An analyzer for a grease interceptor for measuring identity of materials and levels of fat, oil, and grease (FOG), water, sludge and air having a probe which includes a controller and a sensor sub-unit. Sensor circuits include a microcontroller, timers, and sampling capacitors. The sensor sub-unit includes a plurality of electrode ring pairs coupled to a plurality of timers for converting capacitance measurements to frequencies under the control of a microprocessor in the controller. The frequencies identify the measured levels. A calibration of the probe converts a range of frequency values of each sensor circuit to an arbitrary scale for improved accuracy.