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The description of the event determines participants must develop an ORP/Redox Probe, but otherwise in the rules it says nothing about what is considered one. It focuses on measuring NaCl concentration; is it possible to use a conductivity sensor instead of an ORP sensor?

TLDR: no you can’t use an ec probe

Think of an electrolytic cell, it’s basically that. You an electrode connected to the negative side, it would be made out of platinum or silver. On the positive side you have a reference electrode. That is a bit more complex, you need something like a .1 M solution of CuSo4 or AgNO3 and a membrane that can emit electrons(some sort of cloth or string)

Rule 3.b specifies the only requirement as having a salt bridge, though what counts as a salt bridge is up to interpretation if we don't get further clarification. However, conductivity probes don't usually have salt bridges. I would also probably not bring a conductivity probe to competition since the rules clearly want you to build a redox probe, and building something else would be against the spirit of the rules.

Whether or not building a redox probe to accurately measure NaCl concentration is possible is another question altogether, and is something I suppose we will all find out soon enough. Good luck!

Yeah, I suppose you just have to make your own formula for ppm and whatnot based on analog inputs. Very strange