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I wish I knew how an ORP meter works!

If you know pH meters, you’ll breeze through this. Why? Because essentially an pH meter and an ORP meter work the same way. They both read the difference of potential between a reference electrode and a sensing electrode.

For y’all who don’t do pH, let’s break down the process. Just like a pH measurement, ORP measurement uses a formula, the Nernst formula:

ORP meter-the nernst formualr
Courtesy of PhysiologyWeb


Don’t panic. You don’t need to remember it. But it helps to understand how an ORP meter measures. The formula gives you the relation between the ratio of oxidizing and reducing agents and the electrical signal detected by the sensor.

The reference electrode uses a silver/silver chloride (Ag/AgCl) element in a potassium chloride (KCl) solution, with a junction open to the process. The sensing electrode has a noble-metal pin, normally platinum or gold. The noble metal of the pin will gain or lose electrons to the solution. Thus, it creates a potential difference between it and the reference element. We then calculate the ORP value from that difference between the two elements. Piece of cake!

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