I‘m making 100 Meg(+) standard resistors(and as 10+ Meg Hamons as well) - Page 1
Forum section: electronics / general

author: zlymex
author_rank: Frequent Contributor
timestamp: March 29, 2016, 07:02:34 am
content: Current status: Samples of FR4 board for Hamon connection finished.Also, waiting the DIY bridge to test those 10 Meg resistors used as the basic building elements. The bridge hopefully will be completed in early May.I'm going to build a series of high resistance standards, 100 Meg, 1G, 10G, 100G and 1T. Each standard hopefully consist of 10 resistors in series, with all leads connected outside, forming a Hamon as well. The three way connection of a Hamon(series, parallel and mixed) will be done by additional devices attaching/detaching thru BNC connectors.Below is the plan for 100 Meg standard resistors(and 10 Meg Hamons)RequirementsNot quite sure, depends on what I use or what I can find for the resistors. Probably <50ppm/year, <5ppm/K.The best 100M I know of is MI 9331G and G9334, both specified as around 20ppm/year and 5ppm/K.Edit: On second thought,I decided not to pursue long term stability for this 100Mand any value above. Rather, I'll rely on frequent transfer from my 10k for calibration. In this way, I can focus on the low tempco, which is important to ensure the stability in an test session.Resistors1. One Fluke 81 Meg, from 5450A, plus other WW, ready.Fluke specified their 100 Meg as 175ppm/year and 10ppm/K, which is not very good.I suspect that it is WW, I asked DiligentMinds.com and he is not very sure either. But he suggested 3RLab2. 3RLab LTCAvailabe 2ppm/K(nice), Load Life Stability of typ 250ppm/1000hrs, no spec for stability or shelf life.http://www.3rlab.com/I'll try to find representation/sales here.3. Ten 10 Meg from HP3455There is one PWW 10 Meg in each old HP3455 DMM. So far I've gathered 6, could be long way for me to obtain the other 4. These resistors are superb by preliminary testing and certainly the best candidates for building a 10 Meg Hamon.4. Ten RX-9-20Some of these are from an old instrument, WW. The drift and tempco may be problematic5. SHALLCROSSTen 10Meg in series on a rotary switch made in 1966(?), originally used in a high-value resistor box, look like WWThe good thing is, there is a small resistor(7.85k) in series with the main 10M, it must be design this way to allow easy adjustment/trim. If some 10M is drifted too large, I'll just parallel a resistor onto that 7.85k.6. CADDOCK TF020R-3I got these second hand in poor condition, but seem still good property wise, the resistor element is in between two ceramic plates that not affected by dust.Caddock specified it as 5ppm/K and 25ppm/year shelf life(very nice), but only up to 2 Meg for TF020R, I had no idea where these 20 Meg were used for.Tested 20 and 19 of them within 0.1%. Tested 3 for TC, all <10ppm/K, one positive, two negative.The disadvantage of the film resistor is the relatively large voltage coefficient although Caddock not mentioning it in the specification.7. Five ULT A50100No idea for these WW resistors, can be used together with others8. Resistor taken out of a 106TThere are ten 5 Meg pair PWW in a 106T making it a good choice for 10 Meg Hamon/100 Meg standard resistor.I measured some of the wire-wound 10M, some are good, others are poor.ConstructionAluminium diecast case, PTEE support, and guarded.Terminals could be triaxial BNC, like that of Agilent 16353HEdit: I've decided that this is the way I'll use. I figure it out why one end is normal BNC but the other end is a triaxial: it is guarded! A normal BNC socket will expose it's guard voltage outside and dangerous.There must be a triaxial plus but no need to use a triaxial cable. I'll use normal insulated BNC socket in 9 intermediate Hamon output terminals.or N-type like those in 9331G,or like those used by NIST, but no idea what it is.If I were using ten 10Meg, probably constructed in a Guarded Hamon way, easy to test individual resistors later.Measurements of resistor elementsDIY a guarded hi-resistance bridge for testing of 1M, 10M, 100M, 1G, 10G, test voltage 100VUse 100k hamon to transfer 10k to 1MUse SR1050 to transfer 1M to 10M and 100MMeasure 10M for value/drift/tempco before actual use.Compensate tempco if necessary.I will build the bridge first, the test of 10Meg by 3458A is very unstable.

author: quarks
author_rank: Frequent Contributor
timestamp: March 29, 2016, 07:34:10 am
content: Looking forwad to see it.On my wishlist still is a 1 GOhm (like the one for Fluke 8508A, does anyone know what is used inside)and Caddock MG745 40MOhm 0.1% resistors are so far my best candidatesAre you also planning a 1GOhm one?

