One measurement artifact of a bubble tube system is a slight variation in pressure each time a
new bubble breaks away from the end of the tube. The amount of pressure variation is approximately
equal to the hydrostatic pressure of process fluid at a height equal to the diameter of the bubble,
which in turn will be approximately equal to the diameter of the bubble tube. For example, a
1-4 inch diameter dip tube will experience pressure oscillations with a peak-to-peak amplitude of approximately 1-4 inch elevation of process liquid. The frequency of this pressure oscillation, of
course, will be equal to the rate at which individual bubbles escape out the end of the dip tube.
Usually, this is a small variation when considered in the context of the measured liquid height in
the vessel. A pressure oscillation of approximately 1-4 inch compared to a measurement range of 0 to
10 feet, for example, is only about 0.2% of span. Modern pressure transmitters have the ability to
“filter” or “damp” pressure variations over time, which is a useful feature for minimizing the effect
such a pressure variation will have on system performance.