Re: Voltage Measurement on a Capcitor

From: James Howe (concentricnews_at_wingspread.imap-mail.com)
Date: 12/13/04 

Date: 13 Dec 2004 09:24:58 EST

On Sun, 12 Dec 2004 17:56:23 -0800, John Larkin
<jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote:

> On 12 Dec 2004 18:13:47 EST, "James Howe"
> <concentricnews@wingspread.imap-mail.com> wrote:
>
>> I'm analyzing a circuit which contains a capacitor. The capacitor is
>> fed a constant current and is discharged periodically. The capacitor
>> is a
>> non-polarized .01uf capacitor connected on one side to a -12v supply and
>> the other side to the constant current source. If I measure voltage on
>> one pin, I get approximately -7.5v, the other pin measures around
>> -11.94. [...] What I'm trying to figure out,
>> being new to both electronics and using oscilloscopes, is what the -7.5v
>> volt meter value represents.
>>
>> I'm sure this is a really dumb question and when I see the answer I'll
>> probably go 'Doh!'
>>
>> Thanks.
>
>
> A DC voltmeter reads the average voltage. The average voltage of an 8
> volts p-p sawtooth, riding on a base of -12, should be
>
> -12 + (0.5 * 8) = -8,
>
> close to what you're seeing.
>
> John
>

Ok, that's what I suspected. There was some doubt about whether the cap
was really discharging completely back to -12 before ramping again, but
given the wave is 8v p-p and the -7.x v is close to the average if the
swing was from -12 to -4 I feel pretty comfortable that the cap is
draining to -12 before recharging.

Thanks. 

-- 
James Howe
Contact: http://public.xdi.org/=James.Howe

Relevant Pages

  • Re: HELP! Capacitor identification needed
    ... This encoder is probably 30 years old. ... > The capacitor is made, I think, by NEC, because it has marked +NEC at ... The reason I think it's a capacitor is because the circuit ... This could be a 6.8 Microfarad 20 Volt tantalum cap if it is across a power ...
    (sci.electronics.basics)
  • Re: signal and capacitor
    ... > power or signal to the capacitor in a circuit. ... The maths behind a capacitor is simply i = C*dV/dt. ... the impedance at DC is infinite, ie the cap is an open circuit. ...
    (sci.electronics.design)
  • Re: How to test capacitors in-circuit?
    ... Sure you can desolder it, test it out of the circuit, and resolder it ... reading from the test cycle on the capacitor. ... In many cases where a cap test ... using this LCR meter that showed a below normal reading to be false. ...
    (sci.electronics.basics)
  • Re: ESR Meter Chart
    ... i find that many times i need to use a scope in the circuit to detect ... if there is a faulting cap because many times a cap may test ok but ... I think that when ESR meters became ... that bad capacitor was in your grey area catagory. ...
    (sci.electronics.repair)
  • Re: A circuit demonstrating exponential decay....
    ... >>series, close the circuit, and watch the lamp come on and slowly go off ... >>as the capacitor charges up. ... >>Now I'm thinking an electrolytic cap and maybe a 10 ohm ... Professional Circuit Designer ...
    (sci.electronics.basics)