Capacitance level gauge detection principle: two plates that are insulated from each other and close to each other, parallel to each other, form a capacitor. The capacitance of the capacitor changes with the height of the liquid level. The change amount is converted into a standard current signal of 4 to 20 mA by the transmitter , and transmitted to a secondary instrument or a computer to display the liquid level height, and finally reaches the detection liquid level . purpose. As shown in Figure 5.1
1, is a conductive cylinder
2, for insulation materials
3. A coaxial capacitor C is formed between the conductive cylinder 1 and the measuring tube wall 3 for the measurement of the tube wall or the container wall.
Basic calculation formula:
The above formula, 0.885 is the calculation constant, is the invariant; ε is the dielectric constant of the measured medium, and is not variable; d is the distance between the two plates, the distance between the two plates in the formed level gauge is fixed; the only change Only S, the area where the medium invades the plate .
In the above formula, all invariants are negligible, and the formula can be converted to:
The formula shows that the change in capacitance is only ΔH, which is the change of the height above and below the liquid level. The change is independent of the temperature and pressure. The function of each part of the capacitive liquid level transmitter is shown in Figure 5.2.
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