Determination of Flow Rates Using the Radar Method

Flow rate determination

The determination of flow rates is indispensable for many processes when it comes to monitoring water or wastewater volumes. In order to ensure continuous flow determination, however, a measurement system is required which enables optimum velocity detection for the application. The radar measurement method allows contactless flow velocity metering, therefore it is ideal for applications with strong sedimentation on the channel bottom or if sensors cannot be installed on the channel bottom or within the medium. In contrast to other measurement systems, radar metering entails the advantage that it is largely independent from the properties of the measurement medium such as conductivity, density, temperature or viscosity. Moreover the microwave-based method stands out from the crowd of other flow measurement methods due to low maintenance and easy installation.

Measurement principle

Radar sensors are installed outside of or above the measurement medium. The radar sensor sends out a signal with a certain frequency. The signal is reflected as soon as it impinges on the water surface. A frequency shift is induced once the signal is reflected from the water surface. The reflected signal is detected by the radar sensor and will be evaluated using the Doppler principle. The precondition for the radar method is wave formation on the water surface. The sensor measures the movement of the waves and hence the surface velocity of the water. On the water surface a single velocity is measured selectively. With the aid of the hydraulic COSP model developed by NIVUS it is possible to compute the average flow velocity from the selective single velocity. The flow level is measured by utilizing an extra level sensor which enables to determine the wetted area. Flow is calculated from the average velocity v and the wetted area as follows: