The advantages and disadvantages of ultrasonic flowmeter

Ultrasonic flowmeters are non-contact meters that measure both medium flow with large pipe diameters and media that are not easily accessible and observable. Its measurement accuracy is very high, almost no interference with the measured parameters of the media, in particular, can solve other instruments can not strong corrosive, non-conductive, radioactive and flammable and explosive media flow measurement problems.

The main disadvantages that exist today are that the temperature range of the measurable fluid is limited by the temperature tolerance of the coupling material between the ultrasonic transducer and the transducer and the pipeline, and that the raw data of the measured velocity of the fluid under high temperature is incomplete. At present, China can only be used to measure fluids below 200°C. In addition, the ultrasonic flowmeter's measurement circuit is more complex than the general flowmeter. This is because the flow rate of the liquid in general industrial measurement is often several meters per second, and the propagation speed of the sound wave in the liquid is about 1500m/s or so. The change in the flow velocity (flow rate) of the fluid to be measured gives the maximum change in the speed of sound. 3 orders of magnitude. If the accuracy required to measure the flow rate is 1%, then the accuracy of sound velocity measurement needs to be of the order of 10-5 to 10-6, so it must be completed by a complete measuring line, which is also the only ultrasonic flowmeter in the integrated circuit The reasons for practical application can only be obtained under the precondition of rapid technological development.

Ultrasonic flowmeter consists of three parts: ultrasonic transducer, electronic circuit, flow display and accumulation system. Ultrasonic emission transducer converts electrical energy into ultrasonic energy and transmits it to the fluid to be measured. The ultrasonic signal received by the receiver is amplified by the electronic circuit and converted into an electrical signal representing the flow. It is supplied to the display and integrating instrument for display. And totalization. This realizes the detection and display of traffic.

Ultrasonic flowmeters are commonly used in piezoelectric transducers. It uses the piezoelectric effect of the piezoelectric material and uses a suitable transmitting circuit to apply electrical energy to the piezoelectric element of the transmitting transducer to generate ultrasonic vibrations. Ultrasound is injected into the fluid at an angle and propagates, and is then received by the receiving transducer and converted to electrical energy via the piezoelectric element for detection. The transmit transducer utilizes the inverse piezoelectric effect of the piezoelectric element, while the receive transducer utilizes the piezoelectric effect.

Piezoelectric elements of ultrasonic flowmeter transducers are often made as circular sheets that vibrate along the thickness. The sheet diameter exceeds 10 times the thickness to ensure the directionality of the vibration. Piezoelectric element materials are mostly lead zirconate titanate. In order to fix the piezoelectric element, the ultrasonic wave is injected into the fluid at a suitable angle, and it is necessary to form the transducer as a whole (also referred to as a probe) in the vocal wedge of the element. The material of the acoustic wedge not only requires high strength and aging resistance, but also requires that the energy loss after the acoustic wedge passes through the acoustic wedge is small, that is, the transmission coefficient is close to 1. The commonly used acoustic wedge material is organic glass because it is transparent and the assembly of piezoelectric elements in the wedge can be observed. In addition, some rubber, plastic and bakelite can also be used as wedge material.