5uF.Best

author: Perrold
author_rank: Contributor
timestamp: July 22, 2025, 04:20:23 am
content: Flash x-ray isfun. Amazing testing and diagnostic tool that can work what otherwise would be perceived as miracles. Impressive peak power and intensity, even with smaller FXR systems. No PP caps in one system that I looked inside of though the PFNs can get very creative. Some designs dispense with lumped components altogether and have what is effectively a spiral transmission line.

author: mawyatt
author_rank: Super Contributor
timestamp: July 22, 2025, 08:31:04 pm
content: Don't know if we would refer to Flash X-Ray as "fun", more like we didn't want to be anywhere around that lead lined room when they triggered the Flash!!Same for the Explosive Decompression Test, but the campus did have an Alarm and Count Down for that!!Best

author: EC8010
author_rank: Frequent Contributor
timestamp: July 23, 2025, 11:31:25 am
content: Some 11n 0.5% silvered mica capacitors have just arrived and appear to be very low loss. Remembering that muscovite (from Moscow) is considered to be the best electrical mica, it would make sense for the best mica to be retained and only the poorer stuff exported. Date code is April 1991, so they just qualify as being Soviet. IM3536 is being warmed up prior to open-circuit calibration before an accurate assessment of D is made. Series inductance is unexpectedly high at 39nH. Interestingly, they are in hermetically sealed steel cans, so they shouldn't be sensitive to changes in humidity.

author: mawyatt
author_rank: Super Contributor
timestamp: July 23, 2025, 01:10:27 pm
content: Quote from: EC8010 on July 23, 2025, 11:31:25 amWill be interesting to see what you find. 39nH would indicate a long current path thru the cap, 30~40mm, and a series resonance of ~7.6MHz!!Best

author: gamalot
author_rank: Super Contributor
timestamp: July 23, 2025, 02:06:19 pm
content: Quote from: TimFox on June 15, 2025, 03:04:32 pmIt is not very difficult for an LCR meter to measure Q values greater than 1000, and even my old cheap second-hand one can do it without any problem.

author: TimFox
author_rank: Super Contributor
timestamp: July 23, 2025, 02:13:43 pm
content: Quote from: gamalot on July 23, 2025, 02:06:19 pmYes, but you need careful connections. For my purposes, knowing thatQ> 1000 suffices, since the rest of the circuit will dominate the totalQ. However, an accurate measurement of very highQis difficult.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 23, 2025, 02:19:31 pm
content: Letting the tester warm up properly and doing open and short circuit correction before measurement enabled better data. Series inductance now looks to be 36nH, so the resonance isn't quite within range of the Hioki. 36nH could be about 40mm, so 20mm from each Kelvin contact point point to the capacitor within the steel case. That seems an entirely reasonable length.The discrepancy between model and measurement is interesting because it suggests that this silvered mica capacitor is essentially a pure capacitance to 100kHz. Although the model I fitted allowed for shunt resistance across the capacitance, the least squares fit didn't change it from the initial value I entered of 400M.Apropos TimFox's comment, I am increasingly finding that the contact provided by the Mueller Kelvin clips is the limiting factor.

author: gamalot
author_rank: Super Contributor
timestamp: July 23, 2025, 02:23:53 pm
content: Quote from: TimFox on July 23, 2025, 02:13:43 pmYes I totally agree, I carefully polished the two thin copper wires before measuring, otherwise the contact resistance would have a big impact.

author: mawyatt
author_rank: Super Contributor
timestamp: July 23, 2025, 03:29:35 pm
content: The uncertainty in DUT contact impedance is why we are using the direct BNC connections to the LCR Meter shown above. Here the DUT is soldered directly to the BNC fixture connectors which plugs directly into the LCR Meter BNCs eliminating any additional wiring or extra electrical length.We have an exceptionally good Polypropylene 1uF (pair) that consistently shows a Dissipation factor of 0.00005 or a Q of 20,000!! We have measured this multiple times with the direct BNC connection 3D printed fixture with same results, and have another 1uF cap, same type, that also shows similar level of performance. This equates to a series loss of just a few mΩ, so extreme care must be exercised in measurements to get repeatable results.Our TH2830 can't measure this low a dissipation factor tho, consistently showing D of 0.00017, whereas the IM3536 consistently shows 0.00005. Of course the IM3536 has the better dynamic range but costs ~5X the TH2830!Best

author: gamalot
author_rank: Super Contributor
timestamp: July 23, 2025, 03:54:40 pm
content: Quote from: mawyatt on July 23, 2025, 03:29:35 pmYour 3D printed fixtures are impressive, and I'm curious about how much they cost. I bought an LCR extension cable on Taobao that came with two small aluminum boxes for 190 RMB (about $27 USD).

