Electromagnetic flowmeter measurement error reason explanation

by:KAIDI     2021-01-08
Electromagnetic flowmeter measurement error mainly because of improper product selection, interference problems, liquid measuring these three factors. A, sensors, improper selection of 1. Measurement problem of electromagnetic flowmeter can measure liquid flow velocity range is generally for ~ 10 m/s, economic velocity range for ~ 3 m/s. According to actual use for measuring the flow and the electromagnetic flowmeter is flow speed range is to determine the tube diameter measurement. 2. Lining and lining and electrode material and electrode material, direct contact with the measured liquid, should according to the characteristics of measuring liquid ( Such as corrosion resistance, abrasion resistance, etc. ) And working temperature selective electrode and lining material, if choose undeserved, can cause adhesion speed, corrosion and fouling, wear, lining deformation problems, and then the measuring error comes into being. 3. Mixed phase fluid with electromagnetic flowmeter measurement solid-liquid mixed phase fluid ( Such as silt-laden water) Traffic, if choose by electromagnetic flowmeter calibration, single-phase liquid will produce measurement error, should choose at this time does not cause the liquid-solid phase separation of straight pipe installation of sensors. 4. Stability excitation of electromagnetic flowmeter with dc field, ac sine wave excitation and excitation type double frequency rectangular wave excitation, such as dc excitation prone to electrode polarization and dc interference problems, communication sine excitation to zero, the dual-band rectangular wave excitation is both low-frequency rectangular wave excitation of excellent stability of the zero point, and the high frequency rectangular wave excitation of fluid noise inhibition ability, is an ideal way of excitation. The actual application, should ensure the stability of the power supply voltage and frequency, as far as possible to ensure that the magnetic field intensity is constant, decrease due to the measuring error caused by the magnetic field strength changes. Second, the interference problem 1. Space electromagnetic interference asked converter and sensor cable is longer, in the strong electromagnetic environment, are susceptible to interference, triggering instrument measurements nonlinear condition, it is difficult to normal display. For this kind of situation, *, shielding measures introduced, can be carried out within the grounding steel cable introduced separately, and using standard shielded cable; Second, the reasonable shorten the cable length; Third, with the strong magnetic field to keep the distance. 2. Connecting cable question the essence of electromagnetic flow application is using specific cable, realize the converter connected to the sensor, form a complete system, therefore the cross-sectional area of conductors, capacitors, such as cable field will produce adverse effects. Aiming at this situation, to ensure that the cable models meet the requirements, realize effective connection, at the end of the phenomenon of preventing the middle joint; Control the length of the range, usually the shorter the better. 3. Grounding problem because of the sensor output signal is very small, usually only a few millivolts, in order to improve the anti-interference ability, sensor's zero potential must be reliable grounding alone, and the sensor output signal ground should be current and electrical connection. Sensors of grounding resistance should be less than 10 & Omega; In connecting the sensor pipe coated with insulation layer or using non-metallic pipelines, should be installed on both sides of the sensor ground loop, and reliable grounding, grounding to make fluid, fluid potential is the same as the ground potential. 4. Electrodes and the symmetry points installed vibration excitation coil excitation coil of electromagnetic flow meter and electrode ensures the symmetry, once the asymmetry, deviation is caused in the process of production, it is difficult to ensure accurate measurement results. In addition, the installation location need to achieve high standard of vibration, otherwise can't guarantee the measurement precision of the numerical, even induce instrument does not work properly. Three, the influence of measuring liquid 1. With dramatic change measuring liquid conductivity with liquid conductivity is bigger, can lead to display value of the larger fluctuations, if the problem is very serious, the control system is difficult to achieve normal operation; And stay at low liquid conductivity measurement, the electrode is difficult to realize the normal output, if the operation scope of liquid conductivity under test in a lower value in the following, then the electromagnetic flowmeter is hard to work. According to these situation, first of all, should be based on actual needs, combined with the relevant standards and requirements, select the type of electromagnetic flowmeter; Second, reactor or straight pipe installation, in order to ensure the material mix, facilitate the smooth implementation of the chemical reaction; Again and again for flow meter type selection. 2. Air bubbles or a full package for under test fluid, mainly comes from the gas dissolved in the liquid for the development of the free state of inhaled air bubbles bubbles and the outside world. Contains a large number of bubble volume of flow, influence the accuracy of measurement. If the bubble diameter is too big, even more than the electrode diameter values, in the process of the measurement shows will appear unstable state, volatility is inevitable. For this kind of situation, first of all, the gas collector can be installed on the electromagnetic flowmeter, at the same time according to exhaust the operating cycle; Second, the reasonable replacement installation location; Again, the vertical pipe installed on the electromagnetic flowmeter, ensure bottom-up direction; Fourth, the installation of sensors, avoid too close with outfalls;
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