Microwave flow sensor for a harvester

A flow sensor system for sensing flow rate of moving crop material, comprising:

• a microwave transparent duct for containing flowing crop material;
• a microwave transceiver for transmitting a transmitted microwave signal towards the transparent duct and receiving a reflected signal;
• an in-phase mixer electrically connected to the microwave transceiver for combining the transmitted microwave signal and the reflected microwave signal and outputting an in-phase Doppler signal;
• a quadrature mixer electronically connected to the microwave transceiver for combining the transmitted microwave signal and a delayed reflected microwave signal and outputting a quadrature Doppler signal;
• and
• an electronic circuit electrically connected to the in-phase mixer and the quadrature mixer and having a flow rate output.

A method of measuring crop material flow rate within a duct comprising:

• transmitting a first microwave signal towards the crop material duct;
• receiving a reflected microwave signal;
• mixing the first microwave signal and the reflected microwave signal to produce an in-phase Doppler signal;
• mixing the first microwave signal and a delayed reflected microwave signal to produce a quadrature Doppler signal;
• sampling the in-phase Doppler signal and the quadrature Doppler signal to form a set of complex numbers;
• computing a frequency domain spectrum having corresponding amplitude components and phase components;
• computing a frequency domain power spectrum;
• and
• summing the products of the components of the power spectrum and their corresponding frequencies to produce a crop material flow rate.