1%  capacitors to calibrate a meter - Page 1
Forum section: electronics / projects

author: JoeyG
author_rank: Regular Contributor
timestamp: August 24, 2022, 01:23:47 am
content: I'm in Australia looking for some 1% capacitors to calibrate (roughly) a capacitance meter (Electronics Australia Aug 1985)47pF, 4.7pF 4700pF 4.7uF Other values are OK to use.Any suggestions.

author: srb1954
author_rank: Super Contributor
timestamp: August 24, 2022, 03:34:07 am
content: Quote from: JoeyG on August 24, 2022, 01:23:47 amYou can get the smaller values from the usual suppliers Mouser, Digikey etc in mica or polyproplyene dielectric.The 4.7uF 1% capacitor will be quite difficult and might require scouring the usual auction sites to see what is available - look for General Radio (GR) or IET Labs products. 1% or better capacitors up to 1uF, either as single units or in a decade box, are generally reasonably available for up to several hundred $US. Anything over 1uF is going to be exceedingly rare and/or expensive.

author: TimNJ
author_rank: Super Contributor
timestamp: August 24, 2022, 03:41:00 am
content: Do you have access to a good calibrated LCR meter? You can buy a bunch of normal tolerance caps and bin them and choose the caps which are closest to the nominal value you are after.

author: beanflying
author_rank: Super Contributor
timestamp: August 24, 2022, 04:08:33 am
content: Wander over to Clayton and Rockby Electronics or give them a call firsthttps://www.rockby.com.au/index2012.cfmVery very likely they will have some more accurate options available.In particular dipped silver Mica is a good place to starthttps://www.rockby.com.au/searchresSql_12.cfm?select=07&subcode=330Most of the other formally good alternatives like Radio Parts or Jaycar (shudder) will be way less likely. The only others I know that would have something to suit are wholesale suppliers and want to sell you 1000 of each.Other than that Element14, Mouser, Digikey would be the best options and even E14 won't carry stock in Oz.Last option is if you get desperate I am down in western Vic and have a HP/Yokogawa 4440B Capacitance Decade box which is 0.2-1% fitted across the range. So post your toy and supply a return bag and I could hold my tongue at the correct angle and twiddle the sticks

author: Warpspeed
author_rank: Contributor
timestamp: August 24, 2022, 09:21:00 am
content: I don't think super accurate reference capacitors like 4.7pF or even 47pF are even possible.As soon as you connect something to it, or put your hand near it, the capacitance will be changed.As mentioned above, good quality silver mica capacitors can sometimes be had, especially surplus military grade capacitors.A lower cost alternative are 1% polystyrene capacitors which are both temperature stable and accurate.

author: beanflying
author_rank: Super Contributor
timestamp: August 24, 2022, 09:57:34 am
content: Quote from: Warpspeed on August 24, 2022, 09:21:00 amI did a very quick trawl of the Styrene Caps and while most are 10% they did have some 1% listed too in some values. The OP is likely a 10-15 drive if his location is correct to Rockby so well worth asking.

author: CaptDon
author_rank: Super Contributor
timestamp: August 24, 2022, 02:03:41 pm
content: I agree with TimNJ. I was lucky to have some high precision bi-annual calibrated lab gear and a vast inventory of electronic parts used to build our prototypes and so forth. The need to have a drawer with room temperature precision values for my home experimenter lab was important. I grabbed some of the precision meters and went through our inventory to find the most accurate values I could. 1, 10, 100, 1K, 10K, 100K, 1Meg all at .1% or better hand selected. Also 10pf, 100pf, 1000pf, .01uf and .1uf. I also built a super accurate voltage source with low output impedance so I could calibrate measuring devices having either a 10meg or 1meg input impedance. I was very lucky to have access to these meters and parts inventory and I keep those 'calibration standard parts' in a drawer of their own in my parts inventory here at home. I know your situation is different, but you may have some ham radio buddies or electronic prototyping design engineer buddies with an 'after hours' lab key? It pays to network with people and groups with similar interests. I got a lot of very nice damaged or non-functional but indeed repairable laboratory grade equipment from the dumpsters of the companies I worked for. One company even insisted that we 'tinker' at home and allowed us to sign out test equipment to take home and even reimbursed us for magazine subscriptions to QST, 73, Popular Electronics and so forth. Best wishes in your journey!!

