的发展和应用与其抗干扰技术的发展进步密切相关，特别是近几十年来采用三直低频矩形波动励磁技术和双频矩形波励磁技术，以及微处理器硬件和软件技术明显地提高了电磁流量计抗干扰能力和测量精度，扩大了电磁流量计的应用领域，改变了人们长期认为电磁流量计测量精度低，抗干扰能力差的概念。 The development and application of electromagnetic flowmeters are closely related to the development and progress of its anti-jamming technology, especially in the past few decades, the use of three straight low frequency rectangular wave excitation technology and dual frequency rectangular wave excitation technology, as well as microprocessor hardware and software technology have significantly improved The anti-interference ability and measurement accuracy of the electromagnetic flowmeter were expanded, the application field of the electromagnetic flowmeter was expanded, and the concept that the electromagnetic flowmeter has long been regarded as having low measurement accuracy and poor anti-interference ability was changed.
The electromagnetic flowmeter is a measuring instrument that estimates the fluid flow based on the induced potential generated by the movement of a conductive fluid in a magnetic field. Its basic working principle is the law of electromagnetic induction. Therefore, electromagnetic coupling electrostatic induction is the primary source of interference noise of electromagnetic flowmeters; electrochemical interference noise generated by the characteristics of the fluid medium being tested is the second source of interference noise of electromagnetic flowmeters; power supply interference such as voltage and frequency fluctuations of the power supply of electromagnetic flowmeters Noise is the third source of interference noise from electromagnetic flow meters. The sources, mechanisms and characteristics of the above three types of interference noise are different. Different ways of affecting the electromagnetic flowmeter, the corresponding anti-interference measures are also different. Based on the research work of the dual-frequency rectangular wave excitation intelligent electromagnetic flowmeter, the author focuses on the anti-interference technology of the intelligent electromagnetic flowmeter, and proposes some anti-interference countermeasures for reference of intelligent instrument research and design.
Development history of anti-interference technology of electromagnetic flowmeter
的发展历史就是其抗干扰技术的发展历史。 The development history of electromagnetic flowmeter is the development history of its anti-jamming technology. As early as 1832, British physicist Faraday conceived the earth's magnetic field to measure the velocity of the Thame River water, and conducted field experiments, but failed. The main reason is that there is a polarization effect and a thermoelectric effect of the fluid medium under the DC excitation magnetic field, and the interference noise overwhelms the flow signal potential. The riverbed short-circuited the potential of the flow velocity signal, and the flow technology at that time was far from reaching the level of suppression of various interference noises and the measurement of high impedance signals, which led to the failure of the first electromagnetic flowmeter experimental research. It is true that from the beginning of the research of electromagnetic flowmeters, it was difficult to overcome various interference noises. Because of this, in the future research of electromagnetic flowmeters, people have listed their anti-interference technology as the first technical problem.
The development of the electromagnetic flowmeter excitation technology has greatly promoted the progress of its anti-jamming technology. The first industrial application of electromagnetic flowmeters began in the late 1950s. The development of electromagnetic flowmeter anti-jamming technology has gone through several stages. Each advancement is to solve the problem of its anti-interference ability, which has caused a leap in the electromagnetic flowmeter anti-interference technology. The performance index of the electromagnetic flowmeter is improved. In the late 1950s and early 1960s, in order to reduce the influence of the serious polarization potential of the electrode surface under the DC excitation magnetic field, power frequency sine wave excitation technology was used, but it caused power frequency interference such as electromagnetic induction and electrostatic coupling, which led to the use of complex Various anti-interference measures, such as orthogonal interference suppression circuits, are difficult to completely eliminate the influence of power frequency interference noise, which makes the zero point of electromagnetic flowmeters difficult to stabilize, low measurement accuracy, and poor reliability. In the mid-1970s, with the development of electronic technology and the advent of synchronous sampling technology, low-frequency rectangular wave excitation technology was used to change the morphological characteristics of power frequency interference. Using power frequency synchronous sampling technology, electromagnetic flowmeters with better resistance to power frequency interference were obtained. Capability, improved measurement accuracy, zero point stability, and enhanced reliability. In the early 1980s, the three-value low-frequency rectangular wave excitation technology and dynamic zero calibration technology, synchronous excitation, and synchronous sampling technology were used to obtain the best zero point stability of the electromagnetic flowmeter, which further improved the ability to resist power frequency interference and polarization potential interference. At the end of the 1980s, the dual-frequency rectangular wave excitation technology was adopted, which can overcome the mud disturbance and fluid flow noise generated by the fluid medium, and also has the zero-point voltage stability of the low-frequency rectangular-wave excitation electromagnetic flowmeter, which achieves the zero-point stability and resistance of the electromagnetic flowmeter. The best unification of interference ability and response speed. Therefore, the advancement of the electromagnetic flowmeter excitation technology changes the shape and characteristics of the orthogonal interference potential on the one hand, and reduces the order of mud interference and flow noise on the other hand, thereby improving the anti-interference ability of the electromagnetic flowmeter. Is the most effective anti-interference measure.
干扰噪声的物理机理、特性及其对策 Third, the physical mechanism, characteristics and countermeasures of electromagnetic flowmeter interference noise
In order to discuss the anti-interference technology of electromagnetic flow meters, we must first analyze the physical mechanism and characteristics of electromagnetic flow meter noise, and then adopt corresponding anti-interference countermeasures according to the characteristics of various interference noises to improve the resistance of electromagnetic flow meters. The ability to interfere. 1 Power frequency interference noise Power frequency interference noise is the electromagnetic coupling of the electromagnetic flow sensor's excitation winding and the input circuit of the fluid, electrode, and amplifier. In addition, the power frequency common mode interference of the electromagnetic flowmeter's work site, and the power frequency string introduced by its three power supplies The physical mechanism of mode interference is electromagnetic induction. First, the power frequency interference generated by the electromagnetic coupling of the electromagnetic flow sensor's excitation winding and the fluid, electrode, and amplifier input circuits has the greatest impact on the operation of the electromagnetic flowmeter, and its performance and form are different under different excitation technologies. Therefore, anti-interference is adopted. Measures are also different