The handheld flowmeter ultrasonic flow meter is designed to measure the velocity of liquid within a closed conduit. It uses well-known transit-time technology. The transducers are a non-contacting, clamp-on type. They do not block the flow, thus no pressure drop. They are easy to install and remove.
The handheld flow meter utilizes a pair of transducers that function as both the ultrasonic transmitter and receiver. The transducers are clamped on the outside of a closed pipe at a specific distance from each other. The transducers can be mounted in V-method where the sound transverses the pipe twice, or the W- method where the sound transverses the pipe four times, or in Z-method where the transducers are mounted on opposite sides of the pipe and the sound crosses the pipe once. The selection of the mounting methods depends on pipe and liquid characteristics.
The handheld flow meter operates by alternately transmitting and receiving a frequency-modulated burst of sound energy between the two transducers and measuring the transit time that it takes for sound to travel between the two transducers. The difference in the transit time measured is directly and exactly related to the velocity of the liquid in the pipe, as shown in the following figure.
FIGURE 1: TRANSIT TIME FLOW MEASUREMENT PRINCIPLE
Whereθ is the angle between the sound path and the flow direction
M is the number of times the sound traverses the flow
D is the pipe diameter
Tup is the time for the beam traveling from upstream the transducer to the downstream transducer Tdown is the time for the beam traveling from the downstream transducer to the upstream transducer
ΔT = Tup – Tdown