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Re: Power Compacts and pH Probes
>I discussed this with Kim(?) from AH Supply at the AGA conference. I'm
>having the same problem but only when I try to use an AC
>adaptor. Everythings fine when using the nine volt battery. He
>recommended twisting the wire from the ballast to the bulb. I believe this
>is similar to wrapping grounding wire around those same wires. He seemed
>to think the problem was one of induction. He also suggested grounding the
>water in the tank to the ground wire on the hood. I haven't gotten around
>to trying either yet.
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
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Waveform Technology
UNIX Systems Administrator