long LCR meter cables - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: April 13, 2025, 06:11:07 am
content: Out of curiosity, how long can you make LCR meter cables? Like for a DE-5000.I thought 4x coaxial cablescan you put like 30 feet test leads on it?

author: coromonadalix
author_rank: Super Contributor
timestamp: April 13, 2025, 08:02:54 am
content: and why this long ?you'll add stray capacitance, resitance etc ... with long wires, and mess with the readings ... on some yo do have 2 wires probes / kit, maybe 1meter maximum, but precision ?to me it would render any good lcr worthless

author: Smokey
author_rank: Super Contributor
timestamp: April 13, 2025, 08:07:53 am
content: I wonder how much the cable parameters change as the long cables move around. I would think this is one of the big benefits of the short compact housed fixtures is that the parameters are stable and easy to calibrate out.

author: coppercone2
author_rank: Super Contributor
timestamp: April 13, 2025, 08:18:15 am
content: I know it will have problems but "don't engineer that" is not a very useful answer

author: Kean
author_rank: Unknown
timestamp: April 13, 2025, 11:50:01 am
content: You definitely want to use coax to avoid pickup of noise. I believe the DE-5000 has a guard connection which you would connect to the coax shields.Ideally I think you want low noise coax intended for small signal sensors which will help with noise from cable movement better than common coax intended for higher frequency RF or outdoor use.Unfortunately that low noise coax can be a pain to strip and terminate.e.g.https://www.newenglandwire.com/why-low-noise-cables/There might be practical or implementation limits as to what the short/open calibration process can handle, and that will vary between devices.You can estimate the capacitance and resistance of 4 x 30ft of your selected coax and see if using similar value capacitors and resistors on the DE-5000 will be accepted during an open and short cal.

author: EC8010
author_rank: Frequent Contributor
timestamp: April 13, 2025, 12:09:21 pm
content: Cable capacitance gets converted into series inductance by a four-wire impedance measurement. I thought all electrolytic capacitors had 100nH of series inductance until I replaced the (supplied) 600mm cables with a test fixture that hangs off the front of the meter. By extension, I would expect 10m cables to be even more significant. But if you wanted to measure a large inductance, you wouldn't care. It really depends on what you want to measure. I'd far rather pay for a 10m mains extension cable than four 10m lengths of decent coax...

author: TimFox
author_rank: Super Contributor
timestamp: April 13, 2025, 03:15:15 pm
content: The ideas above should work at the lower frequencies of the DE-5000.Low-noise coax often has graphite on the outside of the dielectric to maintain the dimensions against flexing.The DE-5000 has a female 4 mm banana jack for guard that must be connected to all four coax shields.If the parasitic impedances are too bad, the DE-5000 will not complete the open/short calibration.

author: mawyatt
author_rank: Super Contributor
timestamp: April 13, 2025, 03:28:10 pm
content: Some of the higher end bench type LCR meters have a cable length parameter to help deal with longer test cable effects.Generally for better measurements (repeatability and accuracy) the shorter the test cable/fixture length the better, especially so for higher frequency measurements.BTW there's a new low cost handheld LCR Meter that looks promising.https://www.eevblog.com/forum/testgear/new-lcr-meters-zoyi-zt-dq01-and-zoyi-zt-dq02-(march-2025)/Best

author: laichh
author_rank: Regular Contributor
timestamp: April 14, 2025, 02:01:39 am
content: The Keysight E4980A support cable length correction up to 4 meter (~13 ft.), see datasheet page 5.https://www.keysight.com/us/en/assets/7018-01355/data-sheets/5989-4435.pdf

author: pdenisowski
author_rank: Super Contributor
timestamp: April 14, 2025, 07:56:16 am
content: We (R&S) specify a maximum cable length of 1 meter and provide a special fixture for this30 feet seems rather ... ambitioushttps://youtu.be/jc6ByW1Uusg?t=538

author: stevebyan
author_rank: Contributor
timestamp: April 14, 2025, 10:31:51 am
content: Henry P. Hall wrote that the General Radio 1617 Capacitance Bridge could in theory accurately measure the C and D of a 1 uF capacitor through 1,000 feet of cable, though it requires using all five terminals of the bridge. See the June 1966 issue of the General RadioExperimenter.

