The double-flange level gauge shows a lower reading than the on-site magnetic flip-level gauge
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The EJA double-flange level gauge is used to measure the level of liquefied gas, and it has been in normal use for several years. Recently, however, its readings no longer match those taken on-site – they are lower than the values measured on site. Upon disassembly and inspection, the diaphragm box showed no leakage of silicone oil; both positive and negative pressure measurements were normal, and the migration amount was correct as well. I just don’t know why?
I’ve been using it for a few years now, and normal wear and tear is to be expected. It could be a change in the density of the liquefied gas resulting from the manufacturing process, or it might be a deviation in the transmitter itself over time. Based on the liquid level at the site, adjust the upper and lower limits of the transmitter accordingly.
This post was last edited by feng*aosa on 2019-10-16 at 16:02. 1. Since the measurement principles of differential pressure level gauges and magnetic flap level gauges are different, discrepancies may occur when the density of the material changes； 2. Once it is confirmed that one level gauge is functioning properly, the other level gauge should be checked as well ； 3. In the level measurement of low-boiling-point materials, the insulation, heating, and routing of the pressure intake pipe can all affect the measurement results.
Consider the process – why has the pressure difference decreased?
It’s confirmed to be a problem with the remote transmission gauge, not an inaccurate magnetic flip switch?
If the settings are correct, has there been any change in the process medium? Because the differential pressure level gauge is calculated based on the density of the medium.
Consider temperature factors, such as temperature changes and insulation issues
Run the calibration again; if that doesn’t work, switch to another gauge.
Have the process team check whether there has been any change in the liquefied gas components, which could have caused a change in density. Secondly, you can perform a migration; if the value remains low, after ruling out issues with the pressure Guide tube, diaphragm, and signal interference, the most likely cause is density. Another scenario is the heating of silicone oil; the density of silicone oil varies at different temperatures, and this situation can also occur when there is a large temperature difference between the upper and lower flanges.
After several years of normal use, I believe that changes in density have little impact; otherwise, such differences in density due to temperature variations would have occurred earlier. As for the linear relationship with the actual liquid level, should we take into account any deviation in the instrument’s zero point? It’s necessary to level the double flanges and calibrate the zero point – I’m not sure if this is correct