[Test-Equipment] ESR meter

[Richard Knoppow]

----- Original Message ----- 
From: "Ken Kaplan" <krkaplan at cox.net>
To: <ka4inm at tampabay.rr.com>; "Discussion of Electronic Test 
Equipment" <test-equipment at mailman.qth.net>
Sent: Tuesday, June 28, 2011 8:48 PM
Subject: Re: [Test-Equipment] ESR meter


> Not sure where the term "electrostatic capacitor" 
> originated but that's
> what they are called in the Sprague TO-6A manual. As 
> Sprague knows a
> little sumthin 'bout capacitors, I thought I'd use the 
> term.
>
> Now that we are talking about it, what does the suffix 
> lytic mean with
> regards to electrolytic? The electro part I have (I 
> think).
>
> Maybe I should replace all those electrostatic caps in my 
> receivers with
> electroquiet ones? All these years I thought that noise 
> was in the aether.
>
> Ken
>
     All capacitors are electrostatic just as all inductors 
are electromagnetic. The lytic in electrolytic comes from 
the use of a chemical solution to generate the dielectric 
layer under the influence of voltage by means of 
electrolysis. It is this electrolytic action that explains 
why electrolytic capacitors are polarized, the dielectric 
forms in the right place only when the current passes 
through the capacitor in the correct direction. The 
requirement for an electric current to form the dielectric 
layer also explains some of the problems electrolytic 
capacitors have when they are not used for a long period of 
time. Electrolytic capacitors have the advantage over fixed 
dielectric types in being comparatively small for their 
capacitance. However, even the best of them has relatively 
high leakage, that is parallel resistance, in comparison to 
other types. In many applications this is of minor 
significance compared to the large capacitance value 
possible.
     In the past the main dielectric used in capacitors were 
air, special paper, selected types of mica, and ceramic 
materials of certain sorts. Paper capacitors were often 
impregnated with oil. The oil increased the dielectric 
constant and breakdown resistance allowing a higher voltage 
rating. Very high quality capacitors for high voltage use 
especially were sealed in cans with oil. The oil was similar 
to transformer oil but originally plain mineral oil was 
often used.
     Paper capacitors were also frequently impregnated with 
wax and the enclosure was sealed and coated with wax. The 
wax helped to prevent the entry of subsequent absorption of 
moisture by the paper in the capacitor, moisture leading to 
a breakdown of the paper.
     Mica capacitors were of two general types: silvered 
mica, and stacked mica. The former had the electrodes formed 
by electroplating the mica with silver except at the edges. 
The silvered mica plates were stacked in a sealed enclosure 
and the leads were directly soldered to the end plate. 
Stacked mica caps had separate foil electrodes interleaved 
with the mica dielectric, the entire assembly being held 
under pressure and sealed in a case. Silvered mica caps can 
be made to  a very high standard of accuracy and stacked 
mica caps were capable of being made to withstand very high 
voltages and were often used in transmitter.
     Other types of capacitors were vacuum types used mostly 
in very high voltage circuits like the plate circuits of 
vacuum tube transmitters. They are less likely to arc over 
under conditions of high humidity than air capacitors.
     Modern capacitors use a plastic film as the dielectric. 
The film is plated with the electrode in a way similar 
silvered mica capacitors but the form is similar to the old 
paper types, that is a long strip of plastic is coated on 
both sides and rolled up into a cylinder, the leads being 
fastened to the plating on the two sides. There are various 
techniques of winding the element to reduce stray 
inductance. These caps have very low leakage, very low ESR, 
and are much more accurate and stable than the older paper 
types.
     There are some web sites with much more on electrolytic 
capacitors including a description of the various types with 
their virtues and vices.
     All of this is very over simplified but much more 
detailed information is available on the web.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com