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technical article
Common problems and treatment methods of electromagnetic flowmeter
2011-5-22 17:04:42

,在日常使用中多少会遇到一些问题? How many electromagnetic flowmeters will encounter some problems in daily use? We Jiangsu Dongxiang Instrument Co., Ltd. specializes in the production and sale of electromagnetic flowmeters . In the years of production and sales, some methods to deal with the problems encountered in the use of electromagnetic flowmeters are summarized.

1. Failure during debugging

Debugging expects that the fault generally occurs during the installation and commissioning of the instrument . Once eliminated, it will not occur again under the same conditions in the future. Common faults during commissioning are usually caused by improper installation, environmental interference and the influence of fluid characteristics.

1) Installation

It is usually caused by the incorrect installation position of the electromagnetic flowmeter sensor . Commonly, if the sensor is installed at the highest point of the piping system that is prone to accumulate gas; or it is installed on a vertical pipe from top to bottom, it may be empty; or after the sensor Without back pressure, the fluid is directly discharged into the atmosphere to form a non-full tube in the measuring tube.

2) Environmental aspects

Usually it is mainly stray current interference of pipelines, strong electromagnetic interference in space, and magnetic interference of large motors. Pipeline stray current interference usually achieves satisfactory results with good separate ground protection. However, if a strong stray current is encountered (such as in electrolytic workshop pipes, sometimes the peak AC voltage Vpp induced on the two electrodes can be as high as 1V). Additional measures need to be taken and the flow sensor is isolated from the pipeline. Space electromagnetic wave interference is generally introduced through signal cables and is usually protected by single or multiple layers of shielding.

3) Fluid aspect

The measured liquid contains uniformly distributed tiny air bubbles, which usually does not affect the normal operation of the electromagnetic flowmeter. However, as the air bubbles increase, the output signal of the meter will fluctuate. If the air bubbles are large enough to cover the entire electrode surface, Passing the electrode will cause the electrode circuit to be momentarily disconnected and make the output signal fluctuate more.

When the low frequency square wave excitation electromagnetic flowmeter measures the slurry with excessive solid content, it will also generate slurry noise, which will cause the output signal to fluctuate.

When measuring mixed media, if the flow sensor is used for measurement before the mixing is not uniform, the output signal will also fluctuate.

Improper selection of electrode material and measured medium will also affect normal measurement due to chemical interaction or polarization phenomenon. The electrode materials should be correctly selected according to the instrument selection or relevant manuals.

2. Runtime failure

The fault during operation is a fault that occurs after the electromagnetic flowmeter is debugged and operated normally for a period of time. Common faults during operation are generally caused by factors such as the adhesion layer on the inner wall of the flow sensor, lightning strike, and changes in environmental conditions.

1) Adhesive layer on the inner wall of the sensor Because electromagnetic flow meters are commonly used to measure dirty fluids, after a period of operation, it often accumulates on the inner wall of the sensor and causes failure. These failures are often caused by the conductivity of the adhesion layer being too large or too small. If the attachment is an insulating layer, the electrode circuit will be disconnected and the meter will not work properly; if the conductivity of the attached layer is significantly higher than the fluid conductivity, the electrode circuit will be short-circuited and the meter will not work properly. Therefore, the scale layer attached to the measuring tube of the electromagnetic flowmeter should be removed in time.

2) Lightning strike

Lightning strikes can easily induce high voltages and surge currents in the instrument wiring, which can damage the instrument. It is mainly introduced through power lines or field coils or flow signal lines between sensors and converters, especially from control room power lines.

3) Environmental conditions change

During the debugging period, because the environmental conditions are good (for example, there is no interference source) and the flowmeter works normally, it is often easy to neglect the installation conditions (for example, the grounding is not very good). In this case, once the environmental conditions change, new interference sources appear during operation (such as welding on the pipeline near the flow meter, a large transformer is installed nearby, etc.), which will interfere with the normal operation of the meter and the output of the flow meter. The signal will fluctuate