Application of Ultrasonic Level Transmitters in Water and Sewage Treatment Procedures

Ultrasonic level transmitters are commonly found throughout water and sewage treatment processes. Over the last few years, ultrasonic level has become the industry standard for most liquid level requirements. There is simply no other technology that can offer the same level of performance for the price of a typical ultrasonic level transmitter. Ultrasonic level instruments have evolved to come preconfigured with the functionality needed in the water and sewage treatment industry; for example, pump control, cycling and monitoring and open channel flow calculation with totalizer.

Sewage Treatment Procedure

Sewage treatment is generally divided into three procedures. Primary treatment (i.e. physical treatment) lets the raw sewage pass through the coarse grid then lifted by wastewater lift station, moves wastewater from a lower elevation to a higher elevation by the gravity, and then enters the grit chamber, the sewage after grit separation enters the primary sedimentation pool. Secondary treatment is that the effluent from primary sedimentation pool enters into biological treatment equipment, including activated sludge process and biofilm process. Then enters into secondary sedimentation pool, and the effluent is sterilized and discharged or classified into the third procedure, which includes biological nitrogen and phosphorus removal, coagulation sedimentation, sand filtration and activated carbon adsorption. A portion of the sludge from the secondary sedimentation tank flows back to the primary sedimentation tank or biological treatment equipment, and the rest goes into the sludge thickener, finally into the sludge digestion pool. After dehydration and dryness, the sludge can be eventually used.

Problems in Level Measurement

In the three procedures of sewage treatment, level sensors play a significant role in every link, so as to ensure the orderly injection of wastewater, disinfectant and other chemical solutions as well as the smooth discharge after the third stage chemical treatment.

The client has used float level indicators for the past years, but the cables were easy to twine, breakage, and the sensors frequently output false alarms, so the pumps had to be stopped for maintenance by manual care.

In addition, the sewage is corrosive and explosive gas is released, plus the measuring space is limited, also with stir, foam, steam and condensation.

Characteristics and Advantages of Ultrasonic Level Transmitter

According to the special working conditions, Jiwei recommended Uson-21 Flameproof Ultrasonic Level Transmitter to the end user.

Specifically, one set of Uson-21 Flameproof Ultrasonic Level Transmitters are installed in the wastewater lift pump and anaerobic feed pump in the first-procedure to measure the level, and transmits the values to PLC controller and upper computer in real time for system analysis. Hence, the operation of pumps can be automatically controlled corresponding to the measured values.

Uson-21 Flameproof Ultrasonic Level Transmitter is a non-contact sensor without any mechanical movable part, it is not affected by the viscosity and density of liquid, which is suitable for liquid level measurement of open pool and channel. Besides, its reliable operation, simple calibration and easy maintenance greatly reduce the cost. Uson-21 has the following characteristics and advantages:

●　Certified for high level of Flameproof Enclosure explosion protection: Ex d IIC T6 Gb.

●　With three measurements for selection, including 5 meters, 10 meters and 15 meters.

●　With temperature compensation function, offering high accuracy and strong adaptability.

●　With RS-485 communication interface.

●　Special echo signal processing algorithm is used, effectively avoiding false echo signals.

●　With IP66/IP67 Ingress protection rating.

●　Probe made of corrosion-resistant PVDF, suitable for corrosive liquid or applications under corrosive environment.

●　High cost-effective ratio and low maintenance cost.

●　EMC design of the product complies with IEC61000-4 (GB/T 17626.2) standard in EFT (LT: A), ESD (LT: A) and surge.

Selection and Application of Ultrasonic Level Transmitter

A reasonable range should be clarified, larger range should be selected on steam or foam occasions. In weak acid or alkali environment, standard probe (such as ABS) is suitable, and anti-corrosion probe (such as PVDF) is for the strong corrosion area. In the case of explosive gas area, such as urban drainage pumping station, collecting well, biochemical reaction tank, sedimentation tank, etc., the ultrasonic liquid level meter with explosion-proof function should be considered for safety concern.

Key Using Points

1. Adjust the height between sensor and level surface. Signal is weak in long range; and blind area occurs in short range.

2. Ensure that the probe surface is perpendicular to level surface at levelness 2°. At the same time, there are no obstacles in the area that ultrasonic beam emits, especially avoid the ladder, switch, pipeline, etc.

3. Electromagnetic is an interference. The signal cable needs an independent threading pipe, and far away from power and lighting cables. To ensure good signal shielding, conductive steel pipe is recommended, and single point-grounding shall be adopted as a shielding layer, so as to avoid circuit potential difference interfering with sensor.

4. To prevent poor contact, do not leave a connector in the middle of signal wire, and the crimping part of the connecting terminal should be tightened, otherwise the contact resistance will be large.

5. To prevent signal line effect from moisture, it needs to be laid on the cable trench support.

According to the suggestion, the client selects Uson-21 Flameproof Ultrasonic Level Transmitter with a measuring range of 10m. So far, all the sensors have been installed and fully operated.