Electromagnetic flowmeter use empty tube alarm causes and solutions

Causes and solutions for empty pipe alarms when using electromagnetic flowmeters

In general pipeline fluid measurement, the flowmeter can only measure one-way fluid. If the direction of the fluid changes, the measurement cannot conduct. There are only a few flowmeters that can measure bidirectional flow. Normally, we know electromagnetic flowmeters and ultrasonic flowmeters. The forward and reverse flow directions of the electromagnetic flowmeter can be completed through settings. When installed horizontally, flow selection provides a lot of convenience on site. However, when installed vertically, fluid can only pass through the flowmeter from bottom to top. The electromagnetic flowmeter has strict requirements for full pipe. When the fluid passing through the flow meter does not meet the full pipe requirement, the flow meter will issue an empty pipe alarm and the meter will display no flow.

Electromagnetic flowmeters often encounter empty pipe alarms during use. The so-called empty pipe alarm of electromagnetic flowmeters refers to detecting whether the measurement fluid is filled with the sensor measuring tube and detecting the cause of the empty pipe alarm. , we can use wires to short-circuit the converter signal input terminal and the ground. If the measurement result is that the empty pipe becomes full, it means that the converter of the electromagnetic flowmeter is normal. The cause of the failure may be the conductivity of the fluid being measured. Low or empty pipe threshold is set incorrectly. In addition, if there is a problem with the electrode of the electromagnetic flowmeter, an empty pipe alarm may also occur.

The empty pipe alarm threshold is often used in conjunction with the empty pipe alarm. The empty pipe alarm threshold is usually set at 500%. The empty pipe alarm is a relative value, which is directly related to the full pipe status and the conductivity of the medium. The size of the empty pipe alarm threshold will determine the sensitivity of the empty pipe alarm. Before determining the empty pipe alarm threshold, the measured medium (i.e. conductivity) and the resistivity rate of the medium when the pipe is full should be determined. Then consider the time for the fluid to hang on the wall and set the alarm response time appropriately. Therefore, the threshold of the empty pipe alarm should be an adjustable parameter.

In actual use, the resistivity value when the fluid is in the full pipe state is defined as 100%, that is, when the fluid is in the full pipe state, the "empty pipe alarm threshold" is used to calibrate the empty pipe measurement value to 100 %. When the fluid level in the pipeline is lower than the measuring electrode, the relative resistivity will increase. When it is higher than the empty pipe alarm threshold, the instrument will display an empty pipe alarm signal. Theoretically, if the empty pipe alarm threshold is set to 900%, the empty pipe alarm can be displayed when the pipe is empty. The smaller the empty pipe alarm threshold, the more sensitive the empty pipe alarm will be. Each is set according to site requirements.

What to do when an empty pipe alarm occurs in the electromagnetic flowmeter:

1. Measure whether the fluid is full of the measuring tube;

2. Connect the converter signal with a wire Input terminals SIG1, SIG2 and SIGGDN are short-circuited. If the "empty pipe" prompt is canceled at this time, it means that the converter is normal. It may be that the conductivity of the fluid being measured is low or the empty pipe threshold and empty pipe range are set incorrectly;

3. Check whether the signal line is connected correctly;

4. Check whether the sensor electrode is normal;

5. Make the flow rate zero and observe the displayThe conductivity ratio should be less than 100%;

6. When there is current, the resistance of terminals SIG1, SIG2 and SIGGDN measured respectively should be less than 50kΩ.

7. Use a multimeter to measure the DC voltage between DS1 and DS2 and it should be less than 1V. Otherwise, it means that the sensor electrode is contaminated and should be cleaned.