Abstract: A system for detecting when a fluid product, which may be highly viscous and have a variable density such as milkshake, fills to a predetermined level in a container and for automatically terminating flow of the product into the container in response thereto. The system includes a capacitive proximity sensor positioned adjacent the outer wall of the container near the predetermined level. The sensor is connected in a conventional oscillator circuit which generates an oscillating signal having an amplitude and frequency which is a function of the capacitance of the sensor. When product enters the electrostatic field generated by the sensor, an electrical characteristic of the oscillating signal changes thereby causing the current drain of the sensor to increase. The current to the sensor is compared to a preset level, and the flow to the container is terminated when the preset level is exceeded.