Re: slow response time of Ph circuit
From: Yukio YANO (yano_at_shaw.ca)
Date: 03/11/05
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Date: Fri, 11 Mar 2005 01:40:28 GMT
aman wrote:
> I have a simple PH circuit following is the description
>
> A pH probe involves measurement of the DC Voltage created between one
> Silver/Silver Chloride reference electrode - that has connection to the
> conductive water via a low impedence salt bridge (a porous plug filled
> with highly conductivie potassium chloride) - that creates a known and
> very constant voltage.
>
> It has an instrumentation amplifier as it is not possible to measure
> the voltage directly as it is a high impedance circuit.
>
> It was working fine but lately it takes like 15 minutes to settle down.
> So it has a long long response time of 15 minutes now.
>
> What can this be due to ? Any ideas ?
>
Bad Reference Electrode !, or bad Combination Electrode
Plugged Reference Electrode Junction
Ultra pure water, Very high Resistance ~10/15 Megohm !
What are you measuring ! Standard Buffers are ~0.05/0.10 Mol.
If it's slow response to Standard Buffers then likely a plugged Junction
Fast Test, Hold beaker in one hand while measuring pH and shuffle foot
across floor, with Bad Junction, readings will swing wildly due to
static electric build-up.
Yukio Yano
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