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Re: Power Compacts and pH Probes

Bill Wichers wrote some excellent advice and info and I think it bears
repeating.  Like Kim, I also thought the problem was probably one of
radio waves being emitted into the atmosphere.  Bill picked up on the
noise that the ballasts put on the power line too.  That's a rarer
problem, in my experience, and calls for a filtering device as Bill
points out.  If you're curious many ballast manufacturers will give you
a rating for THD or Total Harmonic Distortion, which is the noise.

Scott H.


> Sounds like a problem of conducted RFI. I suspect what is happening
> (since
> you said it works OK with a battery) is that the ballast is creating
> some
> kind of noise that is travelling back down the power cord and getting
> into
> your pH system through the AC adapter. Usually AC adapters provide
> for some
> EMI/RFI filtering for this, but many of the cheap "wall wart" types
> do not.
> The easiest way to solve this would be to purchase a *Tripp-Lite
> Isobar*.
> The reason I mention this particular model (I have no affiliation
> with
> them) is that it provides EMI/RFI isolation between each pair of
> receptacles. Get one of the 4 or 6 plug units, or the 8 plug if you
> need
> lots of plugs and plug the ballast into the NEAREST plug to the
> switch (-20
> dB I think it is), and the pH meter into the FARTHEST plug from the
> switch
> (-<biggest number> dB). The unit will isolate the two units from each
> other
> so that the noise doesn't leak between them. The Isobar units are not
> cheap, about $40 for the 4-plug, and can be purchased from
> http://www.cdw.com among many other places.
> 
> It is possible that the lead from the AC adapter to the pH meter may
> still
> pick up some noise. In this case, if a ground wire twisted around the
> length of it in a spiral doesn't work, you might try getting a piece
> of
> washing machine hose from a hardware store. Use the kind with an
> external
> stainless steel braid, and *ground the braid*. This will provide a
> pretty
> good shield for the wire.
> 
>      -Bill

Like Kim, I also thought the problem was probably one of radio waves
being emitted into the atmosphere.  Bill picked up on the noise that
the ballasts put on the power line too.  That's a rarer problem, in my
experience, and calls for a filtering device as Bill points out.  If
you're curious many ballast manufacturers will give you a rating for
THD or Total Harmonic Distortion, which is the noise.

Scott H.


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