The Rosemount electromagnetic flowmeter shows no reading at low flow rates
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There is a DN200 electromagnetic flowmeter used for measuring industrial wastewater; conditions such as a full pipe and appropriate conductivity meet the requirements for accurate measurement. Due to selection issues, the actual flow rate is around 30 m3/h; based on the pipe diameter, the flow velocity is slightly less than 0.3 m/s. The instrument’s range is set at 150 m3/h, and the cutoff value for low flow rates is set at the lowest level, namely 1.5 m3/h. At first, it was able to display the flow rate, but after about a month of use, it frequently failed to show the flow rate (i.e., the display showed 0). The electrodes were removed twice to check for any deposits on their surface, and they were cleaned with a toothbrush, yet there was no improvement. The insulation of the coils and electrodes with respect to ground is greater than 20 MΩ. I consulted Emerson’s after-sales support, and they said that even though the flow rate is low, the gauge still displays a flow value, although it may not be accurate. I was wondering if any experts with similar experience could share their insights.
The choice of flow meter is a bit problematic; at low flow rates, the flow velocity is too slow, making it likely that no measurement can be taken. It is recommended to use an electromagnetic flow meter with a smaller size
Should the flow meter be powered independently with 24V? What’s the voltage drop at the site, ma’am? Maybe it doesn’t work properly below 18V?
It’s likely that the flow rate is too low; the process wastewater is pumped in, right? Is it possible to increase the pressure used for pumping it in?
It is powered by 220V, and the process wastewater is pumped in. Is the purpose of increasing pressure to reduce any bubbles that may be present in the medium? As far as I know, there are basically no bubbles in the medium Also, the pipes upstream and downstream of this instrument are made of stainless steel; therefore, there are no grounding rings or electrodes. The instrument does not either make any connections across the upstream and downstream pipes. I was wondering if this could be the cause of the aforementioned phenomenon?
If no static grounding is performed, such problems may occur; it is recommended to carry out static grounding. I still suspect that the traffic isn’t sufficient.
Grounding mainly includes protective grounding and anti-interference grounding, to prevent the absence of flow display.
It’s unlikely that this situation will occur when the device isn’t grounded; it’s mainly a problem with the flow rate – when the diameter is large but the flow volume is low, increasing the pressure is done to bring the flow rate within a measurable range