First, use 
 Used in conjunction with the weir trough, measuring the flow of water in the nullah. Mainly used for measuring the wastewater treatment plant, units of enterprises do liquid sewage outfall, city sewer flow and irrigation channels. 
 The Company instrument using ultrasonic wave through the air, non-contact method of measurement. Therefore, in the case of dirt, corrosive liquid with higher reliability than other forms of instrumentation. 

 Second, the principle 
 This series of instruments to directly measure the physical quantity is level. Used for open channel measuring flow in open channel to install the weir trough. Weir tank the size of open channel flow into the level of the liquid level. Instrument measuring the water level of the weir tank, and then the corresponding slot weir water level - discharge relation to anti-calculated flow. 
 An ultrasonic measurement level principle 
 Transmit ultrasonic transducers transmit the ultrasonic pulse, transmitted through the propagation medium to the measured surface sound transmission medium, by reflection and then return to the receiving transducer, measured by the ultrasonic pulse propagation from the transmitter to the receiver in the sound transmission medium time. According to the speed of sound in the sound transmission medium can be described as the distance from the transducer to the surface. To determine the liquid level. 
 Therefore, we can calculate the distance of the probe to the reflecting surface D = C * t / 2 (in addition to two trips because of the acoustic path, D is the distance, C is the speed of sound, t is the time). The level value can be obtained by subtraction. 
 Weir trough measuring flow principle 
 Smooth flow of the open channel flow the greater the level the higher; the smaller the flow, the lower level (Figure 2.1). Calculated by measuring the water level can be anti-traffic. The correspondence between the common open channel flow and water level, channel slope and surface roughness. Weir tank is installed in the channel to produce the throttle effect, open channel flow and level are fixed corresponding relationship, this correlation depends primarily on the weir trough the structure size, the impact of the channel is reduced to a minimum .