6
1. Overview of Dilution
Monitoring
The Cannonball 3 sample dilution system
allows the user to accurately sample
combustible gases from otherwise inert
environments.
Note: This dilution manual assumes
that the user is familiar with the basic
menu functions of the Cannonball 3.
If questions arise as to how to access
certain menu items, see the
Cannonball 3 Reference Manual.
Dilution monitoring is
extremely hazardous and should only
be performed by individuals trained in
the safe monitoring of inert
environments. Failure to follow
established procedures while
performing dilution monitoring may
lead to dangerous and potentially life-
threatening conditions.
Note: The ability to perform dilution
monitoring is automatically disabled
by the Cannonball3 software upon
recognition of an installed HC/LEL
sensor.
1.1 Theory
Catalytic hot bead LEL sensors, such as
the type used in the Cannonball 3,
require oxygen levels of at least 10% by
volume to produce an accurate LEL
reading. Catalytic hot-bead LEL sensors
physically burn the combustible gas that
is present in the environment in order to
produce a reading. Since inert
environments are devoid of oxygen by
definition, it is necessary to add oxygen
to the sample stream to allow the
combustible gas sensor to operate.
The Cannonball 3’s sample dilution
system utilizes two separate sample
draw pumps to overcome this obstacle
by accurately mixing the inert sample
with a fresh air sample. This method
provides enough oxygen to the LEL
sensor to allow it to respond to the
combustible gas. The Cannonball 3’s
microprocessor then calculates the level
of combustible gas in the sample by
dividing the LEL sensor’s response by
the percentage of flow taken from the
sample pump versus the amount of flow
taken from dilution pump.
Note: The Cannonball 3 must be
located in a fresh air atmosphere
containing 20.9 percent oxygen while
conducting dilution sampling. The
sample draw probe must be inserted
into the inert atmosphere to collect
the sample.
2. Operation in dilution mode
2.1 Start up procedure in
dilution mode
The start up procedure for dilution
capable instruments is similar to the start
up procedure for non-dilution instruments
except for a few minor changes. The
software in the Cannonball 3 includes
two additional oxygen alarms for use with
the dilution pump in inert or nearly inert
environments. At start up, the
Cannonball 3 automatically checks for
the dilution pump.
Checking for
Dilution Pump…..
Once the dilution pump is recognized,
the instrument will display the dilution
Oxygen alarm settings in the current
alarm settings screen.
CURRENT ALARM SETTINGS
LOW CEIL
O
2
STD
19.5 22.0
O
2
DIL OFF 5.0
LEL 10
CEIL STEL TWA
CO 100 35 100
H
2
S 10 15 10
Current alarm settings screen with
dilution-capable instrument.
Although standard and dilution alarms
are provided in dilution-ready Cannonball
3 instruments, only one set of oxygen
alarms can be enabled at any time.
Whenever the Cannonball 3’s dilution
system is enabled or disabled, oxygen
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