45
The Cannonball3 offers a choice of two different calibration gas
settings for the CO Plus sensor. Calibration gas settings
determine whether the Cannonball3 is configured for the direct
detection of CO or H
2
S. When the calibration gas value is set
to CO, the Cannonball3 will show CO+ on the current gas
readings screen. Alternately, when the calibration gas value is
set to H
2
S, the Cannonball3 will show H
2
S+ on the current gas
readings screen.
O
2
LEL
20.9 0
CO+
SO
2
0 0.0
Time 8:30 RT 1:15
Current gas readings screens with CO Plus sensor; calibration
gas value set to CO.
O
2
LEL
20.9 0
H
2
S+
SO
2
0 0.0
Time 8:30 RT 1:15
Current gas readings screens with CO Plus sensor; calibration
gas value set to H
2
S.
Note: The procedure for changing the calibration gas
value setting for the CO Plus sensor is covered below in
section 4.7.2.2.
4.3.1.2.1
Relative response of the CO Plus sensor to
carbon monoxide and hydrogen sulfide
The “CO Plus” sensor will accurately and directly measure the
gas type to which it has been successfully calibrated. OSHA
has assigned an 8-hour TWA of 35 PPM as the permissible
exposure limit for carbon monoxide. If the “CO Plus” sensor is
successfully calibrated to carbon monoxide, and then exposed
to 35 PPM carbon monoxide, the display will show 35 PPM.
Appendix A discusses Permissible Exposure Limit alarm
calculations in greater detail.
The “CO Plus” sensor will also show a “relative response” to
other interfering gases. When calibrated with carbon
monoxide, the “CO Plus” sensor responds to hydrogen sulfide
in a ratio of about 3.5 to 1.0. This means a concentration of
about 10 PPM hydrogen sulfide would produce a reading of 10
X 3.5 or 35 PPM in an instrument that has been calibrated to
CO.
This is a very convenient relative response. The 8-hour TWA
permissible exposure limit for hydrogen sulfide is 10 PPM.
This means that the CO Plus gas alarms will be tripped any
time the concentration of hydrogen sulfide exceeds the
permissible exposure limit.
Note: The procedure for changing the calibration gas
value setting for the CO Plus sensor is covered below in
section 4.7.2.2.
4.3.2 Cl
2
and ClO
2
sensors
Four different sensors are currently available for the PhD5 for
the detection of chlorine (Cl
2
) and chlorine dioxide (ClO
2
). The
non-specific versions of the Cl
2
and ClO
2
(part numbers 54-25-
08 and 54-25-12) have built-in cross-sensitivity as follows:
The Cl
2
(non-specific) and ClO
2
(non-specific) sensors are
actually the same sensor. When calibrated to Cl
2
the sensor
will respond to ClO
2
in a ratio of 1:3.1. As an example, if a Cl
2
non-specific sensor is exposed to 1 PPM ClO
2
the readout on
the gas detector will be 3.1 PPM.
The OSHA short term exposure limits (STEL) for Cl
2
and ClO
2
relate to each other in approximately the same ratio. The
OSHA permissible exposure limits (PEL) for an 8-hour time
weighted average (TWA) for Cl
2
and ClO
2
relate to each other
in a ratio of 1:5. The table below details the OSHA alarm
setpoints for Cl
2
and ClO
2
.
Substance STEL
TWA
Cl
2
1.0 PPM
0.5 PPM
ClO
2
0.3 PPM
0.1 PPM
Based on the relationships between the OSHA alarm set points
and the relative response, one benefit of the Cl
2
(non-specific) /
ClO
2
(non-specific) sensor is that the same sensor (with a
limited degree of accuracy) can be used for the detection of
both gases.
Note: For more information on cross sensitivity for any of
the sensors available in the PhD5, see Appendix B.
The specific version of the Cl
2
sensor is not cross sensitive to
ClO
2.
The specific version of the ClO
2
sensor is not cross
sensitive to Cl
2
.
Note: Cannonball3 instruments equipped with a chlorine
dioxide (ClO2) specific sensor (54-25-20) require a chlorine
dioxide generator as a calibration gas source.
4.4 Functional (bump) test
The accuracy of the Cannonball3 may be verified at any time
by a simple functional (bump) test. During the bump test, each
of the sensors is challenged with calibration gas sufficient to
cause the alarms to activate (when the alarms and calibration
gas levels are set at the default levels).
The Cannonball3 includes a built-in continuous sample draw
pump that draws the gas sample into the sensor compartment.
As such, there are two viable methods for delivering the gas to
the sensor chamber for the bump test. Either use a standard 1
liter/minute regulator with the calibration balloon that is
included with every Cannonball3, or use a demand flow
regulator and a small piece of tubing to deliver the calibration
gas directly into the inlet coupling on the front of the
instrument.
To perform a functional (bump) test, do the following:
1. Turn the Cannonball3 on and wait at least three minutes to
allow the readings to fully stabilize.
2. Make sure the instrument is located in fresh air.
3. Verify that the current gas readings match the
concentrations present in fresh air. If the Cannonball3 is
operated in Basic, Basic/Peak or Technician operating
mode the fresh air readings should equal 20.9% O
2
, 0%
LEL or 0.0% CH
4
, and 0 or 0.0 PPM for any toxic sensors
installed. If the instrument is operated in the Text Only
mode all readings should indicate that conditions are “OK”.
If necessary, perform a fresh air calibration as discussed
in section 4.5.1.
Summary of Contents for Cannonball3
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