author: tszaboo
author_rank: Super Contributor
timestamp: March 29, 2016, 07:43:31 am
content: Caddock USG also seems pretty nice off the shelf. BTW any reason to have this, other than resistance nutting? High voltage or something?

author: zlymex
author_rank: Frequent Contributor
timestamp: March 29, 2016, 08:07:23 am
content: Quote from: NANDBlog on March 29, 2016, 07:43:31 amYes, the nutting mainly. I do have other plans to build >=1G as well, which may be used for precision small current, but not for voltage higher than 1000V.I did quote for USG, and got this:USG1110-100M-0.1% 10ppm 10 pieces - RMB:1300/pcs(TC is 10ppm, load 0.025% for 1k hrs)also Super MOX and got this:MOX92021006BWE 25PCS MIN RMB:920/pcs(6.5 RMB = 1 USD)

author: quarks
author_rank: Frequent Contributor
timestamp: March 29, 2016, 08:19:08 am
content: the USG1110-100M-0.1% 10ppm looks good (and is way better than my MG745 80ppm/K)

author: zlymex
author_rank: Frequent Contributor
timestamp: March 29, 2016, 08:27:36 am
content: Quote from: quarks on March 29, 2016, 07:34:10 amNo idea about that 1G for Fluke 8508A.Yes, my 1G would be 50 pieces of TF020R-3 in series for the complex version(Hamon style), and two 500M mini-mox in series for the simple version.Another reason preferring WW for 100M is their very small voltage coefficient. As for the 1G, it's not feasible to use WW any more, but a lot of resistors in series will reduce the effect.Quote from: quarks on March 29, 2016, 08:19:08 amAnd very pricy.

author: quarks
author_rank: Frequent Contributor
timestamp: March 29, 2016, 09:59:27 am
content: Hello zlymex,do you know if the TC of the possible candidates can be expected to be some positive and also some negative when you check a batch?If not, how do you compensate for that?thanksquarks

author: babysitter
author_rank: Frequent Contributor
timestamp: March 29, 2016, 11:03:57 am
content: Did you consider a OCR, oven controlled resistor? This should get the TCR down as long as oven is poweredA thermister should be there anyway, so maybe put it all into a heater box?Put all the resistor elements and the thermistor on or inside some lump of metal inside the box. The heating resistor might be on the metal lump too or external.

author: zlymex
author_rank: Frequent Contributor
timestamp: March 29, 2016, 11:13:57 am
content: Quote from: quarks on March 29, 2016, 09:59:27 amThat's why I have to test those candidate, and select the ones that the sum of individual TC is zero. If they are biased towards one direction, I'll try different batch or different types. If none of these work, I have to compensate by NTC or PTC. I've developed a compensation technique for normal-value resistors and you will see very soon.

author: zlymex
author_rank: Frequent Contributor
timestamp: March 29, 2016, 11:27:36 am
content: Quote from: babysitter on March 29, 2016, 11:03:57 amWhat I'm trying to make is not one but a lot of resistors, even more than one for each decade value, each one is the result of at least 10 resistors in series(Hamon style), thus is large in volume, and has to have its own metal box. Adding oven to all of these will be too much work for me. However, I may consider to ovenize my room

author: manganin
author_rank: Regular Contributor
timestamp: March 29, 2016, 02:34:30 pm
content: Guildline 9330-100M, wire-wound, specified for 30 ppm per year. Unfortunately this specific resistance value is not often seen in the used market. My experience is limited to only one 9330-100M. The first years it drifted randomly up and down but eventually stabilized to 5-6 ppm per year upwards.http://www.guildline.ca/Datasheet/Guildline9330Datasheet.pdfMicroprovod P4033, wire-wound. Stability not specified, but selected units are common in East European primary labs.http://www.microprovod.md/en/portfolio/catalog/standards/onevalued_standard.aspxBe carefull with the used or NOS units in Ebay, because these resistors don't age well. Very high risk of receiving unstable or open-circuit resistor whatever the seller says. Better buy a brand new directly from the factory. Original CCCP design, but still manufactured in Moldova! Prices are quite reasonable.http://www.microprovod.md/docs/pricelist_en.pdf

author: e61_phil
author_rank: Frequent Contributor
timestamp: March 29, 2016, 06:31:07 pm
content: What about Caddock USF 270? I planed to use 20 of them (5Meg 0.01% 2ppm/K ovenized) for some precision high voltage measurements.

