L & C measurements and references - Page 1
Forum section: electronics / general

author: rhb
author_rank: Super Contributor
timestamp: April 26, 2018, 01:00:29 am
content: I have seen very little on L & C measurements and calibration here. What are people doing? I'm sure few people in this group are buying IET capacitor standards on eBay for $15,000. But there may not be many people with an interest in RF.As soon as you start making AC measurements things get a *lot* harder. One need only compare the accuracy specs for any good DMM on AC and DC. And once you get above 1 MHz or so, it gets really hard and becomes VNA territory as you have to deal with self resonance and all sorts of parasitic strays.

author: dl1640
author_rank: Regular Contributor
timestamp: April 26, 2018, 10:32:37 am
content: a LCR meter will do?but that is not chasing ppm

author: TiN
author_rank: Super Contributor
timestamp: April 26, 2018, 10:48:07 am
content: Chasing farad-nuts are using capacitance bridges...

author: rhb
author_rank: Super Contributor
timestamp: April 26, 2018, 01:02:19 pm
content: I'm referring to the problem of being able to calibrate an LCR meter. My interest in metrology is being able to perform calibrations of other equipment. I need a power meter and a noise figure setup and I should be good to go except for calibration.I must plead guilty to having been seduced by the problems of aging, hysteresis and irreducible noise. There is nothing to be done about the latter as it sets the uncertainty. But I think I can do something about aging and hysteresis.My impedance bridge is an old General Radio unit. And I've got a Heathkit impedance bridge my Dad built and a wheatstone bridge he built from scratch. That's likely to be the more interesting of the two as it is likely to have a high precision wirewound pot.Certainly no one is going to make even a 100 ppm capacitance measurement using the setup in the photot.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 26, 2018, 01:16:18 pm
content: I have a General Radio 1615-A bridge system, along with two voltnut friends. Fortunately for me, they have a total of three 1000 pF GR caps. Though long out of cal, everything agrees within maybe 10 ppm. At work we have three Agilent LCR meters that, in theory, are nearly as good. I'm in pretty good agreement with those, but I find them noisy and less certain even with long averaging. They're also long out of cal. That's about the best I can do, since a proper calibration is far out of reach. If you have very good physical metrology you could build a NIST calculable capacitor, but my shop isn't quite that good for the dimensions involved. I do have a few GR inductance standards, and I doubt they could drift much, but ppm level inductance isn't very exciting.

author: rhb
author_rank: Super Contributor
timestamp: April 26, 2018, 01:29:55 pm
content: Mine is a 1650A. I suspect that a good Wien bridge oscillator would significantly improve the accuracy over the internal source.

author: quarks
author_rank: Frequent Contributor
timestamp: April 26, 2018, 02:41:39 pm
content: on my personal wishlist I had a GenRad 1693 RLC Digibridge for a very long time, but I ended up with HM 8118 LCR Bridge (see link below)https://www.rohde-schwarz.com/de/produkt/hm8118-produkt-startseite_63493-44101.htmlit is compared to my other gear not really metrology grade, but nevertheless really good and I am very happy with itfor calibration/reference I use a mix of parts from GenRad, Burster and a set of "Precision Standard Capacitors"

author: precaud
author_rank: Frequent Contributor
timestamp: April 26, 2018, 06:16:04 pm
content: Well the standard depends on frequency range, impedance range, and type of measurement.Some 20 years ago I obtained a near-complete set of GR 1409 standard capacitors, from a Western Electric facility that was closing.All of them had been characterized (by whom and how, I do not know) to 6 significant digits at 100Hz, 1KHz, and 10kHz.Totally fine for 2- or 3-terminal instruments in the audio freq range.Over the years, as I have moved more toward 4-terminal and VNA measurement instruments, I sold the 1409's except for the 100nF one.I have never felt the need to have inductance standards, most LCR instruments don't require them for calibration.For 4-terminal instruments you really need 4-terminal standards, characterized as high in freq as you need.When using a VNA, I find I don't really need L or C standards. Having a short, an open, and a load R that has flat impedance at a value near the range you'll be measuring, works fine. The calibration of the phase response of the VNA then determines its accuracy measuring reactances. For that you need phase standards or generators. The HP 8904A with opt 002 works well below 600kHz. For 1MHz, the HP 16344A Phase Standard.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 26, 2018, 06:20:11 pm
content: I've also got a few 1409s that somebody had measured. They agree well with my borrowed standards and don't drift much. Probably more than adequate for most anybody.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 26, 2018, 10:01:50 pm
content: That AH 2500A needs some TLC. What owner would treat an instrument like that? Broken handles and dirt.To think it contains a capacitance standard worth about as much as a new 3458A or more.