author: mawyatt
author_rank: Super Contributor
timestamp: July 23, 2025, 04:03:50 pm
content: Quote from: gamalot on July 23, 2025, 03:54:40 pmThe 3D printing didn't cost anything other than the filament cost, so <$2 each. The BNCs were about $2~3 each, and the Cu tape probably another couple $. Also needed to 3D print the 4 BNC lever arms.Best

author: gamalot
author_rank: Super Contributor
timestamp: July 23, 2025, 04:40:59 pm
content: Quote from: mawyatt on July 23, 2025, 04:03:50 pmAlmost the same cost. I would probably go with an aluminum box and add a 3D printed jacket on it to give it a more customized look.

author: Hydron
author_rank: Super Contributor
timestamp: July 24, 2025, 01:50:26 pm
content: Quote from: EC8010 on July 23, 2025, 11:31:25 amCan you share a pic of what you received? I have some silver mica caps on order from Ukraine, but they are taking their time to get here (and of course it's Royal Mail that are pissing about, they've had it sitting in their hands without moving for twice as long as the Ukranian postal service took to do their bit shipping it out of a war zone)

author: EC8010
author_rank: Frequent Contributor
timestamp: July 24, 2025, 02:49:40 pm
content: I ordered mine from:https://www.ebay.co.uk/itm/167631592212?_skw=SSG+mica+capacitor&itmmeta=01K0YE9GNKJ90FWP5TZ0MBXPY3&hash=item27079f1b14:g:ZfsAAeSweB9oatv8&itmprp=enc%3AAQAKAAAA0FkggFvd1GGDu0w3yXCmi1dFbvPwmgKT6rBLNUthXVjODI5T1RMGJxx3VWgWwq%2BRmiCVEkuq80jriYLnzrJOk6juYvUbFnZEDgOAhd3D7eK727iQry7llwPonC72jFxXucHIEcfnE7CO39rMxSA0KaXt4%2BuuWC%2FZmyWBkXkqgdCHHOVvl4mRytLqX8PkFVsaTj39KGg5Fe6VVf1ah41Z3dKdS72u4YPnAmWQ%2FI0mwrsGROmAaJzBLrtJKYm84MvvnEJeqTbBIi1KGxkMLcMxuoU%3D%7Ctkp%3ABk9SR_qKps6HZgThey look exactly as in the vendor's pictures. They were ordered on Sunday morning and arrived on Wednesday, so I've no quarrel with the postage.

author: mawyatt
author_rank: Super Contributor
timestamp: July 24, 2025, 03:01:09 pm
content: Quote from: EC8010 on July 24, 2025, 02:49:40 pmThat's quick service!! Was that standard postal service?What sort of Dissipation Factor or "Q" are you seeing with these?Best

author: EC8010
author_rank: Frequent Contributor
timestamp: July 24, 2025, 03:14:56 pm
content: I thought it was satisfyingly quick too. Standard postage.I can't get a sensible answer for dielectric loss - it's too good. If I do a simple 1kHz C, D measurement after having done short and open circuit calibration, I get a very small negative number for D, and phase angle of fractionally over 90 degrees at low frequencies. That's why I tried fitting a model that included a shunt resistance as well as ESR and ESL, but I wasn't able to get anything there, either. These are far and away the best silvered mica capacitors I've seen. Possibly even the best capacitors I've seen (nothing else has fitted pure capacitance so tightly all the way up to 100kHz).

author: mawyatt
author_rank: Super Contributor
timestamp: July 24, 2025, 04:03:58 pm
content: Yeah that's getting into region where <3ns represents 0.001 degrees and easily within the Open/Short Cal and Fixture uncertainty.We've seen a phase of -89.998 degrees at 1KHz with the 1uF PP types and ventures beyond -90.000 as the test frequency goes up. How does the capacitance hold up as you go from ~100Hz to 1MHz?Anyway, good news is these Soviet Micas are really good it seemsBest

author: TimFox
author_rank: Super Contributor
timestamp: July 24, 2025, 04:13:41 pm
content: Quote from: EC8010 on July 24, 2025, 03:14:56 pmCan you see any change in apparent capacitance at very low frequencies?

author: mawyatt
author_rank: Super Contributor
timestamp: July 24, 2025, 04:40:01 pm
content: With our Molded Micas and Fixtures we see a slight rise in capacitance reading as frequency drops which is consistence with both the IM3536 and TH2830 LCR Meters.Best

author: TimFox
author_rank: Super Contributor
timestamp: July 24, 2025, 04:49:30 pm
content: What, roughly, is the frequency where the capacitance change becomes noticeable?

