Liquid level meters make up a large percentage of wastewater treatment applications and are used in almost every aspect of the entire wastewater treatment process. In wastewater treatment, liquid levels need to be measured for wastewater, sludge, chemical solutions, and so on.

In the use of automatic control of the sewage system, the level meter in addition to measuring the level meter, many also involves automatic control of the chain pump start and stop and control the opening and closing of the valve. Therefore, the proper selection of the level meter is very important to reasonably meet the requirements of the production process.

I. Radar level meter

The antenna of the radar sensor transmits electromagnetic wave signals in the form of a beam, the transmitted wave is reflected on the surface of the measured material, and the reflected return signal is still received by the antenna. Each point in the emitted and reflected beam is collected by ultrasonic sampling method. The signal is processed by the intelligent processor to derive the distance between the medium and the probe, and sent to the terminal display for display, alarm, operation and so on. Distance from the surface of the material D is proportional to the pulse time travel T: D = C × T / 2 where C is the speed of light due to the distance of the empty tank E is known, then the level L is: L = E - D

Radar level meter features:

(1) Radar level meter adopts integrated design, no moving parts, no mechanical wear and tear, long service life.

(2) Due to the characteristics of electromagnetic wave, it is not affected by the environment. Therefore, the application occasions of its measurement are relatively wide. The probe of the radar level meter has no contact with the surface of the medium, which is non-contact measurement, and can accurately and quickly measure different media. The probe is almost unaffected by temperature, pressure, gas and so on. Can be used in poor working conditions, large changes, water, steam, foam and other ultrasonic level meter can not be competent occasions.

(3) Radar level meter is also suitable for use in the agitator, the liquid level is unpredictable, changeable occasions.

(4) radar level meter price is relatively expensive, but almost can be applied to sewage treatment process level control process.

II. Magnetic flap level meter

Principle: The liquid level gauge works according to the principle of buoyancy and magnetic coupling. When the liquid level in the measured vessel rises and falls, the float in the main tube of the liquid level gauge rises and falls with it, and the magnet inside the float is transmitted to the field indicator through magnetic coupling, driving the red and white flip column to turn 180°, when the liquid level rises, the flip column turns from white to red, and when the liquid level falls, the flip column turns from red to white, and the red and white boundaries of the indicator are the actual height of the level of the medium in the vessel, so as to realize the indication of the liquid level. When the liquid level drops, the flip column turns from red to white.

Features of Magnetic Flip Plate Level Gauge:

(1) Simple structure, clear display, intuitive reading, especially suitable for on-site display.

(2) Less equipment openings, generally use the magnetic flap level meter with remote output, so that the site and remote monitoring.

(3) According to the media, such as easy to dirty and easy to block the media, it is necessary to regularly clean the dominant tube to remove the deposits in the pipeline, in order to ensure the accuracy of the measurement.

In the sewage treatment process, the magnetic flip-flop level meter is commonly used in chemical solvent tanks, acid tanks, alkali tanks and other liquid level measurement.

III. Ultrasonic level meter

Ultrasonic level meter is the use of ultrasonic reflection principle at the liquid surface for liquid level away from the degree of detection, that is, the application of echo measurement distance principle work. When the ultrasonic probe transmits a short ultrasonic pulse to the liquid surface, after a time t, the probe receives the echo pulse reflected back from the liquid surface.

Therefore the distance from the probe to the liquid surface can be found according to the following formula: set the distance from the ultrasonic probe to the bottom of the container as h, then the actual liquid level. Where, v is the speed of ultrasonic propagation in the measured medium (that is, the speed of sound m / s), which shows that as long as you know the speed of sound v, you can accurately measure the time t, to find out the height of the liquid level H.

Features of ultrasonic level meter:

(1) ultrasonic level meter can do non-contact measurement, stable and reliable operation: ultrasonic level meter installed in the silo, liquid tank above, not directly contact with the material, to overcome the other models of liquid (material) level meter direct contact with the material and the resulting drawbacks.

(2) Can measure a wide range of liquid, lump, powder level can be measured.

(3) Can be fixed-point continuous measurement, and can easily provide telemetry and remote control of the measurement signal.

(4) Simple and convenient installation, and does not require safety protection.

