The use of ultrasonic liquid level sensor in the salt industry

1 the working principle of ultrasonic level meter

we generally called the waves of more than 20 KHZ frequency ultrasound, ultrasound is a kind of mechanical wave, is one of the mechanical vibration in elastic medium propagation process, it is characterized by high frequency, short wavelength, small diffraction phenomenon, additional directional well, to be ray and directional transmission. Ultrasonic attenuation in liquid and solid is very small, so penetrating ability, especially in light of opaque solid, the length of the ultrasonic wave can penetrate tens of meters, touching the impurities or can have significant reflection interface, ultrasonic level measurement is the use of the characteristics of it. In ultrasonic testing technology, regardless of the ultrasonic instrument, must transform electricity ultrasonic launch out, can be converted to electrical signals, receive back to finish the function of the device is called ultrasonic transducer, also known as the probe. Will be above the liquid, ultrasonic transducer in the down side of launch ultrasonic wave, ultrasonic wave through the air medium, reflected back when meeting water, and is received by the transducer and converted to electrical signals, electronic detection section detects the signal after turning it into liquid level signal display and output.

the principle of ultrasonic wave propagation in a medium shows that if the medium pressure, temperature, density, humidity conditions must, the propagation velocity of ultrasonic wave in the medium is a constant. As a result, when measured ultrasonic from launch to meet liquid surface reflection the time required to be received, the conversion of ultrasonic wave through the journey, quick to liquid level data, as shown in figure 1.

ultrasonic sensors under the microcomputer control, transmit and receive ultrasonic, and by ultrasonic transmission t to calculate ultrasonic sensor is apart from the measured level of hb, under the condition of the ultrasonic wave velocity c known, can be calculated according to the hb = ct2 hb. For ultrasonic sensor distance of tank bottom height h is constant value, it can calculate the liquid level height. 哈= h - Hb

2 ultrasonic level meter selection application and installation requirements selection

21 according to needs and conditions to choose the appropriate model is vital to guarantee the accuracy of the measurement result is reliable.

　　( 1) Ultrasonic level meter measuring range: you can configure the 4, 6, 8, 10, 20, 30 m different models of transducer, etc. When choosing a transducer, the need to consider the characteristics of the material to be tested, interface dielectric properties, environmental conditions and operating conditions of production system. Ultrasonic attenuation degree after launch, and the interface reflection features has a great influence on the measurement range. When ultrasonic attenuation, reflection interface is poor, in order to avoid ultrasonic probe the received ultrasonic signal is too weak, not with the noise signal, will increase the emission power of the transducer.

　　( 2) Temperature compensation: ultrasonic probe is adopt the materials, has the acoustoelectric effect when above a certain temperature, the piezoelectric element will lose their effect, and cannot be used. General ultrasonic transducer in the - 20 ℃ ~ 80 ℃ more suitable work conditions. In addition, due to the ultrasonic level measurement is based on the measured material interface on the transfer medium of ultrasonic sound velocity C for fixed value, in practice, the velocity of medium, besides is decided by the composition of medium is influenced by temperature. Along with the change of seasons, the environment temperature change is very big, in order to ensure the accuracy of measurement, should choose any thing with temperature compensation of ultrasonic level meter.

　　( 3) Sound velocity correction: material nature of the interface on the transfer medium of sound velocity and ingredients affect the measurement result, in order to adapt to the measurement of different medium, ultrasonic level meter internal configuration of sound velocity correction system, to correct errors due to the composition change of medium.

22 installation testing instrument can obtain accurate measurements, not only related to the precision of the instrument itself, but also related to the instrument installation and debugging. The correct installation besides can obtain more accurate testing data, still can guarantee the stability of instrument working, maintenance is convenient. Ultrasonic level meter when installation should pay attention to the following:

( 1) Ultrasonic transducer should be installed in only 'see' places on the surface of the measured medium, the sound waves in the container, storage tank, and have no flap transfer in the bunker, mixer, silo wall and other objects to generate interference, measurement error is produced.

　　( 2) Between the ultrasonic transducer in the send and receive pulses, part of itself does not recognize the blind area, in order to measure is reliable, the highest level should be measured object outside the blind area.

　　( 3) When measuring bunker inside the solid material level, want to consider solid materials on the interface is not smooth, usually in the inlet of the material is higher than the surrounding the storage, therefore, transducer should be installed in the position of average height can reflect the material.

　　( 4) Another important point transducer installation is to avoid zero reflection. Ultrasonic transducer on the tank bottom or discharge outlet inclined wall, ultrasonic pulse emitted, but don't get echo, detector gives alarm or adjustment to the maximum, and, with the clutter echo as a dangerous level echo receiving. Effective way to solve this problem, in the bottom of the liquid storage tank is put in a small piece of reflection board or install the transducer in near the tank line.

　　( 5) Ultrasonic transducer should be used between the detector and shielded cable connection, and shielding grounding on both ends of the line, to avoid electrical noise interference.