A level transmitter can generate a level measurement signal according to the position of a float that follows fluid level in a tank. The transmitter can comprise an optical encoder with a patterned disk that is linked to the float so that fluid level change produces disk rotation. An array of optical sensors positioned on one side of the disk can read reflective and absorptive patches attached to the disk's surface to identify disk position and disk rotation. One or more of the sensors can collect a signal from a reference area of the disk. Circuitry can compare the signals output by each data sensor to the reference signal to enhance binary classification of each acquired data signal. The transmitter can operate in multiple encoding modes, each of which can provide a level of redundancy.