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Description of the correctness of the electromagnetic flowmeter

The accuracy of electromagnetic flowmeters The scope of application of electromagnetic flowmeters is common.
Large-diameter instruments are used in water supply and drainage projects. Small and medium-sized calibers are rarely used for solid-liquid double equal unpredictable fluids or high-demand applications, such as measuring paper pulp and black liquor in paper industry, pulp in non-ferrous metallurgy industry, coal slurry in coal preparation plant, strong erosive liquid in chemical industry, and blast furnace in steel industry The tuyere cooling water masters and monitors the leakage, and the flow measurement and mastery of the long-distance pipeline coal. Small calibers and small calibers are rarely used in applications such as the pharmaceutical industry, food industry, and bioengineering. The performance of general-purpose electromagnetic flowmeters on the market is quite different, some have high precision and many functions, some have low precision and simple functions. The instrument basic error with high utility is (0.5% ± 1%) R, and the instrument with low precision is (1.5% ± 2.5%) FS. The price difference is 1 to 2 times. Therefore, when the measurement accuracy request is not very high (for example, non-trade accounting is only for the purpose of mastering, only the field body with high reliability and excellent repeatability is required to cut the magnetic field lines. If the pipe section is perpendicular to the diameter of the magnetic field, one end is installed. The counter electrode (Fig. 3-17) can confirm that only the flow velocity in the pipe is distributed as an axisymmetric dispersion, and the induced electromotive force is also generated between the two electrodes: e=BD (3-36) where is the uniformity of the pipe section The flow rate. The volumetric flow rate of the pipe thus obtained is: qv=πDUˉ = (3-37) As can be seen from the above formula, the volume flow rate qv is linear with the induced electromotive force e and the inner diameter D of the measuring tube, and is proportional to the magnetic induction intensity B of the magnetic field. It has nothing to do with other physical parameters. This is the measurement principle of electromagnetic flowmeter. It should be explained that in order to make the formula (3-37) strictly established, the following assumptions must be satisfied: 1 The magnetic field is a uniformly distributed constant magnetic field; The flow velocity of the fluid to be measured is axisymmetrically dispersed; 3 the liquid to be tested is non-magnetic; 4 the conductivity of the liquid to be measured is uniform and isotropic. Figure 3-17 Schematic diagram of the electromagnetic flowmeter Magnetic pole; 2-electrode; 3-pipe (2) Excitation method The method of excitation is the method of generating magnetic field. From the above, in order to make the formula (3-37) strictly established, the first condition that must be satisfied is to have a uniform and constant condition. The magnetic field. For this reason, it is necessary to choose a suitable excitation method. At present, there are three kinds of excitation methods, namely DC excitation, exchange excitation and low-frequency square wave excitation.

1. DC Excitation The DC excitation method uses a DC to generate a magnetic field or an eternal magnet that produces a constant uniform magnetic field. The biggest advantage of this DC excitation transmitter is that it is little affected by the exchange electromagnetic field disturbance, so it can neglect the influence of the self-induced scene in the liquid. However, the use of a DC magnetic field tends to cause the electrolyte liquid passing through the measuring tube to be polarized, that is, the electrolyte is electrolyzed in the electric field, causing positive and negative ions. Under the action of the electric field force, the negative ions run to the positive pole and the positive ions run to the negative pole. As shown in Figure 3-18. In this way, the positive and negative electrode breakups will be entrapped by ions of opposite polarity, which will greatly affect the normal task of the electromagnetic flowmeter. Therefore, DC excitation is only used to measure non-electrolyte liquids, such as liquid metal. Figure 3-18 DC excitation method
2. Exchange Excitation At present, most of the electromagnetic flowmeters used in industry use the power frequency (50Hz) power exchange excitation method, that is, its magnetic field is generated by sinusoidal alternating current, so the magnetic field is also an alternating magnetic field. The important advantage of the alternating magnetic field transmitter is to remove the polarization of the electrode surface. In addition, because the magnetic field is alternating, the input signal is also an alternating signal, and the release is compared, and the sealing condition of the downhole string is determined according to the increase or decrease of the flow rate. If there is a leak in the water injection pipe column, the ultrasonic flowmeter will have a high-level and low-low condition in the upper part; if the bottom of the ball is not well sealed, the flow will not be zero in the impact tube. On May 5, 1999, when the T5-XXX well was tested with the Qing 106 type float flowmeter, the difference between the whole well flow and the airborne measurement was 15m3/d. The personnel concerned were suspicious of the leakage of the water injection pipe column. Because it can't be verified by the float flowmeter, it is measured by the electromagnetic flowmeter. The measurement result is shown in Figure 3. In Figure 3, several flow steps (from left to right) between 10:40 and 11:07 are measured at 1000m, 500m, and 100m underground, except for 500m, which is the full well flow value, and other with over-the-air measurement. The consequences are consistent and explain that the foundation of the downhole string is not leaking.

5 Several problems and countermeasures in application

There are several important reasons for the use of electromagnetic flowmeters: fine pressure gauges
(1) The problem of accurate position in the downhole of the instrument. Because the instrument itself is not deeply positioned, the instrument's penetration depth is measured by the depth counter on the winch. The accuracy of the depth counter measurement results is related to the counter itself and to the task environment. If the depth error is too large, the measurement consequences will be meaningless. Therefore, deep proofreading is a crux problem in field testing. (2) The impact of pipe diameter changes on the measurement consequences. The commonly used electromagnetic flowmeter is a central flow rate type. The calibration of the instrument is realized in a special pipeline. If the measurement environment is different from the calibration environment, the measurement error will appear. Taking an in-flow instrument as an example, if it is calibrated in a Ф62 mm illuminating tube, it will introduce a maximum error of 15.28% when measured in a coating tubing with an inner diameter of Ф59 mm. This is the system error, so in the instrument measurement process, it is necessary to clear the inner diameter of the pipe to be tested, and the measurement error caused by the pipe diameter change should be deducted when interpreting the material. A small amount of practice measurement data indicates that the error caused by the change in pipe diameter is within 10%.
(3) Calibration of the instrument. The instrument is calibrated with clear water. If the injection medium is changed to sewage or other non-clear water medium, it will affect the measurement results. It is also a problem to be considered in the application. In practice, it is often necessary to calibrate the instrument on site and to ensure the correctness of the calibration results.
(4) Measurement cannot be continued. If the flowmeter can continue to measure the active profile in the column, it can intuitively reflect the water absorption in the entire wellbore, which is beneficial to the interpretation of the logging material. Due to structural design shortcomings, electromagnetic flowmeters are currently unable to fully implement continuous measurements. Through the analysis of the operation status of the underground storage electromagnetic flowmeter in Henan Oilfield, this technique was invented to fully meet the stratification test request for water injection development in Henan Oilfield. It has the characteristics of high test victory rate, correct material and inconvenient use, and the results of material application are good. This technique is a fantasy technique for stratification testing in place of a float flow meter.

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