Ultrasonic level meter solution
Ultrasonic liquid level meter is using the echo ranging principle. Due to the ultrasonic can travel in different medium, so ultrasonic liquid level meter is divided into: gas interface type, three types of solid liquid interface type and medium type, is the most commonly used gas medium type and liquid interface type.
For liquid medium type, electromagnetic flowmeter detector installed in the bottom of the liquid level, sometimes also can be installed on the outside of the container (bottom). Form of single probe, the probe of ultrasonic pulse passes through the liquid to liquid level, then through liquid surface reflection back to the original transmitter, the transmitter has now become a receiver, receiving the ultrasonic pulse.
With single probe with double probe scheme, main should consider from electromagnetic flowmeter measurement object specific situation. More commonly the scheme of single probe for single sensor is simple, easy installation, maintenance workload is small. In addition, it can be directly measured distance, don't have to be corrected. But in some special circumstances, also have to choose double probe solutions, such as the detection distance is far away, in order to guarantee a certain sensitivity, must increase the transmission power, with high power transducer, but these high-power transducer as receiving detector sensitivity is very low, even can't used to receive. In this case, so we have to use another high sensitivity receiving detector.
In addition, the single probe scheme and a receiving probe "blind spots" problem. In the application of the same probe as a transmitter and as a receiver, the launch ultrasonic pulse, to probe on the plug-in electromagnetic flowmeter to higher excitation voltage, the voltage while the duration is shorter, but when stop firing, still exists on the probe over a certain time of vibration, 0 - t, is the time of launch ultrasonic wave pulse, ti - t2 time for vibration over time. If the residual vibration time will probe to receive amplification circuit, the input end of the amplifier will also have a strong enough signal, obviously in this period of time, if can receive the echo signal, it is hard to be distinguished, so according to the time period for the blind area. The blind area of time, the receiver can discern the echo signal. The probe's blind spot time and structure parameters, working voltage, frequency and other factors, can be determined through the experiment. After know the blind area, and then obtain sound velocity, can determine the blind area. Because of the limitation of blind area distance using single probe solutions can't distance is less than the blind area of liquid level measurement. Adopt double probe, in fact, the hard to avoid the coupling circuit, and the function of the directional sound waves to the receiver, the launch ultrasonic pulse, weak output will be generated in receiving circuit, also can be thought of as a certain blind area, but it is much smaller than single probe.