Interface detectors enable the operator to precisely control the interface level in the most difficult of applications. These detectors are made of two basic components: antenna and the power supply/signal conditioning circuitry. By measuring the energy absorption of the fluid surrounding the antenna, the interface detector senses the water concentration in an emulsion regardless of fluid density, viscosity, density, temperature, pressure or pH. The high frequency signal from the antenna allows the interface detectors to see through coatings that may adhere to the probe, a problem that is common with capacitance probes. The output can be a simple on/off adjustable relay to activate a solenoid valve. The interface detector is not limited to oil/water applications but may be used wherever an accurate interface control is a priority such as, desalter/dehydrator and production separators, automatic dewatering of crude and refined storage tanks, waste water treatment and slop oil recovery systems.