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 24, 2022, 05:02:21 pm
content: Quote from: Warpspeed on August 24, 2022, 09:21:00 amSmall value reference caps are in housings with shielded connections. You can have a 1 pF reference cap that's known to 0.01% or better. The large calculable capacitors used by NIST give you a precise change in capacitance of about 0.4 pF, from which all other values are scaled. OTOH, if just dealing with a typical 2-lead component, getting better than a couple percent on 100 pF can be challenging.

author: mawyatt
author_rank: Super Contributor
timestamp: August 24, 2022, 05:27:00 pm
content: Quality (Venkel) chip caps with NP0 or C0G ceramic are a good source for stable small values up to ~1nF. Using a dedicated SMD test fixture with good pre-calibration (open-short) for measurements is a must for highly repeatable results.Best,

author: JoeyG
author_rank: Regular Contributor
timestamp: August 25, 2022, 02:49:43 am
content: Yep - Rocker's is 15min from my place. I might start there

author: Kleinstein
author_rank: Super Contributor
timestamp: August 25, 2022, 07:04:32 am
content: For low tolerance one may have to look at low loss also. Lossy capacitors have a more frequency dependent capacity. In this respect mica capacitors can be a bit tricky as they are usually made for RF use and they are not that low in loss. So they may be spot on at 1 MHz, but could be more than 1 % off at 1 kHz.

author: trobbins
author_rank: Frequent Contributor
timestamp: August 25, 2022, 11:52:26 am
content: Joey, I'm in Endeavour Hills and have a good LCR meter and two decade boxes (100p to 1uF) that have all been cross-compared to better than 1% tolerance. Although the boxes are vintage, one includes 0.25% original tolerance parts, and the other has graded parts by Cambridge Instruments. I also have a 4.7u and 5.6u Philips 344 series polycarb that were measured a few decades ago on lab HP LCR and show less than 0.5% tolerance with my LCR meter now. I have also cross-compared using a soundcard technique that indicates better than 1%, and a switched R-C comparison technique (Mariscotti method). Like beanflying, if you drop over (or post parts over) I can quickly make measurements that should be better than 1% for any parts you have (preferably of a type with known low tempco and ok stability).Ciao, Tim

author: JohanH
author_rank: Frequent Contributor
timestamp: August 25, 2022, 12:18:25 pm
content: This thread reminded me, so I just ordered from Ebay a couple of NOS USSR capacitors:1,000 pF (1 nF) 0.3% SGM3-A Silver Mica10,000 pF (10 nF) 0.5% SGM3-A Silver Mica100,000 pF (100 nF) 0.3% SSG-2 Silver MicaI'm still looking for some NOS USSR polystyrene 0.5% caps.You can get these quite affordably from eastern Europe. And note, no import tax from Ukraine to EU, for the time being!

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2022, 01:56:51 pm
content: The precision capacitors in my older test gear were trimmed by adding low value parallel capacitors. So what I might do, especially for larger values where 1% parts are not available, is make a test circuit for measuring capacitance based on frequency and resistance, and use that to calibrate a capacitor.Note that doing this means selecting the largest capacitor for the lowest temperature coefficient.Quote from: Warpspeed on August 24, 2022, 09:21:00 amFixture capacitance can be calibrated out. Even the capacitance function on my digital multimeter can accurately measure picofarads to 10s of picofarads down to a picofarad.Tektronix gave a detailed procedure for accurately measuring the input capacitance of a 1 megohm oscilloscope input using their capacitance meter. Calibration is interesting since it involves negative capacitance.

