Common problems of electromagnetic flowmeter in coal chemical production

Electromagnetic flowmeter, as a flowmeter widely used in the current process industry, often has some problems in coal chemical production. Therefore, the analysis of common problems is as follows:

1. There are bubbles in the liquid and the phenomenon that the tube is not full

The scene where there are air bubbles in the liquid will lead to inaccurate measurement or fluctuation of the measured value (output fluctuation). The formation of bubble-like gas in the liquid has two ways: from the external suction and the transformation of dissolved gas (air) in the liquid into free bubbles.If the liquid contains large air bubbles, the entire electrode can be covered when the electrode is wiped, so that the input circuit of the flow signal is opened instantaneously, resulting in fluctuations in the output signal.Partial pipe phenomenon can be regarded as an extreme case of liquid containing air bubbles.The liquid is not filled with the pipe can be divided into two situations where the liquid level is higher than the level of the measuring electrode or lower than the level.When the liquid level in the pipe is higher than the electrode level, if the straight pipe section before and after the pipe system is ideal, the measurement of the electromagnetic flowmeter can mostly be stable, but the liquid volume measured by the flowmeter includes the gas volume in the pipe, so this kind of measurement exists. There is a large measurement error.When the liquid level in the tube is lower than the electrode surface, the electrode is exposed to the air, and the measurement circuit is actually in an open state.The measured value and output of the electromagnetic flowmeter are in a random state, constantly fluctuating or full scale.This is also in the non-working state, that is, when the pipeline has no liquid medium, the electromagnetic flowmeter indicates a random value, and the craftsman sometimes thinks that the flowmeter is faulty.

The easiest way to judge is to cut off the excitation circuit current of the magnetic field when encountering fluctuations. If the instrument still displays and is unstable at this time, it means that it is mostly caused by the influence of air bubbles or non-filled tubes.If you measure the electrode resistance with a multimeter at this time, you can measure that the loop resistance of the electrode is higher; most of the phenomena in this area are caused by the installation. Whether the installation of the electromagnetic flowmeter is suitable or not directly affects the measurement effect. If the air is contained in the measuring medium, if it is judged that it is caused by the installation location, such as the electromagnetic flowmeter is installed at the high point of the pipeline and the gas stays or the flowmeter fluctuates due to the inhalation of air from the outside, changing the installation location is the most thorough solution. , Installed at the lowest point of the pipeline or with a U-shaped pipe.However, in many applications, the caliber is large or the installation position is not easy to change. It is recommended to install an air collecting bag and an exhaust valve upstream of the flowmeter. After installing the exhaust device, the measurement will return to normal.When installing the flowmeter, try to avoid the situation of partial pipe, such as the installation at the lowest end of the pipeline mentioned above or intentionally install the flowmeter on U-shaped pipes and vertical pipes.Typical failure: the outlet flow rate of coal gasification 33 unit P-3301AB, because it is installed on the horizontal pipeline at the high outlet of the pump, the process water is not filled with the electromagnetic flowmeter, resulting in large fluctuations in the indication, that is, the measured value and output are in a random state, Constantly fluctuating or full scale; the process cannot be referred to, and the problem can be completely solved by refitting the electromagnetic flowmeter to a vertical pipeline or a suitable horizontal pipeline; 33FT-0002, 36FT-0001, 36FT-0002 have the same problem , all due to the improper installation position causing large fluctuations in the indication.

2. Electrode corrosion

After eliminating the factors of air bubbles, the measured value may fluctuate due to electrode corrosion, and all of them end in sensor failure.

Due to improper selection of electrode materials, the electrodes are corroded by the liquid to be measured, resulting in fluctuations in the output of the flowmeter.Once the electrode is corroded, the only solution to the result is to replace it with a new electrode.

3. Electrode fouling and electrode short circuit

The identification of electrode short circuit is relatively simple. If the measured medium contains metal substances, it is easier to diagnose electrode short circuit. At this time, the measured value is obviously small or tends to zero.But this phenomenon is rare in daily operation.Because electromagnetic flowmeters are often used in measurement environments such as raw water and sewage, the probability of electrode fouling is relatively high.When the electrode is fouled, the signal will gradually decrease until the insulation makes the signal circuit open, and the flow signal is isolated at this time.

When the viscosity of the measured medium is high, it is easy to adhere and precipitate on the tube wall. If the adhered medium is a special conductive substance, the signal potential will be shunted and cannot work, that is, the electrode is short-circuited. If it is a non-conductive layer, it is what we use every day The so-called electrode scaling will make the electrode open and unable to work.It is a more thorough method to remove and clean the electromagnetic flowmeter in combination with the process conditions.

4. Lining deformation

Inaccurate measurement or damaged magnetic flowmeter.The deformation of the lining mostly occurs in the lining of fluoroplastics. The process structure of the fluoroplastic lining, especially the polytetrafluoroethylene (PTFE) lining itself, because the PTFE and the pipe wall are only pressed and pasted, there is no adhesive force, so it cannot For negative pressure piping.The practical temperature of polytetrafluoroethylene (PTFE) cannot be greater than 150°. Therefore, the electromagnetic flowmeter with polytetrafluoroethylene (PTFE) lining cannot be used in high-temperature pipelines. If negative pressure is formed instantaneously at high temperature, the lining will be deformed.Therefore, to provide convenience for users, Huayi sincerely provides services for you, and hopes that you will also be interested in metal rotameters.