Hach 3400 Analogue Contacting Conductivity Sensors. These enhanced performance sensors are manufactured to exacting tolerances using high quality, rugged materials for demanding applications including ultra-pure water, clean-in-place (CIP), and boiler/condensate monitoring. The sensors measure from theoretically pure water (0.057 µS/cm or 18.2 MΩ) up to 200,000 µS/cm.