Ultrasonic level meter is a continuous level gauge applied to various tanks. It emits high-frequency ultrasonic pulses in an ultrasonic transducer (probe). When the ultrasonic pulse meets the surface of the measured liquid level, it is reflected, and part of the reflected echo is received again by the converter and converted into electrical signals.
Therefore, the ultrasonic measurement environment and the sound conversion capability of the instrument circuit will affect the ultrasonic measurement accuracy. Ultrasonic pulses propagate at sonic velocity. The time interval from transmission to reception is proportional to the distance from the transducer to the surface of the test medium. The relationship between the distance value S, the speed of sound C and the transmission time T can be expressed by the formula S=CxT/2.
According to the transmission characteristics of ultrasonic waves, the ideal condition for the application of ultrasonic water level meter should be a smooth liquid surface.
If the liquid level is not constant or the liquid level is waveform, there will be errors in measuring the actual water level by ultrasonic measurement. Therefore, in order to obtain the actual water level, the internal circuit needs to optimize the algorithm of the measurement signal. In practical application, the factors affecting the accuracy of ultrasonic level measurement mainly include:
(1) Complex working conditions
In a stirred, curved or relatively dynamic liquid level environment (such as fluid level measurement), the measurement accuracy of ultrasonic water level meter may be greatly reduced due to the dynamic fluctuation and uncertainty of liquid level. Therefore, it is necessary to improve the stability of the instrument in hardware and software. For software, adding delay average algorithm can better adapt to the complex and dynamic working conditions of instruments. At the same time, an efficient and strict signal filtering circuit should be used in hardware to filter the auxiliary noise caused by the ultrasonic signal contacting the complex liquid surface during measurement.
(2) Wrong instrument installation method
Improper installation may reduce the measurement accuracy. For example, the direction of the ultrasonic transducer is not perpendicular to the liquid level.
(3) Temperature sensor
The speed of sound wave propagation in air medium is affected by temperature. Ultrasonic wave is a kind of sound wave, and its propagation speed is also affected by temperature. Therefore, when designing an ultrasonic transducer, a temperature sensor is usually embedded in the probe to monitor the ambient temperature and compensate the ultrasonic speed of the algorithm. However, due to the structure that the temperature sensor is sealed by the protective material as a part of the probe and the limitation of the protective material (most of which are materials with large mass and low thermal conductivity), the probe temperature may not be able to follow the change of the ambient temperature in real time. For example, if the ultrasonic water level meter is installed in an unobstructed outdoor environment, the exposure of sunlight will continue to heat the probe, but the ambient temperature will not continue to heat like the probe.
(4) Environmental factors
In addition to the influence of temperature mentioned in the third point, air humidity, air pressure, air flow and different gas media will also affect the propagation speed of sound waves, thus reducing the accuracy of ultrasonic measurement.