author: lowimpedance
author_rank: Super Contributor
timestamp: March 29, 2016, 11:42:47 pm
content: Nice collection of old resistors there.Had a look at some high value standards at work for the connector side of things and found both N (on Guildline 100M ohm), and 4mm banana binding posts with extra isolation using custom plastic mounting washers on the IET 100M ohm and 1 G ohm boxes. Not sure what the extra washers are made of but look like acrylic (polycarb ?maybe). Can take a pic if you need.Also the connectors used by NIST are called BPO (Musa), silver plated with PTFE insulator and are not that easy to come by these days. My preference would be to use N connectors.https://en.wikipedia.org/wiki/Musa_connectorMight be able to find a data sheet if i dig deep enough and one is not on line somewhere !.

author: zlymex
author_rank: Frequent Contributor
timestamp: March 30, 2016, 01:57:13 am
content: Quote from: e61_phil on March 29, 2016, 06:31:07 pmThat is one of the best.I assembled a table of high value resistance, not meant accurate nor complete, just for reference.

author: zlymex
author_rank: Frequent Contributor
timestamp: March 30, 2016, 02:16:34 am
content: Quote from: lowimpedance on March 29, 2016, 11:42:47 pmThanks for the info, I finally know that Musa.I came across that 'BPO' connector several times in 'NIST Technical Note 1458', they say it is British Post Office, could that be the same thing?www.nist.gov/calibrations/upload/tn1458.pdfPls do take pic of the extra washers, very interested.

author: lowimpedance
author_rank: Super Contributor
timestamp: March 30, 2016, 04:37:20 am
content: Some pic's of the additional insulator on the IET standards. The same construction applies to the 100 M ohm, 1 G ohm and 10 G ohm boxes.The BPO connectors used at work and are generally just referred to as BPOs and not Musa!. (same thing though)

author: lowimpedance
author_rank: Super Contributor
timestamp: March 30, 2016, 04:40:09 am
content: Plus the N connectors on two Guildline boxes.

author: zlymex
author_rank: Frequent Contributor
timestamp: March 30, 2016, 09:47:18 am
content: Thanks lowimpedance for the photo. It looks to me that Guildline use extra insulation for high voltage and reduce leakage because there is no guarding. Being a HAM, I have some N-connectors as well, it's bulky, and difficult for guarding of Hamon devices(there are at least 11 sockets for a guarded Hamon). Therefore I think I'll go for BNC instead.

author: quarks
author_rank: Frequent Contributor
timestamp: March 30, 2016, 10:04:48 am
content: here is a link to an interesting comparison of 13 labs measuring 1GOhm (from Ohm-Labs)"North American One Gigaohm Interlaboratory Comparison: 2006–2008"http://www.ohm-labs.com/pdfs/1%20G%20ILC%20Paper.pdfalso the Ohm-Labs Resistance Standards look very interestinghttp://www.ohm-labs.com/resistance-standards/index.html#highand they seem to offer custom resistors

author: manganin
author_rank: Regular Contributor
timestamp: March 30, 2016, 10:18:17 am
content: Quote from: zlymex on March 30, 2016, 02:16:34 amMUSA (Multi User Steerable Array) is another name for the BPO (British Post Office) connector. It provides low contact resistance and excellent repeatability, making it suitable for impedance metrology, especially high capacitance and low inductance. Not the best alternative for high resistance, type N connectors have usually higher insulation resistance and lower thermal EMF than MUSA.Canare more or less copied the MUSA design for their video patch connector system. Similar performance, but not interchangeable, the female pin was changed to male pin and vice versa. Also minor changes in the mechanical dimensions. Surplus Canare is probably much easier to get on your side of the world.

author: zlymex
author_rank: Frequent Contributor
timestamp: March 30, 2016, 10:25:51 am
content: Thanks quarks, indeed interesting, especially comes the comparison method.MI6000 bridge is based on Cutkosky Divider(A kind of binary divider), For Active Arm Bridge, someone say it is easy to realize in a lab if you have two programmable voltage sources but involves a lot of programming. I'll try to make a Wheatstone Bridge instead, it is very simple, the detector is worrisome though.Yes, I'll borrow some ideas from Ohm-Labs

author: Gyro
author_rank: Super Contributor
timestamp: March 30, 2016, 10:30:18 am
content: Quote from: zlymex on March 30, 2016, 09:47:18 amWhat about the good old SO239 UHF socket? It's 500V RF rated, so good insulation and in addition to being screened, I believe the center hole will accept a 4mm banana plug.