author: TERRA Operative
author_rank: Super Contributor
timestamp: April 14, 2025, 12:13:34 pm
content: Why do you need 10m cables?Could you use an IR/USB adapter module and extend the readings to a PC or similar instead?

author: coppercone2
author_rank: Super Contributor
timestamp: April 14, 2025, 08:10:37 pm
content: Quote from: stevebyan on April 14, 2025, 10:31:51 amvery interesting I look forward to reading this

author: Smokey
author_rank: Super Contributor
timestamp: April 14, 2025, 08:34:15 pm
content: Quote from: TERRA Operative on April 14, 2025, 12:13:34 pmmaybe the meter is already right next to the DUT, but it's 60ft long end to end

author: coromonadalix
author_rank: Super Contributor
timestamp: April 14, 2025, 09:13:52 pm
content: apparently the hp 4363B and maybe A can support 4m lenghts ?? they seems to have a setup menu for that ?and for the General radio is it with time constant or frequencies ?? or unless it work like a tdr ?found this :https://www.grwiki.org/wiki/1617-AManualhttps://www.grwiki.org/grwiki/images/4/47/GR_1617_Capacitance_Bridge_1617-0100-E_1978.pdf

author: RoGeorge
author_rank: Super Contributor
timestamp: April 14, 2025, 09:18:07 pm
content: Quote from: stevebyan on April 14, 2025, 10:31:51 amThanks!Found the June 1966 of GR Experimenter athttps://www.worldradiohistory.com/Archive-Company-Publications/Archive-General-Radio/GR%20Exp%201966_06.pdfAccidentally found this one, too, about error types and why a five-terminal bridge:https://www.worldradiohistory.com/Archive-Company-Publications/Archive-General-Radio/GR%20Exp%201970_03.pdf

author: TimFox
author_rank: Super Contributor
timestamp: April 14, 2025, 09:33:55 pm
content: Quote from: RoGeorge on April 14, 2025, 09:18:07 pmThe second article (GR Experimenter, Mar/June 1970), page 16, shows actual results for measuring a 10 nF capacitor with 100 feet of cable and a GR 1683 bridge, with a 5-terminal connection.The capacitance values measured at the bridge itself, and after 100 feet of cable, agreed to within +/- 1 count, and the indicatedDvalue increased by only 0.0040 after the cable.

author: coppercone2
author_rank: Super Contributor
timestamp: April 14, 2025, 09:45:33 pm
content: I can tell you with a impedance analyzer at 100MHz-1GHz you start getting balony pretty quick, even when you do the coaxial calibration standards at the end of it. When I put my 'unknown' I had trash after a calibration when I put like 12 feet of coaxial cableI did also hear before that bridges are the best for this sort of thingactually it might have failed to calibrate one of the standards too. I don't feel like messing with that, it was just an idea to see if you can plug it into a remote antenna. That one I am leaving alone, but the lower frequency measurements seem.. more approachableIt looks like a boondoggle anyway. The picture in the article is confusing. They call it a guard. Its not a driven guard though? And its not instrument earth?I know of guard in a triaxial cable. That one I understand to deal with leakage using a amp. But the picture in that genrad document makes it look like its just chassis?? So the idea is they are star grounding the shields to the chassis? So the coaxial outer connector of sense and source are all floating, and you connect the source return to earth ?I.e.1) Source current : Shield floating2) differential amplifier 1 : shield floating3) differential amplifier 2 : shield floating4) source current return : Shield connected to guard shield5) guard : shield connected to earth6) guard center pin=So the star looks like this:Guard -> source return current -> branches to #1,2,3Why not actually have a 5th wire from the star to go to guard, why are you 'daisy chaining' the return current shield to act as star? Like thisIs it just the matter of being easier to wire?And yes, my question is for DUT of unusual size. So IDK how you would short that shit together at the end either. I imagined just unrolling a roll of copper

author: TimFox
author_rank: Super Contributor
timestamp: April 14, 2025, 10:20:54 pm
content: Quote from: coppercone2 on April 14, 2025, 09:45:33 pmYour original post was about a DE-5000, which has a maximum frequency of 100kHz.The General Radio 1683 and 1617 bridges discussed above have a comparable frequency range.Read the actual GR articles about the use and necessity of the guard terminal: guard and ground are different concepts.In the second article, the guard terminal is discussed on page 16. There, it does connect to the bridge chassis, but the terminals connected to the unknown component are not grounded.The guard connections minimize the effect of stray capacitance.The DE-5000 measuresV/Ias a complex quantity, while the bridges balance out the "null" voltage by adjusting the components in the bridge, but the four terminals plus guard are connected similarly.At 100 MHz, you need a reflection bridge, and many wavelengths of cable in series with the unknown will give substantial errors.

