# Shifty Capacitors

Discussion in 'Electronic Basics' started by Ron Hubbard, Aug 9, 2003.

1. ### Ron HubbardGuest

In checking out some surplus caps using the capacitance
function of my wavetek multimeter, there were a few that
flickered between values. For most occasions I wouldn't worry
about it, but I have a project requiring matched capacitors.

My question, if the value is flickering between say 0.334uF
and 0.335 uF, how do I know if the cap is the higher or lower
value?

Thanks

2. ### Bob MastaGuest

It's probably around 0.3345 uF and the meter is just doing
the best it can.

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
Shareware from Interstellar Research
www.daqarta.com

You don't know which value it is. The two are within 1% of each other
and that's a good enough definition of 'matched' for most projects.
Forge ahead, and make enough money to get a .1% meter!

4. ### DarkMatterGuest

You give a *cheap* handheld way to much credit in the realm of
capacitance or inductance testing. Even an *expensive* handheld is no
substitute for a good RLC bridge for the level of resolve he is
apparently after.

5. ### John LarkinGuest

Almost everyone manages to say something intelligent on occasion.

*Almost* everyone.

John

6. ### Roy McCammonGuest

.----R1----+-----C1------.
| | |
| | |
Signal Source -----+ meter +--- gnd
| | |
| | |
'----R2----+-----C2------'

Get matched resisters R1 = R2.
Choose R1 close to the reactance of C1 at the frequency of interest.

Match C1 and C2 by minimizing meter reading.
You should be able to match the caps to almost
the same matching as the resisters.