author: manganin
author_rank: Regular Contributor
timestamp: March 30, 2016, 10:35:32 am
content: Quote from: lowimpedance on March 30, 2016, 04:37:20 amThose spacers turned from Acrylic or Teflon bar are an old trick to increase the insulation resistance and breaktrough voltage of the off-the-shelf binding posts.I haven't seen ready made spacers for a while, but they were available in the past for Hirschmann binding posts at least.

author: zlymex
author_rank: Frequent Contributor
timestamp: March 30, 2016, 10:40:25 am
content: Quote from: manganin on March 30, 2016, 10:18:17 amNow I understand what is a BPO.Because I'm going to make the resistor as Hamon(a lot of sockets in a box), I'll first try the quick BNC(no twist needed) widely used in LCR test fixtures

author: zlymex
author_rank: Frequent Contributor
timestamp: March 30, 2016, 10:44:57 am
content: Quote from: Gyro on March 30, 2016, 10:30:18 amIs that the M-type connectors often used in mobile antenna? May be it's too big, and need crew in.And yes, I've just measured, the center hole is 4.0mm in diameter. That is very convenient, I'm considering to use it on the bridge, hi-volt input say.There are hi-ohmetic standards that use this connect, but only one.

author: manganin
author_rank: Regular Contributor
timestamp: March 30, 2016, 10:55:36 am
content: Quote from: zlymex on March 30, 2016, 10:40:25 amHow about using cheap insulated BNC connectors and a built in Guard divider feeding the BNC shells? Saves a lot of trouble and connector cost if the goal is higher than 100 Mohm.

author: manganin
author_rank: Regular Contributor
timestamp: March 30, 2016, 11:23:12 am
content: Quote from: Gyro on March 30, 2016, 10:30:18 amQuote from: zlymex on March 30, 2016, 10:44:57 amThe SO-239 when used with the mating plug (PL-259) is so unreliable that it is wrong to call it a connector. OK when used with a banana plug.

author: zlymex
author_rank: Frequent Contributor
timestamp: March 30, 2016, 11:32:29 am
content: Quote from: manganin on March 30, 2016, 10:55:36 amThat's right, I'm going to use these, I have a few samples, it's easy to make guarding on a metal box.

author: lowimpedance
author_rank: Super Contributor
timestamp: April 01, 2016, 03:54:53 am
content: Just found a box when tidying up a lab that contained some interesting old standards that were not mounted in any enclosure of any sort !. pics below.1 Box lid2 inside of box and3 end on pic of construction, Teflon plug each end with a alum. tube then an outer plastic sleave to protect the hand written value etc.Dont know if they were made here or not (I suspect they might have been and maybe contain glass envolope resistors)

author: zlymex
author_rank: Frequent Contributor
timestamp: April 01, 2016, 08:45:13 am
content: Quote from: lowimpedance on April 01, 2016, 03:54:53 amLooks very good in quality, and they are individually numbered. They reminds me of old analog null meters that have 1-3-10 range steps.

author: Lowpass30Hz
author_rank: Newbie
timestamp: April 01, 2016, 04:38:48 pm
content: Are you interested in the Voltage Coefficient? It is an important consideration for precision measurements of a 100 Mohm resistor, if you want to use it over a large voltage range.Of course if you are only planning on using it with the same applied voltage this isn't an issue. However, if you ever decide to have the resistor externally calibrated you would have to careful of the difference between the lab's test voltage and your own.Standard resistor design example - The inside of a Welwyn 100 Mohm standard:

author: zlymex
author_rank: Frequent Contributor
timestamp: April 01, 2016, 04:58:56 pm
content: Quote from: Lowpass30Hz on April 01, 2016, 04:38:48 pmThanks very much. Interesting to see inside photo of the Welwyn 100 Mohm standard. The metal cans must be hermetic 10M(or slightly less) resistors, any idea of what is made of?I'll consider the voltage coefficient, that's why I decide to use wire-wound type for my 100 Meg as the 1st choice, they have very small voltage coefficient. If I build higher values such as 1G, 10G, 100G, then I must use none-WW. Apart from selection of resistors with small voltage coefficient, I will use 10 resistors of 1/10th the nominal value to reduce the voltage coefficient effect. In one earlier DIY, I use 100 resistors in series.

author: Lowpass30Hz
author_rank: Newbie
timestamp: April 01, 2016, 08:16:25 pm
content: I have no idea I'm afraid. I can have a proper look next week when I have access to it again.What did you use for your earlier 100 resistors in series design, foil type?Thank you for another engaging thread, these DC/LF topics really interest me. Looking forward to the finished item!

