Redox and fluorescent lighting

[Moggs]

I have noticed that the indicated redox value falls dramatically whenever a twin ballast 54w fluorescent control unit is switched on. The value falls from around 300mV to 200mV, switching on an ozone generator. The problem is repeatable. I have moved the sensor without any effect. You can imagine that this causes a big control problem when trying to maintain a steady redox value and I am concerned that I may be overdosing ozone at times.

Advice appreciated.

[GHL Support]

You have already tried to move the sensor away from the ballast as far as possible?
Which kind of lamp is it that contains this ballast?

[Moggs]

Hi Carolin
Yes, I have moved the sensor around. The ballast is a standard twin-choke unit for a dual T5 fluorescent tube system each tube rated at 54w. It's a standard aquatic control unit. I would imagine that the choke (coil, capacitors and starter) are influencing the sensitive ORP probe. Are these sensors screened at all? All other electrical equipment is properly earthed (grounded). I have recently cleaned and calibrated the sensor and it reads reliably in a 235mV standard solution (with the lighting unit switched off !).

Regards

[Moggs]

Matthias/ Carolin
You made some suggestions to try to solve the problem with the Redox values as mentioned above - thank you. Mathias, I have electrically 'earthed' the tank as you suggested and it has indeed had some interesting effects. The mV value drops very quickly on the application of the earth, (with lighting unit switched on) and eventually stabilises at a negative value of 45mv. Immediately upon removing the earth, the value increases to around 140mV (also with lighting switched on) but the real value is around 300mV (as measured by a separate ORP meter). The sensor returns the correct value with the fluorescent unit switched off (there are a number of other LED units which have no effect).

I am reluctant to attempt to calibrate the redox sensor with the earth in place as it would just appear to be applying an offset and would probably not address the problem of the step-change reading when the lights are turned on.

Any other advice would be appreciated as this is causing me some difficulty with ozone dosing.

Thanks and regards.

[Matthias]

is this a dimmable lamp and is this lamp connected over a control line with ProfiLux?

if you measure redox of the tank water in an extra cup - what happens then?

is this a redox card or a built-in redox port?