Redox reading erratic

[Dalmerjd]

My redox reading can jump 5-20 points in seconds. Should the probe be replaced, cleaned? The tolerance is set at 5, it calibrates in 220 in less than 120 seconds and is about 1 year old.
If cleaning is required, what is the correct procedure. My instructions went AWOL.

[Blahenazo]

Cleaning info can be found here
http://www.aquariumcomputer.com/Forum/showthread.php?t=1606

they say probes don't last very long but mine became more stable when I added an earth pin to my tank (but it was measuring 30 /40 less when my T5's where on.)

[almost]

Want to control nitrareductor filter with reedox, setting point -250.

Readings change constantly, reedox is about -150 always.

Now I can measure No3 in the aquarium as a result of bad controlling of the nitrareductor filter.

I changed the signal filter to 1, the same occurs.

What can I do to stable up the reading so it can control the filter in the area of -250 -200 that it should be operated?

Please advice.

.

[Matthias]

Readings change constantly, reedox is about -150 always.
how do the readings change? range? frequency?
do the readings also change if the probe is immerged in glas of water?

[almost]

how do the readings change? range? frequency?
do the readings also change if the probe is immerged in glas of water?

It changes +-5 in a second.
I didn't test it in a glass of water, I can try if needed.
The probe is that of Aquamedic because it has o 13mm thread and it was calibrated in your fluids, calibration went well.

The same probe in another ORP controller, gives very stable readings.

I have one of your ORP probes, waiting to connect it to the expansion box.

Tell me what you want me to try.

[boboxx]

can you see if setting the Operation Mode of the redox sensor to "Twooption controller" will fix your problem?

[almost]

It was allready in 2potition controller.

[boboxx]

have you tried changing it and setting it back?

[almost]

Just did it, nothing changed.

[Matthias]

A change of +/- 5 can be normal, it depends on several things, e.g. the flow.

If you incease the hysteresis the controlling should work without issues.

Where is the technical problem with it? Maybe I just don't understand.

[almost]

The nitrareductor filter depends on low level of O2.
It needs to be operated in -250,
From the manual of Aquamedic nitratereductor:


"If it exceeds -50 mV, the denitrification reaction may stop at the nitrite stage!
If it falls below -300 mV, all the nitrate is reduced. The bacteria then start to use sulphate. This is a very undesired process because the end product of this reaction is Hydrogensulfide.
Hydrogensulfide (H2S) is toxic and smells very strange like fouling eggs."


I have set it to work, in area of -250.
So, in one sec it is above the next sec is bellow.
I changed the hysterisis so that powerbar is not allways in a on/off status.
But, when it goes to -260mV, it opens the flow of the filter, when the flow stops (pump connected to powerbar) I see readings of -150mV.
It should stop the flow of the filter earlier, but due to hysterisis and that values changes +-5 all the times, P3 stops the flow much later than I wanted.

My goal was to open on -250 and close on -230 and I can't do that (untill you help me :) ).

[Matthias]

The hysteresis covers the range between the upper switching point to the lower switching point.
This means
if you have a set value of -250 and a hysteresis of 50 the upward control will be activated at -250 - (50/2) = -275, the downward control will be activated at -250 + (50/2) = -225, both controls (up and down) will be activated when the wished value is reached.

-> hysteresis must be large enough to reduce frequent switching (in your example due to the +/-5mV)
-> and must be small enough in order not to switch too late (in your example: -150mV)

if you want to open on -250mV and close on -230mV you need these settings:
nominal value -240mV (center of wished range), hysteresis 40mV (effective hysteresis for upward control = 40mV / 2 = 20mV)

if it does still switch too late:
Consider the time lag of your system (so-called "overshot"). Switching off will not immediately stop the raising of the redox!

[almost]

O.K. Matthias, I just put the settings you told me, I will inform about the readings of mV (about the correct controlling of the nitratereductor).

PS: I just saw that when I put -240mV and press save, it saves the value -239mV, so I put -241mV and with save it went to -240mV. I do not know if this is critical or not, I just thought I should share it since it made me wonder why this happens (in possitive values, whatever I put, pressing save doesn't change it).