Digital Turbine Flowmeter Flow Sensor Manufacturer Guangdong Sensor

Knowledge extension:

Requirements for medium conductivity of electromagnetic flow meters

The condition for using an electromagnetic flowmeter is that the measured liquid must be conductive and cannot fall below the threshold (i.e. lower limit value). Conductivity below the threshold can cause measurement errors and even render it unusable. If it exceeds the threshold, it can still be measured even if it changes. The indication error does not change much, and the threshold of a universal electromagnetic flowmeter is between 10-4 and (5 × Between 10 and 6 S/cm, depending on the type. When used, it also depends on the length of the flow signal line between the sensor and the converter, as well as its distributed capacitance. The signal line length corresponding to the conductivity in the manufacturer's operation manual is generally specified. The surface of non-contact capacitance coupled large area electrodes can measure low conductivity * * * 5 × Liquid of 10-8S/cm.

The working principle of electromagnetic flow meters is based on the conductivity of the measured medium, which is also closely related to temperature and the doping level of impurities in the medium.

Temperature conductivity is highly correlated with temperature. The conductivity of metals decreases with increasing temperature. The conductivity of semiconductors increases with increasing temperature. Within a temperature range, the conductivity can be approximated as proportional to temperature. In order to compare the conductivity of substances at different temperature conditions, it is necessary to set a reference temperature together. The correlation between conductivity and temperature can often be expressed as the slope of conductivity to the temperature plot. The degree of doping in solid-state semiconductors can result in significant changes in conductivity. Increasing the doping level will result in an increase in conductivity. The conductivity of an aqueous solution depends on the concentration of solute salts or other chemical impurities that can decompose into electrolytes. The conductivity of water samples is an important goal for measuring the salt content, ion content, impurity content, and other components of water. The purer the water, the lower the conductivity (higher the resistivity). The conductivity of water is often recorded by its conductivity coefficient; The conductivity coefficient is the conductivity of water at a temperature of 25 ° C.

The conductivity of industrial water and its aqueous solution is greater than 10-4S/cm, and the conductivity of acid, alkali, and salt solutions is between 10-4-10S/cm. There is no problem with its use, and there is also no problem with low alcohol distilled water at 10-5S/cm. Petroleum products and organic solvents cannot be used if their conductivity is too low. From the data, it was found that some pure or aqueous solutions have a relatively uneven conductivity, which makes them unsuitable for use. However, in practical operations, there may be situations where impurities can be used, which increase the conductivity of the medium. Regarding aqueous solutions, the conductivity in the data was measured in the laboratory using a pure water ratio. The actual aqueous solution used may be mixed with industrial water, and the conductivity will be higher than what was found, which is also beneficial for flow measurement.

There are significant differences in the performance of universal electromagnetic flow meters on the market, with some having high accuracy and multiple functions, while others have low accuracy and simple functions. The fundamental error of high precision sanitary electromagnetic flow meters is (± 0.5%~± 1%) R, while the appearance of low precision meters is (± 1.5%~± 2.5%) FS, with a price difference of 1-2 times between the two * * *. Therefore, it is economically uneconomical to choose places with low measurement accuracy requirements, such as places where non trade accounting is only intended for control and only requires reliability and repeatability.

Some types of sanitary electromagnetic flow meters claim to have a certain height, with a fundamental error of only (± 0.2%~± 0.3%) R. However, there are strict equipment requirements and reference conditions, such as an ambient temperature of 20-22 ℃, and the length of the front and rear straight pipe sections should be greater than 10D and 3D (usually 5D and 2D). It is even proposed that the flow sensor should be integrated with the front and rear straight pipe for real flow calibration on the flow standard equipment to reduce the impact of clamping. Therefore, when selecting multiple types with high selection, do not just focus on the * * * target, but carefully read the manufacturer's samples or instructions for comprehensive analysis.

The functions of electromagnetic flow meters in the market vary greatly, as the simple one is to measure one-way flow and only output analog signals to drive the rear appearance; Multifunctional sanitary electromagnetic flow meters include bidirectional flow measurement, range switching, upper and lower limit flow alarm, air traffic control and power cut alarm, small signal cutoff, flow display and total calculation, automatic verification and fault self-diagnosis, communication with upper computer, and motion configuration. Some types of external serial digital communication functions can be equipped with multiple communication interfaces and chips (ASICs) to connect to HART protocol systems, PROFIBUS, Modbus, PROFIG, FF fieldbus, etc.