The main sources of electromagnetic flowmeter failures caused by piping systems and related equipment are as follows

1. Poor installation
2. Not full tube
3. Gas storage in the piping system
4. Constantly inhale gas
5. Flow status changes during use

1. Poor installation

Poor installation is manifested in:

1. The flow sensor and the inner diameter of the connecting pipe are incorrectly matched, and the difference is too large. Without the manufacturer’s recommendation, the inner diameter of the connecting pipe shall not be less than the inner diameter of the flow sensor, and shall not be greater than 3% of the inner diameter.
2. The gasket between the flow sensor and the pipe protrudes into the flow pipe. 3. The front spoiler adjacent to the flow sensor produces severe flow velocity distribution distortion or rotating flow, and the straight pipe section is insufficient. These reasons mainly cause the flow measurement value to be inconsistent with the actual, and sometimes the output shakes.

2. Not full tube

Due to insufficient back pressure or poor installation position of the flow sensor, the liquid in the measuring tube cannot be filled. The failure phenomenon has different manifestations due to the degree of underfilling and the flow condition. If a small amount of gas is in a stratified or wavy flow in a horizontal pipeline, the fault phenomenon is manifested as an increase in error, that is, the flow measurement value does not match the actual value; if the flow is bubble flow or plug flow, the fault phenomenon is except that the measured value does not match the actual value. In addition, the output will fluctuate because the gas phase instantly covers the electrode surface.

If the gas phase part of the flow area in the horizontal pipeline stratified flow increases, that is, the degree of liquid underfilling increases, output sloshing will also occur. If the liquid is not full to the surface of the liquid below the electrode, the output will be overfull.

3. Gas storage in the piping system

One reason for the gas storage in the piping system is that the air in the pipe cannot be drained before it is activated. The remaining gas accumulates at the high point of the piping system and is entrained by the liquid when flowing and flows out in the form of bubbles; the other reason is that small bubbles are gradually entrained in the liquid. Gather and store at the high point of the pipeline system. The fault is manifested as the flow measurement value does not match the actual value and the output shaking.

4. Constantly inhale the gas

The reciprocating pump is pumping liquid and the measuring point is not far away from the pump. The pulsating flow will cause the output of the electromagnetic flowmeter to sway and sometimes cause measurement errors. In order to slow down the influence of pulsation on the instrument, it is usually possible to increase the excitation frequency of the electromagnetic flowmeter or increase the resistance; in the piping system, damping devices such as air chambers can be added. The flow control mismatch of the piping system causes the opening and closing oscillation of the control valve to also form a pulsating flow.

5. Flow status changes during use

Normally, after a period of the normal operation of the instrument during debugging, malfunctions may also occur due to changes in the flow state. Although the probability of occurrence of this failure cause is not high, this factor should not be forgotten when analyzing the cause of failure.