Making Kelvin Test Leads For My LCR Meter | Voltlog #326

in a previous video of all log 303 i reviewed this lcr meter from hand tech and this is a nice unit performs well for this price range comes with a nice eva carry case for storage but it doesn't come with four wire kelvin test leads which are kind of needed if you want to take precise measurements if you think about a standard pair of test leads these will have about 0.1 ohm of resistance per lead and if you have two of these when doing a measurement that's 0.2 ohms added to the value you are measuring now imagine measuring a 0.1 ohm resistor with that 0.2 ohm included in the measurement with a four wire kelvin connection you have two wires carrying the current that's used for the measurement and another two wires doing the sensing which improves the measurement accuracy a common mistake when building kelvin four wire test leads is to use these standard alligator clips because in a standard alligator clip the top and bottom jaw are connected electrically at the hinge point and let me prove that to you with the multimeter on the continuity tester if i measure between the top jaw and the bottom we have a continuity and this kind of defeats the purpose of having separate sense lines if they are getting shorted at some point with the current carrying trace for a true four wire kelvin connection you would need a special type of alligator clip like these ones and these have a plastic hinge uh and the top and bottom jaws are not electrically connected between them these can be quite expensive they are made by a good manufacturer but i got mine from aliexpress for cheap these are no name they do not excel in quality but they're good enough for the type of instruments i'm going to be using them with and with the amount of work volume they're going to be seeing on my bench uh they should last a while for the other end of these test leads i have designed this pcb which will be part of the connector that slides into the contacts on the front of the lcr meter and these pcbs were manufactured by pcb way they are the sponsor of this video and as you can see they look very nice with this gold plating finish the thickness of the pcb is 1.5 millimeters and i've experimented with different thicknesses this seems to be the best for a nice fit in the lcr meter and while i did try to space these apart so that you can't physically plug this in uh backwards i didn't quite manage to get that result and i don't think it's worth to order another set of boards just for that reason alone the design of this is open source i will place a link in the description so you can download the files and if you want you can build one of these for yourself i have also designed and 3d printed an enclosure for this so i don't have any exposed electrical connections and this is a pretty simple design this was designed to be like a press fit connection between the top and bottom side but depending on how well your printer is tuned this might end up too tight or too loose so then you can just maybe use a bit of glue to hold it together as for the connection wires that go between the clips and the connector i got some of this 28 awg 2r shielded cable this should be thin enough to still be flexible and at the same time still provide good connection and we are talking about small currents here so 28 awg is gonna be fine ideally we want this cable shielded and we want the shield to be connected to the guard terminal on the instrument the connection uh to the uh probes should be done like this like force plus and force minus inside the same shield which is then connected to guard sends plus and sense minus inside the same shield which is also connected to guard these two holes on the pcb are in here so that you can run a very thin zip tie to secure the wires to the pcb once they're soldered in and this way they will be very rigid mechanically and will not break the solar connection if stress is applied from the outside soldering through the clips is kind of difficult the connection tabs are located deep inside the handle but they do appear to be pre-tinned my main concern here is not to melt the plastic handle while soldering and i did notice that they used lid free solder to thin these tabs but in the end uh the handle seemed to handle the heat pretty well there was no obvious melting of the plastic i did manage to solder this the clips don't have any way of mechanically securing the the wire so i just used some hot glue inside the handle with some heat shrink sleeving to wrap everything up and hide it under the heat shrink and this is the end result it's not as pretty as with some higher quality connectors that you can buy but still this is results and it will get the job done i have about 50 centimeters of wire length on these i don't need more than this and you probably don't want to go very long on these test leads this is how it goes together it just it's just a press fit now let's put these to a test and they just seemed like a good fit for the connection on the meter with the wire going up to the right side this will work fine for me but the first thing i want to do is to calibrate these test leads so i can take some measurements after calibration everything seems to be working fine here is for example a 33 picofarad ceramic capacitor being measured there are also another couple of options you could consider besides building this from scratch like i did and one way is to buy a ready-made compatible kelvin test lead set i'll put a picture of one of those on screen i think there are some available that use kind of the same spacing on the slot connector so they might just work like a plug-and-play solution but i haven't tested that so uh i don't know you'll have to try it and the second option is to buy one of these kelvin test lead sets that come with banana jacks and you can cut away the banana connectors and solder the these test leads to these custom made pcbs that i design one downside of doing that is that i'm not sure if these wires are shielded i think not so that's a slight disadvantage over the method of building it yourself having a shield on test leads connected to guard terminal plays a role in porosity capacitance i'm not sure how important that is i guess it also depends on the level of accuracy you expect from the meter i'm pretty happy with these results and i think this is a nice little weekend project that you can try if you have an instrument that does four wire type measurements link for all of the parts used in the project will be in the description below the video so check them out if you like the video please consider supporting the channel on patreon you can do that with as little as one dollar per month or you could just hit the like button which is also good enough thank you for watching and i will see you next time

Channel: VoltLog

Views: 6,096

Rating: 4.9346051 out of 5

Keywords: Voltlog, Kelvin Test Leads, DIY Test Leads, Making LCR Test Leads, 4 Wire Test Leads, Kelvin Test Clips, 4 Wire Measurements, Guard Terminal, Shielded Test Leads, LCR Meter Test Leads, LCR Meter, Kelvin Leads, Shielding Guard, Kelvin Alligator Clips, LCR Meter Calibration, Sense Terminals, Force Terminals, DIY Kelvin Leads, lcr meter

Id: MpJgCks37lE

Length: 7min 53sec (473 seconds)

Published: Mon Aug 24 2020