pH probe - US standard plugs, and spiral reference electrode help
I got an almost-free Orion pH electrode, stored dry (bad). It is a double-junction probe with the reference electrode in a glass spiral, in its own
gel, at the top of a glass spiral. Typically quite expensive.
Currently the probe is showing just a few mV in vinegar. But the 10 MΩ input impedance of my DVM is probably not enough for the typical 400MΩ
impedance of the probe circuit, so I might need to make a high impedance pre-amp (or buy a cheap old probeless meter), or try a null detector circuit.
Some sites suggest you can revive dried out probes. I'll start soaking the outside in mildly acidic 3M KCl soon, the recommended storage solution.
I have 2 questions:
what is the purpose of the 2nd little plug in the legacy "US Standard" plug style? Some probes don't have this. There's almost no info on
the US plug style. How is this probe wired? A BNC probe just has the primary and reference electrode in series.
The white-ish gel (?) in the glass spiral leading to the reference electrode is broken in spots, from drying out. The gel is behind a porous
glass (?) plug. I'm soaking the inside with distilled water in the belief that the KCl is still present in the gel, so it might swell back up to
the right concentration when water enters the plug and makes its way up . Is there any hope of rescuing a probe once the gel of the reference
electrode has dried out?
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