View Full Version : ORP calibration

06/18/2010, 03:57 AM

I am one of the DIY guys and recently I added an ORP meter to my Arduino controller. For the last a few months I keep checking the ORP value in parallel with a Pinpoint meter and I get very closed readings (+/- 5), but I need to end this exercise.

Question: Is there any way we can have two different calibration solutions ?
I can buy 400 ORP calibration, but to establish the slope I need another reference point. Any idea ?


06/18/2010, 07:08 AM
My OPR calibration fluid is 225 - 275.

Randy Holmes-Farley
06/18/2010, 11:07 AM
There are other fluids if you want to test other values. I discuss some here:

ORP and the Reef Aquarium

from it:

ORP Standards

Many ORP meters do not permit calibration, but some do, and for detailed ORP measurements, including situations where ORP is being controlled (such as when using ozone), it is worthwhile calibrating (or checking the proper operation of) the meter. Usually, the calibration is quite easy given commercial ORP standards. A variety of standards are available, including Zobell solution which can be obtained from Cole Parmer for $21. It is a solid that is reconstituted from deionized water, and has an ORP of 231 10 mv. Another common standard ORP solution involves putting quinhydrone into pH 7 and 4 calibration solutions to make standards of 86 and 263 mv, respectively. A third standard is Light's solution, which uses the Fe++/Fe+++ reactions described above.

This pdf has some detailed directions:


06/19/2010, 04:00 PM
Thank you jtma508 and Randy. I will get in touch Monday with Sensorex. Seems to be a nice calibration kit allowing both pH and ORP correction.