forget about the RC oscillator, build a simple series RC circuit and
conect the input to a function generator producing 1hz output.

Find a proper value of R so the capacitor will just have enough time to
charge with the incomming square wave.

monitor the charging of the capacitor using an oscilloscope, you can use the
exponential equation for the charging of a capacitor in a series RC circuit
and solve it for C.


For more precise results, you can monitor the capacitor charging process
with a digital oscilloscope and hook up a computer to it using GPIB
(IEEE-488, HPIB)

Write a program to do a "data dump" from the oscilloscope to the computer
carefully look at your data and determine where 1 time constant is.

In an exponential curve, voltage changes quickly at the begining of the
charge curve and then things slow down.

TAKE your measurement at the begining (t,v) if you wait until the cap is
almost fully charged, a very small error in Vc can result in the wrong value
of t (curve is almost horizontal)


Option 2 don't use function generator, use a constant current source
instead!!

IF you charge a capacitor with a constant current source, the result is a
linear ramp, and the capacitance can be obtained from simple arithmetic!!!

V = (1/C) * I * t



"gmv" wrote in message
news:JQwMd.18007$C24.14251@attbi_s52...
Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.

These capacitors are to be used at frequencies
under 1 Hz.

Everytime I try to use my meter to measure, the
capacitance will change from one range scale
to the next, I guess because the frequency changes too.
When I use a typical non-electrolytic capacitor
these changes in readings are not there.

I have been thinking of making
a simple RC inverter oscillator and using
the resulting frequency to determine the
true capacitance in the small signal
application I want to apply them to.

Maybe there are non-electrolytic capacitors
in the 10uf to 100uf range but if so
I have never heard of them before.

I do not know if any of you have ever seen
the SCI FI movie THIS ISLAND EARTH
but I am in need of several of those
fantastic capacitors.

I am trying to get a reading
within 1% of reality.

Help here is appreciated.


--
Regards;
gmv