author: Hydron
author_rank: Super Contributor
timestamp: July 24, 2025, 05:00:47 pm
content: Ah right - I had that seller on my list too but got caps from elsewhere to get a bigger range of values. I have a few of the exact same type ("SSG-1") coming in 10nF and 4.4nF values, plus some 100/99.5nF "SSG-2" capacitors that appear to be the same style, just in a physically larger can.Good to hear that they measure well, hopefully mine are similar (they are used rather than new).RE postage - pretty normal to get next working day via the postal service in the UK, the distances are much less than in the US and it's practical to do via land transport other than from the most far flung areas. Reliability has been a bit hit or miss since covid though!My issue is that the package is sitting in a warehouse at an airport in the UK somewhere and isn't properly in the postal system yet (though it looks like it should have cleared customs at least) - Ukrainian post took an impressive <2 days to get it out of the country once received (by road/rail - no commercial aviation right now!) but it's been waiting in the UK for nearly 4 days at this point with no progress, which is rather frustrating (would have totally understood a delay on the Ukrainian end of course given the situation there)!

author: EC8010
author_rank: Frequent Contributor
timestamp: July 24, 2025, 05:51:55 pm
content: Quote from: TimFox on July 24, 2025, 04:49:30 pmI've seen that too in my lossy capacitor tests and it's usually below about 300Hz. I've measured quite a few lossy capacitances around the 5pF mark and needed a series CR network across the main capacitor to get a reasonable fit. The discrepancy graph in my earlier post appears to show a different form of dielectric loss above 100kHz.

author: TimFox
author_rank: Super Contributor
timestamp: July 24, 2025, 08:31:42 pm
content: The old General Radio decade boxes were available with mica or polystyrene capacitors.Both have highQ.G R noted the better tempco of mica, but the increase in capacitance at low frequency. Did that relate somehow to the water of crystallization in crystalline mica?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 24, 2025, 09:13:23 pm
content: Water could contribute to the dielectric losses. However there can be other impurities that can contribute. Mica is a natural material and can thus vary by source.

author: d-el
author_rank: Regular Contributor
timestamp: July 24, 2025, 09:45:03 pm
content: I have two LCR meter. HP 4285A (75kHz - 30MHz) and Keysight 4980AL (20Hz - 300kHz).SMD fixture crafted for Hioki axial fixture. It is quite convenient to measure components of size 0402.In search of standards of inductance and capacitance I look at old Gen Rad standards.Some photos:Keysight 4980AL have inside configurable DC bias, 1.5V and 2V.This allows to measure polar electrolytic aluminum and tantalum capacitors.But for the future, I will make or buy an adapter for external DC Bias. This would be useful for measuring the capacitance versus voltage dependence for ceramic capacitors. Since the devices are connected to the central server via GPIB, it will not be difficult to script and organize automatic measurement.P.S. Tell me why the image is blurry in the preview.

author: TimFox
author_rank: Super Contributor
timestamp: July 24, 2025, 09:56:48 pm
content: Quote from: Kleinstein on July 24, 2025, 09:13:23 pmI’m not referring to dielectric loss, but a change in dielectric constant, hence capacitance, at low frequencies.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 24, 2025, 10:06:10 pm
content: Quote from: Kleinstein on July 24, 2025, 09:13:23 pmMy limited understanding is that stating "mica" is like stating "glass" - there are lots of different types and it's a mix of an awful lot of elements. Electronic wisdom is that Muscovite mica (from Moscow region) has the lowest losses. I am perfectly happy to accept that water could cause variable dielectric losses as I believe that Muscovite mica contains 4.5% water, and that's probably variable.Thank you TimFox for your comment about dielectric constant; that is consistent with what I have measured. Again, I have a limited understanding of what is going on, but I have been told that the Debye theory predicts a peak in losses at high frequency. Yet I also find that the Debye theory predicts dielectric absorption that can be crudely modelled as a cascade of series CR networks in parallel, which tends to work at low frequencies. Still, for all that, capacitors are far nearer to being perfect reactive components than inductors!@d-el: I hope you can upload better photographs because what you uploaded was tantalising but unreadable; looks like the autofocus didn't work.

author: Hydron
author_rank: Super Contributor
timestamp: July 24, 2025, 10:31:47 pm
content: Quote from: EC8010 on July 24, 2025, 10:06:10 pmThe blurry pics are links to higher res images - click on them to reveal.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 24, 2025, 10:36:37 pm
content: So they are! Thank you for that.

