What to consider when choosing level timing

What to consider when choosing level timing

(1) Measurement objects, such as the physical and chemical properties of the measured medium, as well as the working pressure and temperature, installation conditions, and the speed of liquid level changes;

(2) Measurement and control requirements, such as measurement range, measurement (or control) accuracy, display mode, on-site instructions, remote instructions, interface with computers, safety and corrosion protection, reliability and ease of construction.

The commonly used level gauges in water supply engineering and the key points of selection are as follows:

A. Static pressure (or differential pressure) level gauge

　　 Since the static pressure of the liquid column is proportional to the liquid level, the liquid level can be measured by measuring the static pressure of the liquid column on the reference surface with a pressure gauge. Calculate the pressure or differential pressure range based on the density of the measured medium and the liquid measurement range, and then select a pressure gauge or differential pressure gauge with suitable range and accuracy. The accuracy of this level gauge is ±(0.5~2)%.

B. Ultrasonic level gauge

　　 The sensor of the ultrasonic level gauge is composed of a pair of transmitting and copper solenoid valve receiving transducers. The transmitting transducer emits ultrasonic pulses facing the liquid surface, and the ultrasonic pulses are reflected from the liquid surface and received by the receiving transducer. According to the time from transmission to reception, the distance between the sensor and the liquid surface can be determined, which can be converted into liquid level. Its accuracy is ±0.5%.

C. Float level gauge

　　Put a hollow float in the liquid. When the liquid level changes, the gas solenoid valve float will produce the same displacement as the liquid level changes. The displacement of the float can be measured by mechanical or electrical methods, and its accuracy is ±(1~2)%. This level gauge is not suitable for high-viscosity liquids, and its output terminal has switch control and continuous output. In the design of water purification plants, this type of level gauge is often used for level measurement of collection wells to control the automatic start and stop of drainage pumps.

D. RF capacitance level gauge

　 Insert an electrode in the container. When the liquid level changes, the internal medium of the electrode changes, and the capacitance between the electrodes (or between the electrode and the container wall) also changes. The change in capacitance is then converted into a standardized DC signal. Its accuracy is ±(0.5~1.5)%.

　　Capacitive level gauge has the following advantages: the sensor has no mechanical moving parts, simple and reliable; high accuracy; low power consumption at the detection end, fast dynamic response; convenient maintenance and long life. The disadvantage of the solenoid valve is that the instability of the dielectric constant of the measured liquid will cause errors. Capacitance level gauges are generally used for liquid level measurement in regulating tanks and clean water tanks.

　　 When the measuring range does not exceed 2m, rod-shaped, plate-shaped, coaxial electrodes are used; when it exceeds 2m, cable-type electrodes are used. When the measured medium is water, an electrode with an insulating layer (polyethylene can be used) is used.

This liquid level gauge has no mechanical moving parts, high reliability, simple and convenient installation, non-contact measurement, and is not affected by the viscosity and density of the liquid, so it is mostly used in medicine pools, medicine tanks, sludge pools, etc. Level measurement. But this method has certain blind spots.

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