Background of electromagnetic flowmeter usage
During our initial visit to a customer's wastewater treatment plant Phase II, we found a DN500 electromagnetic flowmeter installed on the inlet pipeline. The design maximum flow rate is 3000 m³/h, the normal operating flow rate is approximately 800 m³/h, and the inlet valve is typically kept at around 30% opening. Shortly after commissioning, the transmitter readings began to fluctuate wildly, with a range as high as ±300 m³/h, severely affecting the operators' judgment and process control.
The usage issues of the electromagnetic flowmeter discovered on site
During the on-site investigation, our technical staff discovered several installation-related issues:
1. The sensor installation did not meet straight-pipe requirements. The flange connection was visibly misaligned, causing the sensor and the upstream/downstream pipelines to be out of alignment. This type of installation creates vortices inside the sensor, disrupting the flow velocity profile and leading to unstable signals picked up by the electrodes.
2. The position of the degassing valve was incorrect. The degassing valve was installed downstream of the sensor rather than upstream, preventing gases from being effectively removed before entering the measurement area, further exacerbating measurement interference.
3. Grounding issues. The inner wall of the metal pipeline was coated with anti-rust paint, resulting in poor grounding between the pipeline and the earth. ADC was even measured on the pipeline. Additionally, the sensor itself had no grounding treatment. Poor grounding creates a potential difference between the upstream and downstream sections of the pipeline. This interference signal directly couples onto the electrode's measurement signal, causing abnormal readings.
4. Presence of large amounts of air bubbles and partially filled pipe. When the valve was only 30% open (or less), a loud humming noise could be clearly heard from the pipeline. As the valve opening was increased to above 50%, the noise gradually diminished and eventually disappeared, and the flow fluctuation simultaneously narrowed to ±50 m³/h. This further confirmed that air bubbles and partially filled conditions are major causes of unstable electrode induction voltage.
On-site modification suggestions
To address these problems, our on-site technicians took the following corrective actions:
- performed proper grounding for the sensor;
- recommended that the user install degassing valves dispersedly along the upstream pipeline to ensure the medium is in a full-pipe condition before entering the measurement area;
- and re-aligned the sensor installation to ensure the sensor and upstream/downstream pipelines are in a straight line.
After these corrections, the interference current on the pipeline disappeared, and the flow readings returned to stable.
Summary
From this troubleshooting experience, the core causes of flow data fluctuations due to electromagnetic flowmeter installation issues can be summarized into three points: First, poor grounding contact creates a potential difference between upstream and downstream sections, interfering with the sensor electrode signal; Second, the sensor and upstream/downstream pipelines are not aligned in a straight line, causing vortices inside the sensor; Third, a large amount of air bubbles mixed in the medium and a partially filled pipe prevent the electrodes from obtaining a stable induced voltage.
Regarding our services
The long-term stable operation of an electromagnetic flowmeter is built on product performance as the foundation, but proper installation and precise adaptation to site conditions are the true guarantees. Site conditions vary greatly - pipeline configuration, grounding environment, fluid characteristics - if any factor is not carefully considered, measurement anomalies can occur. This is exactly why LEEG Instrument emphasizes the principle of "Survey first, select later". As a professional flow measurement manufacturer, we provide full-process technical support from pre-sales to after-sales: during the selection phase, our technical personnel can visit the site to conduct condition surveys, comprehensively evaluate pipeline conditions, installation environment, and process characteristics, and provide targeted solutions and selection guidance based on actual site conditions, rather than simply applying standard models; during the installation and operation phase, our engineers can provide on-site installation guidance to ensure key aspects such as straight-pipe requirements, grounding, and degassing are done correctly the first time. For applications like wastewater treatment plants, which are prone to low flow rates and gas bubble precipitation, we also provide long-term operational recommendations and ongoing follow-up services. Solving problems before installation is far more efficient and worry-free than troubleshooting afterward. If you are planning a flowmeter selection or encountering on-site difficulties, feel free to contact LEEG Instrument. Let the professionals do the professional work.
Recommended Product: MFE600E Intelligent Electromagnetic Flowmeter
Measurement Accuracy: ±0.5%, ±0.2%
Size/Range: DN3 ~ DN2400
Installation Type: Flanged, Wafer, Threaded, Clamp (Tri-clamp)
Electrode Materials: Stainless Steel (316L), Titanium (Ti), Hastelloy (HC, HB), Tantalum (Ta), Tungsten Carbide (WC), Platinum-Iridium (Pt)
Lining Materials: Chloroprene Rubber, Natural Rubber, Polyurethane Rubber, PTFE, F46, PFA
Medium Temperature: -20℃ ~ 150℃
Power Supply: 100~240V AC, 12V DC, 24V DC, Battery, Solar
Signal Output: 4~20mA DC, 1-5V, Frequency/Pulse, Relay Output, RS485/RS232 (standard ModBus protocol), HART, Profibus-DP/PA
Protection Rating: IP65, IP67, IP68 (sensor part of remote type)
