Analysis of the advantages and disadvantages of electromagnetic flowmeter

Features:

1. The measurement is not affected by changes in fluid density, viscosity, temperature, pressure and conductivity;
2. There are no obstructing parts in the measuring tube, no pressure loss, and the straight pipe section requirement is low;
3. The series nominal diameter is DN15~DN3000. There are many options for sensor lining and electrode materials;
4. The converter adopts a novel excitation method, with low power consumption, stable zero point and high accuracy. The flow range can reach 1500:1;
5. The converter can be integrated or separated with the sensor;
6. The converter adopts a 16-bit high-performance microprocessor and 2x16LCD display, which is convenient for parameter setting and reliable programming;
7. The flow meter is a bidirectional measurement system with three integrators: forward total, reverse total and difference total; it can display positive and negative flow, and has multiple outputs: current
   , pulse, digital communication, HART;
8. The converter adopts surface mounting technology (SMT) and has self-test and self-diagnosis functions;

advantage:

1: Electromagnetic flowmeter can be used to measure industrial conductive liquid or slurry.
2: No pressure loss.
3: Large measurement range, the diameter of electromagnetic flow transmitter ranges from 2.5mm to 2.6m.
4: Electromagnetic flowmeter measures the volume flow of the measured fluid under working conditions, and the measurement principle does not involve the influence of fluid temperature, pressure, density and viscosity.

shortcoming:

1: The application of electromagnetic flowmeter has certain limitations. It can only measure the liquid flow of conductive media, but cannot measure the flow of non-conductive media, such as gas and water with better heating water treatment. In addition, its lining needs to be considered under high temperature conditions.
2: The electromagnetic flowmeter determines the volume flow rate under working conditions by measuring the speed of the conductive liquid. According to the measurement requirements, for liquid media, the mass flow rate should be measured, and the measurement of the medium flow rate should involve the density of the fluid. Different fluid media have different densities and change with temperature. If the electromagnetic flowmeter converter does not consider the fluid density, it is inappropriate to only give the volume flow rate at normal temperature.
3: The installation and commissioning of the electromagnetic flowmeter are more complicated than other flowmeters, and the requirements are more stringent. The transmitter and converter must be used in conjunction, and two different types of instruments cannot be used between the two. When installing the transmitter, from the selection of the installation site to the specific installation and commissioning, it must be carried out in strict accordance with the requirements of the product manual. There must be no vibration or strong magnetic field at the installation site. During installation, the transmitter and the pipeline must have good contact and good grounding. The potential of the transmitter is equal to the potential of the measured fluid. When in use, the gas remaining in the measuring tube must be exhausted, otherwise it will cause a large measurement error.
4: When the electromagnetic flowmeter is used to measure viscous liquids with dirt, sticky substances or sediments adhere to the inner wall of the measuring tube or the electrode, causing the output potential of the transmitter to change, resulting in measurement errors. When the dirt on the electrode reaches a certain thickness, the instrument may not be able to measure.
5: Scaling or wear of the water supply pipeline changes the inner diameter size, which will affect the original flow value and cause measurement errors. For example, a 100mm diameter instrument with a 1mm change in the inner diameter will bring about an additional error of about 2%.
6: The measurement signal of the transmitter is a very small millivolt potential signal. In addition to the flow signal, it is also mixed with some signals unrelated to the flow, such as in-phase voltage, orthogonal voltage and common mode voltage. In order to accurately measure the flow, various interference signals must be eliminated and the flow signal must be effectively amplified. The performance of the flow converter should be improved. It is best to use a microprocessor-type converter to control the excitation voltage. The excitation mode and frequency are selected according to the properties of the measured fluid, which can eliminate in-phase interference and orthogonal interference. However, the improved instrument has a complex structure and high cost. Correct installation is very important.