Plating shops ask whether they need pH or ORP monitoring. The answer is usually both, but for different reasons.
pH Measures Acid Concentration
pH measures hydrogen ion activity. In plating baths, it tells you the acid concentration. In a sulfuric acid anodizing bath, pH 1.2 means about 15% sulfuric acid by weight. In an acid chloride zinc bath, pH 4.5 indicates the correct balance of acid and zinc chloride.
If pH drifts, deposition rate changes, coating adhesion suffers, and hydrogen embrittlement risk increases. pH control maintains the correct chemistry for the electrochemical reaction.
ORP Measures Oxidation State
ORP measures the solution's tendency to gain or lose electrons. In a hexavalent chromium bath, ORP tells you the ratio of Cr⁶⁺ to Cr³⁺. If ORP drops, the bath is reducing. Hexavalent chrome converts to trivalent. Plating efficiency collapses.
In electroless nickel, ORP monitors the oxidation state of the reducing agent, usually sodium hypophosphite. When ORP drifts, the bath approaches depletion and stops depositing nickel.
When You Need Both
Hexavalent chromium plating needs pH to control sulfuric acid catalyst concentration and ORP to monitor chrome oxidation state. Electroless nickel uses pH as the primary control variable and ORP as a secondary indicator of bath health. Anodizing typically needs pH only.
The SP100 series offers combination pH/ORP sensors with a single housing and cable. One installation point. Two measurements. No additional wiring.
Send me your process chemistry. I will recommend the right sensor configuration.