1 Overview
With the advancement of science and technology,portable ultrasonic flowmeters came into being, and they have been widely used in flow measurement and online verification at the production site. FLB type portable flowmeter has the following characteristics
(1) Small size, light weight and easy to carry;
(2) The instrument does not directly contact the fluid, does not affect the operation of the pipeline system, and is easy to install;
(3) Data input is carried out through man-machine dialogue, which is convenient for operation.
(4) Wide measuring range of pipe diameter: (small probes are used for pipe diameters of Φ25~Φ350mm, and large probes are used for pipe diameters of Φ200~Φ6000m). Both AC and DC power supply are available, with strong versatility.
(5) The measurement data and placement data can be easily read and recorded by the digital liquid crystal display and printer.
(6) The measurement result data can be displayed and printed out, and can also be stored in the internal register.
The portable flowmeter is composed of a host and a probe. The host can display parameters, measurement results, etc. The probe is installed on the pipeline to transmit and receive ultrasonic signals.
2. Working principle
When the ultrasonic wave propagates in the fluid, its propagation speed or phase is affected by the fluid flow velocity, and the ultrasonic signal passing through the fluid is properly processed, the fluid velocity can be detected, and the fluid flow rate can be obtained. The time difference method ultrasonic flowmeter uses the time difference caused by the difference in the propagation speed of the ultrasonic wave in the fluid forward and backward to measure the fluid velocity and calculate the flow rate.
3. Application
Portable flowmeters are mainly used in two aspects: on the one hand, to measure the flow of the pipeline without meter; on the other hand, to perform online flow verification on the pipeline that has been metered.
3.1 Flow measurement
Install the probe on the pipe correctly and connect the probe cable to the host. After power on, input the pipe parameters (including pipe outer diameter, pipe material, pipe wall thickness, fluid type, installation method, etc.), and correctly install the probe according to the installation distance, so that the portable flowmeter enters the normal measurement state. We can see a variety of flow displays, including instantaneous flow value, instantaneous flow rate value, positive cumulative flow and negative cumulative flow receiving strength A12. In the measurement state, we can print the measurement data. It is also possible to transfer data from an external device.
3.2 Calibration of online flowmeter
Due to the continuous operation of the production system, some flowmeters cannot be calibrated at the same time. The portable flowmeter is calibrated to the online flowmeter, which not only completes the regular verification work, but also ensures the continuity and accuracy of the measurement. In the same period of time t, record the cumulative flow value Q1 of the online flowmeter, and record the cumulative flow value Q2 of the portable flowmeter at the same time. After the time is completed, if the measurement data of the online flowmeter is out of tolerance, according to the formula:
The new correction value = (Q2/Q1) × the original correction value of the online flow meter to correct the online flow meter.
4. Precautions for probe installation
The installation position of the probe, that is, the pipeline condition of the flow to be measured, has a considerable influence on the measurement accuracy, and the position that meets the following conditions should be selected:
(1) The length of the upstream straight pipe is more than 10D, and the length of the downstream straight pipe is more than 5D.
(2) Within 30D on the upstream side, there is no interference flow factor.
(3) The pipeline must be filled with fluid and there should be no air bubbles.
(4) The Z method should be selected when the pipe diameter is 200mm or larger, and the Z method should also be selected when the appropriate installation distance cannot be provided or the fluid concentration is high.