RE: Non-linear capacitance
Ceramics are complicated formulations,
including dopants to tailor characteristics
like NPO, HV, firing temperature, etc.
more complicated than just "ferroelectric".
Reference for all interested in Ceramic Capacitor properties:
Properties Devices and Appication
edited by Lionel M Levinson
General Electric Co.
Marcel Dekker, Inc. NY
TK787115.C4E418 (1987) CR 1988
From: Tesla List [mailto:tesla-at-pupman-dot-com]
Sent: Friday, January 07, 2000 8:02 PM
Subject: Re: Non-linear capacitance
Original Poster: Ed Phillips <evp-at-pacbell-dot-net>
Tesla List wrote:
> Original Poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com>
> I am sloooowly gathering materials to build a fiber optic probe set.
> I do that, I decided to build a passive HV scope probe. Knowing that
> capacitance in high-value resistive dividers will cause probe anomalies, I
> decided to use a capacitive divider approach. For the "hot" end of the
> divider I used a string of forty 680 pF/1KV ceramic disk capacitors. When
> tested the probe with 120VAC input, the division ratio was as expected.
> when I cranked the input voltage up, it appeared that the impedance of the
> string decreased as the voltage increased.
> My first thought was that since I did not immerse the cap string in oil,
> perhaps corona was responsible for a change in apparent impedance. I was
> just about to try the oil immersion thing when I saw in a post today:
> >This is sort of like those ceramic capacitors that have different
> >capacitance at different voltage levels
> Is this a real phenomenon with ceramic disc capacitors?
> Gary Lau
> Waltham, MA USA
Sure you've gotten response to this, but in case not the answer is
the titanates used are "ferroelectric", and indeed do have capacitance
which is a non-linear function of voltage.