Help converting orp probe ph value to orp value

[nivram]

I'm running a denitrator and trying to obtain negative orp values via my Apex. Unfortunately the Apex does not report values below 0 for orp. Based off the below post from an old thread on a similar issue. I believe I have come up with the formula to do this. Can anyone confirm? This makes me wish I paid attention in algebra.
7+(x/58)= y

X = orp value
Y= ph value using orp probe



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

[Randy Holmes-Farley]

How would you calibrate that?

I'm worried that using the pH measuring part allows the calibration to mess with the zero point. Some ORP probes allow no calibration and force the zero point, and some allow calibration of the actual ORP, but in either case, if you do not calibrate the ORP probe when it is attached to an input that allowed the zero point to float (as the pH measurement input does), then I'd think you'd have to calibrate with a known ORP standard of some sort.

FWIW, I can't confirm that the equation is right for how you intend to use it (the change in mv/pH unit is correct, but I worry about the zero point), but I don't have the time just now to check it. Sorry.