Ultrasonic levlmeter called ultrasonic liquid level gauge, ultrasonic level gauge, ultrasonic level meter, is an excellent interface non-contact measurement equipment, used in petroleum, chemical industry, tap water, sewage treatment, water conservancy and hydrology, iron and steel, coal mine, electric power, transportation, food processing and other industries. The utility model has the advantages of simple and convenient installation, wide applicability, low cost and good quality and low cost. 1 ultrasonic levlmeter principle of ultrasonic level meter installed on the upper part of the container, under the control of the electronic unit, the probe to the object emits a beam of ultrasonic pulse waves by surface reflected, part of echo received by the probe and converted into electrical signals. From time to time, from time to time, the distance between the probe and the probe is proportional to the distance between the probe and the measured object. The electronic unit detects the time and calculates the measured distance according to the known sound velocity. Probe to the bottom of the tank to the liquid level probe distance distance is equal to the actual level or the level of material, the liquid level height into 4 ~ 20mA, 1 ~ 5V current signal to voltage signal output; or through the 485 communication, Hart communication, GPRS communication transmission to the control center. Because the temperature has a great influence on the sound velocity, the instrument should measure the ambient temperature to correct the sound velocity. The measurement principle of ultrasonic level meter is shown in figure 1. 2 ultrasonic level meter used in the system block diagram of the ultrasonic level meter system diagram shown in figure 2. In the system application, the ultrasonic level meter measuring liquid height and converted into a standard signal sent to the control center, the control center to the liquid level detection instrument information sent, and according to the height of the liquid level and the actual needs of the material or material reduction control. 3 the main technical indicators of ultrasonic level meter 3.1 range and blind area and blind area are the two important indicators reflecting the ultrasonic level meter

The range represents the maximum range of the meter to measure the sensitivity of the transducer. In other words, the larger the range, the higher the sensitivity. Most manufacturers are the nominal range for smooth surface, but at the time, the actual measurement of the liquid level fluctuation, surface floats, solid material measurement, dust, steam, which is likely to lead to the range can not reach the nominal value. For example, 50m range of equipment, if the measurement of corn, the actual can only be measured 20m. The blind zone is also called the dead zone, which is not measured by the ultrasonic liquid level meter. For example, blind area 30cm, that is, the distance between the surface and the probe is less than 30cm, there will be unable to measure the situation. Then the same range of products, the smaller the blind area, indicating that the design of the transducer the better; for some closed tank or short range of measurement, the more convenient installation. Therefore, the blind area is an important index to measure the performance of the transducer. 3.2 temperature and temperature range is the range of most of the nominal accuracy of 20 to 60 DEG C. Because most of the liquid crystal display with the meter, the LCD screen operating temperature can only be in this range, beyond the scope of the liquid crystal display will appear abnormal. If you do not consider the liquid crystal display, generally can do range of-40 to 80 DEG C. The piezoelectric ceramic has a Curie temperature of about 300 DEG C. The Curie temperature is generally safe temperature, under normal circumstances, ultrasonic transducer working temperature is less than 150 DEG C; when more than 150 degrees, easy to damage the inside of the piezoelectric ceramic, so 150 degrees can be regarded as an absolute failure temperature. In addition, part of the material used in the manufacturing process of ultrasonic transducer can not work at a temperature above 100 DEG C for a long time.
Therefore, the limit temperature of most transducers is about 100. Why consider the accuracy and temperature together? Because in the air, the measurement error of the temperature is 1 DEG C, the impact on the sound velocity is 0.6m / s, 20 DEG C, the sound velocity of about 1 340m / s. It can be concluded that the influence of the measurement error is 0.17%; if the temperature measurement error is more than 3 DEG C, the error of the measurement of the material level exceeds the nominal range of most manufacturers of 0.5%. In fact, the accuracy of 0.5% is for the normal temperature and pressure, on the high or low temperature, are likely to lead to the measurement accuracy of more than 0.5% of the situation. When the temperature gradient and the temperature change quickly, the measurement error will increase. In addition, the greatest impact on the measurement accuracy is the gas composition, such as in the case of a number of volatile liquids, liquid evaporation caused by changes in the composition of the air, and then lead to changes in the sound velocity of the gas, and finally cause the measurement error. 3.3 pressure in the case of negative pressure, generally do not recommend the use of ultrasonic measurement, because the ultrasonic transmission is achieved by gas. Negative pressure means that the thin air inside, the propagation of ultrasound in thin air, a sound speed will change, causing the error is two, the thin air inside, the acoustic attenuation increases, resulting in reduced or even measure the measurement range. Positive pressure is the main structure of the probe, as long as the probe structure is not a problem, will not cause leakage phenomenon, in the case of large pressure ultrasonic meter can work. 3.4 corrosion of the material level meter is the main test of the material. In weak acid and weak alkaline environment, the ordinary plastic shell can be. PTFE shell, can withstand most of the strong acid alkali. It is worth noting that, if the material being tested has a relatively strong corrosion and volatility, with an integrated level meter, it is best to the circuit board for the peak. Because most of the waterproof shell, can not prevent gas; gas into the device, but it will corrode the circuit board. 3.5 orientation and installation