Can a tank with an internal floating roof use a differential pressure transmitter to measure the liquid level?
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The new unit is to be started up, and raw benzene is being fed in. The temperature is currently very low, and the magnetic level gauge does not have any heating for insulation; therefore, the magnetic level gauge at the site has not been put into use. The benzene tank is equipped with 3 level gauges and 2 radars; a single-flange pressure transmitter is installed at the bottom, and another single-flange pressure transmitter is placed at the top of the tank. These two single-flange pressure transmitters are subtracted from each other in the configuration, and the height is calculated based on density. Now the readings from both radars are consistent, and the level calculated based on pressure is higher than that indicated by the radars. According to the formula, pressure = Mg/S; m should be the sum of the mass of benzene and that of the internal floating roof. Doesn’t this mean that the liquid level measured using a pressure transmitter is higher when there is an internal floating roof?
There will definitely be some deviation; it depends on how much that deviation is. The actual height can be measured using a dipstick to calibrate differential pressure level gauges and radar levels.
Did the calculation not take into account the zero-point drift issue?
When using a differential pressure transmitter, it is necessary to take into account the deviation caused by the pressure generated by the floating roof; if this is not corrected, the measurement values will definitely be too high
Even without the issue of floating platforms that you mentioned, the measurements would still be inaccurate; there is still a gap between theory and reality. Rosemount has an electronic remote transmission option that you might want to consider. At the very least, it can **help reduce measurement errors**
Just calculate it directly with ρgh; what’s the need to add mass?
Measurement is based on radar, with differential pressure as a supplement. But the radar can also be interfered with, and in such cases differential pressure must be used as a reference. Actually, if interlocking is used, tuning fork switches can be added. Your problem is related to the discrepancy between two liquid levels. The differential pressure method for determining liquid level assumes that the density remains constant, whereas the density of liquids is greatly affected by temperature, which leads to a deviation from the actual liquid level.
The pressure value on the positive pressure side should be obtained by subtracting the mass of the floating roof component; subtraction is performed on the negative pressure side
Without making any adjustments to the differential pressure level gauge, it is normal for the indication to be slightly high—by a few dozen to a couple of hundred centimeters. First, figure out what a floating roof tank is. Refer to the figure below: the upper part of the floating roof as measured by radio radar ； Steel strip level gauges, differential pressure level gauges, and guided wave radar are used to measure the liquid level in the measurement well. Additionally: Using two pressures to measure the differential pressure is theoretically fine. In fact, it will result in significant errors.