An apparatus and method for measuring air flow in a duct, e.g. in a ventilation duct, includes a sensor fittable into connection with the duct, the sensor including an ultrasound transmitter and at least two ultrasound receivers, and a control unit to which the ultrasound transmitter and ultrasound receivers are connectable. The control unit is adapted to measure, during the measuring of air flow, the phase difference of an ultrasound signal received at the same moment in time by at least two ultrasound receivers fitted into connection with the duct and, based on the measured phase difference, to determine the flow velocity and/or flow direction of the air. The apparatus is adapted to perform a calibration of the apparatus by transmitting with an ultrasound transmitter at least one calibration signal and by receiving the calibration signal with at least two ultrasound receivers. The apparatus is further adapted to analyze the received calibration signal and based on the analysis to select the parameters to be used in measuring to be such that at least one analysis result of the calibration signal meets predetermined criteria with the parameters.

Techniques are described herein for displacing liquid away from a signal path of sonic signals in a signal anemometer. A sonic anemometer may include a membrane positioned between a sonic transducer and the open environment. The membrane may be formed of a hydrophobic material that repels the liquid. The membrane may also include a plurality of pores that impede the flow of liquid through the membrane but enables sonic signals to pass through the membrane. The sonic anemometer may also include a reflector that displaces liquid away from the signal path of the sonic anemometer. The reflector may include one or more pores that wick liquid away from the signal path.

A measurement device is provided for determining a distance of the measurement device from a medium and a flow speed of a medium by evaluating a transmission signal emitted by the fill level measurement device and reflected by the medium. The measurement device includes an antenna arrangement for emitting the transmission signal in two different directions. The flow speed of the medium can be determined using the Doppler shift of the transmission signal.

An impact sensor is mounted in a duct of a grain cleaning system above an upper sieve. The impact sensor has an upstream-facing impact-sensing surface with respect to a cleaning airstream, and is configured to transduce impact events and generate impact signals. An electronic control unit (ECU) is configured to generate control signals based upon a particle energy value that is determined from the impact signals. The control signals may serve to adjust various working units of a combine harvester including, by way of example, a cleaning fan and sieves.

In order to determine a level and the flow speed of a medium, FMCW transmission signals and CW transmission signals are emitted alternately. Using the Doppler effect, the flow speed of the medium can be determined from the reflected CW signal. The level is determined from the reflected FMCW signal.

A measurement device is provided for determining a distance of the measurement device from a medium and a flow speed of a medium by evaluating a transmission signal emitted by the fill level measurement device and reflected by the medium. The measurement device includes an antenna arrangement for emitting the transmission signal in two different directions. The flow speed of the medium can be determined using the Doppler shift of the transmission signal.

A measurement device is provided for determining a distance of the measurement device from a medium and a flow speed of a medium by evaluating a transmission signal emitted by the fill level measurement device and reflected by the medium. The measurement device includes an antenna arrangement for emitting the transmission signal in two different directions. The flow speed of the medium can be determined using the Doppler shift of the transmission signal.