Phase fraction measurement using light source adjusted in discrete steps

An apparatus comprising:

• a structure containing a multiphase fluid;
• a transparent window structure formed in the structure;
• a collimated light source configured to emit light through the transparent window structure and into the structure, the emitted light having a wavelength at which a component of a desired phase of the multiphase fluid is absorptive;
• a photodetector positioned such that the emitted light passes through the multiphase fluid in the structure and out through the transparent window structure to impinge upon the photodetector;
• wherein the photodetector has an actual dynamic range for collimated light detection;
• processing circuitry coupled to the collimated light source and photodetector, the processing circuitry configured to:
• adjust a power of the collimated light source in a series of steps dependent upon a relationship between an output level of the photodetector and at least one threshold so as to cause measurement of the emitted light by the photodetector over an effective dynamic range greater than the actual dynamic range;
• determine at least one property of the multiphase fluid as a function of the measured emitted light.