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Introduction
The Flowmeter is the device which measure flow through differential pressure, it developed base on the measurement principle of the Pitot tube. It can measure the flow of liquid, gas and steam, etc. It consists of no moving parts and has no pressure losses, so it is convenient for setup and repair, low operation cost, and highly favored by customers.
Structure
Sensor parts:
The sensor is composed of detected rod, pressure tapping and guide rod, which pass across internal pipe and perpendicular to axis of pipeline.A number of pressure measuring holeson face flow side of the rod can measure the total average pressure, and on the back and side of the stream surface have static pressure measurements holes, respectively, guided by the main connecting pipe and the static pressure pipe .According to differential pressureof the total pressure and the pressure to calculate flow through the pipe. Static pressure of the back stream surface of sensor can also replaced with flow pipe wall static pressure.
Transmitter parts;
The Flowmeter transmitter is composed of sensors, guiding pressure accessories and differential pressure transmitter, pressure transmitter, flow integrating instrument and other supporting components.
The Flowmeter flow sensor can make up varied types of flowmeter with differential pressure transmitter, pressure transmitter, temperature transmitters, and temperature transmitter manufactured by our company. It can also be adopted differential pressure transmitter, pressure transmitter, temperature transmitters and flow integrating instrument areproduced in any factory, to make up various types of Flowmeter.
Operation principle;
The Flowmeter is based on the principle of Pitot tube, which is determined by the product of the average flow velocity and effectivesection area of pipe. In general, the flow velocity distribution in the pipe is uneven. For the fully developed fluid, the velocity distribution appears on an exponential law. In order for accurate calculation, the entire circle section is divided into a number of half circles and half rings with the same area. The detect rod in the sensor is made of a hollow metal tube. A number of holes are drilled in the rod at the face-flow side which are located in the center of each divided sections and represent flow velocity of each section. Due to the total pressure tapping is interconnecting, total pressure be transmitted to each point and averaged, be guided to
high-pressure terminal through total pressure tube and be transmitted to the positive pressure room. When the sensors correctly installed on long straight pipeline, there no vortex in the flow cross-section and the static pressure of the entire section can be considered as constant. Detected holes are located on the back or side of the sensor which represent the static pressure of the entire section. The static pressure is transmitted from low-pressure terminal to the negative pressure chamber of sensor through the static-pressure tube. Since square of the differential between the positive and negative pressure chamber is proportion to the average flow of section, the flow can be get from the pressure differential. Based on this relationship, the flow can be calculated according to the formula as the following by Bernoulli equation and continuity equations
Installation;
The I-sensors, the detect rod and a section of pipe has been welded together, the sensors must be installed in the direction of the fluid flow.Technology requirements of the pipeline diameter and the diameter of the sensor are in line, or at least in the upper reaches of the pipe above the required length of the sensors within the framework of the pipe axis and the axis formed angle as far as possible to zero.
Other types of sensors that the detect rod is inserted in the process piping, installation, besides the total pressure tapping should be the direction of flow velocity, must ensure that the sensors detect rod perpendicular to the process pipeline, which allows the location of the angular pressure deviation as shown in Figure Six.
The angle between the center of sensors total pressure tapping and pipe axis should be less than 7 °.
pitot tube flow meter