author: PA4TIM
author_rank: Super Contributor
timestamp: April 27, 2018, 07:21:28 am
content: Here an other Farrad-nut.My "standard" is a 1620.http://www.pa4tim.nl/?p=3398Henry Hall recognized it as being the bridge from there standards lab. Besides that a GR1424A, two Philips adjustable (0-1000pF and 0-100pF), a HP-4440B and a Hatfield model 2977. I have a box with a bunch of caps in the pF and nF range I measured very carefull with the 1620.Also a couple of LCR meters: HP-4260, HP-4261(my daily driver, ex-cal-lab with cal report), IET DE-5000, GR-1608, GR-1650, ESI-277, ESI-250, WK CT-492, Tek-130, Peak LCR meter and a Hameg 8018I regret not to have a GR digibridge but on the other hand, the 4261 works great and fits above the bench. The 4261 is a lot faster as the DE-5000, for me important. Two years ago I repaired it for the cal-lab that was my first customer and the one that stimulated me to start a repair company. I really liked that meter. A few months ago he bought a new more advanced LCR meter and I bought it from him.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: April 28, 2018, 08:12:32 pm
content: If I may, what size, style and value capacitors?same question for inductors.A few calibrated samples and a LC bridge (Heathkit for example) will work wonders.If you want digits, go to eBay with $12 dollars and search "Mega328 Component Tester Transistor Diode Capacitance ESR Meter Inductance".These are amazing. Not as accurate perhaps for a Nut, but amazing none the less. Hook anything to it, it can usually tell you if it's a resistor or a transistor and if the later, it shows which is the base-emitter-collector.If you want to do testing at RF frequencies, check out Q Meters.If you want to send me a handful of typical values, I'll calibrate them for you and send them back.George Dowell

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 28, 2018, 09:45:40 pm
content: Just an interesting side note. The GR 1657 (and probably others in the series, brilliantly designed by Henry Hall I should add) has no provision for calibration at all. It's accuracy is based on precision resistors and the crystal based timing.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: April 28, 2018, 09:56:39 pm
content: Wow Fred, you have a bunch of capacitor testers. Have you tested the capacitor in your Simpson 260?You can without taking the back off.Quiz- where is it?Geo>K0FF

author: rhb
author_rank: Super Contributor
timestamp: April 28, 2018, 10:30:28 pm
content: Would 70 year old air core inductors on ceramic forms be good candidates for reference inductors? I've got a bunch of TU-10-B tuning units. Or perhaps wind new coils and anneal them. I'm thinking about this in the context of the calibration club. I've got full metal working facilities and some old high grade components. So making some itinerant references seems like a worthwhile project.I found a couple of very nice NOS roller inductors today, so I'm thinking an inductance bridge would be a good project after I put the 1.5 KVA autotransformer into a somewhat safer enclosure. All the connections are bare metal binding posts!BTW what is the accuracy limitation of a GR 1650? The components or the THD of the oscillator? I'm wondering it it would be worth building one of the designs in "Max Wien, Mr. Hewlett and a Rainy Sunday Afternoon" by Jim Williams to replace the original oscillator.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: April 29, 2018, 12:11:18 am
content: "Would 70 year old air core inductors on ceramic forms be good candidates for reference inductors?"In my opinion yes, absolutely, if they pass the visual and smell test.George Dowell

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: April 29, 2018, 12:25:28 am
content: Basic accuracy for the 1650A is: ±1% for RCL and ±5% for D and 1/Q. It is a middle accuracy instrument, lab grade is considered ±0.1% for RCL or better. The ESI 707 Capacitance bridge is ±0.01%.

author: rhb
author_rank: Super Contributor
timestamp: April 29, 2018, 02:34:11 am
content: The inductors have been cycled from 10 F to 130 F for 56 years, so they ought to be pretty stable. I think I'll look into how IET packages their references.My question about the 1650 was not about what the error was. I already knew it was a 1% instrument. The question was what is the dominant source of error. My spectrum analyzer only goes to 9 KHz, So more detailed work would require calibrating a sound card.Given the quality of the hardware, I think augmenting it with a sound card and some software might improve the accuracy a good deal.

author: precaud
author_rank: Frequent Contributor
timestamp: April 29, 2018, 02:42:47 am
content: Quote from: rhb on April 29, 2018, 02:34:11 amFor D, the main source of error is the accuracy of the taper of the potentiometer in conjunction with the etched labels on the dial. Amazing that they could hold it to 5% over each range, really. I bet Conrad knows more about the pots in the GR bridges.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 29, 2018, 02:52:40 am
content: With enough patience you can get a 1650 about as accurate as you can read the dial. More accurate bridges have either mechanical reduction and/or individual digits, like the 1608.AFAIK, the GR inductors were wound on inert toroids, probably ceramic, then placed in a bed of ground cork to cushion and protect them.On oscillator purity, I don't know how much it matters, since tuned detectors are almost always used. You do need frequency to be accurate since, depending on bridge design, a frequency error will show up as either a value or loss error.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 01, 2018, 02:42:41 am
content: Quote from: PA4TIM on April 27, 2018, 07:21:28 amI brought my HP 4260A to work. The people there say it sounds like a sewing machine!

