Applications in petroleum chemical industry production process of ultrasonic liquid level meter liquid level measurement, often because of some fault causes inaccurate measurement, this paper introduced the principle and the use of the advantages of the ultrasonic liquid level meter, analyses the common problem of ultrasonic, and puts forward some matters needing attention in the process of use.
The preface ultrasonic liquid level is simple and convenient, it is non-contact measurement, and it is not affected by the viscosity and density of the liquid. But the accuracy is low, the test is easy to have blind area, cannot measure pressure vessel, cannot measure easy wave hair medium. However, the use of reliable and small maintenance is widely used in petrochemical production equipment.
The principles and advantages of ultrasonic liquid level
The idea of an ultrasonic liquid level is to measure the amount of time that an ultrasonic pulse will take to return the entire process. Three chang ultrasonic level meter vertical installed on the surface of the liquid, it give an ultrasonic pulse to liquid level, after a period of time, ultrasonic level meter sensor to receive back from liquid surface reflection signal, signal through transmitting circuit selection and processing, according to the SC transmitting and receiving ultrasonic time, ultrasonic level meter distance to calculate the liquid level to the sensor. The ultrasonic liquid level meter measures the material that is corrosive (acid, base), the environment that is polluted, or the material that can produce adhesion. Suitable for liquids that are not physically accessible. The three-way ultrasonic liquid level is an ideal measuring tool for corrosive, stratified or acid alkaline wastewater. Ultra sonic level meter can measure the medium including hydrochloric acid, sulfuric acid, hydrogen chloride, waste water, resin, paraffin, mud, alkali and bleach agent used in industry, widely used in water treatment, chemical, electric power, metallurgy, petroleum, semiconductor and other industries. Advantages of ultrasonic liquid level: non-contact measurement; No moving parts, simple structure, long service life; Corrosion resistant (most probe USES PVDF, PP etc.); Automatic temperature compensation function; It is not affected by the humidity and viscosity of the medium; It is not affected by dielectric constant, conductivity, and thermal conductivity. Excellent performance price ratio.
The ultrasonic liquid-gage problem
At the top of the blue light, the top lights are on the top and the output current is 22MA. And after a period of time, the failure will not be automatically relieved when the liquid level is restored. This failure is a matter of installing attachments. The emission of ultrasound is also emitted from the thread, except for the flat head. If the remaining zero is added, the mounting parts are selected for the metal support. The SCCSB ultrasonic liquid level will recognize the strength of the signal strength greater than the signal strength of the plane head. There is a blind area between the metal scaffold and the launch wave. So the ultrasound is protected, the lights are always bright, the output is 22MA. The solution is to use non-metal scaffolding. Because of the use of non-metal stents, the firing waves of the thread can penetrate through, and the backwave signal of the zero level will be greater than the echo of the thread.
At the top of the error lamp, the top failure light is always bright and the output current is 22MA. This failure occurred in the course of programming and debugging, which failed to comply with the specification. The resulting program is dysfunctional and self-insured. It is not possible to wait for the indicator lamp to move normally when debugging the ultrasonic liquid level of the program, or if the method step in the programming method is not correct, it is in unstable programming and debugging. If no programming is required for multiple iterations, the ultrasonic liquid level will refuse to work. The solution to this failure is to reset the three-way ultrasonic liquid level in order to reprogram. If you reprogram multiple times in an unreset situation, the above failures will occur.
Ultrasonic liquidometer is a common problem in measurement
4.1 due to the power supply voltage fluctuation measurement is not allowed With single probe measurement device, the same measuring probe as it did on the transmitter and receiver, then in the side of launch ultrasonic wave, when the probe with high driving voltage, can make the blind area distance increased, the measurement range of produce, may be beyond the scope of measurement; When the probe on the voltage is too low, because of the distance measurement, signal may not accept returns, this could have a normal job, now you can't work normally, or producing measurement errors, when need to adjust the supply voltage to the rating, probe to normal work.
4.2 the selected measuring range is not appropriate As a result of the existence of blind area distance and ultrasonic produces in the process of transmission attenuation, so the use of ultrasonic measuring liquid level measuring range to a certain extent, is not unlimited, so you should choose suitable probe and the way to work.
To measure the fault caused by the propagation medium
In measurement, when the larger droplets particle in the propagation medium, this paper is for gas measurement methods, liquid type measuring method and solid type measuring way, transmission medium to other impurities, and gas type produces results basic same, only a little different, there is no longer much above), when ultrasonic encounter these droplets scattering and reflection of these droplets will absorb ultrasonic, cause of ultrasonic attenuation, causing the measurement error, false or measurement probe will not work, this kind of phenomenon in China's northern region, especially in winter is more common. When these droplets attached to the surface of a measuring probe, more dangerous, on the one hand can make the measuring probe can not work, on the other hand, time is too long the droplets may probe surface corrosion, the measuring probe forever is not available, so should be timely by ventilation and wipe, and equipped with filter device, the measuring probe equipped with shield. When the droplet particle is small and not attached to the surface of the probe, it can also be solved by using a high-power probe or double probe measurement.
The 4.4 measures the failure of the liquid level
When the liquid level measuring liquid level with other impurities or liquid level is not very usual, ultrasonic diffuse or beam reflection to the other direction, and back to the little ultrasonic measuring probe and beyond measuring probe sensitivity, measurement probe beam, so do not reflect, can't work normally, at this time should be placed at the bottom of the measuring probe wire trunk, etc.
Failure caused by the installation method
Ultrasonic liquid level meter is a blind spot, like a person's eyes, blind area when the object is near the eyes is very close, but can't see clearly, this distance is called blind spots. In the blind area of ultrasonic liquid level, the blind area is different according to the range. The range is small, the blind area is small, the range is large, the blind area is big. But it's usually between 30cm and 50cm. So in general, the blind area must be taken into account when the ultrasonic liquid level is installed. Ultrasonic measuring probes should be installed vertically to the right place, when installation tilt measuring probe of ultrasonic beam will be reflected to the other direction, ultrasonic beam measuring probe and doesn't work, so should be corrected reinstall, when measuring probe from the liquid level too close or too far, also affect the measurement, so the measuring probe shall be installed to their proper locations from the liquid level, liquid level height range in the range of the measuring probe, highest level should be in the blind area distance. On special occasions, will ask blind area is small, this time can consider small blind area of ultrasonic level meter, the blind area usually only 4 ^ "6 cm. But its range is very small, only 0. 6 m. In a lot of level measurement field, because of the limitation of space, constraint of installation and need blind area small three chang ultrasonic liquid level meter.
The ultrasonic liquid level meter USES caution
Because of the power of the probe, the measuring probe also has a certain life span, which can be measured by measuring the voltage or current variation of the probe output. Measurement technology of intelligent instrument is widely used now, ultrasonic liquid level measurement and intelligent transmitter, mostly due to the complex environment of on site, the possible causes of the intelligent instrument damage and loss of setting parameters, so that the measuring system can not work normally, then replace the transmitter or to setting parameters measurement system.
Ultrasonic liquid level considerations:
Heat-resistant ability is limited, most less than 60 ° C, the individual special product of up to 100 ° C; It is impossible to measure in a vacuum, the large fluctuations of pressure affect the measurement precision; Try to avoid the bubbles, obstacles, waves, etc.
6. Conclusion
Ultrasonic liquid level meter is contact measurement is widely used in intelligent instrument, has the advanced measurement technology, high measurement precision, wide measuring range, long-term operation stability is good wait for a characteristic. Ultrasonic liquid level measurement technique plays an important role in the measurement of liquid level of petrochemical enterprises.
