A kit to build a pair of double contacts kelvin probes. Used with LCR, battery tester, or 4 wire instruments like micro-ohmeter or bench multimeter.

This type of probes, used as an alternative to the classic alligator clips, allows you to easily carry out measurements on flat surfaces and small components, thanks to the two tips with 3 mm center distance. It is therefore ideal for measurements on materials, SMD components, batteries.

Dual layer probe PCBs are just a support for the contacts and the cable(s), and provide guarding. The gold plated spring contacts provide accurate and repeatable measurements. The silkscreen identify the injection (Cur) and sense (Pot) terminals, useful for a correct application of the probe on the workpiece.

The kit includes:

• 2 probe PCBs

• 4 gold plated spring contacts

• cable ties to fix the cables

• heat shrink tube to insulate and protect the probes

The PCB provide connections for the wiring on both sides, allowing the use of different types of cables:

• two single conductor shielded calbles, tipycally for use with bench LCR with 4 BNC inputs,

• one double conductor shielded calble, tipycally for use with battery tester and handheld LCR meter (with an adapter, see below),

• two non shielded conductors, tipically for use with micro-ohmeter or bench multimeter provided with 4 wire (kelvin) measurement

Assembly suggestions

In order to easily weld the spring contacts, it is advisable to hold them with a clothespin. The length of the cables must be, compatibly with use, as short as possible.

Characteristics

Maximum voltage 30V

Maximum current 1A

Probe PCB dimensions 60x7 mm

The supplied gold plated spring contacts have a force of 250g with a useful stroke of 4.2mm

Use for battery measurements

Note that to use the probes to measure battery internal resistance or impedance with an LCR, an adapter is necessary to insulate the instrument from the battery voltage and avoid to damage the LCR.

Use with handheld LCR

To connect the probes to an handheld LCR, it shall provide 4 wire (kelvin) measurement method. All bench LCR make kelvin measuremnts, but handheld LCR sometimes not. An example is the Keysight U1730C series.

To connect the probes to an handheld LCR some kind of adapter is necessary. The adapter allows to reach the contacts inside the instrument slots used to insert the tested component leads.

User Voltlog designed a very nice adapter pcb for Hantek LCR meters, it can be bought on tindie.

I derived from his project a version suitable for other LCR models, that can be bought as an option. I have also foreseen the way to mount the capacitors necessary for the measurement on the batteries.

The LCR adapter PCB is designed for theese LCR models:

• MCP BR2832
• B&K Precision 878B / 879B / 880
• Tonghui TH2822A / TH2822C / TH2822D / TH2822E
• Eucol U822,
• Sourcetronic ST2822/ST2822A/ST2822C

I have no information regarding other models. You can chek compatibility to your model by comparing your LCR adapter with the provided dimesions and pad signal description. PCB thickness is 1.2 mm.