50Hz 60Hz AC Electromagnetic Flowmeter 4-20mA 316L Stainless Steel / Hastelloy Material
An AC Electromagnetic Flowmeter Refers To An Electromagnetic Flowmeter
An AC electromagnetic flowmeter refers to an electromagnetic flowmeter that excites the excitation coil with industrial frequency (50Hz or 60Hz) sinusoidal alternating current.
Core technologies
- Mechanical zero adjustment method: An early approach, which involves manually adjusting the position of the transformer core in the signal loop to generate a reverse compensation voltage. This method is cumbersome and has limited effectiveness.
- Hardware quadrature suppression circuit (mainstream solution): A portion of the excitation current is diverted through a 90° phase-shifting circuit to produce a compensation voltage that is equal in magnitude and opposite in phase to the quadrature interference. This compensation voltage is then injected into the signal loop to cancel out the interference.
Comparison with Modern Mainstream Excitation Techniques
| Characteristics | 50/60Hz AC Electromagnetic Flowmeter | Modern Low-Frequency Rectangular Wave Excitation Flowmeter |
|---|---|---|
| Excitation Waveform | 50/60Hz Sine Wave | 1/8, 1/16 of power frequency and other low-frequency rectangular waves (e.g., 6.25Hz) |
| Core Issues | Severe orthogonality interference, unstable zero point. | Orthogonality interference is fundamentally avoided. Sampling is done during the stable DC period of the magnetic field, with no dΦ/dt. |
| Zero Point Stability | Poor, frequent manual zero adjustment is required. | Excellent, intelligent transmitters can automatically track and correct the zero point. |
| Power Consumption | High, coils tend to heat up. | Low, pulse excitation is used, which is energy-saving and results in less coil temperature rise. |
| Resistance to Power Frequency Interference | Poor, susceptible to interference at the same frequency. | Strong, sampling frequency avoids power frequency and its harmonics. |
| Current Status | Has been largely phased out and only exists in extremely old devices. | Definitely the market mainstream, accounting for over 95% of applications. |
The AC electromagnetic flowmeter is a great transitional technology that solved the problem from 0 to 1, but due to inherent defects, it failed to achieve optimization from 1 to 100. It marked the turning point of the electromagnetic flowmeter technology from the exploration period to the mature period. Its historical lessons directly pointed out the development direction of modern electromagnetic flowmeters - low frequency, digitalization and intelligence.
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