author: mawyatt
author_rank: Super Contributor
timestamp: July 24, 2025, 11:22:11 pm
content: Quote from: d-el on July 24, 2025, 09:45:03 pmClever idea!!Here's a link you may find useful wrt a DC Bias Adapter (see towards the end).https://www.eevblog.com/forum/projects/bias-network-for-lcr-meter/These type "Plunger" fixtures like you've created and the ones in the link above for SMD components produce good results with high Z components, but degrade with lower Z components. The main reason is lack of uniform DUT contact impedance and that the Force and Sense for Kelvin connections are far removed from the DUT.This is why we developed the Split-Kelvin type SMD LCR Fixture here.https://www.eevblog.com/forum/projects/different-type-lcr-smd-fixture/msg5798431/#msg5798431Here the Force and Sense are connected by the DUT end terminals and this technique has shown very good repeatability with very low Z components.Anyway, hope this helps!!Best

author: d-el
author_rank: Regular Contributor
timestamp: July 24, 2025, 11:43:07 pm
content: I'm also looking at the China Made SMD fixture. Has anyone tested this?On ebay it costs about $70

author: mawyatt
author_rank: Super Contributor
timestamp: July 25, 2025, 12:03:45 am
content: Quote from: d-el on July 24, 2025, 11:43:07 pmSure have. Search for:cheap-smd-lcr-fixture-the-good-bad-and-uglyBest

author: d-el
author_rank: Regular Contributor
timestamp: July 25, 2025, 12:36:35 am
content: Quote from: Hydron on July 24, 2025, 05:00:47 pmWhat is the accuracy of SSG-1 and SSG-2 capacitors that you bought? I see that in the local flea market there is SSG-2 with an accuracy of 0.3% for sale (used, ~2.4$).

author: Kleinstein
author_rank: Super Contributor
timestamp: July 25, 2025, 06:54:06 am
content: Quote from: TimFox on July 24, 2025, 09:56:48 pmDielectric loss and frequency dependent capacity are linked via the Kramers-Kronig relation. So a lossy capacitor always has a corresponding capacitance that goes up to lower frequency.Relaxation processes in the dielectic act like an RC series element. If there is only one time constant one gets a broad (about a factor of 10 on the frequency scale) peak in the loss versus frequency and a corresponding step in the capacity. In many cases the time constants are smeared out (a superposition of different relaxation processes) and the loss and capacitance change are over an even longer frequency range, so that no clear peak or steps are visible.

author: d-el
author_rank: Regular Contributor
timestamp: July 25, 2025, 04:48:22 pm
content: I am found SSG-1 and SSG-2 0.3% for the price of a cup of coffee.It turned out that the seller was half an hour away from me.

author: mawyatt
author_rank: Super Contributor
timestamp: July 28, 2025, 02:24:44 pm
content: Nice!!How do these large Micas compare to EC8010, do you see a change in apparent capacitance wrt to change in frequency? How does "D" hold up over frequency?Best

author: Hydron
author_rank: Super Contributor
timestamp: July 28, 2025, 03:14:41 pm
content: Just got my batch (ordered before the others, but held up in customs it seems). See pic below.One of them is well out of spec, might be a candidate for dissection (tbh not unhappy to have a bad one, gives me the excuse). Everything else is well within tolerance, and has Q >10002000 @ 1kHz (limit of the DE-5000). Some of the ones I got are MUCH older than those that others have gotten - (range looks to be late-60s (!!) to late-80s, assuming I'm reading the codes right, they seem to move from month,year to year,month at some point in the 80s).Edit: @mawyatt - over freq the 10n capacitance seemed to be consistant, the 100n went up slightly at 10k and 100kHz, but take that with a big grain of salt given I'm looking at the least significant digit on my DE-5000!

author: TERRA Operative
author_rank: Super Contributor
timestamp: July 28, 2025, 07:28:58 pm
content: Now I am intrigued about buying some of these mica capacitors..What's the difference in SSG-1, SSG-2 and SSG-3 rating?

author: Hydron
author_rank: Super Contributor
timestamp: July 28, 2025, 07:40:46 pm
content: Quote from: TERRA Operative on July 28, 2025, 07:28:58 pmAs far as I can tell, just capacitance range.

author: d-el
author_rank: Regular Contributor
timestamp: July 29, 2025, 12:02:00 am
content: Quote from: mawyatt on July 28, 2025, 02:24:44 pmI wrote a small script that makes a series of measurements and displays a graph. HP4285A connected by GPIB.Expandable image:SSG-1 10000pFSSG-2 100000pF

author: mawyatt
author_rank: Super Contributor
timestamp: July 29, 2025, 12:41:16 am
content: Quote from: d-el on July 29, 2025, 12:02:00 amThink your right Y axis is notDissipation but "Q" which is 1/DEdit: We see you've changed these two plots to Quality from Dissipation after our postYour Mica Capacitors seem to behave the opposite of what we see at frequencies below 100KHz, ours exhibit a rising apparent capacitance as frequency drops. Try looking below 100KHz down to 1KHz (100Hz) maybe the trend will reverse?Best

author: EC8010
author_rank: Frequent Contributor
timestamp: July 29, 2025, 08:01:14 am
content: Unfortunately, since D = Xc/Rp, it's only a useful metric at the conventional 1kHz, allowing different dielectrics to be compared, so plotting D or Q against frequency isn't useful.I have found that the low frequency issue often needs very small capacitances (5pF, or so) to be visible at the frequencies LCR testers use. I suspect that the 10nF capacitors still show the effect, but that it occurs far too low in frequency for any conventional LCR tester to see.

