Electromagnetic flowmeter selection and verification method and signal is too weak and no signal fault treatment method
Electromagnetic flowmeter is the first choice in flow instruments. It is a mature and perfect electromagnetic flowmeter in process technology measurement. It has high-quality performance characteristics and is not affected by changes in fluid density, viscosity, temperature, pressure and conductivity, as well as wear resistance. Many advantages, electromagnetic flowmeter has become a popular flow meter in industrial production.
Electromagnetic flow has been widely used in the water supply industry due to its good linearity, wide range ratio, strong reliability and high accuracy.
(1) Selection of electromagnetic flowmeter: selection of caliber, electromagnetic flowmeter can continuously measure the flow rate in a wide flow range, and can be adjusted arbitrarily within the specified flow rate range (0.5~10m/s). In order to promote the flow meter to work within a suitable flow rate range, when the flow rate in the process pipeline is low, the flow rate is relatively stable, and on the basis of allowing a certain pressure loss, the diameter of the meter can be selected smaller than the diameter of the process pipeline. Reducing pipes are reinforced at the front and rear ends to promote the increase of the internal flow rate of the instrument. In addition, in order to ensure the measurement accuracy of the instrument, the central cone angle of the reinforced reducer should not be greater than 15°, and the upper section of the reducer should have at least a straight pipe section equal to 5 times the diameter of the process pipe.
The setting of the flow rate, according to the considerations of economy, practicality, accuracy, etc., when using the electromagnetic flowmeter, the appropriate flow rate range is 1~5ms; for the fluid medium containing solid particles in the liquid, the flow rate range used should be controlled within 1~3m/s; if it is a fluid medium that may cause sediment to the pipeline, the range used is preferably 2~5m/s.
(2) Characteristics of electromagnetic flowmeter: Because the measurement results of electromagnetic flowmeter have little relationship with physical parameters such as water pressure, temperature, conductivity, etc., it has strong reliability and high accuracy. There are no obstructions in the measuring tube, so there is no additional pressure loss in the flow meter. During the measurement process, only the pipeline and the electrode are in contact with the liquid to be measured, so it is only necessary to select the appropriate electrode material to achieve the effect of anti-corrosion. In addition, the electromagnetic flowmeter also has the characteristics of long service life and low maintenance requirements. Electromagnetic flow meters can measure the flow of forward water. And compared with other flow weight counters, its output signal mode is more flexible and diverse.
(3) Use and installation of electromagnetic flowmeter: In the selection of diameter, we mentioned that the upper section of the reducer should have at least a straight pipe section equal to 5 times the diameter of the process pipe, and its lower section needs at least 3 times the length of the straight pipe section . The length of the front pipe of the flowmeter should be at least 10 times the pipe diameter. In the process of installing the electromagnetic flowmeter, the grounding ring of the sensor must be tightly grounded, and the grounding resistance should not be greater than 10Ω. At the same time, in the environment where the electromagnetic flowmeter is used to measure, special attention should be paid to the external electromagnetic interference, especially to avoid the interference of the industrial electromagnetic field. In addition, installing a rectifier in a straight pipe with a diameter of 5 to 10 times the diameter of the electromagnetic flowmeter is the best way to stabilize the water flow.
(4) The way of online verification of electromagnetic flowmeter. There are two main methods of online calibration of electromagnetic flowmeters: electrical parameter method and standard table method. The electrical parameter method is used to test the relevant parameters of the pipeline electromagnetic flowmeter through a certain measurement principle, including the resistance of the excitation coil, the resistance of the surrounding insulation of the excitation line, and the resistance of the electrode to the ground. By detecting the degree of change of these parameters and comparing with the original data from the factory, if it is within the limited range, its accuracy will not be affected, and it can be used with confidence; the standard table method is to use the principle of the standard table, at the same interval, in the Let water (fluid) continuously pass through the calibrated meter and the standard meter, and compare the output flow value generated to determine the accuracy of the calibrated meter.
After the electromagnetic flowmeter is selected, shipped, and installed, the electromagnetic flowmeter can run normally for a long time without maintenance. Of course, the electromagnetic flowmeter also needs maintenance and daily inspection. During the use of the electromagnetic flowmeter, there may be a problem that the signal cannot be received or the signal is too weak. If the failure occurs, the following steps can be taken seriously to solve it.
1. First confirm whether the pipeline is full of fluid. The electromagnetic flowmeter must be measured with a full tube, and the full tube measurement can ensure the preparation and stability of the signal.
2. If the pipe is too close to the wall, the probe can be installed on the diameter of the pipe with an inclined angle instead of the diameter of the horizontal pipe, and the Z method should be used to install the probe
3. Carefully select the dense part of the pipeline and fully polish it, apply sufficient coupling agent to install the probe;
4. Carefully move each probe slowly near the installation point to find the maximum signal point, so as to prevent the installation of strong signals from being missed due to the scaling of the inner wall of the pipeline or the reflection of the ultrasonic beam out of the expected area due to the local deformation of the pipeline.
5. For the metal pipes with severe scaling on the inner wall, the scaling method can be used to make the scaling part fall off or crack, but it should be noted that this method sometimes does not help the ultrasonic wave because of the gap between the scaling and the inner wall. transmission.
In the selection of flow measurement instruments, users must understand the operating environment and consider a reasonable flowmeter in different applications. Experience feedback to ensure the accuracy, reliability and economy of the instrument.
