Electromagnetic flowmeter measurement of pipeline water common problems

Case introduction

Common problems with electromagnetic flowmeters measuring pipeline water and methods to avoid installation errors:

1. Introduction

Common faults in the use of electromagnetic flowmeters, some are due to damage to the components of the instrument itself Some faults are caused by improper selection, improper installation, environmental conditions, fluidity and other factors, such as display fluctuations, reduced accuracy and even instrument damage. It can generally be divided into two types: faults that occur during installation and debugging (faults during commissioning) and faults that occur during normal operation (faults during operation).

2. Failures during commissioning

Debugging expected failures generally occur during the instrument installation and commissioning phase. Once eliminated, they will not reoccur under the same conditions in the future. Common faults during commissioning are usually caused by improper installation, environmental interference and fluid effects.

1. Installation

Usually the fault is caused by incorrect installation position of the electromagnetic flow sensor. Common ones include installing the sensor at the highest point of the piping system where gas is prone to accumulate; or installing On the vertical pipe from top to bottom, emptying may occur; or there may be no back pressure behind the sensor, and the fluid is directly discharged into the atmosphere, resulting in a non-full pipe in the measuring pipe.

2. Environmental aspects

Usually mainly caused by stray current interference in pipelines, strong electromagnetic wave interference in space, magnetic field interference from large motors, etc. For stray current interference in pipelines, satisfactory results can usually be obtained with good single grounding protection. However, if a strong stray current is encountered (such as electrolytic workshop pipelines, sometimes the peak AC potential Vpp induced on the two currents can be as high as 1V), it is still possible to obtain satisfactory results. Additional measures and flow sensors and pipe edges need to be taken. Space electromagnetic wave interference is generally introduced through signal cables and is usually protected by single or multi-layer shielding.

3. Fluids

The measured liquid contains evenly distributed tiny bubbles which usually do not affect the normal operation of the electromagnetic flowmeter. However, as the bubbles increase, the output signal of the meter will Fluctuations occur. If the bubbles are large enough to cover the entire electrical surface, as the bubbles flow through the electricity, the electrical circuit will be instantly disconnected and the output signal will fluctuate even more.

When an electromagnetic flowmeter with low-frequency square wave excitation measures a slurry with excessive solid content, it will also produce slurry noise, causing the output signal to fluctuate.

When measuring mixed media, if the flow sensor is entered for measurement before the mixture is uniform, the output signal will also fluctuate.

Improper selection of electrical materials and the measured medium will also affect normal measurement due to chemical effects or chemical phenomena. Electrical distribution materials should be selected correctly according to instrument selection or relevant manuals.

3. Operational faults

Operation faults are faults that occur after the electromagnetic flowmeter has been debugged and operated normally for a period of time. Common running faults are generally caused by the adhesion layer on the inner wall of the flow sensor. Caused by factors such as lightning strikes and changes in environmental conditions.

1. Adhesion layer on the inner wall of the sensor

Since electromagnetic flowmeters are often used to measure dirty fluids, after running for a period of time, an adhesion layer will often accumulate on the inner wall of the sensor.malfunction occurs. 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 electrical circuit will be open and the instrument will not work properly; if the conductivity of the attachment layer is significantly higher than the conductivity of the fluid, the electrical circuit will be short-circuited and the instrument will not work properly. Therefore, the attached scaling layer in the electromagnetic flowmeter measuring tube should be removed in time.

2. Lightning strikes

Lightning strikes can easily induce high voltage and surge current in the instrument circuit, causing damage to the instrument. It is mainly introduced through power lines or excitation coils or flow signal lines between sensors and converters, especially the majority of them introduced from the control room power lines.

3. Changes in environmental conditions

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