Re: Making an electrode for a conductivity meter

From: WayneL (nospam-mail_at_wlawson.com)
Date: 01/04/05 

Date: Tue, 04 Jan 2005 19:00:47 GMT

Hi Enlevez

                    I understand the overvoltage principle and know that it
applies to biased ac (10-20mV).
But if you had NO bias and just applied AC peak to peak say volt what would
the outcome be?
If the p-p voltage was lower than the cell "overpotential" (not overvoltage)
then there would be know effect apart from the oscillations of ions species?

Cheers

Wayne

"n2mp" <mcteguy@nospam.club-internet.fr> wrote in message
news:41da7466$0$23337$7a628cd7@news.club-internet.fr...
> Hello
>
> "Nick J." <nospam@nospam.com> a écrit dans le message de news:
> 4GjCd.274729$5K2.200722@attbi_s03...
>
>> I can see how Pt would be especially good for EIS where very small
>> amplitude
>> signals are used (e.g. the MacDonald EIS book suggests < 20mV, in order
>> to
>> stay well below most redox potentials).
>
> No that's not the reason why very small amplitude signal must be used in
> EIS.
> I suggest you to have again a look to both descriptions of EIS principle
> measurement and to relationship between current density and overvoltage
> (i.e. Butler-Volmer relation), in Bard & Faulkner's book. In the former,
> it
> will be said that determined impedance is the ratio between the excitation
> signal and the response signal (deltaE/deltaI) and that the main
> assumption
> is that the response is linear. In the latter, you'll see that the
> variation
> of charge transfer resistance vs current density is logarithmic. Thus, the
> only way for both items to be compliant is to use very small amplitude
> signal. Note that, here, we talk about the sinusoidal signal and that you
> can superimposed this signal to any DC signal.
> However, taking into account the initial poster's aim (i.e. measuring
> electric
> conductivity), this restriction is not applicable for you... on the
> condition that you excitation signal has a high enough frequency that
> charge
> transfer resistance doesn't interfere with your measurement or is
> negligible.
>
> Best regards.
>
>
> --
> Enlevez ".nospam" de mon adresse e-mail pour me répondre.
> --------------------------------------------------------------------------------------------------------
> Remove ".nospam" from my email address to reply me.
>
>
>

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