workaround for reading -orp values?

Avast Marine

.Registered Member
Looking to be able to read ORP in negative values. I made a bnc crossover cable to switch the positive and negative wires but I can't get the controller to read past zero. Shouldn't the crossover "trick" the controller to be reading the -orp value as a positive one? Any tricks to get this working would be very helpful. TIA
 

Bryan

New member
From previous posts I have read ORP will not display negative values on the Aquacontroller. I believe this is by design and no workaround.

Hgere is a suggestion though, why not design some circuity a pre-amp in a way that will add voltage to the probe reading to move it into the positive range. If your lowest reading is likely -100mv then add 200mv to bring it to 100mv and base your program on the positive values. If the value drops to 0 on the display then you know the true reading is-200.

Just a thought anyways.
 

Avast Marine

.Registered Member
Would calibrating with 700mv solution to 400mv give me -300mv offset? My target is -200mv coming out of a sulfur denitrator so would calibrating it like this read 100mv with the above calibration technique? Or does it not work like that?
 

Bryan

New member
Hm, i know in my jr I can add a PH offset. Which model do you have, perhaps a offest can be added to the ORP.
 

Avast Marine

.Registered Member
I have the AC3. I will look in the manual to see if that is possible, should be since it is actually a ph meter not a true orp meter, I just wasn't sure if that scale transfered even or if there was something more to it than that.
 

clp

.Registered Member
As a work around, you should be able to use the ORP connector in pH mode. A pH reading above 7.0 is a negative ORP reading. For every 1 unit of pH change the ORP is changing by about 58 mV. An ORP reading of -200 is equivalent to a pH reading of about 7.0 + 200/58 = 10.44.

Curt
 

Avast Marine

.Registered Member
hmmm.... Mine wont read above 10.0 with the AC3. I can drop the ph probe in my kalkwasser to verify this (I actually bought a differant ph monitor so I could monitor my kalkwasser solution). Is there a setting that needs to be changed or maybe a firmware issue?
 

clp

.Registered Member
It just tried it with the latest firmware (3.3) and it does read 12+. I'm not aware of any issues w/ earlier versions though.

Curt
 

Bryan

New member
I don't know if your controller supports this, but in the jr there is a debug menu which allows the user to enter a offset for PH. there might be one for ORP as well.

Go to the second screen self test screen on the AquaController. Press the up button twice, the down button twice, and then the select button. You should now be in the manual cal menu.
 

dadonoflaw

New member
when you say use the orp connector in ph mode do you mean use a ph probe in the orp connector on the controller?
 

clp

.Registered Member
Since you are interested in measuring ORP then you must use a ORP probe. This hack simply allows you to read negative ORP values on a pH meter.

Curt
 

mgroleau

New member
Hi,
The issue I have found is that the Apex prevents you from coding with a Ph probe value greater then 9.99. Can someone from Neptune System look at this and put it on the list of changes for the next firmware update? Apart from that, the probe workaround works great. Obviously, it would be much better if Neptune System implement a firmware update to read negative ORP, like Digital Aquatic did not too long ago. Thank you in advance for your help and I wish you a very good day,

Mathieu
 
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