Flow measurement is very complicated. In order to achieve accurate measurement, it is necessary not only to understand the principle and characteristics of the flowmeter, but also to pay attention to the related matters of the entire measurement system. As far as the usage is concerned, attention should be paid to several links such as selection, installation, use, and maintenance to ensure the correct and reasonable use of the metering instrument.
1 Precautions in selection
(1) The choice of the inner village of the electromagnetic flowmeter will directly affect the correct use and life of the electromagnetic flowmeter. Therefore, it is necessary to decide to choose different ones according to the temperature, pressure, speed of the measured fluid, and the hardness, content and particle size of the solid particles. Inner Village.
(2) The range of the electromagnetic flowmeter should be suitable for the actual needs of the process parameters, and the process range is 80-90% of the selected electromagnetic flowmeter range; the lower limit of measurement should consider the signal-to-noise ratio of the electromagnetic flowmeter detector; its adaptation The fluid pressure range is: -0.098MPa~2.941MPa, because the pressure of the fluid is too high will affect the service life of its electrical level, and if it is too low, it may cause the inner village to fall off.
(3) If the fluid contains magnets such as sand, it will disturb the magnetic field of the instrument and produce corresponding errors; if the fluid contains bubbles, the measured flow rate is the volume flow rate including the bubbles; if the fluid has precipitation or knotting phenomenon , It will cause the electric JI to be covered by foreign matter and cause the zero-point fluctuation of the meter. At present, some electromagnetic flowmeters use the method of adding ultrasonic waves to the measuring electric level to solve the precipitation and knotting of the fluid on the electric JI.
(4) The particles in the fluid may shock the electric JI and form peak noise, which will affect the stability of the flowmeter indication. In this case, an electromagnetic flowmeter with porous porcelain or conductive rubber cover can be used.
2 Precautions during installation
(1) Ensure that the fluid flow rate is uniform. It should be noted that there is a 5d (diameter) straight pipe section in the upstream direction of the electromagnetic flowmeter, and the downstream direction can be omitted; during installation, it is necessary to prevent the process pipeline from increasing too much. The stress, especially on the high temperature and high pressure pipeline, if it is unavoidable, the elbow should be installed to relieve the stress.
(2) In order to ensure that the fluid medium fills the inner cavity of the electromagnetic flowmeter, try to install it on a vertical pipeline, and the fluid should be bottom-up; if the process conditions do not allow it, it can also be installed on a horizontal pipeline. Direction.
(3) In order to facilitate the overhaul of the flowmeter, a cut-off or bypass pipeline should be installed before and after the meter to facilitate the installation and disassembly of the meter; in order to prevent electromagnetic interference, it should be far away from large-scale motors, transformers and other magnetic sources, and the meter should be grounded.
3 Precautions for use
(1) When the newly installed pipeline is put into use, a short tube should be used instead of the flowmeter to prevent foreign matter such as iron slag used in the pipeline from damaging the inner village of the instrument; the inner village of the electromagnetic flowmeter has high compressive strength but poor tensile strength, such as When installing on a vertical pipeline, if the rear valve is closed, the liquid returning from the front will easily form a negative pressure in the pipeline and damage the inner village.
(2) The inlet hole of the electromagnetic flowmeter should be well sealed to prevent corrosive gas and dust from entering and damaging the circuit of the meter.
(3) Regularly check the zero-point drift of the electromagnetic flowmeter to confirm the working status of the electrical and electronic; check the meter regularly, and recalibrate the meter when the main board and power board are replaced.