Shifty Capacitors

[Ron Hubbard]

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

 

[Bob Masta]

On Sat, 9 Aug 2003 01:10:02 -0700, "Ron Hubbard"
<hubbard-ron@hotmail.com> wrote:

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?

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

Bob Masta
dqatechATdaqartaDOTcom

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

 

[Wade Hassler]

"Ron Hubbard" <hubbard-ron@hotmail.com> wrote in message news:<bh2ab4$toq6h$3@ID-43450.news.uni-berlin.de>...

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

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!
Wade H

 

[DarkMatter]

On Sat, 09 Aug 2003 14:07:29 GMT, no_spam@aol.com (Bob Masta) Gave us:

On Sat, 9 Aug 2003 01:10:02 -0700, "Ron Hubbard"
hubbard-ron@hotmail.com> wrote:

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?


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

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.

 

[John Larkin]

On Sat, 09 Aug 2003 12:08:16 -0700, DarkMatter
<DarkMatter@thebarattheendoftheuniverse.org> wrote:

Damn... he sports some brains every now and then.

Almost everyone manages to say something intelligent on occasion.

*Almost* everyone.

John

 

[Roy McCammon]

Ron Hubbard wrote:

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?
.----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.


--
local optimization seldom leads to global optimization

my e-mail address is: rb <my last name> AT ieee DOT org