[pcm81]

I have Extech PH220-C, which display's pH or mV. My question is: are these mV the same as ORP or is it just the raw signal from pH probe but not an actual ORP?

[pcm81]

I have Extech PH220-C, which display's pH or mV. My question is: are these mV the same as ORP or is it just the raw signal from pH probe but not an actual ORP?

OK, so doing some googling it seems that the mV output is the output from the pH probe, not an actual ORP measurement. For ORP measurement id need an ORP probe. Soooo, now the question becomes: is mV output of ORP probe equal to ORP value? If so, I might just buy ORP probe and read it with my pH meter or even my multi-meter (my hp3457A needs some use) that has bnc connection. On a flip side if mV output of ORP probe is drastically different from ORP reading i'll probably just buy ORP meter with a probe... What yalls think?

[Borek]

Technically pH meter is just a specialized voltmeter, ORP meter is just a voltmeter too. pH meter uses an ion selective electrode and is scaled not in volts, but in pH units - which are directly proportional to the electrode potential (compare http://www.ph-meter.info/pH-measurements-potentiometry ). ORP can use any electrode, usually including ion selective ones, and is scaled in volts - but converting these volts to concentration is trivial (especially taking into account fact all voltmeters made these days are digital and use some kind of microcontroller).

[pcm81]

Technically pH meter is just a specialized voltmeter, ORP meter is just a voltmeter too. pH meter uses an ion selective electrode and is scaled not in volts, but in pH units - which are directly proportional to the electrode potential (compare http://www.ph-meter.info/pH-measurements-potentiometry ). ORP can use any electrode, usually including ion selective ones, and is scaled in volts - but converting these volts to concentration is trivial (especially taking into account fact all voltmeters made these days are digital and use some kind of microcontroller).

Thanks. What i was interested in is if Volts output of the ORP probe is the same as the actual ORP value or if a given probe will have some sort of scaling coefficient between volts it outputs and ORP value.
If there is scaling (especially non-trivial one like for thermocouples) that the actual orp meter is doing math on, then i'll probably buy an ORP meter with a probe. If the scaling between probes output and actual ORP is trivial then i can just buy and cal ORP probe. I don’t want to mess with non-linear calibrations between ORP standards and mV output of the probe...

[Borek]

What i was interested in is if Volts output of the ORP probe is the same as the actual ORP value

That's the idea.

When you use specialized ion selective electrodes ORP can have another mode of work, that allows calibration, temperature compensation and so on, but when using normal electrode (that is just a piece of metal) these are not necessary.