author: coppercone2
author_rank: Super Contributor
timestamp: April 14, 2025, 10:24:53 pm
content: but why do they daisy chain it through I- instead of making the 5th a independent braid? I feel like the core idea is a star ground. But its not really implemented like that. The piggy backing is confusing me.And that was just a side note about the IA. People might have other things in mind then a De-5000.

author: TimFox
author_rank: Super Contributor
timestamp: April 14, 2025, 10:33:06 pm
content: You asked about the DE-5000.Most people now seem to have forgotten about bridges.I proudly own the largest collection of impedance/admittance bridges on Chicago's Northwest Side: General Radio, Wayne-Kerr, and others.

author: coppercone2
author_rank: Super Contributor
timestamp: April 14, 2025, 10:40:03 pm
content: I feel that if you jumper the 4th wire to a '5 wire' instead of using a real 5th wire you are concentrating shield currents in that path and effecting the circuit more.Especially if it was really long and picking up alot.

author: TimFox
author_rank: Super Contributor
timestamp: April 14, 2025, 10:41:49 pm
content: No. Read the 1970 G-R article comparing 4-terminal and 5-terminal connections.The point is to minimize the effects of unwanted shunt capacitance, not interference pickup.

author: coppercone2
author_rank: Super Contributor
timestamp: April 14, 2025, 10:48:13 pm
content: I'm having trouble finding what you are talking about.I see it as a star connected coaxial tube. You can either use a 5th part to get to guard, or route a jumper between the 4th part and guard. All the terminals are floating in both cases, and its connected to guard/ground through one point, either a jumper or a separate wire.4-wire connected where the shield is grounded at 4 points is totally different arrangement.They are showing that its only grounded at one point. Why are they using a jumper instead of a 5th wire.

author: coppercone2
author_rank: Super Contributor
timestamp: April 14, 2025, 10:54:35 pm
content: Why do they do the left one instead of the right oneI only drew the shields.

author: TimFox
author_rank: Super Contributor
timestamp: April 14, 2025, 10:55:01 pm
content: Two each of the four terminals go to the two sides of the unknown impedance, and none of them is grounded.

author: coppercone2
author_rank: Super Contributor
timestamp: April 14, 2025, 11:00:10 pm
content: clearly I wrote floating . I will wait for someone else to explain.That article is bullshit anyway, they don't draw half the circuit elements

author: TimFox
author_rank: Super Contributor
timestamp: April 14, 2025, 11:06:58 pm
content: Another discussion of guarding is section 2.4.7 of the lengthy -hp- handbookhttps://www.cmc.ca/wp-content/uploads/2019/07/Keysight-Technologies-impedance-measurement-handbook.pdf

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 15, 2025, 07:49:10 pm
content: Quote from: stevebyan on April 14, 2025, 10:31:51 amThey also made the 716-P4 Guard Circuit for the model 716 capacitance bridge. It was designed for things like measurements inside an environmental chamber; not sure just how far one could go, but probably many feet. The manual is readily available and studying the circuit might be useful. Here's my write-up-https://conradhoffman.com/GR716P4.htm

author: Aart
author_rank: Newbie
timestamp: May 08, 2025, 08:36:11 am
content: For some research setup at work i have successfully used tens of meters RG58 on a Agilent U1733 for measuring the capacitance of a sensor.Shields connected to the guard terminal. I do not remember the exact numbers, but it might be worthwhile to try.[Offtopic: First post on this forum. Hi everyone! from the Netherlands. ]

author: EC8010
author_rank: Frequent Contributor
timestamp: May 08, 2025, 09:14:48 am
content: Quote from: TimFox on April 14, 2025, 11:06:58 pmIn the unlikely event that anyone here hasn't read that handbook, they should. It is excellent. My measurements improved markedly after reading that and making screened test boxes that hang directly off the front of my LCR amalyser and have short internal leads to Kelvin clips.