Disadvantages of ultrasonic level meters:

(1) ultrasonic level meter measurement will have a blind spot, the installation needs to avoid the blind spot, when the liquid level into the blind spot, the ultrasonic transmitter will not be able to measure the liquid level, so in determining the range of ultrasonic level meter, must leave a margin of the blind spot, installation, the transmitter probe must be higher than the highest level blind spot or so. This will ensure accurate monitoring of the liquid level and ensure the safety of ultrasonic level meter.

(2) ultrasonic level meter in the case of foam, because the sound wave can not penetrate the foam, the sound wave will be reflected back in the foam, so that the measurement of the actual level with a large deviation. Foam can be added to the tank container defoamer to reduce the generation of foam to ensure accurate measurement.

(3) Ultrasonic level meter in the container with agitator will be affected by the agitator, resulting in the reflection of false reflection echo, resulting in inaccurate measurement. By reducing the speed of the stirrer and installing the level meter away from the center of the stirrer, the influence of the stirrer on the ultrasonic level meter measurement can be reduced.

(4) The temperature of the measurement medium also has an impact on the ultrasonic level meter, especially in the closed container, the temperature of the medium and the surrounding temperature temperature temperature difference, the probe will be condensed around the water droplets, which will affect the accuracy of the measurement. Can be installed in the ultrasonic level meter, connected to the compressed air pipe blowing against the probe, to reduce the temperature difference between the medium and the container and the probe condensation of water droplets on the measurement of the impact.

IV. Hydrostatic Level Gauge

Hydrostatic level measurement method is based on the principle that the hydrostatic pressure of the liquid column is directly proportional to the height of the liquid column to achieve the realization of the liquid level measurement through the measurement of the hydrostatic pressure generated by the height of the liquid column. Differential Pressure Level Gauge, which is the use of the principle of working when the level of the liquid in the container is changed, by the hydrostatic pressure generated by the liquid column is also changed accordingly.

Hydrostatic level gauge is to measure the liquid level by measuring the static pressure generated by the liquid level height to determine the liquid level. According to P = ρgh, and the density of the liquid ρ, the acceleration of gravity g is known, as long as the measured pressure P, you can find the liquid level h.

A kind of pressure instrument for liquid level measurement is input level meter, that is, the level measurement instrument is put into the liquid level to be measured in the medium plants, with the change of liquid level, the pressure transmitter in the diffusion silicon and other pressure detecting elements will be the static pressure is converted into a resistance signal for the detection of the liquid level, the input level meter can be directly put into the medium to be measured.

Characteristics of the input pressure level gauge:

(1) Simple structure, solid state structure, no moving parts.

(2) Quite easy to install and use, long service life.

(3) Measuring range is relatively wide, can be measured from water, oil to the viscosity of the phase, etc..

(4) It is not affected by the measured medium blistering, deposition, electrical hold, no material fatigue wear, vibration, shock insensitive.

(5) Cheap and relatively high reliability.

(6) installation, pay attention to choose a relatively smooth fluid, fluctuations in the installation of small places, if you can not avoid the impact of water flow, friction vibration, the need to install isolation pipe, reduce the impact of water flow, to ensure the accuracy and stability of measurement.

(7) When installing the input level meter, it is best to leave the bottom of the pool or the bottom of the tank 100mm to 200mm, in order to reduce the bottom of the pool or the bottom of the tank because of silt and sediment media, affecting the accuracy of measurement.

(8) in the poor water quality environment, especially when the medium has a lot of suspended solids, impurities, easy to block the pressure hole, affecting the accuracy of measurement. Need to regularly clean the level meter, dredge the pressure hole to ensure accurate and stable measurement.

Pressure level meters are suitable for use in processes with good water quality, such as supernatant catchment pools, filtration pools, clearing pools, external discharge pools and SBR pools. It can also be used in thickening and regulating tanks with agitation by installing isolation tubes to avoid sludge impurities at the bottom of the tank.

V. Summary

In summary, due to the process of sewage treatment involves a lot of occasions need to measure the level, but also due to the characteristics of the process of sewage treatment itself, in the selection process, the need for each process and the characteristics of the medium, select the appropriate level meter, the accuracy and reliability of the process measurement of the stability and the economy of service life will have a great impact.

It is recommended that in the case of funding allows, try to choose a high precision, low maintenance, long life of the liquid level meter. Make the whole sewage treatment level measurement and control in reliable, stable, safe operation.