The principle of electromagnetic flowmeter measurement is Faraday's law of electromagnetic induction. The main components of the sensor are: measuring tube, electrode, excitation coil, iron core and yoke housing. It is mainly used to measure the volumetric flow in conductive liquids and slurries in closed pipes. It includes highly corrosive liquids such as acids, bases, and salts. The product is widely used in petroleum, chemical, metallurgy, textile, food, pharmaceutical, paper and other industries as well as environmental protection, municipal management, water conservancy construction and other fields.
Features:
1. Measurements are not affected by changes in fluid density, viscosity, temperature, pressure, and conductivity;
2. There is no obstructive flow component in the measuring tube, no pressure loss, and the requirements of the straight pipe section are low;
3, series nominal diameter DN15 ~ DN3000. Sensor lining and electrode materials are available in a variety of options;
4. The converter adopts novel excitation mode, low power consumption, stable zero point and high precision. The flow range can reach 1500:1;
5. The converter can be integrated with the sensor or separated;
6. The converter adopts 16-bit high-performance microprocessor, 2x16LCD display, convenient parameter setting and reliable programming;
7. The flowmeter is a two-way measuring system with three totalizers: positive total, reverse total and total difference; can be displayed. Zhuang, anti-flow, and has a variety of outputs: current, pulse, digital communication, HART;
8, the converter uses surface mount technology (SMT), with self-test and self-diagnosis function;
advantage:
1: Electromagnetic flowmeters can be used to measure industrial conductive liquids or slurries.
2: No pressure loss.
3: The measuring range is large, and the diameter of the electromagnetic flow transmitter is from 2.5mm to 2.6m.
4: The electromagnetic flowmeter measures the volumetric flow rate of the fluid under test. The measurement principle does not involve the effects of temperature, pressure, density and viscosity of the fluid.
Disadvantages:
1: The application of electromagnetic flowmeter has certain limitations. It can only measure the liquid flow of conductive medium, and can not measure the flow of non-conductive medium, such as gas and water for better heating. In addition, the lining needs to be considered under high temperature conditions.
2: The electromagnetic flowmeter determines the volume flow rate under working condition by measuring the speed of the conductive liquid. According to the measurement requirements, for liquid media, mass flow should be measured. The flow rate of the medium should be related to the density of the fluid. Different fluid media have different densities and vary with temperature. If the electromagnetic flowmeter converter does not consider the fluid density, it is not appropriate to give only the volume flow at normal temperature.
3: The installation and commissioning of the electromagnetic flowmeter is more complicated than other flowmeters, and the requirements are more stringent. The transmitter and converter must be used together and cannot be used with two different types of instruments. When installing the transmitter, the selection from the installation site to the specific installation and commissioning must be carried out in strict accordance with the product specifications. The installation site must be free from vibration and strong magnetic fields. The transmitter and piping must be in good contact and well grounded during installation. The potential of the transmitter is equipotential to the fluid being measured. When using, the gas remaining in the measuring tube must be drained, otherwise it will cause a large measurement error.
4: When the electromagnetic flowmeter is used to measure the viscous liquid with dirt, the sticky substance or the precipitate adheres to the inner wall or the electrode of the measuring tube, so that the output potential of the transmitter changes, which brings measurement error, and the dirt on the electrode reaches a certain thickness. , may cause the meter to be unable to measure.
5: The scale of the water supply pipe or wear changes the size of the inner diameter, which will affect the original flow value and cause measurement error. If the inner diameter of the 100mm diameter meter changes by 1mm, it will bring about 2% additional error.
6: The transmitter's measurement signal is a small millivolt potential signal. In addition to the flow signal, it also contains some flow-independent signals, such as phase voltage, quadrature voltage and common mode voltage. In order to accurately measure the flow rate, various interference signals must be eliminated to effectively amplify the flow signal. 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 can be selected according to the nature of the fluid to be tested, and the in-phase interference and quadrature interference can be eliminated. However, the improved instrument structure is complicated and the cost is high. The correct installation is very important.
1 The transmitter should be installed in a dry and ventilated place indoors. Avoid installation in places where the ambient temperature is too high, should not be subjected to strong vibration, try to avoid equipment with strong magnetic fields, such as large motors, transformers, etc. Avoid installation in corrosive gases. The installation location is easy to overhaul. This is an environmental condition that guarantees proper operation of the transmitter.
2 In order to ensure that the measuring tube of the transmitter is filled with the measured medium, the stacker is preferably installed vertically, and the flow direction is from bottom to top. Especially for liquid-solid two-phase flow, it must be installed vertically. If the site is only allowed to be installed horizontally, it must be ensured that the two electrodes are at the same level.
3 The transmitter should be equipped with valves and bypass at both ends.
4 The electromagnetic flux measured by the electrode of the electromagnetic flow transmitter is based on the liquid potential in the transmitter. In order to stabilize the liquid potential and the potential transmitter and the fluid to maintain the same potential to ensure stable measurement, the transmitter shell and the metal tube should have good grounding at both ends, and the converter housing should also be grounded. The grounding resistance should not be greater than 10 and cannot be shared with the grounding wire of other electrical equipment. If the transmitter housing is not guaranteed to be in good contact with the metal pipe, connect them with metal wires. Re-reliable grounding.
5 In order to avoid interference signals, the signal between the transmitter and the converter must be transmitted with shielded wires. It is not allowed to place the signal cable and power cable in parallel in the same cable. The length of the signal cable should generally not exceed 30 m.
6 converter installation site should avoid AC and DC strong magnetic field and vibration, ambient temperature is -20 to 50 ° C, does not contain corrosive gases, relative humidity is not more than 80%.
7 In order to avoid the influence of the flow rate on the relative measurement, the flow regulating valve should be placed downstream of the transmitter. For small-caliber transmitters, since the distance from the center of the electrode to the inlet end of the flowmeter is equivalent to several times the length of the diameter D, the upstream straight pipe may not be specified. However, for a flowmeter with a large diameter, generally there should be a straight pipe section of 5D or more in the upstream, and the downstream pipe section is generally not required.
Reasonable selection and correct installation of electromagnetic flowmeters are important to ensure measurement accuracy and extend the service life of the instrument. The following is a brief introduction to the selection principle of electromagnetic flowmeter, installation conditions and precautions for use.
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Label: Analysis of the advantages and disadvantages of electromagnetic flowmeter
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