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TEK DMM 4020

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GigaJoe:
ah ..  it seems connector split in half

shakalnokturn:
That's only to detect insertion to that socket, for 4 wire measurements you need 4 banana plugs, 2 to high, 2 to low.

Edit: Well correct me if I'm wrong... That's at least what I'd expect from a DMM with High and Low sockets.

bdunham7:

--- Quote from: shakalnokturn on April 13, 2023, 04:55:05 pm ---That's only to detect insertion to that socket, for 4 wire measurements you need 4 banana plugs, 2 to high, 2 to low.

--- End quote ---

No, the Fluke 2X4W system has the source and sense connections on the same jack.  So if you look at it, the left half of the jack is the source connection and the right half is connected to the sense.  With normal test leads the single banana would short the two together, so you'd just have normal 2W ohms and any other function.  In 4W mode, the right half would be disconnected and the sense circuit would be connected to the jacks to the right.  The 2X4W test leads use a matching split banana jack that connects to the two halves independently and then keeps the two circuits isolated via a coax cable all the way to the probe tips.  The result is 'almost 4W' operation because you still have the probe tip and tip contact resistance in common.  In practice it works pretty well down to the single-digit milliohm level.  You could construct a true 4W system using this setup by replacing the probe ends with Kelvin clips, but Fluke doesn't sell them this way.

bdunham7:

--- Quote from: shakalnokturn on April 13, 2023, 04:55:05 pm ---Edit: Well correct me if I'm wrong... That's at least what I'd expect from a DMM with High and Low sockets.

--- End quote ---

Your expectations actually aren't unreasonable, this case is just a fluke.  ::) You might expect that for a single-probe near-4W result you could just use something like this (and you can).

https://us.rs-online.com/product/pomona-electronics/6303/70198464/?gclid=CjwKCAjw0N6hBhAUEiwAXab-TZvrW4SWl5qIght7jQBfHM05xa5YTs7FUF1dW_XrpbJB4ShA9GOlyRoCqEUQAvD_BwE&gclsrc=aw.ds

As far as I can tell the only significant advantage of the Fluke 2X4W system is that you can use the same set of probes for 2X4W resistance and all of the other voltage functions, whereas you might not want to measure 1000VAC with the 4W probes still connected, at least on some meters. 

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