Points to Be Noted in Electromagnetic Flowmeter Engineering Application

In the petrochemical, chemical, electric power, metallurgy, municipal, pharmaceutical and other industries, the technical difficulty and complexity of flow measurement are quite high. Research on flow measurement plays an important role in improving product quality, reducing business costs, and solving energy conservation and environmental protection. The electromagnetic flowmeter has the advantages of no resistance and no pressure loss, which can fully reduce the resistance in the pipeline and meet the requirements of energy saving and consumption reduction, so the electromagnetic flowmeter has been widely paid attention in the industry. However, although the electromagnetic flowmeter has the above advantages, and it is much better than most other types of flowmeters in reliability and stability, but in actual use, some problems will occur, the following magnetic flow meter factory will list the main points that need to be paid attention to in the application of electromagnetic flowmeter.

1. The transmitter should be installed at a position where the measurement tube can be filled with liquid at any time to prevent the illusion that the pointer is not at zero because of no liquid in the measurement tube. It is best to install it vertically to reduce the error caused by the liquid flowing through the bubble generated on the electrode. If placed horizontally, the two electrodes of the flowmeter must be kept on the same level, in order to prevent sediment or air on the top of the tube to insulate it.

2. If necessary, the tube can be emptied. The built-in empty tube detection circuit will stop the accumulation and flow signal output.

3. For the fluid flowing in the anode-protected pipeline, the following points should be observed when installing the electromagnetic flowmeter: To make the fluid well grounded, a ground ring should be used; when the sensor is connected to the pipeline, there must be insulation between the flanges Insulation sleeves should also be used on the pads and screws.

4. When the electromagnetic flowmeter is installed on the grounded metal pipeline, the system potential balance is achieved through the grounding terminal on the electromagnetic flowmeter transmitter, that is, the copper core wire with a cross-sectional area of not less than 6mm2 is connected to the grounding terminal; When the electromagnetic flowmeter is installed on an ungrounded metal pipe, the two flanges are connected to the pipe flange through a copper core wire with a cross-sectional area of at least 6mm2 and are grounded. Connect the transmitter or sensor junction box to the ground terminal. Achieve system potential balance; when the electromagnetic flowmeter is installed on a plastic pipe or a pipeline with an insulating lining, the system potential balance is achieved through an additional ground ring, which is connected to the ground terminal through a copper core wire with a cross-sectional area of at least 6 mm2.

Insertion Magnetic Flowmeter with differential welded nipple and ball valve

Insertion  Magnetic Flowmeter with differential welded nipple and ball valve   can be used for differential size . 

How JCDP Capacitive Differential Pressure Transmitter Work

JCDP/JCBP Capacitive Pressure Transmitter  operates on the principle that, if the sensing  diaphragm between
two capacitor plates is deformed by a differential pressure, an imbalance of capacitance will occur
between itself and the two plates.This imbalance is detected in a capacitance bridge circuit and
converted to a D.C. output  current of 4 to 20 mA.
 Another type of capacitor uses concentric hollow metal cylinders. The capacitance of this type just like theflat-plate type is proportional to the area.

This principle can be applied to differential pressure measurement, as shown in Figure. The pressure actingon the isolating diaphragms set up similar pressures in the silicone oil filling the space between them.

A net force proportional to the difference between the two pressures acts upon the metal sensing diaphragm and deflects it to one side or the other, depending on which input pressure is the greater.
 

he sensing diaphragm and capacitor thus form a differential variable separation capacitor. When the two input pressure are equal, the diaphragm is positioned centrally and the capacitances are equal.

A difference in the two input pressures causes displacement of the sensing diaphragm and is sensed as a difference between the two capacitances.

This change in capacitance is measured using a bridge circuit to measure the equivalent pressure signal.

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Cases for Wrong Installation of Electromagnetic Flowmeter

Case 1: The Flow Value Jitters Seriously. 


    
Analysis: There is pump tightly closed to the flow meter on the spot. When the liquid flows through the flow meter, it will be in the turbulent condition,
which exists strong interference in measurement. That is why the value of flow meter always jitters.
Solution: Be far away from the pump and choose the straight pipe distance, at least five times of pipe diameter longer, to guarantee the flow steady.
   As below is the similar case that is installed closed to valves.


 
 
Case 2: The Measurement Is Always Not Correct. Sometimes ATC Alarm And Lower Limit Alarm Will Occur Sometimes.



Analysis: From the picture above, there is half pipe of water inside, which means it isn’t full pipe measurement for electromagnetic flow meters.
That is why its measurement is not correct.
Solution: reduce and extend the pipe, let the liquid fulfill the pipe.
 
Case 3: The Electromagnetic Flow Meters Always Damage.




Analysis: If installed in the places where there is water immersion risk, the flow meters have to be IP68.

Solution: choose IP68

Why is the installation of electromagnetic flow meters so strict?

1. The measurement principle of electromagnetic flow meters is based on Faraday induction, conducting medium’s cutting magnetic line generates inductive emf,
2. and the signal is collected by the electrodes in the central axis.

That is why the liquid has to be fulfilled in the pipe, otherwise, limit alarm or Atc alarm will occur.
In which conditions will guarantee the liquid is fulfilled in the pipe?
It is surely full pipe in the vertical pipe. It is also full pipe in the horizontal pipe if installed correctly.

2. The flow velocity of liquid through the pipe has to be uniform and stable. Why? The flow measurement is actually the product value of velocity and pipe CSA.
2. Then if velocity is not steady, the flow measurement will jitter.

       That is why we choose to install the flow meters as far as possible. Certainly, there has to be long enough straight pipes, whose function is gentling the flow velocity
and let the liquid go through the flow meters uniformly and steadily. (5 times of pipe diameter longer upstream and 5 times of pipe diameter longer downstream)