1 Introduction
Acoustic properties of ultrasonic technology have long been recognized. However, the use of ultrasound technology to industrial measurement, it is nearly two decades, with the micro-computer and electronic technology, ultrasonic signal transmission, means of capture and handling was able to achieve more perfect. At present, the ultrasonic level meter and ultrasonic flow meters have been widely used.
2 Acoustic properties of ultrasound
Ultrasound is sound waves at frequencies exceeding 20kHz. In order to fully understand the ultrasonic instrument, it is necessary to understand their specific properties.
    (1) the speed of sound characteristics of ultrasonic technology
Ultrasound can be solids, liquids and gases to spread at different speeds, the speed by the medium temperature, pressure and other factors, but in the same external environment, the ultrasonic propagation in the same medium speed is a constant. This is all the basis of ultrasound measurement instruments.
    (2) the reflective properties of ultrasonic technology
Ultrasonic wave from one medium into another medium, because of two medium density, and therefore the interface between two media, will change its direction of propagation: part of the refraction into another medium, and some is reflected back.
When the ultrasonic wave to spread to the solid or liquid gas, due to significant differences between two medium density, almost all of the reflected sound waves, ultrasonic level meter full advantage of this feature.
When the ultrasonic wave propagation in solid to liquid (or vice versa), the sound waves as transmission medium density similar to almost all of refraction, ultrasonic flow meter is used to this feature.
    (3) the ultrasonic attenuation characteristics of technology
Ultrasound in the dissemination process, due to media and media in the obstruction or absorption of impurities, its intensity will produce attenuation. Whether or Ultrasonic Flowmeter Ultrasonic Level Meter, on the strength of the acoustic waves have accepted certain requirements, must be restrained on a variety of attenuation.
3 Ultrasonic Meter and Its Application Overview
    3.1 The two types of ultrasonic flowmeter
Currently used in industrial measurement ultrasonic flowmeter main categories, namely, Doppler ultrasonic flow meter and the time difference ultrasonic flowmeter. They have adopted modern technology to handle high-precision ultrasonic signals are applied to the relevant acoustic characteristics of ultrasound, but the working principle and applications so there are very different, as shown in Table 1.
    3.2 The measurement principle of two types of ultrasonic flowmeter
 To correct selection and rational use of ultrasonic flow meters, and on the problems in the practical application of the analysis, summarize and address the need to understand the working principle of two types of instruments.
    (1) Doppler ultrasonic flowmeter
Two probes mounted symmetrically on both sides of the pipe fluid under test, launch probe firing frequency f1 of the ultrasonic signal, through the pipeline or liquid particles suspended in air bubbles, the frequency shift, to the frequency f2 to the receiving probe reflection This is the Doppler effect, f2 and fl shall be the difference between the Doppler frequency shift fd.
Set flow rate for the v, ultrasonic velocity as c, Doppler frequency shift fd is proportional to fluid velocity v:
Namely: fd = f2-f1 = × v
Therefore, flow rate: v = × fd
When the channel conditions, the probe mounting location, firing frequency, speed of sound determined later, c, f1, θ shall be constant, fluid flow velocity and Doppler frequency shift is proportional to frequency shift can be obtained by measuring the flow rate, fluid flow and thus obtained .
    (2) The time difference type ultrasonic flowmeter
Time difference type ultrasonic flowmeter of the two probes installed in the tested pipe, upstream and downstream, for small diameter pipeline, installed in the pipeline side, for the V mode, for large diameter pipeline (diameter greater than 200mm) were installed on both sides for the Z mode. Two probes (ie, transducer) can transmit and receive ultrasonic signals. As the role of fluid flow, from upstream to downstream side of the probe made to increase the speed of sound; otherwise reduced. Time difference between transmission and fluid flow rate directly proportional to the time difference detection by a hydraulic body velocity can be calculated, and then obtain the flow.
    3.3 Application of Ultrasonic Flowmeter in Shanxi Aluminium Profiles
Currently, Shanxi Aluminum Plant on the site have used two types of ultrasonic flowmeter. According to actual situation, the production process of alumina slurry, semen, lotion, etc. for use Doppler ultrasonic flowmeter, such as the Bayer process on the dissolution of lotion on the use of the measuring instrument, while the measurement of clean water the time difference ultrasonic flowmeter for use. From the use of effect, the former operation is not stable, the effect is not satisfactory, which already reached a satisfactory result.
According to our analysis, on the one hand, using Doppler-type flow meter measured over output wave tube for the thick multi-media, high temperature fluid properties vary, but lead to long-term movement of the wall scaling, affect the normal transmission of ultrasonic and dissemination; the other hand, the available data to see, the time difference is more mature technology than the Doppler technique, and more reliable.
4 Ultrasonic Level and Application of the Principle
4.1 Ultrasonic Level measurement principle
     Ultrasonic level meter using an ultrasonic acoustic characteristics, that is, under certain conditions, ultrasonic wave in the air transmission speed is certain, so by measuring the ultrasonic wave from the probe spread to Level the surface and return to probe the time used to calculate the probe to Level of distance, and then trough the total height minus the distance you can get the actual material level.
That is: L = H-h = H-CT / 2 = H-(Co + at) T  2
Where: H is zero material level to probe the distance, m;
h for the material level surface to probe the distance, m;
T is time, s;
C. 0 ℃, ultrasonic propagation velocity in air, m  s;
α is the temperature coefficient of ultrasonic velocity, m  ℃;
t is temperature degrees, ℃.
Ultrasonic level meter to measure the core component of the probe, microprocessor, signal sending, receiving and processing is accomplished through both.
   4.2 Application of Ultrasonic Level Meter Overview
Practical application in the field of ultrasonic material level timing, have a variety of factors on the stable and reliable measurement of impact, the following we will combine the practical, about the various kinds of interference on the use of ultrasonic level meter, use and installation of.
   (1) media and environmental temperature
Ultrasonic reflection from the material surface, its frequency will be reflected the influence of material temperature changes, to compensate for this change, ultrasonic probe that has the temperature sensor, the probe sends to the processor, the reflected signal, but also the temperature signal to microprocessors, the processor will automatically compensate for temperature on the material level measurement.
In addition, in order to ensure the reliability of the probe, and asked the ambient temperature does not exceed 60 ℃.
    (2) the measurement of stirrer on the Level of
If the material container in blender, it's also reflected ultrasonic signals, resulting in false echo, and was sent to the microprocessor. According to statistical theory dealing with the microprocessor will return true mask, so they requested that ultrasonic echo reflected from the material surface should be at least as reflected echo from the agitator arm 3 times. Appropriate to reduce the mixer speed, or to deviate from the mixing center of the probe, can effectively eliminate reflection mask mixer produced the impact on the level measurement.
    (3) Ultrasonic Level Meter measurement of the limit
      1) Maximum Level
When a bunch of ultrasonic pulses to the material surface of the transmission process, if received from the material surface to the reflected wave, will not be able to measure the distance that is blind. Materials shall not exceed the maximum expected bit blind.
      2) Minimum Level
Minimum material level is to make the distance ultrasonic sensor can reach the most remote, and so echo can be received sensor. As the ultrasonic attenuation in the communication process and the material surface on the acoustic absorption, the transmission distance depends heavily on the material properties.
In short, as long as the instrument selection, installation of appropriate application of ultrasonic level meter result is quite satisfactory.
5 Conclusion
Ultrasonic instrumentation of modern science and technology class in the industrial measurement of the specific application, is the latest electronic and acoustic product of the combination principle. Compared to conventional instruments, they are more intelligent, more advanced applications of technology, but also to users greater convenience.