author: mawyatt
author_rank: Super Contributor
timestamp: August 25, 2022, 04:08:28 pm
content: Quote from: David Hess on August 25, 2022, 01:56:51 pmWe just did a quick test (8/15) of a new KS34465A and compared to a Tonghui TH2830 Lab Type LCR meter. With a stable fixture, proper "Open Short" calibration on the TH and a "Open" Null on the KS, then using a quality DUT Venkel 0603 C0G 4.7pF cap the KS measured 4.678pF and TH 4.69388pF. This same cap was measured awhile back (5/15) with a new Hioki IM3536 as 4.6885pf.So yes a quality DMM with a stable fixture, proper calibration, and a stable DUT can indeed resolve pF levels.Whats interesting about these measurements is the techniques utilized by the DMM are totally different than that used by a Lab Grade LCR meter, but with proper care and use can yield very good agreement like with a 10nF Polystyrene.....KS 10.0907nF, TH 10.0851nF, IM 10.0860nF.Best,

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2022, 09:09:08 pm
content: Quote from: mawyatt on August 25, 2022, 04:08:28 pmI usually would not rely on my digital multimeter for accurate capacitance measurement, but I wanted to compare the three methods available to me when measuring the capacitance of a coaxial cable. My DE-5000 LCR meter, ESI DA250 impedance bridge, and my digital multimeter all returned the same value which came out to 29.4 picofarads per foot, within a picofarad.

author: mawyatt
author_rank: Super Contributor
timestamp: August 25, 2022, 09:21:50 pm
content: Like you, would not normally rely on a DMM for accurate capacitance measurements, and why we undertook the effort to compare the Keysight KS34465A, Keithley DMM6500 DMMS with the Lab type Tonghui TH2830 and Hioki IM3536 LCR meters. The statistics feature of the DMMs was employed to get a good "average" readings.With a stable fixture and proper initialization the DMMs perform quite well indeed!!Best,

author: beanflying
author_rank: Super Contributor
timestamp: August 26, 2022, 12:59:42 am
content: Much as it is nice to talk about setting accurate Capacitance standards or tweaking them the OP currently doesn't own a device capable of measuring Caps.Apart from visiting someone that does or owns a few known ones then buying sensible and reasonable ones is the only other choice for what is a kit/home brewed box.This is why they obviously need to buy a better meter or two preferably calibrated, standards to match then join the TEA thread

author: The Electrician
author_rank: Frequent Contributor
timestamp: August 26, 2022, 01:20:34 am
content: Quote from: JohanH on August 25, 2022, 12:18:25 pmHave a look here:https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=polystyrene+capacitor+ukraine&_sacat=0&LH_TitleDesc=0&_odkw=capacitor+ukraine&_osacat=0I have some of these and they are extremely low loss.

author: The Electrician
author_rank: Frequent Contributor
timestamp: August 26, 2022, 01:28:09 am
content: Quote from: JoeyG on August 24, 2022, 01:23:47 amHow does your project meter connect to the cap to be measured? Do you have Kelvin clips, or are there a couple of banana terminals on a project box, or what?Do you have a link to the project description?

author: trobbins
author_rank: Frequent Contributor
timestamp: August 26, 2022, 04:45:36 am
content: Quote from: The Electrician on August 26, 2022, 01:28:09 am2x Banana 4mm sockets on front panel.Tempco of internal parts would be dominant source of drift over time, so regular nulling and recal to reference caps would be advisable.The test frequency depends on the DUT value, as the DUT forms part of a simple RC oscillator (the magazine article doesn't describe the test frequency range), so cross-comparison to an LCR meter at a specific test frequency is part value related.Google is your friend for the article.

author: gamalot
author_rank: Super Contributor
timestamp: August 26, 2022, 06:56:13 am
content: Quote from: JoeyG on August 25, 2022, 02:49:43 amI was there at M-City last night trying to find a Harry Potter costume for my son.I don't know there is an electronics store nearby, thanks guys for letting me know!

author: MegaVolt
author_rank: Frequent Contributor
timestamp: August 26, 2022, 09:24:09 am
content: Quote from: David Hess on August 25, 2022, 01:56:51 pmDo you have a link to this document? Or any tips on where to find it?

author: David Hess
author_rank: Super Contributor
timestamp: August 26, 2022, 09:40:53 am
content: Quote from: MegaVolt on August 26, 2022, 09:24:09 amThe capacitance meter is the Type 130. Documentation is availableherebut I don't remember if that includes the oscilloscope input measurement.

author: JoeyG
author_rank: Regular Contributor
timestamp: August 27, 2022, 10:15:20 am
content: I got some caps from Rockby, but it seems there is someting not quite right wth the Capacitance meter with the Adj pots.I may take up your offering later!

