we discussed this a while back, how it might be done, today i stumbled
across that:
When Hydrogen Peroxide and Hydrochloric Acid (HCl) are used to replenish
the Cupric Chloride () etchant, the Hydrogen Peroxide additions are
controlled by an Oxidation/Reduction Potential (ORP) meter, which
functions very similarly to a pH meter. The Hydrochloric Acid additions
are controlled by a very sensitive conductivity meter, which has only
recently been commercially available.
here:
<
http://www.pcbfab.com/iepart3.html>
I still think automatic maintainance is pointless in our low volume
applications, but i wanted to have it mentioned as we did discuss it at
some point and that text provides hints.
ST