Intelligent ultrasonic liquid level gauge interference analysis and ruled out

Intelligent ultrasonic level meter with its advanced technology, high measurement precision, long-term stability is good wait for a characteristic, measurement has been applied in many domestic enterprises of the sewage treatment plant. Jinhua group company in order to achieve the standard of sewage discharge, the original of the technical renovation of the sewage treatment plants on a large scale in the measurement, monitoring of sewage adopted many advanced instrumentation equipment, including the water level of Canadian Milltronics measuring all with the company of intelligent ultrasonic level meter ( Range of 5 m) 。 The ultrasonic level meter integrating ultrasonic probe, converter and electronic display. Made by probe continuous ultrasonic pulse through the echo of the surface measured medium, received by the sensor and after internal intelligent ultrasonic detection and filtering processing processing technology, the reflection of the real echoes from the media and the environment noise and ZUI after converted into liquid level numerical display on the LCD screen, at the same time corresponding 4 ~ 20 ma current signal output. And the output signal in the DCS for centralized monitoring. 1. Liquid level control of the company in the sewage treatment by activated sludge and biological oxidation concatenated process method. Treated by activated sludge sewage pump to the biological oxidation pool to continue processing. Technical requirements of the pump suction of the sewage pool level interlock control ( See figure 1) Sewage pool level ground plane as zero water level, water level value is displayed above the ground water level is positive, whereas shows negative. Liquid level interlock stop value for - low 2. 10 m, that when the water pump, sewage water will be a smoking to - 2. 10 m, the liquid level interlocking system automatically stop, to prevent the water was drained. Sewage pool inlet pipe by continuous water level difference. After stopping the pump for water level rises to close to zero when the surface of the water, again by artificial kai pump. A total of 3 pump, the operator according to sink into the water at any time one or two of them decided to open. 2. Problems and analysis the operating personnel under the normal control and interlocking level gauge LISA - in the DCS 1603 AI trend of complex curve is shown in figure 2. After a period of operation, the operator response sometimes water not to set value ( - 2. 10m) Interlock stop pump phenomenon. Bring up the LISA - in DCS AI trend of 1603 level gauge complex curve view, found abnormal curve shape, as shown in figure 3. Look from the curve, acoustic or electronic noise interference phenomenon existence environment. Under normal circumstances, the rule of water level control curve showed similar to sine wave shape, and there will be no irregular with broken line and the shape of the peak. Remove the ultrasonic level meter calibration, there is no problem. After days of on-site sewage pool water observation found that when the water level to pressure pipe leaking out of the water in the inlet pipe mouth will form the forward flow washout for the fan surface accompanied by a little bubble, bubble to burst when water quality is poorer, when water inflow is larger, Into the water with the chemical plant of open parking and whether running at full capacity) , there was an obvious rotating or surge phenomenon, the surface of the water as the water flow in the water a little bubbles under the ultrasonic probe would show no sometimes. And when the are too many bubbles appear, on the water level gauge will show echo invalid & other; 吗? ” Symbol, until the return to normal. See AI trend complex curve, found obvious interference with a line shape, but interference interlock that do not meet the set value. Obviously, flowing water and the surface has a bubble has the effect of interference on the ultrasonic measurement, and when the interference peak value - are met or exceeded 2. 10 m, interlock stop pump phenomenon. 3. Because Canada Milltronics company to resolve the problem of ultrasonic level meter for intelligent liquid level meter, meter inside have a variety of operating parameters, can be set according to specific conditions. A total of 4 SP one parameter Settings, such as table 1 list 1 Measurement Response: the selection of the parameters to make the sensor can keep pace with the change of the corresponding level; Open Agilator Discrimination: the parameter for bubble of the difference between the water motion and the actual liquid level; Open the Filter: this parameter is used to invalid acoustic and electronic noise from the environment and on the surface of the measured medium echo apart; Fls Timer( 失败- - - - - - 安全定时器) : the choice of this parameter is set the instrument measuring waiting time. Disappear when the echo signal disappears, if echo time reach the FLS Timer set by time value, the echo is not normal, the instrument will display & other; 吗? ” Symbolic representation measurement is invalid at this time. Bring up the instrument parameters of SP, according to the actual change of liquid level is set SP is 4, Agitator Discrimination function and Filter function are open ( ) 。 For a period of time the actual measure, the original fault phenomenon disappears, the issue is resolved. 4. Conclusion loose container liquid level measurement by ultrasonic level meter application in many domestic enterprises is not fresh, in addition to the correct installation, to ensure the good reflection echo, requirements on the surface of measured medium without large fluctuations, no floating foam. When the condition can not completely guarantee, can choose intelligent ultrasonic level meter measuring. In addition, contains a lot of foamy substances on the surface of a medium should choose ultrasonic measurement, and still can take action, the practice of the author is to do a secondary outer casing ( Material can choose corrosion resistance of glass fiber reinforced plastic) As shown in figure 4. The length of the outer casing guarantee when ZUI low level liquid level can not be revealed. Outer casing diameter than the ultrasonic probe diameter as far as possible big, install the outer casing and the ultrasonic probe fixed, ensure outer casing under vertical to surface. So that it can guarantee of casing that the ultrasonic liquid level, no bubble, and the measured liquid level and the actual value, the effect is very good.
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