The relationship between electromagnetic flowmeter and excitation mode
1. DC Excitation Technology: The use of permanent magnet or DC power supply to the electromagnetic flux sensor excitation winding power supply, to form a constant excitation magnetic field. It has the characteristics of simple and reliable method, small influence by power frequency interference and small self inductance phenomenon in fluid. However, the biggest problem is that the DC induction potential on the surface of the two electrodes to form a fixed positive and negative polarity, will cause the measured medium of electrolysis, resulting in the electrode surface polarization phenomenon. The existence of this phenomenon will increase the effective resistance between electrodes, the electrode polarization and potential drift, and seriously affect the signal conversion put most of the work.
2. The power frequency sine wave excitation technology: is uses the work frequency 50Hz sine wave electricity supply to the electromagnetic flux sensor excitation winding power supply, causes it to form the sine wave excitation magnetic field. It can basically eliminate electrode surface polarization phenomenon, reduce electrode electrochemical potential influence and sensor internal resistance. In practical application, phase-sensitive rectification, line compensation and automatic orthogonal suppression must be used to eliminate the power frequency interference voltage which is consistent with the flow signal frequency.
3. Low frequency rectangular wave excitation technology: it is a kind of excitation technology between DC excitation and power frequency ac excitation. It not only has the advantages of DC excitation technology, such as Eddy current effect, orthogonal interference and phase interference, but also has the advantages of power frequency sine wave excitation technology not producing polarization effect, and the flow signal is easy to enlarge and deal with. However, when the liquid-solid two-phase conductive fluid is measured, the surface of the electrode can cause peak potential interference.
4. Low-frequency three-value rectangular wave excitation technology: the use of frequency one-eighth for the excitation current in accordance with positive • 0 • Negative 0 • Positive law changes. The maximum characteristic is that it can automatically correct 0 points in 0 states with 0-point stable characteristics. It can also use the logic judgment function and operation function of microprocessor to solve the effect of peak jamming potential.
2. The power frequency sine wave excitation technology: is uses the work frequency 50Hz sine wave electricity supply to the electromagnetic flux sensor excitation winding power supply, causes it to form the sine wave excitation magnetic field. It can basically eliminate electrode surface polarization phenomenon, reduce electrode electrochemical potential influence and sensor internal resistance. In practical application, phase-sensitive rectification, line compensation and automatic orthogonal suppression must be used to eliminate the power frequency interference voltage which is consistent with the flow signal frequency.
3. Low frequency rectangular wave excitation technology: it is a kind of excitation technology between DC excitation and power frequency ac excitation. It not only has the advantages of DC excitation technology, such as Eddy current effect, orthogonal interference and phase interference, but also has the advantages of power frequency sine wave excitation technology not producing polarization effect, and the flow signal is easy to enlarge and deal with. However, when the liquid-solid two-phase conductive fluid is measured, the surface of the electrode can cause peak potential interference.
4. Low-frequency three-value rectangular wave excitation technology: the use of frequency one-eighth for the excitation current in accordance with positive • 0 • Negative 0 • Positive law changes. The maximum characteristic is that it can automatically correct 0 points in 0 states with 0-point stable characteristics. It can also use the logic judgment function and operation function of microprocessor to solve the effect of peak jamming potential.
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