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Re: A stable and repeatable low value capacitance meter


 

On Sun, 4 Sep 2022 at 11:57, Hans Wagemans <on4cdu@...> wrote:
I use this LC meter and am very satisfied with it:
LC meters on Ebay that look the same have a much worse specification.

73, Hans, ON4CDU
I don¡¯t have one, but this LCR meter from Hungary quite impressed me




Note it is 4-terminal, and works on the principle of an autobalancing bridge, like at least some of the HP/Agilent/Keysight ones do. My Agilent 4284A (0.05% basic accuracy) works on that principle.

On my HP 4284A one has to enter the length of the test leads (either 0 m, 1 m, 2 m or 4 m). There¡¯s no facility to enter the test lead length on that meter.?

I don¡¯t know why HP consider the test lead length important, but they obviously do. On the 4284A, option 006, which adds support for 4 m test leads, was an extra cost option. It¡¯s a software only option, but the instrument needs recalibration - I assume to check the 4 m results meet the specification. My meter didn¡¯t originally have that option, so I asked Keysight the cost of upgrading. They said when I sent it for calibration they would add it free of charge. The maximum frequency of the 4284A is 1 MHz (wavelength of 300 m), so even 4 m test leads are very small compared to the wavelength.?

Obviously 2 different imp¨¦dances would present the same impedance at the end of test leads, if those leads were of a different length. But I would have thought that as long as the 4 test leads were of the same length, the 4-wire Kelvin connection would have compensated fully for the length.?

Dave?
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

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