Electromagnetic flowmeter In general pipeline fluid measurement, the flowmeter can only measure one-way fluid. If the fluid direction changes, the measurement cannot be performed. There are only a few flow meters that can measure two-way flow. Normally, we know that there are electromagnetic flowmeters and ultrasonic flowmeters. The positive and negative flow directions of electromagnetic flowmeters can be completed by setting. When installed horizontally, the flow selection provides a lot of convenience on site. However, in vertical installation, the fluid can only pass through the flowmeter from bottom to top. The electromagnetic flowmeter has strict requirements on the full pipe. When the fluid does not reach the full pipe requirement when the flow passes through the flowmeter, the flowmeter will have an empty pipe alarm, and the meter head shows no flow.
The electromagnetic flowmeter often encounters an empty pipe alarm phenomenon during the use process. The so-called empty pipe alarm of the electromagnetic flowmeter refers to detecting whether the measuring fluid is filled with the sensor measuring tube, and detecting the cause of the empty pipe alarm, we can use the wire to The converter signal input terminal and the ground three-point short circuit, if the empty tube becomes full, the converter of the electromagnetic flowmeter is normal. The cause of the fault may be the low conductivity of the measured fluid or the empty tube threshold setting. error. In addition, if there is a problem with the electrode of the electromagnetic flowmeter, an empty pipe alarm may occur.
Empty pipe alarm thresholds are often used in conjunction with air traffic control alarms. The empty tube alarm threshold is usually set at 500%. The empty tube alarm is a relative value. It has a direct relationship with the full tube status and the conductivity of the medium. The empty tube alarm threshold will determine the sensitivity of the empty tube alarm. Before determining the empty pipe alarm threshold, the measured medium (ie, conductivity) and the resistance value of the medium under full pipe conditions should be determined. Then consider the time of the fluid wall and other appropriate settings of the alarm reaction time, so the threshold of the empty pipe alarm should be an adjustable parameter.
In actual use, the value of the resistivity in the full tube state is defined as 100%, that is, when the fluid is full, the empty tube measurement is calibrated to 100% with the "empty tube alarm threshold". When the fluid level in the pipeline is lower than the measuring electrode, the relative resistivity will increase, and when the pipeline is above the empty pipe alarm threshold, the meter will display an empty pipe alarm signal. In theory, an empty pipe alarm threshold can be displayed when the empty pipe alarm threshold is set at 900%. The smaller the empty pipe alarm threshold, the more sensitive the air traffic control alarm. Each is set according to site requirements.
Huaheng Instrument reminds you: when the electromagnetic flowmeter has an air traffic control alarm:
1. Measure whether the fluid is filled with the measuring tube;
2. Use a wire to short-circuit the converter signal to terminals SIG1, SIG2, and SIGGDN. If the "empty pipe" prompt is cancelled, the converter is normal, which may be the conductivity of the measured fluid or the empty pipe threshold. The empty pipe range setting is incorrect;
3. Check if the signal cable connection is correct;
4. Check if the sensor electrode is normal;
5, the flow is zero, the observation shows that the conductivity ratio should be less than 100%;
6. In the case of current, the resistance of the terminals SIG1, SIG2 and SIGGDN should be less than 50kΩ.
7. Use a multimeter to measure the DC voltage between DS1 and DS2 should be less than 1V. Otherwise, the sensor electrode should be contaminated and should be cleaned.
The empty pipe alarm should mean that the pipe is not completely filled. Not full but there is flow which occurs on the horizontally placed pipe. Mounting the sensor on the riser should eliminate this problem.
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