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Introduction to the zero point stability of electromagnetic flowmeter

First, zero stability
The low-frequency rectangular wave excitation instrument has good zero stability, and the exchange excitation instrument is poor. The causes are:
1. Noise caused by eddy currents in liquids;
2. Signal line, the electrode and the liquid cause loop induced (orthogonal) noise;
3. In-phase noise introduced by the signal line is also present when the power frequency exchange is excited.
If the magnetic field, the measuring tube diameter, the tube axis and the fluid resistance are completely symmetrical with respect to the electrode axis, even if there is eddy current, no noise will appear on the electrode, but the electrode of the practical process is easily purified, damaging the symmetry of the electrode itself, and the coaxial is emerging. Orthogonal noise.
That is, the power frequency exchange excitation and the low frequency rectangular wave excitation in the aluminum hydroxide slurry are measured at 165 days of zero offset. The zero point stability of low frequency excitation is significantly better than exchange excitation. Orthogonal noise does not indirectly affect the flow signal in principle, but the iron loss caused by it causes the signal voltage to phase shift and cause in-phase noise.
The author thinks that despite these unfavorable factors in the practice of exchange excitation flowmeter design, different levels of improvement, and the exchange excitation method is not the mainstream, it seems that you do not mind, but some foreign manufacturers still exchange excitation as a slurry. Leading the instrument, so you should familiarize yourself with these features when making analysis.
Second, the electrode adhesion layer effect
In order to verify the change of the differential noise caused by the electrode adhesion layer, the application of the phenolic resin was equal to half of the electrode for the simulation experiment.
The power frequency exchange excitation bias is as high as 9%, and the low frequency rectangular wave excitation is lacking 0.2%. This experiment gives us a quantitative concept of electrode attachment.
Third, the activity noise
Electromagnetic flowmeters have been attracting attention due to the influence of fluid noise. The active noise is the charge generated by the fluid and the lining of the lining. These charges cause noise when the fluid moves. The active noise depends on the conductivity, dielectric constant, viscosity, and flow rate in the fluid parameters, and the relationship between them is as shown in the following equation. This set of diagrams allows us to understand the relationship between them and also has a numerical concept.
Dielectric constant
Activity noise ∝────── × (flow rate)
Conductivity × viscosity

The active noise is low-conductivity such as alcohol and pure water and noise specific to low-viscosity liquids.

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