In this post, I present a DIY 3D printed adapter for 4-wire Kelvin measurement of SMD components with an LCR meter. The adapter has been tested with the Multicomp Pro handheld LCR meter (rebranded Hantek 1833C) and should work with the DER DE-5000 LCR meter.
In previous posts, I’ve presented Kelvin clamps and SMD tweezers for use with the Multicomp Pro LCR meter. This new design was inspired by a comment Jan Cumps made in the post on Kelvin clamps. My friend Adrian also made suggestions and modified the PCB so that it can be used with both the Multicomp Pro or DER meters.
There were 6 major iterations made during the design process. Major modifications included:
- Changed contacts from copper foil tape to brass bar stock
- Adjustments for improved slide movement
- Added 4-wire capability
- Constructed jig for ease of contact fabrication
- Modified PCB to allow use with DE-5000 LCR meters
- Added screw mechanism to slide
The design was done in Fusion 360 and all parts were modeled with the exception of wiring. The image below from a screenshot in Fusion 360 shows how the mechanism works.
Fusion 360 also allows me to show you gratuitous see-through shots like the one below.
Printing Plastic Components
The 3D printed components were all done with PLA on an Anycubic I3 Mega. The components are comprised of the top, bottom, slide, and screw. The image below shows the parts prior to the final assembly.
Fabricating Brass Contacts
Two brass contacts are used to clamp SMD parts in place during measurement. The contacts are cut from 5/32 inch (3.97 mm) brass bar stock into 10 mm lengths with 1/16 inch (~1.6 mm) holes drilled partially through the lower center on one face for connecting wire leads to the PCB. Two wires are required for each contact to get a 4-wire measurement. 26 AWG silicon insulated multi-stranded wires were used for the leads.
Cutting the brass bar stock to length and drilling the holes is difficult by hand so a jig was 3D printed to guide the hack saw while cutting and properly position the drill bit in the drill press. This made the fabrication of the contacts both quicker and more accurate.
Revising the PCB
Thanks to Adrian for revising and testing the PCB so that it can be used with both the Multicomp Pro and the DER LCR meters. Note that the DE-5000 contacts are reversed from the Multicomp Pro but the PCB can be flipped over and used. The ends of the “fingers” were tapered and the PCBs made 0.8 mm thick which allows easier insertion into the DE-5000. The modifications work equally well for the Multicomp Pro.
The PCBs were manufactured at OshPark and can also be used with the earlier 4-wire Kelvin clamps.
I subsequently made a second version with the PCB trimmed a bit in width and the mounting holes symmetrically placed to allow a smaller enclosure with the SMD adapter.
Assembling the Adapter
The top and bottom are held in place with M3 x 16 mm long screws and M3 x 5.8 mm brass heat inserts. The high side of the enclosure is embossed with a "+" for polarized components and colored in with a pencil. The screw that moves the slide is M3 x 30 mm and is held in place by an M3 nut in the knob and another M3 nut in the body of the slide.
The most difficult process in the assembly is attaching the contacts. Super glue didn’t adhere well and epoxy takes some time to set and is more difficult to place keep out of undesired places. The leads are soldered first and then the “high” side contact is glued to the slide. Once the high side contact is dry the “low” side contact is glued to the bottom of the enclosure with the slide in place.
The close-up below shows a 1.3-ohm 0805 resistor being held by the contacts during measurement.
Using the Adapter
In the image below the adapter is shown measuring a 1.3-ohm 0805 resistor.
Below is a 1uF 1nF 0603 capacitor.
And here is a 4.7pF 0603 capacitor. This is out of range for this instrument but it is giving a reasonable result.
Limitations: The adapter cannot measure 0402 sized parts - They are so small they can get under the sliding contact. It also cannot measure capacitors and inductors with contacts that don't protrude sufficiently out the sides. However, these parts could be soldered to the PCB directly and measured given the attachment pad design suggested by Shabaz.
Thanks to Adrian for help adapting the PCB for use with the DER-5000 and for providing some additional parts for testing. Thanks to Jan, Shabaz, and others for the many comments and suggestions.
Areas for improvement if I were to pursue this further include:
- Tweak tolerances on the slide
- Modify design for easier assembly of the contacts
A word about the overall usefulness of the DIY designs in this series and linked below. I've been very happy with the Kelvin clamps and imagine they are as good as anything one could buy. The tweezers aren't as good as what can be bought and the tip design needs further work. This SMD adapter is useable and while almost certainly not as good as the devices commercially available can be made at a much lower cost.
Thanks for reading and comments are always appreciated and welcome.
Changes and Corrections
7 Oct 2021: Corrected typos