Test Kit for constructors

Posted: 2/1/2011 8:23:51 AM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................

Joined: 12/7/2007

Measuring small capacitances is, IMO, extremely useful for theremin builders / developers..

I have used several instruments (some made myself) but these are sometimes awkward (my Peak inductance / capacitance analyser is great, but takes a long time to aquire a reading, and does not automatically update, and my analogue home-made LCR bridge is fiddly)

I have just bought a Newcason XC6013L (http://www.mib-instruments.com/servlet/the-129/Capacitor-Capacitance-Meter-tester/Detail) capacitance meter for £14, and this cheap instrument is great!

On its 200pF (most sensitive) range, one has a display showing xxx.x pF (199.9pF to 00.0pF) and the value updates about twice a second..

The standard multimeter probes provided are useless for the 200pF range - one needs to construct a screened probe with low capacitance (<10pF) [b] Not so sure about what follows .. something is going wrong.. [/b][i]or a probe with twin screened leads, one being a dummy lead to balance the capacitance of the leads against the differential inputs - the probes can be adjusted to 0pF on the meter.[/i]

With the above, it is possible to resolve 0.1pf +/- 0.05pF .. One can, for example, connect an antenna to the probe, ground the common, and measure antenna capacitance with different positions accurately enough to determine the maximum value - and get a rough idea of minimum value of capacitance.

Only had this meter for one day, so not yet able to comment on reliability etc.. but it does seem well made. The 'manual' is a single page of gobbldygook - but, apart from the use of the difference inputs (which is not mentioned) the instrument is self explanatory.. [b] updated -> [/b]I am not yet sure how / if the C+ and C- inputs work differentially (I thought they did, but am getting results from my newly constructed probes which seem to indicate that I am misunderstanding something..

I have been buying a few low-cost Chinese instruments lately - and will post reviews on this thread.

If anyone else has information on useful instruments, I hope you join in!


[b] Seems I may have posted on this too soon [/b] - Everything works fine with a short screened lead, but it seems that one cannot use C+ and C- inputs for difference measurements / compensation... They seem to add! Still good - but not quite as good as I first thought.

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