METER TUBES FOR ULTRASONIC FLOW METERS
MATTECH, s.r.o. supplies meter tubes as well as complete sets consisting of ultrasonic flow meters and straight lengths at the inlet and outlet. The design of the meter tube is divided to three sections: inlet, in which the flowing fluid is straightened (conditioned), measuring one (ultrasonic flow meter) and outlet. Ultrasonic flow meter is subcontracted by our suppliers. Straight lengths required by the customer are manufactured directly in our company. If the customer requires so, the meter tube manufactured according to the documentation of the ultrasonic flow meter can be supplied separately.
The ultrasonic flow meters have the following disadvantage: higher sensitivity to pipeline vibrations, in which the flow meter is installed, and shorter service life of the flow meter with regard to limited service life of its inner electronic components. Their advantage is, that they do not contain moving parts as the turbine flow meters and they show almost no pressure loss. Identically as throttling bodies the meter tubes require min. straight lengths of 10D upstream and 5D downstream the flow meter for proper functioning of the meter tube. D symbolizes the inner diameter of the pipeline.
The principle of ultrasonic flow meters functioning differs in various equipment. Nowadays the most often used principle is the one based on the measurement of period the signal goes through the measured fluid. In certain distances in the pipeline there are installed sensors against each other. One of them has a function of an ultrasonic signal transmitter, the other one of a receiver. Their functions are being changed during the measurement. There is measured the period during which the signal covers a distance between the sensors. Upstream the signal covers the distance in a longer period of time than downstream the fluid flow. Knowing the measured periods, distances between the meters and angle of the measuring beam to a pipeline axis, we get medium velocity of the measured medium flow. Volumetric flow rate is determined indirectly based on the knowledge of flow cross-section and medium velocity of the flowing medium that is evaluated by the ultrasonic flow meter. This method is used not only for the measurement of flow rate, but for the identification of the fluid in the pipeline, too.
The meter tubes for the ultrasonic flow meters are made of carbon, stainless steel and refractory alloyed steels. If it is not possible to keep required straight lengths, it is recommended to install the flow conditioners in the pipeline. Concept of meter tubes minimizes eventual mismatches during assembly of ultrasonic flow meters and their operating. Division of the meter tube to individual sections also enables easier maintenance control and subsequent verification of the meter.