Anemometer for Agricultural Pneumatic Installations: With Application in the Design of Combine Harvester Cleaning Systems

The cleaning system of combine harvesters is an important component whose efficiency directly depends on the uniform distribution of the air velocity profile on the sieve surface. However, the experimental evaluation of the air flow rate is often limited by the high cost and the impossibility of simultaneous multi-point acquisition using commercial anemometers. This paper presents the design, development, and calibration of a low-cost anemometric sensor, based on an NTC thermistor, intended for aerodynamic optimization in the design and laboratory testing phase of cleaning systems. The proposed system replaces the need to use Wheatstone bridges by combining a constant current source, a 16-bit ADC converter, and an RC filter, allowing it to resolve fine voltage variations at low velocity. The algorithm integrates temperature compensation in the 3rd degree polynomial equation by simultaneously reading the environmental temperature using a digital sensor with an accuracy of ±0.1 °C. Experimental validation on the bench against the reference anemometer testo 405i showed excellent agreement (R2 = 0.998, mean bias = 0.017 m/s, and a maximum error of ±0.08 m/s), falling within the tolerance of the reference anemometer. By the ability to use multiple sensors and parallel acquisition in real time, the proposed solution offers an alternative for 2D/3D aerodynamic mapping of sieves under controlled laboratory conditions for the design of combine harvester cleaning systems.