The effect of vibration and negative pressure on electromagnetic flow meter measurements

Electromagnetic flowmeter is a commonly used instrument for flow measurement in industrial pipelines. As long as the medium in the pipeline is conductive, electromagnetic flowmeter can be used to measure instantaneous flow and cumulative flow. But today we are talking about the impact and solutions of vibration and negative pressure on electromagnetic flowmeter measurement. The editor will briefly introduce it to you below.

1. The impact of vibration on electromagnetic flowmeter and its solutions

1. When the electromagnetic flowmeter is installed near the pump, the pump will cause the pipeline to vibrate when it is started, which will affect the electromagnetic flowmeter. Measurement;

Solution: Install the electromagnetic flowmeter more than 3 meters away from the pump, but it must be 10D in front of the straight pipe section and 5D in the back.

2. The bracket used to install the electromagnetic flowmeter is not strong enough, and some even have only one bracket. When the vibration stress of the pipeline is transmitted to the instrument pipe section, the accuracy of the instrument will be reduced because the bracket is not enough to resist the vibration stress;

Solution: The position of the support should be installed as far as 15D away from the upstream and downstream as much as possible Inside, install two brackets in the electromagnetic flowmeter to resist sufficient vibration stress. The diameter of the bracket must be sufficient to support the weight of the instrument and tubing and to isolate vibration.

3. If the bracket is installed at the flange connection of the electromagnetic flowmeter, stress will also be generated, which will affect the accuracy of the instrument;

Solution: Install the outlet pipe of the electromagnetic flowmeter The pipeline should be as high as possible higher than the second bracket of the electromagnetic flowmeter to generate a small back pressure and avoid siphoning.

2. The impact of negative pressure on electromagnetic flowmeters and solutions

The lining of the electromagnetic flowmeter is actually glued on, because the electromagnetic flowmeter works based on the principle of electromagnetic induction. Electromagnetic flowmeters generally have a set of coils and three electrodes. The function of the coil is to add an electric field to the fluid. The flowing conductive liquid is equivalent to a conductor. According to Faraday's law of electromagnetic induction, when the conductor cuts the magnetic lines of force, a corresponding magnetic field will be generated that is proportional to the speed. The electromotive force, the function of the electrode is to measure this induced electromotive force, so only the electrode in the measuring tube is connected to the conductive liquid, and the other parts are lined, and insulation must be ensured so that the electromagnetic flowmeter can work normally. If the metal pipe with a magnetic field is also in contact with the liquid, and there is a short circuit between the conductive liquid measured by the electromagnetic flowmeter and the metal pipe, there will be conduction, which will cause the electromagnetic flowmeter to be unable to measure the potential, so the electromagnetic flow rate The inside of the meter is lined to isolate the electrodes and the measured medium from contact with the electromagnetic inner wall. This is one of the key conditions to ensure that the electromagnetic flowmeter can work normally

When the measurement medium is corrosive to a certain extent, we must use polytetrafluoroethylene lining material. However, electromagnetic flowmeters made of PTFE material cannot withstand negative pressure. The generation of negative pressure will easily cause the lining to fall off and crack, causing water to come into contact with the electromagnetic inner wall, making the flow meter unusable. Therefore, when negative pressure is generated in the pipeline, it is equivalent to pulling the lining down from the inner wall of the electromagnetic field. The lining cannot withstand the damage of the negative pressure and the flow meter cannot be used, so onceGenerally, it is required that there should be no negative pressure in the measuring pipeline.

Solution: Change the original vent valve to a one-way valve (check valve). When a slight negative pressure occurs in the pipeline, the check valve automatically opens and sucks in air from the atmosphere, thereby ensuring safety.