At present, most enterprises have very few spare meters due to the high cost of flowmeters. Generally, they are used online. Once offline verification, pipelines need to be shut down, which will affect production and cause economic losses to enterprises. There are also some flowmeters with diameters greater than 300mm. It cannot be traced in China. 对在线的流量计进行检测。 In order to meet the needs of the measurement market, many companies use portable ultrasonic flow meters to test online flow meters. The portable ultrasonic flowmeter is used to precisely measure liquid fluids in various flow ranges with acoustic conductivity, such as fluids of water, acid, oil, alcohol and other media. Not only suitable for deionized water to highly mixed liquid or high viscosity liquid, but also volume / mass flow or HVAC thermal energy measurement, batch accumulation control, thermal energy transmission detection, pump and valve operation status monitoring, and solids and gases mixed in the product And water monitoring. The transducer matched with the portable ultrasonic flowmeter can be installed on pipes (stainless steel, cast iron, plastic, etc.) with diameters from 12mm to 6m. The whole set of equipment has the characteristics of convenient and fast installation, no need to cut pipes, low maintenance and no pressure loss. Its mainframe housing can be operated in harsh industrial environments. The portable ultrasonic flowmeter uses a two-channel V-method sound velocity measurement method, which is characterized in that the transducer emits a sound beam to the opposite wall emission surface, and then emits and accumulates to the receiving transducer. In this way, the traditional sound wave propagation has developed to Surface propagation, which increases the scanning speed of sound
Due to the diversity and complexity of the industrial site, especially the environment around the pipeline, the reliability and stability of the ultrasonic flowmeter is greatly reduced. Therefore, how to install and debug the ultrasonic flowmeter according to the specific environment has become an important part of the detection field. Topic. The actual measurement accuracy of field applications is often reduced due to measurement errors such as work negligence, transducer installation distance, and flow area. The dual-channel portable ultrasonic flowmeter in our unit can improve the average flow velocity of mono-channel measurements. The uncertainty of the amount of influence reduces the sensitivity of the influence of the oncoming flow velocity distribution, reduces the influence of the length of the front and rear straight pipe sections, eliminates the influence of the location of the installed transducer, and greatly improves the measurement accuracy.
The installation of the ultrasonic flowmeter should be considered from several aspects: (1) understand the site situation in detail; (2) determine the installation method; (3) choose the installation pipeline; (4) calculate the installation distance and determine the probe position; (5) the surface of the pipeline Handle; (6) Probe installation and wiring. During the testing process, you should note:
First, the choice of transducer position
要求管道内液体必须为满管流。 The ultrasonic flowmeter requires that the liquid in the pipeline must be full. The requirements for the front and rear straight pipe sections during installation are to meet at least the first 10D and after 5D (D is the pipe diameter). If obstructions such as elbows, gradually expanding pipes, and shrinking pipes are installed on the upstream and downstream sides, the upstream and downstream straight pipe sections of the ultrasonic flowmeter should be extended to (25 ~ 50) D. Many enterprises did not consider the subsequent detection when installing the flowmeter, did not leave a long enough straight pipe section or installed near the pump / valve, which caused turbulence in the valve and the weld, which brought some trouble to the flowmeter detection. At this time, it is generally necessary to perform inspection after rectification, and try to stay away from valves and welds as much as possible, otherwise the data field will be unstable and the data deviation or accuracy will increase.
Portable ultrasonic flowmeters should avoid interference from strong electromagnetic and acoustic signals during use. Below the high-voltage line, next to the inverter, and near the densely packed road, the measurement accuracy of the ultrasonic flowmeter will be affected. The power supply of the instrument should avoid causing voltage fluctuations. The shielded cable should be used for the connection between the transducer and the instrument.
Gas is easy to accumulate on the top of the pipeline, and debris is easy to deposit on the bottom. Gas, debris and welding seams will cause abnormal reflection of the ultrasonic signal, which will affect the measurement accuracy of the ultrasonic flowmeter, and even cause the ultrasonic flowmeter to fail to work properly. The existence of these factors should be considered in the process.
Installation of the transducer
Before installation, you need to know the outer diameter, material (including cast iron, stainless steel, PVC, aluminum, etc.), wall thickness, lining and lining thickness of the flowmeter installation pipeline, and find the corresponding detection points according to the instructions of the host. For pipeline grinding (the insulation layer needs to be removed in advance), the detection points must be polished and flat, with a certain radius of arc and the transducer, and coated with a coupling agent for meshing.
的测量原理， 换能器的安装是影响测量准确度的关键因素。 According to the measurement principle of the ultrasonic flowmeter , the installation of the transducer is a key factor affecting the accuracy of the measurement. When the V method is used for installation, the horizontal position of the two transducers is easier to ensure. When the Z method is used for installation, the pipe should be wrapped with coordinate paper, folded in half along the center line, and then the horizontal center of the two transducers should be aligned with the two ends of the coordinate paper for installation. This can ensure that the acoustic signals emitted by the transducer pass through Pipeline axis to reduce the impact on measurement accuracy.
However, it should be noted that due to the large changes in on-site process conditions, each flow point of the on-line actual flow test should be completed within a small range of the test flow, pressure, and temperature. Due to the limitation of on-site process conditions, it is difficult to complete the full range verification of the flowmeter. Ultrasonic flowmeters are generally equipped with multiple sets of probes according to the caliber range. Different probes are suitable for different caliber sections. The probes cannot be easily interchanged. Therefore, pay attention to the caliber range when checking.