Electrode electrode-signal out
The electrode is the part where the electromagnetic flowmeter picks up the flow signal. In the measurement process, only it is in contact with the grounding ring (or called the wetted ring), the grounding electrode, and the measured medium.
Therefore, in order to adapt to different medium measurement conditions, such as the temperature, pressure, corrosiveness, and abrasiveness of the fluid medium, different electrode materials, different structural shapes, and different installation methods must be selected.
In practical applications, maintaining the surface condition of the electrode is very important for the correct pickup of the flow signal and the stability of the signal.
In the production process of the flowmeter, the assembly and lead-out of the electrode are related to the magnitude of the orthogonal interference of the sensor, the stability of the flowmeter’s zero points, and the quality of the linearity.
In short, the electrode system is a key component in the electromagnetic flowmeter, and the electrode assembly technology is one of the key technologies of the sensor.
Electrode material
The electrode is in the working magnetic field. In order to prevent the magnetic field lines from being concentrated on the electrode, the electrode material must use non-magnetic metal material.
If the electrode is corroded or worn by the measured medium, the distance between the two electrodes will be changed. To obtain the partial derivative of D in equation (2-1), the measurement error can be obtained, namely
In fact, what is more, serious is that during the corrosion process, a considerable DC drift voltage will appear on the electrode, which will cause a large swing in the measurement output and affect the measurement reading.
The signal influence of electrode material corrosion will be discussed in Section 6. Here we only use Table 3-4 to introduce several commonly used electrode materials and their corrosion resistance to some representative media.
Common electrode materials and scope of application
| Lining material | Features and scope of use |
| Stainless acid-resistant steel | 1. Mainly used for domestic industrial water, raw water, sewage, wastewater 2. Suitable for weakly corrosive acid, alkali, a salt solution such as dilute acid and dilute alkali 3. Price is the cheapest |
| Hastelloy B | 1. Suitable for low-concentration hydrochloric acid and other non-oxidizing acids and non-oxidizing hydrochloric acid 2. Oxidizing acids such as nitric acid are not applicable |
| Hastelloy C | 1. Suitable for room temperature nitric acid, other oxidizing acids, and oxidizing hydrochloric acid, with corrosion resistance 2. Reducing acids such as hydrochloric acid and chlorides are not applicable |
| Ti | 1. Slightly better corrosion resistance than acid-resistant steel 2. Good corrosion resistance to chloride, hypochlorite, and seawater 3. Corrosion resistance to oxidizing acids such as nitric acid at room temperature 4. Reducing acids such as hydrochloric acid and sulfuric acid are not applicable |
| Ta | 1. Has superior corrosion resistance similar to glass 2. Except for a few acids such as hydrofluoric acid, and fuming sulfuric acid, most acid solutions are suitable 3. Sodium hydroxide and other lye are not applicable |
| Zr | 1. Corrosion resistance is better than titanium nickel chromium aluminum alloy and acid-resistant steel 2. Corrosion resistance to sulfuric acid with a concentration of less than 80% |
| Platinum, Platinum-iridium alloy | 1. Corrosion resistance to almost all acids and alkalis 2. Aqua regia, ammonium salt, and a few media are not applicable 3. Price is expensive |
| Tungsten carbide alloy | 1. The special electrode for slurry has good abrasion resistance and can reduce slurry noise 2. Poor corrosion resistance, not suitable for corrosive liquids |
| Conductive rubber, Conductive fluoroplastic, Porous ceramics |
1. Low noise electrode material. Resistance to slurry noise and flow noise 2. Conductive fluoroplastics have good chemical resistance |