700-Bubbler-Man Rev 12 13 Feb 2020 Page 1/51
GENERAL
1.1 INTRODUCTION
The FTS Bubbler is an SDI-12 user configurable system for accurately measuring water stage in
streams and reservoirs using pressure differentials. It is a self-contained, sealed system that
includes an air compressor, control electronics and a high accuracy pressure sensor for measuring
water levels. It must be used with a desiccator (see section 2.5) and can be connected to any SDI-12
capable data logger or data collection platform (DCP) using the SDI-12 Data Terminal Block for data
logging capability. The FTS Bubbler also has the option to output the level value as a 4-20mA signal.
Figure 1-1: Bubbler components
The system forces air at a continuous rate through an orifice line, the end of which is mounted at a
known, fixed position. A sensor measures the pressure required to maintain the air flow down the
orifice line such that bubbles emerge from its end, compares that to atmospheric pressure, and
computes the stage level (water depth). Any change in water level causes the air pressure in the
orifice line to vary resulting in updated stage levels.
FTS’ proprietary design allows for a larger orifice (18 times larger than the standard metering valve
orifice of 0.035mm). Not only does this minimize fouling of the manifold but it also allows the purge
to flush particulates throughout the entire system from the compressor valve to the orifice line end
fitting. The purge is achieved without bypassing a portion of the system, as systems which use a
metering valve must do. This results in highly accurate readings, even in environments with high
humidity or containing airborne particulates.
Compressor Air Intake
Outlet/Orifice Line Connection
Data Terminal Block
plates
Display
Part#18729: Barbed
desiccant line inlet
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