The double-flange level gauge is inaccurate
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Our unit currently has a SMAR LD301 double-flange level gauge. Recently, as the weather has gotten colder, a problem has arisen: the level reading is inaccurate. After resetting it to zero and setting the full scale, the reading was accurate for a few hours, but later it still differed from the actual level, and the magnitude of this discrepancy varied. The medium we are measuring is a mixture of crude oil and water from oil wells. Additionally, temperature fluctuations are significant in cold weather. We installed electric heating elements around the capillary of the double-flange level gauge to provide insulation; this improved the accuracy compared to not using any heating. As far as I remember, the capillary of this type of level gauge doesn’t require insulation – it should function fine even at low temperatures. So why does it fail to work at low temperatures? Could someone please help us solve this problem? How can we adjust it so that the errors are minimized? The adjustment of the scale is done using a magnetic rod
Can you find out what model the capillary filling oil is? Or, what is the lowest ambient temperature that this filling oil can withstand? What is the ambient temperature? For the three types of silicone oils I am aware of, the lowest temperatures are: –45 degrees (some also reach –30 degrees), 0 degrees, and +20 degrees; all of these are products from DOW CORNING. Judging from the appearance, it is estimated that silicone oil with a positive temperature coefficient was used. @jiaguoyun
I’m not really sure about the model of this silicone oil. Based on the current situation, it might be necessary to choose either a positive value or zero. Also, is there any good way to deal with fluctuations in the liquid level? The diaphragm has been cleaned; it was a bit dirty at first. And must the full scale correspond to the height of the upper flange? Any position will do, as we don’t need such a high liquid level here; around 1.7 is sufficient. We set the full scale at around 1 meter. Does this have any impact on the transmitter? What’s the problem with setting it this way? I’m not very familiar with this area; could someone please provide an explanation?
It was quite accurate before, but recently as the weather has gotten colder, there have been greater fluctuations. Additionally, the difference between the actual liquid level and the indicated level keeps changing – sometimes it increases and sometimes it decreases. Could this be related to the electric heating and insulation we use for the capillaries? Is it the varying temperatures of the capillaries that cause these fluctuations in the liquid level?
There’s nothing else to do; we just keep it heated. Heating for capillaries is something normal; for example, Yokogawa’s capillaries use conventional silicone oil, which can maintain temperatures around -10 degrees, while specially customized versions can achieve temperatures of -30 degrees. The Romon DC200 is around -45 degrees. The compression range affects accuracy, by a few percentage points; it’s not that significant. When using a capillary within a range of 1 meter, it is indeed necessary to give careful consideration to the filling fluid; as the range becomes smaller, the influence of the filling fluid increases. What’s the local temperature? Was it the same last winter? @jiaguoyun
The inaccuracy of double-flange level gauges is mainly due to two factors: first, the density of the liquid being measured, as changes in the ratio of water to oil or variations in temperature can affect the density of the medium； The second factor is the ambient temperature of the capillary; significant changes in ambient temperature can cause the liquid inside the capillary to expand, affecting the accuracy of the measurements. Take measures for the above reasons.
Inaccurate measurements caused by low temperatures can be addressed by adding heat tracing as required, or by purchasing a level gauge suitable for use in low-temperature conditions in that area.
Check whether the root valve with double flanges is blocked; this phenomenon may be caused by a blockage in the root valve, leading to pressure fluctuations. Clean and clear the root valve.
There’s no problem with this root valve; it has been under adjustment these past few days, and the valve is fine
Some time ago, the temperature dropped to minus 12 degrees, and then that was no longer allowed. In the past, the temperature was slightly higher than that; the lowest it ever reached was around minus 8 degrees. Back then, there was heat supply, but the temperature wasn’t as high as it is now. Also, the readings fluctuated a lot