author: Hydron
author_rank: Super Contributor
timestamp: July 29, 2025, 09:04:42 am
content: Quote from: EC8010 on July 29, 2025, 08:01:14 amIs there any sort of definitive guide as to how large the low-freq increase can be (and is it similar within a dielectric type, or varies widely between say different mica capacitors)? While it might take very low frequencies to see for nF range capacitors, this is still problematic for some of their potential uses, e.g. for low-current generation by dv/dt (operation region is well <1Hz). Would polystyrene or other film (teflon, PP) be better in this application?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 29, 2025, 09:29:11 am
content: The change of capacitance with frequency is linked to the dissipation. So the lower the dissipation the less frequency dependent the capacity. The Kramers Kronig relation are however not strictly local, so it is the dissipation over a slightly larger (like 1 decade below/above) frequency range that can have an effect. For the low frequency part (like < 10 kHz) there should be essentially only relaxation type processes and thus the capacitance allways going down with higher frequency. It is only at higher frequencies that the parasitic inductance of the the capacitor also has an effect. Series inductance lowers the impedance and thus increases the measured capacitance, if the DUT model does not include the inductance. The self resonance makes the apperant capacitance to go up with frequency.Another point can also be the calibration of the meter - there ref. capacitors used to adjust the LCR meter also show the frequency dependence and this can lead to frequency dependent errors. For this reason it is important to have standards with little (or well known) parasitics and low loss.Looking at the loss at different frequencies can still make sense. However with very low loss one is at the limits of the instruments and the readings have to be taken with a grain of salt. For a comparisone between different capacitors one should still use the same frequency as later used. There may be differences between dielectrics in how the loss depends on the frequency. A few datasheets give such data for higher frequencies (like > 10 MHz).

author: d-el
author_rank: Regular Contributor
timestamp: July 29, 2025, 11:43:41 am
content: Quote from: mawyatt on July 29, 2025, 12:41:16 amThis meter (HP 4285A) measures at a frequency of 75 kHz. I have a second one, it can measure from 20 Hz. But I have not yet developed an API for remote control via SCPI for it.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 29, 2025, 12:07:08 pm
content: Quote from: Kleinstein on July 29, 2025, 09:29:11 amAgreed. Having found some capacitors having losses near the limits of measurement, i have begun to wonder where my discrepancies/uncertainties are coming from. The tester is new (and therefore well within its calibration interval), and the jig is good (but not perfect). A Soviet silvered mica has measured very well with < 0.1% change in capacitance up to 100kHz. I suspect that the next step is a jig where the capacitor has soldered contacts; I can tolerate a little more inductance and ESR because they are accounted for in my model. I am beginning to think that reference capacitors are useful not so much for calibrating an instrument but for periodic checking that it has not suddenly changed. I suspect that a calibration that transfers impedance from a known accurate resistance to the impedance of an unknown capacitor at a known frequency is the way to go.

author: EC8010
author_rank: Frequent Contributor
timestamp: July 29, 2025, 12:19:59 pm
content: Quote from: Hydron on July 29, 2025, 09:04:42 amNot as far as I know. I have seen it in <5pF mica and in polyethylene terepthalate (polyester). Until I measured the Soviet silvered mica last week, I would have said that silvered mica was a bit lossy (better than polyester, but not as good as polystyrene). However, if you look up the composition of mica, you immediately see that stating "mica" is as vague as stating "glass"; there are lots of different types. It is widely known that muscovite mica has the lowest electrical losses, but it seems there is large variation even within this type, which shouldn't really be surprising since it is a naturally occurring material. PTFE is known to be the dielectric of choice for sample and hold applications.When you start looking hard at the dielectrics, they all have flaws. Polystyrene softens at 98C but is still squidgy (technical term) at normal temperatures, so its long-term stability of value is questionable. PTFE has a phase change at 19C, so you have to be careful to avoid that temperature because it is piezoelectric and can cause unexpected currents passing through 19C. Finally, you have to remember that all the films have impurities within them and come off the roll and are wound to become capacitors in facilities that are not clean rooms. Winding tension makes a difference, too.

author: mawyatt
author_rank: Super Contributor
timestamp: July 29, 2025, 12:47:31 pm
content: Quote from: EC8010 on July 29, 2025, 12:07:08 pmAgree. We created our "Capacitor Fixtures" for just that purpose (sanity check not ultimate calibration). Quality instruments like your Hioki IM3536 should hold up long term very wellBest

author: Kleinstein
author_rank: Super Contributor
timestamp: July 29, 2025, 12:51:15 pm
content: The film capacitors have the problem of possible stress from winding / production. The polymer materials can hardly withstand stress long time and will more or less fast creep to reduce the stress. So long term stability can be difficult.Many of the polymers need some catalyst / starting agent in production that is often still present. So not all films are the same.

