A device (102, 302) for measuring a geometry of a fluid meniscus (132, 328), comprising: - a fluid chamber (104, 304) comprising a first fluid (128, 324) and a second fluid (130, 326), which first fluid is electrically conductive, which second fluid is electrically insulating, and which first and second fluids are mutually immiscible and in contact with each other over a fluid meniscus (132, 328), - a main electrowetting electrode (118, 318) located in a main plane and auxiliary electrowetting electrodes (120, 122, 124, 126) partially surrounding the fluid chamber and being located in respective auxiliary planes (121, 123, 125, 127), for controlling the geometry of the fluid meniscus, - a voltage source (134, 33) for providing a voltage between the main electrowetting electrode and a plurality of auxiliary electrowetting electrodes, - a measurement circuit (144, 342) for separately measuring capacitances between the main electrowetting electrode and at least two of the respective auxiliary electrowetting electrodes (320, 322), the measurement circuit comprising a multiplexer (212, 414) for demodulating a signal (210, 412) indicative for said respective capacitances, wherein the multiplexer is a time domain multiplexer, wherein the time domain multiplexer is arranged for employing demodulation signals, each demodulation signal being a square wave signal having a low value and a high value, wherein the voltage source comprises voltage switches (331, 333, 407, 409) for alternatingly disconnecting the voltages corresponding to the high values of the respective demodulating values, or wherein the multiplexer is a frequency domain multiplexer, wherein the voltage source is arranged for providing voltages at specific frequencies and wherein the frequency domain multiplexer is arranged for employing demodulation signals each having a frequency component corresponding to the respective specific frequencies. - a fluid chamber (104, 304) comprising a first fluid (128, 324) and a second fluid (130, 326), which first fluid is electrically conductive, which second fluid is electrically insulating, and which first and second fluids are mutually immiscible and in contact with each other over a fluid meniscus (132, 328), - a main electrowetting electrode (118, 318) located in a main plane and auxiliary electrowetting electrodes (120, 122, 124, 126) partially surrounding the fluid chamber and being located in respective auxiliary planes (121, 123, 125, 127), for controlling the geometry of the fluid meniscus, - a voltage source (134, 33) for providing a voltage between the main electrowetting electrode and a plurality of auxiliary electrowetting electrodes, - a measurement circuit (144, 342) for separately measuring capacitances between the main electrowetting electrode and at least two of the respective auxiliary electrowetting electrodes (320, 322), the measurement circuit comprising a multiplexer (212, 414) for demodulating a signal (210, 412) indicative for said respective capacitances, wherein the multiplexer is a time domain multiplexer, wherein the time domain multiplexer is arranged for employing demodulation signals, each demodulation signal being a square wave signal having a low value and a high value, wherein the voltage source comprises voltage switches (331, 333, 407, 409) for alternatingly disconnecting the voltages corresponding to the high values of the respective demodulating values, or wherein the multiplexer is a frequency domain multiplexer, wherein the voltage source is arranged for providing voltages at specific frequencies and wherein the frequency domain multiplexer is arranged for employing demodulation signals each having a frequency component corresponding to the respective specific frequencies.