In-Situ Aqua TROLL 100 and 200 Operators Manual - Manual (Page 58)

Page 58 Aqua TROLL Operator’s Manual
6 Pressure and Level
The Aqua TROLL 200 Instrument contains a pressure sensor. A
pressure transducer senses changes in pressure, measured in
force per square unit of surface area, exerted by water or other
fluid on an internal media-isolated strain gauge. Common
measurement units are pounds per square inch (psi) or newtons
per square meter (pascals).
Non-Vented (Absolute) vs. Vented (Gauged) Sen-
sors
A non-vented or “absolute” pressure sensor measures all pressure
forces exerted on the strain gauge, including atmospheric
pressure. Its units are psia (pounds per square inch “absolute”),
measured with respect to zero pressure.
Non-vented pressure measurements are useful in vacuum
testing, in short-term testing when atmospheric pressure would
not be expected to change, in very deep aquifers where the
effects of atmospheric pressure are negligible, and in unconfined
aquifers that are open to the atmosphere.
With vented or “gauged” pressure sensors, a vent tube in the
cable applies atmospheric pressure to the back of the strain
gauge. The basic unit for vented measurements is psig (pounds
per square inch “gauge”), measured with respect to atmospheric