In-Situ TROLL 9500 Operators Manual - Manual (Page 63)

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Multi-Parameter
Water Quality TROLL ®
TROLL 9500 Operator’s Manual 0095110 rev. 007 01/09
9 MONITORING BAROMETRIC PRESSURE
WHAT IS BAROMETRIC PRESSURE?
Barometric, or atmospheric, pressure is the force exerted by the
gases in the atmosphere everywhere on the surface of the earth.
Barometric pressure is greatest at or below sea level, and decreases
as altitude above sea level increases.
WHY MONITOR BAROMETRIC PRESSURE?
"AROMETRIC
A logged record of barometric pressure data during a test can be used
to correct water level measurements made with an absolute pressure
SENSOR
To measure barometric pressure, the probe must be vented
to the atmosphere. A submerged Multi-Parameter TROLL
on non-vented cable cannot accurately report barometric pressure.
If your MP TROLL 9500 is used with a non-vented backshell and/or
non-vented cable, a software correction can substitute for barometric
pressure venting. See the procedure in this section.
THE BAROMETRIC PRESSURE SENSOR
Most models of the Multi-Parameter TROLL 9500 include a per-
manent, factory-calibrated internal barometric pressure sensor. Its
primary function is in calibration and measurement of water-quality
parameters, such as dissolved oxygen, that are dependent upon baro-
METRIC
The sensor is automatically included in tests so that its value is avail-
able to compensate water-quality data from other channels.
Units
The following units are available for barometric pressure: Bars, mil-
liBars, inches of mercury (in. Hg or “ Hg), millimeters of mercury (mm
Hg), cm, pounds per square inch (psi)
TIP: To change unit preferences: In Win-Situ, select
Preferences on the Options menu. In Pocket-Situ, select the
Home site, then tap Setup in the command bar.
COLLECTING ACCURATE MEASUREMENTS WITHOUT
VENTED CABLE
Win-Situ and Pocket-Situ cannot determine whether the MP TROLL
9500 is on vented or non-vented cable. However, you can supply the
software with this information, and also enter a fixed barometric pres-
sure value to be used in the absence of cable venting.
Procedure:
1. Select the barometric channel in the Navigation tree.
2. Click or tap Edit.... The Edit Barometric Channel screen appears.
Several options are presented:
TIP: This screen can also be accessed during test setup and
dissolved oxygen calibration.
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