author: PA4TIM
author_rank: Super Contributor
timestamp: May 01, 2018, 09:15:50 am
content: The GR1608 does that to but it also has the size of a sewing machine. I think the 4260 was at that time a very unique bridge. It was the first cooperation between HP and Yokogawa. It is a "semi-automatic" bridge. You crank the handel. The two lamps under the display tell you the direction and the zero. It is 1% but that is because of the resolution. Today many instruments have to much digits, this one could have handled more digits with ease. Mine is spot-on and with a sharp eye you can estimate the value between digits.I use the 4261 the most because of the speed. I use a IET DE5000 besides that for (among other for higher frequencies (10 and 100kHz) ) My ESI 250DE is set up for Rs measurements of batteries (i have a video about that) and I made a fixture to compensate C or L while measuring Rs or Rp . Thew ESI is a very good and very cute little bridge with a beautiful decade knob made from alu disks.http://www.pa4tim.nl/?p=6012(the battery measure video is on that page too, it is a demo of the bridge and the battery measurement is part of that towards the end of the video.http://www.pa4tim.nl/?p=3550the first staps in developing this test. Some manufacturers use this principle in their best battery analysersAbout DIY C "standard"http://www.pa4tim.nl/?p=5123I thought about selling a sort of cap calibrator to test lcr and DMM's, a box/cabinet with a few values like 1, 10, 100 pF, 1, 10, 100 nF and 1, 10, 100 uF. Or an LCR box. three 10 position switches to switch 10 values per function. So 10x R, 10 x C and some L values because L measurements are very tricky. But I think there are not enough people interested in that. There are two ways. I have a collection values I use most for quick tests. I did not bother about making round values, but I calibrated them careful. So instead of trying to get a spot on 100 pF I use a 89.567 pF (numbers only for the idea) This is as good but much saves costs and time.http://www.pa4tim.nl/?p=2929this were my first experiments way back when I had only one bridge and wanted to measure fFBut I better stop, I get over enthusiast if it is about measuring caps

author: PA4TIM
author_rank: Super Contributor
timestamp: May 01, 2018, 09:21:42 am
content: Quote from: GEOelectronics on April 28, 2018, 09:56:39 pmYeah, I use that as my mother of all standards, just kidding, like the picture of the 260 with the esi. Some people contacted me seriously to tell me the 260 is not suited for calibrating a ESI 1010The cap is between the normal input and the socked that is stated as an output. This is for making AC coupled measurements. But why they state it as output

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 01, 2018, 12:27:57 pm
content: I had a 4260 for a while and it's a nice bridge. I sold it because I'm really a GR collector and it didn't get much use. In hindsight I regret selling it just because it was so handy.

author: ap
author_rank: Frequent Contributor
timestamp: May 01, 2018, 12:58:04 pm
content: There is a document about capacitor calibration and standards on my webpage, seehttps://www.ab-precision.de/documents/(also, in case someone here in this forum is interested in one of the C-standards listed, please contact me through mail for a member discount first)

author: precaud
author_rank: Frequent Contributor
timestamp: May 01, 2018, 03:48:40 pm
content: Quote from: PA4TIM on May 01, 2018, 09:15:50 amTrue, there's almost enough room inside a 1608 to lay out a sleeping bag. But that makes it very serviceable too. And it's all over the 4260 in terms of accuracy... the 1608 is the only passive impedance bridge I've owned and still have. One of a kind. But as Conrad said, the real game-changer was the GR 1657. We bought one for production in 1981, batched and sorted 100's of parts daily with it for 15 years, it only needed servicing once.

author: PA4TIM
author_rank: Super Contributor
timestamp: May 01, 2018, 04:44:42 pm
content: Yes., the 1608 is great in every context. I had to repair mine. The 1M was burned when I got it. Replaced it with advise from Henry (the new resistor was 40 euro, the bridge 50) I replaced all the germanium transistor also. Only thing that was not easy was cleaning the contacts of the decades and replacing the lightbulbs. I wanted to adjust the D dial just a tat but that is very difficult (if I remember well) so I left it like it is. I really love using it with those "back lit" scales.My "standard" is my 1620 with known history, according to Henry Hall who recognized it, it was the bridge from GR's own standards lab until it closed.I use the 4261 most because it is much faster as my IET DE5000 and as accurate. (It was from a cal lab and came with two calibration rapports) I had serviced it two times for them in the past so I knew it was in perfect state.