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 27, 2022, 03:16:49 pm
content: If you want to get into voltnuttery, you can make a cap with a very low temperature coefficient by putting a polystyrene in parallel with a mica. That's what General Radio did for the reference cap in some of their more precise bridges. The 1608-A comes to mind, but I'm not completely sure. Some fiddling would be required because the tempco of caps can vary.

author: TimFox
author_rank: Super Contributor
timestamp: August 27, 2022, 04:35:48 pm
content: Quote from: David Hess on August 26, 2022, 09:40:53 amThe Tektronix 130 "L,C meter" is a very interesting device, since it allows a straightforward compensation for roughly 70 pF of cable capacitance (from my memory) between the panel and the test point, and the most sensitive range is 3 pF full-scale.It is a beat-frequency unit, where the test port detunes an oscillator (again, I remember the frequency as being roughly 140 kHz) that is compared with a second oscillator, and the beat frequency drives a charge pump to the analog output; internal calibrations of the different ranges adjust each charge pump current range.The panel zeroing adjustments (coarse and fine) allow the operator to get zero beat with an external coax cable to an open circuit: it is not a full LCR meter, since the adjustment only nulls the capacitance.It also has inductance scales for inductive detuning of the oscillator.As mentioned above, if you overcompensate the panel adjustment, you are in "negative capacitance" territory.Should you obtain one, I recommend immediate replacement of the plastic-packaged paper capacitors in the charge pump with modern polypropylenes, due to moisture absorbed in the original capacitors, but that will require re-calibrating each range to a known capacitor; if you are really lucky, you can obtain an S-30 "Delta standard" to facilitate calibration.Seehttps://w140.com/tekwiki/wiki/130for an overview, and links to documents and manuals.

author: mawyatt
author_rank: Super Contributor
timestamp: August 27, 2022, 05:15:20 pm
content: Since our Lab LCR meters Tonghui TH2830 and Hioki IM3536 are idle now waiting for a upcoming project, we can offer to evaluate supplied capacitors for folks here. PM and we'll need a self addressed prepaid return envelope.Also found a source for various components including some Polystyrene, PolyPropylene, and Mica cap types, and had thought about purchasing a number of somewhat standard values in various types, measuring them and offering those.Least we can do for some of the great folks here that have helped so many, including ourselvesBest,

author: The Electrician
author_rank: Frequent Contributor
timestamp: August 28, 2022, 12:07:04 am
content: Quote from: JoeyG on August 24, 2022, 01:23:47 amJoeyG, I downloaded the article from EA Aug 1985. On page 51 they discuss the calibration procedure. They recommend using 3 capacitors: 4700 pF, .47 uF, and 47 uF. Why are you asking for 4.7 pF, 47 pF and 4.7 uF? Perhaps you just want to check the performance at a wider range of values, but don't you actually need .47 uF and 47 uF to do the calibration procedure described in the article?

author: ledtester
author_rank: Super Contributor
timestamp: August 28, 2022, 03:15:46 am
content: Quote from: TimFox on August 27, 2022, 04:35:48 pmCircuitcellar published an MCU version of the Tek 130 here:https://circuitcellar.com/research-design-hub/projects/building-an-lc-meter/At the end of the article there are references to the Silicon Chip articles on the Tek 130:https://www.siliconchip.com.au/Issue/2020/June/Vintage+Workbench(page 34)https://www.siliconchip.com.au/Issue/2020/July/Vintage+Workbench(page 70)