Shielded cable for DIY Kelvin clips for DE-5000 LCR meter - Page 1
Forum section: electronics / beginners

author: omgfire
author_rank: Regular Contributor
timestamp: July 20, 2014, 06:09:10 pm
content: Greetings.I have ordered Der EeDE-5000LCR Meter and some Kelvin clips to mod TL-21: replace alligator with Kelvin clip (for 4 wire measurement) and replace short cables with longer ones. I planned to usespeaker wire. But according to Dave's video, TL-21 uses shielded cables. I looked at datasheet for CyrustekES51919/ES51920and it declares necessity of shielding:QuoteThere is report atUT612 threadthat probes without shielding did not pass calibration. Is parasitic capacity of unshielded cables big enough to fail calibration?Question 1: How guard (5-th wire) works on Cyrustek based LCRs? Is shielding for isolating "plus" from "minus"? Is shielding for isolation force from sense? Does force and sense have common shielding or separate?I haven't found variety of shielded cables in my cable drawer.Only shielded stranded twisted pair with thin cores.Question 2: Can sense and force wires be twisted or untwisted or indifferent?4 Wire sensing ignore voltage drop at force wires, so it is possible to use thinner wires and not sacrifice measurement accuracy.Question 3: What is appropriate resistance (diameter) for cables for Cyrustek based LCRs?DE-5000 measures up to 100KHz. So wavelength is about 3km. Since cables will be within 0.3m-1m, I would assume that this LCR meter do not need proper coax cable with constant conductor spacing and specific characteristic impedance. Any shielded cable will work. Right?I have looked at ebay for shielded stranded cables and I found these:ID 1.3mm, OD 2.9mm. Area 1.32mm^2. Is PTFE rigid enough to make this cable poor choice for Kelvin probes?H155Core 19 x 0.28mm. OD 5.4mm. Area 1.17mm^2. Is it too thick for 5 wire measurement?RG174Core 7x0.16 mm. OD 2.55mm. Area 0.14mm^2.RG178Core 7x0.1 mm. Will 0.05mm^2 be enough?Silicone AWG 24. It should be flexible, but overseas shipping cost cancels this option.So, the last question 4: which cable should I use?PS: sorry for long post

author: PedroDaGr8
author_rank: Super Contributor
timestamp: July 20, 2014, 06:56:34 pm
content: The tweezers have a pretty large diameter wire on them. Do you want me to take measurements of wire diameters for you?

author: omgfire
author_rank: Regular Contributor
timestamp: July 21, 2014, 01:32:17 pm
content: Quote from: PedroDaGr8 on July 20, 2014, 06:56:34 pmThanks, but I more interested about how cable constructed than outside diameter. Perhaps, I should wait for delivery, and then I'll see is the cable twisted or not and how shielding is done (separate or common).

author: robrenz
author_rank: Super Contributor
timestamp: July 21, 2014, 03:19:17 pm
content: Single shield over both wires. Twisted is optional. Very smallgage probably around 2628 Gage wire is used.Guard or shield From the Agilent impedance handbook:"The guard terminal is the circuit common of the auto-balancing bridge and is connected to theshields of the four-terminal pair connectors. The guard terminal is electrically different from theground terminal, which is connected directly to the chassis (Figure 2-12 (b).) When the guard isproperly connected, as shown in Figure 2-12 (c), it reduces the test signal's current but does notaffect the measurement of the DUT’s impedance (Zx) because Zx is calculated using DUT current (Ix.)"

author: omgfire
author_rank: Regular Contributor
timestamp: July 22, 2014, 06:14:10 am
content: Quote from: robrenz on July 21, 2014, 03:19:17 pmExcuse, non English speaker. What does "single" word mean in your sentence? Like single woman or like single bedroom.(i) Separate shields, like 4 coax for force plus, force minus, sense plus, sense minus.(ii) One common shield, like 2 shielded twisted pairs: force plus and sense plus inside one shield; force minus and sense minus inside another shield.In second case force influences sense.Quote from: robrenz on July 21, 2014, 03:19:17 pmThank you.

author: robrenz
author_rank: Super Contributor
timestamp: July 22, 2014, 12:29:59 pm
content: The DE-5000 attachments are (ii)

author: omgfire
author_rank: Regular Contributor
timestamp: July 22, 2014, 03:38:41 pm
content: robrenz, thank you.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 24, 2020, 02:09:58 am
content: Surfacing a very old thread.What is the impact of the shield (vs. no shield) in Kelvin test leads? With the shield maybe the same leads and clips that could otherwise measure reliably to milliohms without the shield might measure more reliably to microohms with the shield, or is there some other purpose? Thx