| ?Ultrasonic liquid level instrument a wide range of applications, such as: weather water level measurements, large oil tank liquid level measurement. With the concept of intelligent machines. In the electronics and the development of micro-control chip based on the equipment level is also undergoing rapid changes. The current level of functionality and price, different manufacturers and between different models, a difference larger. Relatively inexpensive domestic products, but features a simple, precision is not high. Imported product function relatively well. Accurate, but expensive. For some small and medium-sized users, the more difficult to bear the price, and inconvenient maintenance. Therefore, the development of a simple to use, measurement accuracy, low price and management level with a smart instrument is necessary. Large number of level measuring instruments, the ultrasonic liquid level applications better instrument, it is non-contact type liquid level instrument, with more moderate prices, convenient installation, the advantages of higher accuracy. Familiar with the propagation characteristics of ultrasound and ultrasound probe the structure, working methods, such as Q, the choice of the ultrasonic probe T/R40. Completed the design and production of ultrasonic instrument hardware level, the preparation of the operation of the corresponding software, the debugging and trial operation, the result is satisfactory. Part in the hardware design to the smallest single-chip microcomputer 80C51 single-chip system as the core, the use of ultrasound as a control signal to the liquid level detection and automatic data processing, reduction of measurement in the process of human intervention to facilitate the exercise of the testing staff real-time monitoring, printer and PC via a mini-machine communications, such as print, save the data, to better the situation for the detection of storage management. Mainly includes: ultrasonic transmitter; receiver circuit; temperature compensation circuit and the corresponding control circuit. Ultrasonic transmitter will be sent 40KHZ pulse single-chip signal amplification to 20V, in order to meet the driving requirements of ultrasonic probe. By the ultrasonic receiver circuit for receiving the echo amplification and shaping, the upcoming single-chip echo signal into the interrupt signal. 80C51 single-chip is the core of the main tasks of the issue used to drive ultrasonic pulse launched ultrasonic probe device sent through the timer on the ultrasonic transmission time T1 to time, temperature measurement, based on measured time and the parameters the distance, size, etc., control the input parameters and data display, and the host computer and data communications such as print output. Part of the software design, the use of modular program design, different functions of the respective programming procedures, so that the entire software is not only the level and structure of a clear and favorable and software debug and modify. Software consists of two major modules: The first ultrasound-driven and data processing module, and the other is functional modules. Which is divided into functional modules display module to communicate with the host computer module. Finally, the design of the measurement error analysis, as well as a method of reducing the error to make it a more accurate measurement. In the design, because of the need for longer distance measurement (a few meters to ten meters), for when the ultrasonic amplitude in the dissemination of the characteristics of exponential decay, to maximize the driving capability of multi-level Echo to enlarge, reaching the design requirements. Temperature measurement using a compensation method: the temperature measured using temperature sensors to achieve the speed of sound indirect compensation data in the single-chip computation time to consider adding temperature. To enhance the accuracy and use of the digital temperature sensor DS1820, DS1820 is MAXIM's a three-wire serial digital temperature sensor, with a resolution up to 0.060℃. Can achieve accuracy of the design. The experimental results show that the proposed design method can improve the ultrasonic liquid level measurement precision instrument and not the hardware overhead.(1) as a result of restrictions on the probe, at high temperature, high pressure, such as harsh environment, the measurement error, and can be replaced according to the actual situation of the probe more suitable. Measuring distance and transmission power is directly related to the probe power due to limited space, only small-scale indoor measurements. Replaced high-power probe, the scope will be expanded location(2) Effect of temperature on the impact of the speed of sound.(3) the process of Ultrasonic in the dissemination of the first disturbance, as well as thermal convection air to absorb the impact of dust, receive the echo amplitude with increasing distance from the dissemination of the law of exponential decay, making difficult to detect long-distance echo. At the same time, other error sources, such as thermal noise resistance capacitance circuit delay caused by transit-time error detection. Improved method is to improve the surface under test conditions, and the advancement of the probe power.(4) The system dynamic performance is not high enough, the measured speed of the surface of a very mobile, tracking can be achieved; mobile speed is too large, errors become larger. Quantization error, we take the pulse cycle time 26.7μs, check the speed of sound at 25℃, derived quantization error is 0.5×340×0.00267=4.539mm, to meet the testing requirements.(5) the impact of direct wave. Part of the direct sound waves transmitted from the probe to launch probe to receive, directly added to this part of the signal echo signal, echo signal interference detection. Through experiments and found that the accuracy of the impact of transit-time limited, so the system there are still some areas of improvement: Therefore, the accuracy of level measurement on the time and temperature into the measurement accuracy of. |
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