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HP 4328A Milliohmmeter update and repair

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Tomorokoshi:
I got an HP 4328A Milliohmmeter for a specific technical project 1.

It was rather cheap on ebay, and was missing half of the Kelvin probe. This was clear from the listing, so no surprise.

The update was to replace the original Kelvin probe assembly with independent banana terminals. I used Pomona 3750.

The unit resistance of 12 AWG copper wire is 5.21 mohms/meter. The length of wire between the leads is 0.0762 m. Therefore, one would expect around 5.21 * 0.0762 = 0.397 mohms. This is closely matched by the meter after going through the calibration procedure in the manual.



1 Honest. Not just adding to the collection.

Jay_Diddy_B:
Hi,

I also have one of these meters. Mine was missing the leads. I bought the connector from Digikey.

The part number is RM12BPE-5PH(71) Digikey: HR1732-ND

It is made by Hirose.

Regards,
Jay_Diddy_B

Tomorokoshi:
Mine was the older version, with a permanently attached cable that terminates to a connector that holds the two Kelvin leads. Basically no replacements available. At some point they changed to the updated connector version.

With the Kelvin leads still on the test wire, I transferred it to my 250 mA current source on the Force leads, and measured the voltage on the Sense leads. I got 0.097 mV. Therefore, as a calibration datapoint I get 0.097 mV / 250 mA = 0.388 mOhms. I looks like I'm directly measuring around 0.393 mOhms, so compared to the other values it's doing very well.

Tomorokoshi:
Today is July, 24 2020, so it's appropriate to post this picture:


52 years of reliable service.

HighVoltage:
Sometimes brand new parts show up for this HP 4328A,
like this analog dial.

Someone got lucky for US$ 23,50
https://www.ebay.com/itm/383614194226

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