Controls the brine outlet valve – using its ability to measure small amounts of oil in water to maintain a very high (and unstable) percentage of water several feet above the bottom of the vessel. This allows suspended oil in the water phase to separate, thus inhibiting oil undercarry as a primary control function. While Probe #1 establishes this lower limit for the emulsion layer anything that floats on the water phase stops here.

Monitors the % water content from its position in the oil phase just below the lower grid. This provides real-time detection of the rate and extent of emulsion growth (which must, by Probe #1’s control, occur in the upward direction). Probe #2’s monitoring function allows the operator to avoid downstream upsets by providing advanced warning of such growth, and allows time for the implementation of corrective measures to prevent grid loss (transformer “trip”).

Is an in-line monitor of the water content of the crude feed and is typically located as far as possible upstream of the desalter (generally at or near the tank farm). This probe provides advanced warning of wet/contaminated crude feed, which is necessary to avoid the upsets typically resulting from tank switching and/or the introduction of slop oil.

The fourth probe monitors the condition of the water phase below the control probe, alarming on the presence of suspended oil that does not readily separate and threatens the condition of the brine effluent. This is of particular value when low-quality sources of wash water (e.g. stripped or straight sour water) are utilized that can upset the separation process and form stable oil-in-water mixtures (reverse emulsions). This probe is also used during mud-wash cycles.