author: mawyatt
author_rank: Super Contributor
timestamp: July 29, 2025, 01:07:38 pm
content: Quote from: EC8010 on July 29, 2025, 12:19:59 pmGood point about "Mica" being a generic term!!Was not aware of the PTFE 19C phase change!!In the past we've placed PP as just a slightly better overall cap than Mylar but nothing special, our HV Physically Large 1uF PP pair have changed that view (both have Qs of over 20,000 @ 1KHz)!! Evidently certain PolyPropylene capacitors may exhibit extremely low dissipation factors (high Q) and maintain a stable capacitance at lower frequencies (<100kHz), altho not sure how good the TC is as we haven't looked into that.Best

author: EC8010
author_rank: Frequent Contributor
timestamp: July 29, 2025, 02:53:39 pm
content: Quote from: Kleinstein on July 29, 2025, 12:51:15 pmIndeed, they aren't. I have some TDK 2.2uF 450V capacitors that are surprisingly small for their CV product, implying that the internal field strength must be higher. I expected them to have poorer leakage because of the thinner film, but they measure very well, so I conclude that their film must have reduced impurities compared to most. Thank you for the catalyst/seed comment.

author: mawyatt
author_rank: Super Contributor
timestamp: July 30, 2025, 12:54:22 pm
content: What sort of Q or D do you find with these TDK 2.2uF caps, are they PP?Best

author: mawyatt
author_rank: Super Contributor
timestamp: July 30, 2025, 02:12:31 pm
content: We've been considering making a small "Capacitor Kit" available to folks with the select Mica and PolyPropylene Capacitors mentioned above with our 3D type fixtures. These would include local in-house measurements with our TH2830 and/or IM3536 in the interest of "seeing" what other folks find, so not Metrology grade or NIST traceable measurements.Having just checked with our local UPS Store and USPS over-seas shipping is $50~100, whereas within US shipping is $15~25.Contact us by PM if interested, if we reach critical mass we may move forward with this.Best

author: EC8010
author_rank: Frequent Contributor
timestamp: July 30, 2025, 03:02:18 pm
content: Quote from: mawyatt on July 30, 2025, 12:54:22 pmThey are indeed polypropylene. I've just popped one into the (cold) IM3536 and it says 2.20874uF and D = 0.00008. Yes, four noughts eight!

author: Hydron
author_rank: Super Contributor
timestamp: July 30, 2025, 05:51:33 pm
content: See results from my 9.3nF (meant to be 10nF) teardown:The case is held together with solder, feedthroughs are hollow and are sealed with solder at the top too (lead seen in the pics goes right into the tab on top. Capacitor module itself is potted in wax, with a heavy paper folded cover between it and the case (not shown in the "carnage" pic sorry!).mawyatt - yep it does have a fair bit of lead length internally, as you surmisedGood chance that I'll be stateside in early September - if so I will look into whether I can help facilitate a UK/US exchange of capacitors for testing without international postage costs.

author: Gyro
author_rank: Super Contributor
timestamp: July 30, 2025, 08:59:12 pm
content: Many thanks for the teardown, Hydron.I purchased four 50nF SSG1 0.3% caps a few years ago. On arrival, two were fractionally low and two fractionally high. It turned out that, by pure chance, I was able to combine them into two 100nF pairs that are closer in value than my ability to resolve and presumably rather better than 0.3%. Aside from a closely measured and marked 100nF Polystyrene cap that I acquired, I am the proverbial 'man with two clocks'. I can say though that the 'two clocks' still compare perfectly.In hindsight, I should have purchased more (they used to bereallycheap*), I've been wondering about internal construction ever since (which looks excellent, even after 'disassembly'!).I did buy a bunch of k71-7 500nF 0.5% rectangular Polystyrene caps though which I still need to characterize. They seem to match well though and all appear well within spec. (based on variation).Edit:*It's the highest values in each type that seem to disappear most quickly.

author: Hydron
author_rank: Super Contributor
timestamp: July 30, 2025, 09:11:02 pm
content: Yeah I suspect the price went up due to audiofoolery folks dreaming up some absolute bullshit about them (when I tried to find info about the teflon caps I ran into pages of absolute fucking tripe being spewed about "how the different caps sounded", SNR of the internet on the subject was basically 0). Still pretty affordable if they turn out to be in "reference standard" quality territory though, and the seller I got mine from combined shipping which dropped the price quite a bit.Am interested in how stable the Polystyrene ones are vs the SSR Mica, and what you're using to characterise them.