author: zlymex
author_rank: Frequent Contributor
timestamp: April 02, 2016, 01:55:21 am
content: Quote from: Lowpass30Hz on April 01, 2016, 08:16:25 pmThat one Giga-Ohm is a test resistor consisting of 100 Vishay Dale RN55D-1005F Metal Film Resistors assembled on PTFE sheets.Value adjustment: by some resistors of slightly less than 10M(9.76M say)TemCo adjustment: by test and select those with equal but negative TC from more than 1000 pieces.

author: Vgkid
author_rank: Super Contributor
timestamp: April 02, 2016, 02:42:30 am
content: I read a few months ago about a university in South America(Im thinking possibly Mexico) that built a very stable high value resistance standard. It was rather in depth about the issues that were faced, and how they were overcome. The interesting thing is that it was built with off thelf resistors. Unfortunately I did not save it.

author: Vgkid
author_rank: Super Contributor
timestamp: April 02, 2016, 03:39:26 am
content: Quote from: DiligentMinds.com on April 02, 2016, 03:12:46 amThat is the one. Though i remembered reading the second one as well.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 02, 2016, 05:28:47 am
content: Quote from: DiligentMinds.com on April 02, 2016, 03:12:46 amThanks for the file. That's remind me something similar I found before.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 02, 2016, 05:35:00 am
content: Quote from: DiligentMinds.com on April 02, 2016, 03:21:26 amI've saved this one before. There is another one called 'Evaluation of Guarded High-Resistance Hamon Transfer Standards', too large to upload even if I compressed it to rar file(2.8M).

author: zlymex
author_rank: Frequent Contributor
timestamp: April 02, 2016, 05:50:21 am
content: Quote from: Vgkid on April 02, 2016, 02:42:30 amThanks for the refreshment. The resistors they use (USG1110) are very good at 0.1%, 10ppm/K, but no shelf life specification. I'm going to build my 100G Hamon based on TF020R-3, similar spec(0.1% and 10ppm/K) but has shelf life specified as 25ppm/year. Because I have more than 25 set of these 100M to choose from, I'm going to rival that.

author: lowimpedance
author_rank: Super Contributor
timestamp: April 05, 2016, 01:34:10 am
content: While looking for the reversing switch I also came accross these Keithley 5155 High value standards that go from 10^8, 10^9......up to 10^13.Note the connectors used. The standard BNC is the 'low end'. Inside is a glass encapsulated resistor made by Victoreen.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 05, 2016, 06:28:19 am
content: Here is the spec for Keithley 5155. Interesting to see the guarding, similar to those 100M.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 07, 2016, 09:24:16 am
content: update: case arrived today. However, I will make a FR4 board according to the case on which to put all the BNC sockets. Also, I need the finished high resistance bridge to test all those 10 Meg resistors. The case for the bridge also arrived.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 09, 2016, 08:13:14 am
content: Update: design of the FR4 boards finished and sent to a plant for CNC machining. These boards will be used not only for this 100M standard(10M Hamon) but also for all my high standard resistors/Hamons from 10M to 1T.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 12, 2016, 05:55:17 am
content: In order to test those 10 Meg resistors to be used in these 100 Meg standard, I need a test box for shielding/connection.I have a very old Keithley 6104 test enclosure but it is un-guarded, and is not compatible with my 100Meg/high resistance bridge.I modified the original BNC socket to a triax and added a guarding in between the positive and ground. Also added another BNC socket to let the lower end of the resistor flow thru instead of connecting to the ground/shield.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: April 15, 2016, 07:58:43 pm
content: Just wondering, Why would you need such high value resistors? (e.g anything over 10Meg).

author: zlymex
author_rank: Frequent Contributor
timestamp: April 15, 2016, 11:43:18 pm
content: Quote from: ZeTeX on April 15, 2016, 07:58:43 pmTwo possible applications are- to generate very small current, thus to calibrated/check electrometers such as Keithley 610C, 617, 6517A- to calibrate insulate resistance meters/megaohmeters such as HP4329A

