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Re: PH Probe Problem
>From: Andrew Hamilton <andrewha at tafe_sa.edu.au>
>
>I recently replaced my lighting system and now have my fluro's run from two
>electronic ballasts which I have placed remotely in the aquarium cabinet.
>The tubes are suspended from the inside of the hood which rests on the
>glass. the wiring is therefore also contained under the hood.
>
>As I am not running a sump my Ph probe is also placed under the hood. I have
>it positioned as far away from the wiring as practicle.
>
>The problem I now have is that the lights seem to interfere with the Ph
>reading. Whilst the lid on the hood is closed I am getting a reading of
>close to 6.9, however as soon as I raise the lid the reading plumits to 6.5.
>If I turn the lights off the reading also drops to 6.5. Using a ph test kit
>my ph seems to be around 6.6 (the kit is not very easy to read). I have
>checked the wiring and nothing is coming in contact with the wiring to the
>probe. Obviously there is some electrical interfernce here that I must deal
>with.
>
>Would insulating the lighting section off to the Ph probe area work and what
>sort of insulating material should I use. Has anyone else had simular
>problems? Any advice would be greatly appreciated.
>
>Andrew
>In sunny Adelaide, South Australia.
Alternating currents form the flourescent lights and wiring are being
induced in your PH probe and wiring. These types of problems cause big
headache's for electronic types. You have moved the probe away from the
wiring but the same current that flows throught the wire also flows through
the bulb, and it could be this current in the bulb that induces the
magnetiv field.
There is no pratical way to use non-conductive insulation to solve this problem.
You can try to reduce the electromagnetic energy radiated by your lighting
wiring by twisting the insulated wires from your ballast together (twisted
pairs radiate/pickup less that non-twisted pairs) and by running the wires
to the bulbs close and parallel to the bulbs until they depart for your
ballast. A metallic shield over the wires may also help. You may want to
use steel conduit for the ballast wires.
You can try to limit the pickup to your PH sensor by using a shielded wire
to the PH amplifier, twisting the pickup lead (if it's twinlead),
shoortening the lead, and trying a metallic shield over the PH sensor (does
Vegamite come in cans or bottles?).
Paul,
In sunny So. California.