author: Gyro
author_rank: Super Contributor
timestamp: July 30, 2025, 09:28:22 pm
content: Yes, audiophoolery around these things is a pain! I just looked on ebay and only found a couple of hits for 50nF (I think the highest available value for SSG-1), one out of stock, and the others £8 each and looking very battered. World events have, of course, had an effect, both availability and postage.I'm not particularly well off in terms of high resolution or high accuracy capacitance measurement, hence the wish to establish some 'standards'. I do most of my comparisons by homebrew bridge measurement. The dissipation factor of the Polystyrenes is well below what I can resolve, but I can do comparative temperature runs [and hopefully long term Mica vs Polystyrene comparison]. Edit: From experience of other former Soviet parts I would suggest the buy now, characterize later approach though (I don't see any 500nF listed now).

author: TERRA Operative
author_rank: Super Contributor
timestamp: July 31, 2025, 11:22:55 am
content: I just placed an order for two 100,000pf and two 10,000pf 0.3% capacitors from the Ukranian seller on ebay.I have a feeling they will read better than my test gear can resolve... (I have in working order a 4263B, a 4276A, and the usual DER-EE DE-5000)Do these mica caps come in 1000pF and lower sizes?

author: Hydron
author_rank: Super Contributor
timestamp: July 31, 2025, 11:34:02 am
content: I have seen 970pF from one seller, nothing else close to 1000pF though. I assume 1000pF are or at least were available at some point.

author: d-el
author_rank: Regular Contributor
timestamp: July 31, 2025, 12:16:34 pm
content: I can send you new SSG-1 10000pF for free. I can even measure its parameters for fun.

author: d-el
author_rank: Regular Contributor
timestamp: August 09, 2025, 04:12:16 pm
content: Quote from: Hydron on July 31, 2025, 11:34:02 amI collected these capacitors. I also want to find 150pF and will send them to you.

author: EC8010
author_rank: Frequent Contributor
timestamp: August 10, 2025, 10:24:39 am
content: I'm in the middle of measuring Soviet silvered mica capacitors just like the ones in the previous post inside my screened measuring jig using Mueller Kelvin clips to connect to the DUT. The Hioki IM3536 had been switched on for three hours before being open and short-circuit compensated, and the Kelvin clips had been cleaned by dragging a piece of paper through their (gold-plated) jaws. I had previously noticed that D started negative when a low-loss capacitor was first connected, so I set up a logging experiment to interrogate the Hioki IM3536 every half second, set it running and connected the capacitor. The following plots discard the nonsense data before and whilst I made the connection, then the data at t = 0 because log graphs don't like 0, and the t = 0.5s data to avoid an awkward scale. We see that the measurement takes time to reach stability. I find that if I have left a capacitor in place overnight and switch the Hioki on, I immediately get the final value of D, so it's not to do with the Hioki. I suspect what I'm seeing is mechanical relaxation. Whatever it is, it takes time to achieve stability. Presumably, a capacitor soldered into a fixed jig is instantly stable?

author: Hydron
author_rank: Super Contributor
timestamp: August 10, 2025, 11:40:24 am
content: Huh, that's a non-insignificant change. Certainly suggests doing what mawyatt did and making some little boxes up for use as standards (3d printing should allow a nice snug fitting pocket for the cap to sit in).d-el - impressive work, was not expecting such a haul, appreciate the effort! I also see you were able to get the missing 1000pF "standard" value locally.

author: EC8010
author_rank: Frequent Contributor
timestamp: August 10, 2025, 02:20:07 pm
content: It's not trivial, is it? But I don't think you want a snug-fitting pocket, more a pocket lined with foam that can support the capacitor without imposing mechanical stress, then flexible leads to the four-wire terminals.

author: mawyatt
author_rank: Super Contributor
timestamp: August 10, 2025, 03:00:37 pm
content: Assuming this isn't the Hioki contributions (which is valid IMO), then is this the DUT capacitor or the fixture, or both? If this type behavior is showing with different values and type DUT capacitors, the fixture is suspect. My guess it's more with the Kelvin Clips than the mechanical aspects of the fixture, but thats just a guess!! Having the "D" go from negative thru zero to positive seems to hint at the Zero Calibration which could be attributed to the Kelvin Clips??Directly connecting (soldering) the DUT to the BNC connectors should eliminate any Kelvin or other type clip connection uncertainly. The 3D printed fixture has potential issues tho, being plastic with moisture absorption and temperature deforming effects, as well as aging. None of these are well known to us, but the 4 BNCs provide a stable electrical connection as well as some overall mechanical stability for both the DUT and fixture housing.The 3D fixtures don't weight much, so little flexing stress is placed on the 4 BNC connectors. We designed the fixtures to be easy to print (no supports) with separate front and rear "plates" and a center rectangle "tube". Brass inserts were used to allow 3mm bolts to hold things together. This arrangement also allows relatively easy means for the Cu tape application. We didn't solder things together considering the butt type electrical contacts at the ends were sufficient as this is just a E shield not a H shield.Would be interesting to see how well these 3D fixtures hold up with the Soviet Mica capacitors, they seem to do well with the DUT types we have so farBest