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 16, 2016, 06:18:33 am
content: Quote from: ZeTeX on April 15, 2016, 07:58:43 pmA third application is the verification and calibration of DMMs, which have these high OHM ranges.Frank

author: ZeTeX
author_rank: Frequent Contributor
timestamp: April 16, 2016, 08:19:51 pm
content: Quote from: zlymex on April 15, 2016, 11:43:18 pmFair enough I guess, not that really useful for me.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 20, 2016, 04:31:54 am
content: Update: CNC samples of the FR4 boards finished. The thickness of the board is 3mm.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 29, 2016, 01:03:00 pm
content: Update: FR4 board arrived today, precisely made, fit the case/BNC perfectly. It is crucial that holes on top/bottom part are aligned.

author: acbern
author_rank: Frequent Contributor
timestamp: April 29, 2016, 01:13:10 pm
content: Great! What are the mating connectors for the BNCs?

author: zlymex
author_rank: Frequent Contributor
timestamp: April 29, 2016, 02:29:34 pm
content: Quote from: acbern on April 29, 2016, 01:13:10 pmThanks. Those connectors are of special male type often found on test fixtures of LCR meters.

author: acbern
author_rank: Frequent Contributor
timestamp: April 29, 2016, 02:33:23 pm
content: Yes, I know, but where did you get these from? Is there any part reference (other than from Keysight?).

author: Gyro
author_rank: Super Contributor
timestamp: April 29, 2016, 03:55:02 pm
content: Same question here, where can you get them? That's an impressive alignment, I understand now why you had boards made!

author: zlymex
author_rank: Frequent Contributor
timestamp: April 30, 2016, 02:56:14 am
content: I bought them from Taobao(China ebay) about two years ago but running out, I've just bought some more from here:https://item.taobao.com/item.htm?id=45440995167There is another way as some one has suggested: buy regular BNC male plugs(with PCB mount) such like these(very cheap):https://item.taobao.com/item.htm?spm=a1z0d.6639537.1997196601.230.Wi4im5&id=14163363960and remove the mounting heads yourself after. I've tried this before by two ways, one is by pure force, the other is to gradually lever at the end by s screw driver to let loose the spring, the whole thing will come out.Edit: I found some entries at aliexpress selling the same thing such as:http://www.aliexpress.com/item/Quick-TNC-or-BNC-male-nut-bulkhead-deck-mount-solder-cup-RF-connector/32619733999.htmlDon't buy those with straight head as they often don't contact female sockets such as:http://www.aliexpress.com/item/RF-electrical-terminal-connector-BNC-Plug-panel-mount-Quick-Push-on-bulkhead-with-Solder-cup-connector/32443473110.html

author: zlymex
author_rank: Frequent Contributor
timestamp: April 30, 2016, 04:08:25 pm
content: Update: common Hamon adapters finished. They are common so that they can be used for all my Hamons to facilitate parallel, series and mixed connections.If one of the adapters connect to the short Hamon body, the total height is 67mm

author: doktor pyta
author_rank: Frequent Contributor
timestamp: May 02, 2016, 08:21:29 am
content: Zlymex, fantastic jobP.S. Have You considered using typical laminate with copper (etched only near the connectors). Since You have guard rings this could provide better electrostatic shield. Was it due to the higher cost of this solution or the leakage in the guard divider string ?

author: zlymex
author_rank: Frequent Contributor
timestamp: May 02, 2016, 12:35:03 pm
content: Quote from: doktor pyta on May 02, 2016, 08:21:29 amThanks very much. Probably I did not quite follow you, did you mean to cover large part of the board(probably both sides) with copper? I did plan this, and with copper ring on both side around the connectors, and make isolation rings to separate the guard and earth. That certainly works better. However, the insertion and separation of top part require a tremendous force, board of 3mm thick has to be used, the PCB manufacturer don't seem to do PCBs of this thick(usually 1mm to 2mm), I have to buy bare FR$ board(without copper layers, in any thickness such as 10mm) myself and had them cut by CNC machine.In my current version, there is a gap between top and bottom which might affect the guarding connectors(which are high impedance) as well. I'm going to use flexible, insulated, earth-connected copper foils to wrap around the gap if that is a problem.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: May 02, 2016, 04:27:43 pm
content: Yes, I got my answerThanks.

author: leighcorrigall
author_rank: Frequent Contributor
timestamp: December 02, 2020, 12:06:48 am
content: Quote from: zlymex on March 30, 2016, 01:57:13 amHi zlymex,I realize that this topic is a little old, but do you have a more updated version of your spreadsheet? I am particularly interested in the Ohmite RX-1M temperature coefficients. How did you quantitatively determine the temperature coefficient increases as a function of increasing resistance? This is not included in the datasheet.Also, can you please provide websites to the other manufacturers listed? Some of them I cannot find and am unfamiliar with.Thank you!