Pengukuran Level dengan Bubbler Tubes

Salah satu metoda pengukuran level adalah dengan menggunakan bubbler tubes. Intinya sebenarnya adalah kita mengukur back pressure dari supply udara yg kita berikan ke dalam tanki. metode ini sangat murah dan mudah di buat, tapi kelemahannya akurasi yg 1-2% saja. berikut penjelasannya yg di copas dari http://www.omega.com/ (he..he... artiin sendiri aje, ane males nerjemah2 :-D)


Bubbler tubes provide a simple and inexpensive but less accurate (±1-2%) level measurement system for corrosive or slurry-type applications. Bubblers use compressed air or an inert gas (usually nitrogen) introduced
through a dip pipe (Figure 7-4A). Gas flow is regulated at a constant rate (usually at about 500 cc/min). A differential pressure regulator across a rotameter maintains constant flow, while the tank level determines the
back-pressure. As the level drops, the back-pressure is proportionally reduced and is read on a pressure
gage calibrated in percent level or on a manometer or transmitter. The dip pipe should have a relatively large
diameter (about 2 in.) so that the pressure drop is negligible. The bottom end of the dip pipe should be located
far enough above the tank bottom so that sediment or sludge will not plug it. Also, its tip should be notched
with a slot or "V" to ensure the formation of a uniform and continuous flow of small bubbles. An alternative
to locating the dip pipe in the tank is to place it in an external chamber connected to the tank. In pressurized tanks, two sets of dip pipes are needed to measure the level (Figure 7-4B). The two back-pressures on the two dip pipes can be connected to the two sides of a u-tube manometer, a differential pressure gage or a d/p cell/transmitter. The pneumatic piping or tubing in a bubbler system should be sloped toward the tank so
that condensed process vapors will drain back into the tank if purge pressure is lost. The purge gas supply
should be clean, dry, and available at a pressure at least 10 psi greater than the expected maximum total pressure required (when the tank is full and the vapor pressure is at its maximum). An alternative to a continuous bubbler is to use a hand pump (similar to a bicycle tire pump) providing purge air only when the level is being read. Bubblers do consume inert gases, which can later accumulate and blanket processing equipment. They also require maintenance to ensure that the purge supply is always available and that the system is properly adjusted and calibrated. When all factors are considered, d/p cells typically are preferred to bubblers in he majority of applications.