author: mawyatt
author_rank: Super Contributor
timestamp: August 10, 2025, 03:11:50 pm
content: Quote from: EC8010 on August 10, 2025, 02:20:07 pmIf you are considering the 3D printed fixtures, then a solid wire to the outer BNCs provides good mechanical support while "floating" wrt to ambient. A couple smaller solid wires to the inner BNCs for the Sense connections. This was how we mounted the large PP 1uF cap, but it had thick heavy leads that were directly soldered to the outer BNCs to hold the cap without any other mechanical connection, and added some thin solid wire soldered close to the DUT case for the Sense leads.With these Soviet DUTs wouldn't expect using the large terminals for mechanical support would cause issues with a heavy soldered wire, or even a Cu tab, to the BNCs.Anyway, just some random thoughts.Best

author: EC8010
author_rank: Frequent Contributor
timestamp: August 10, 2025, 03:29:45 pm
content: I've looked into it carefully. I am also suspicious of the Kelvin clips. I have every so often seen a negative value of D (implying negative resistance). I was testing various capacitors including a batch of three Soviet PTFE all of the same value. The capacitors had large silver-plated stub terminals that were quite corroded, so I polished them clean with metal polish. I measured D of -0.00014, -0.00014, and -0.00015. That suggests something solid, not an iffy connection.I had also wondered about the S/C calibration and on one attempt, I got rather larger correction values than expected, leading me to clean the Kelvin clips. A little dirt was visible on the cleaning paper. After that, the S/C calibration produced more familiar values.I'm wondering about a piezo-electric effect and mechanical stress because of the fact that leaving a capacitor in the jig overnight and switching the Hioki on immediately gives a stable and sensible value of D, whereas inserting a silvered mica capacitor seems to require 120s or more for stability; the Hioki now has a kitchen timer nearby. Film capacitors do not seem to show this effect nearly as badly as silvered mica, making me wonder about dielectric absorption.The measurement jig is destined to get an internal RTD so that temperature can be logged, and a couple of white LEDs inside so that I can more easily see what I'm doing. After that, those Kelvin clips may have to go, but I really don't want to have to poke a soldering iron in there every time I want to measure something. One possibility is to make another jig for soldered connections, but it's quite a lot of work...Meanwhile, I logged a Vernitron silvered mica capacitor for two hours. The drift in capacitance is not due to temperature, perhaps supporting the mechanical stress hypothesis. The D for the Vernitron silvered micas was nowhere near as good as the Soviets, suggesting poor quality control of incoming material. Never thought I'd praise Soviet quality control! Of course, Vernitron couldn't send naughty employees to the gulag for ten years. Lab work is stopping now because weather forecast says it's going to be hot for the next week...

author: mawyatt
author_rank: Super Contributor
timestamp: August 11, 2025, 07:04:49 pm
content: Wonder if wrapping a shielded mechanical enclosure hosting the DUT around these LCR Meter Fixtures might work?Best

author: EC8010
author_rank: Frequent Contributor
timestamp: August 11, 2025, 09:19:11 pm
content: With care, it ought to be possible to mount it inside a die-cast box, and hinge the lid like a door. The awkward bit is that the fixture would need to be at the bottom of the box, so the box will obcure a lot of the tester. Another thought that occurs is that a suitable biscuit or sweet tin would work just as well, but be a lot lighter. A hinge would soon bend the box, so the lid would have to just come on and off. But it would require earth bonding. Something involving a 4mm metal socket on the lid and a 4mm chassis mounting plug onto the TH fixture would do the trick.

author: d-el
author_rank: Regular Contributor
timestamp: August 19, 2025, 11:38:57 pm
content: Quote from: EC8010 on August 10, 2025, 10:24:39 amI see a similar effect.Precondition:---------------------------Agilent E4980ALFUNC: Cs-DFREQ: 1kHzLEVEL: 2VRANGE: AUTOBIAS: OFFMEAS TIME: MEDAVG:32Ambient temperature: 26°CHumidity: 34%---------------------------Capacity vs time:I also realized that if connect a capacitor to the generator in advance, like, "warm up the capacitor", the transient time is reduced:

author: EC8010
author_rank: Frequent Contributor
timestamp: August 20, 2025, 07:54:06 am
content: Interesting; I assume your LCR tester had been fully warmed up beforehand? Not sure where it takes us, but it's another nail in the coffin of stable capacitances.

author: d-el
author_rank: Regular Contributor
timestamp: August 20, 2025, 12:58:28 pm
content: I warm up my meter for more than 5 hours. The room temperature fluctuated no more than 1 degree Celsius.I have a SSG-1 10000pF that spent a lot of time in the meter. So if you connect it again, the result normalizes after a few seconds. It seems that there is a transient process when the capacitor has been lying for a very long time without signal.