Disadvantages of ultrasonic flow meters Posted by : admin / Posted on : Feb 28， 2020

The current shortcomings of the ultrasonic flowmeter are mainly that the temperature range of the measurable fluid is limited by the temperature resistance of the ultrasonic transducer aluminum and the coupling material between the transducer and the pipe, and the raw data of the sound velocity of the fluid under test at high temperature. Incomplete. At present China can only be used to measure fluids below 200 ° C. In addition, the measuring circuit of the ultrasonic flowmeter is more complicated than the general flowmeter. This is because the velocity of liquid in general industrial measurement is often a few meters per second, and the propagation speed of sound waves in the liquid is about 1500 m / s. The change in the velocity (flow rate) of the measured fluid brings the largest change in sound velocity, which is also 10- 3 orders of magnitude. If the accuracy of measuring the flow velocity is 1%, the accuracy of measuring the speed of sound needs to be on the order of 10-5 to 10-6. Therefore, it must have a perfect measurement circuit to achieve this. Reasons for practical application can only be obtained under the premise of rapid technological development.
Ultrasonic flowmeter consists of three parts: ultrasonic transducer, electronic circuit and flow display and accumulation system. The ultrasonic transmitting transducer converts electrical energy into ultrasonic energy and emits it into the fluid to be measured. The ultrasonic signals received by the receiver are amplified by the electronic circuit and converted into electrical signals representing the flow. And accumulation. This realizes the detection and display of the flow.
Ultrasonic flow meters often use piezoelectric transducers. It uses the piezoelectric effect of piezoelectric materials and uses a suitable transmitting circuit to add electric energy to the piezoelectric element of the transmitting transducer, so that it generates ultrasonic vibration. Ultrasonic waves are injected into the fluid at an angle to propagate, and then they are received by the receiving transducer and converted into electrical energy by the piezoelectric element for detection. The transmitting transducer uses the inverse piezoelectric effect of the piezoelectric element, while the receiving transducer uses the piezoelectric effect.
The piezoelectric element of the ultrasonic flowmeter transducer is often made into a circular sheet and vibrates along its thickness. The diameter of the sheet exceeds 10 times the thickness to ensure the directivity of the vibration. The piezoelectric element material mostly uses lead zirconate titanate. In order to fix the piezoelectric element, so that the ultrasonic wave is injected into the fluid at an appropriate angle, it is necessary to put the element into the vocal wedge to form the entire transducer (also called the probe). The material of the acoustic wedge not only requires high strength and aging resistance, but also requires a small energy loss after the ultrasonic wave passes through the acoustic wedge, that is, the transmission coefficient is close to 1. The commonly used acoustic wedge material is plexiglass because it is transparent, and the assembly of piezoelectric elements in the acoustic wedge can be observed. In addition, some rubber, plastic and bakelite can also be used as acoustic wedge materials.