Products > Test Equipment

Kelvin leads for DMM

<< < (7/14) > >>

Gary350z:
I have these B&K TLDK1 Kelvin probes:
They work very good and have good build quality.
Mine have a moderate amount of that cheap Chinese plastic smell, which I don't like.
https://www.tequipment.net/BK/TLDK1/Kelvin-Test-Leads/

-----------------------------------------------------------------------
Previously, I bought some of the these GWInstek Kelvin type clips to make my own probes.
https://www.ebay.de/itm/231777696119?epid=1501720482&hash=item35f706f977:g:saQAAOSwp5JWZq5g
They are supposedly made by ETA (Electronic Test Accessories); ETA3105 Kelvin Test Clip
http://www.tw-eta.com/index.php?c=show&id=149
I don't know if I got the real deal or a clone, but mine were very bad. They are supposedly gold plated, but the surface of the metal looks bad, and when testing conductivity of the surface of the metal with good gold plated meter probes, many times they don't even make contact. I threw them away.

Gary350z:
B&K TLDK1 Kelvin probes teardown photo:

mawyatt:
Of course with just a 4 wire Kelvin banana interface this begs the question, "where to connect the shield(s)"?? What's interesting about the above image is that the transition from the 4 wire individually and overall shielded grey cable is that none of these shields is terminated!! The connection to the 2 dual prong banana adapters are using a shielded single wire connection and the shield as the other connection to connect to the dual banana jacks!!

Our DIY versions, we brought all the shields together and a separate banana jack, so a 5 wire setup. The 5th or shield wire can be connected separately, and usually we just connect to the source negative on the DMM since these have no ground or chassis connection on the front panel, although we found little difference in resistive measurements with the shield wire connected or not, or connected to another DMM terminal. This might make a difference with very high resistive measurements, although we haven't done any of these measurements yet (high resistive measurements don't usually require Kelvin measurements tho).

Having the shields connected to chassis or line ground may improve EMI/RFI susceptibility, and may provide a more stable measurement environment (in our case this didn't make much difference).

With any of the Kelvin clip type cables getting accurate small capacitance readings will be difficult, these are best left to a mechanically and electrically stable test fixture, and not generally the place for using banana jacks and DMMs, this is the purpose for dedicated LCR instruments and fixtures.

Here's what the Tonghui TH26011CS Kelvin Clip BNC interface box to the instrument looks like. Note how each individual lead shield is terminated at BNC chassis connection, and all shunted together (doesn't seem the overall cable shield is connected tho).

This illustrates the difference between a LCR instrument and DMM Kelvin Clip banana jack type interface.

Anyway, interesting topic and thanks for posting the innards of the B&K TLDK1.

Best,

2N3055:
Fairly convenient place to connect shield to analog ground of multimeter is a high current input. I use 10A input on my DM3068.

mawyatt:
Yes that is a good spot, however we haven't seen any change in readings when connected or not, but measuring low value resistors (<100k) also.

Best

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod