cootwo User Manual – Rev. 20170512 ©2017 DiveNav, Inc. – www.divenav.com
P a g e 6
7.2
O2 Sensor Replacement
In order to replace the Oxygen sensor you will need first
to open cootwo by removing the 3 screws on the back of the
unit and the large O-ring on the tank adapter.
Then disconnect the molex connector from the old O2
sensor and connect it to the new one.
Make sure you also install on the new O2 sensor the 2
extra O-rings that were previously mounted on the old O2
sensor as they are needed to keep the sensor in place
inside the enclosure.
Once you are done, go the Main
Settings menu and PUSH the button to
position the pointer on the SENSOR
sub-menu.
HOLD the button to enter the
SENSOR sub-menu.
Then select the O2 SEN sub-menu
and enter it.
Scroll down to select the CHANGE
sub-menu and enter it.
Now, PUSH the button to confirm that
you have replaced the Oxygen sensor
and cootwo will acknowledge it and turn
off after a few seconds.
Please note that when you replace the Oxygen sensor
while in stand-alone mode, cootwo will automatically assign
to the O2 sensor a lifetime of 12 months.
WARNING: the Oxygen sensor contains chemicals
which can cause burns if they come in contact with
eyes, skin and other body parts. Dispose of the Oxygen
sensor according to local regulations.
8 CARBON MONOXIDE SENSOR
cootwo comes with a Carbon Monoxide sensor that is
already factory calibrated and its calibration should last
about 1 year from the factory shipment date. More often you
calibrate the CO sensor and more accurate it will be.
cootwo uses an extremely sensitive CO sensor
designed to operate below 100ppm but if it is exposed to a
very high concentration of CO (like putting it behind the
tailpipe of a car - or riding for a long time in heavy traffic) the
CO sensor could take few hours to go back to zero and it
could also get permanently affected as the zero baseline
could go up a bit - but this could be easily solved by
performing a zero calibration.
If you do not have access to certified calibration gasses
or if you do not want to perform the Carbon Monoxide
sensor calibration yourself you can return your cootwo to us
and we will calibrate it for you. Please check with DiveNav
customer service for costs and procedures.
8.1
CO Sensor Bump Test
It is good practice to periodically verify if the Carbon
Monoxide sensor is working properly. The simplest way to
do so is to perform a bump test using your breath.
According to a paper from Ryter and Choi, the exhaled
Carbon Monoxide value of non-smokers could be about 3
ppm while the mean value of exhaled Carbon Monoxide for
smokers was 17 ppm.
Before you perform a bump test, you might want to
enable the display of the decimal digit (to display "0.0"
instead of just "0"). To do so, connect to your cootwo with a
smartphone equipped with the My Nitroxbuddy app, go to
the settings and enable "Display Decimal".
Now, take a long breath .... hold it as long as you can ....
and then slowly exhale it into your cootwo.
If you are a non smoker you might see values up to 3
ppm. If you are a smoker the CO value could be much
higher. The other thing you will notice is that the O2% value
will change too (decrease).
More you hold your breath before exhaling and more the
CO and O2% values will change (CO will increase and O2%
will decrease).
8.2
CO Sensor Calibration
As indicated earlier, with cootwo you can perform a
Carbon Monoxide sensor calibration either with the stand-
alone unit or with the assistance of a smartphone.
To calibrate the Carbon Monoxide sensor while in stand-
alone mode, first turn the unit ON.
Then, while the unit is in the Normal Operating Mode,
HOLD the button and enter the Main Settings menu.
Now, PUSH the button to position the pointer on the
SENSOR sub-menu and HOLD the button to enter it.
Then select the CO SEN sub-menu and enter it.
Scroll down to select the
CALIBRATION sub-menu and enter it.
In this menu you can perform either
a ZERO point calibration or a SPAN
calibration.
8.2.1
ZERO point Calibration
The ZERO point calibration could be used to take care
of the slow aging of the Carbon Monoxide sensor as it
resets the CO display to zero.
In order to perform a ZERO point
calibration you need to have a reference
gas with 0 ppm such as a scuba tank
containing good air or just ambient air.
In the CO CALIBRATION sub-menu
select the ZERO sub-menu and then
enter it.
Now, expose cootwo to a reference
gas with 0 ppm and, when ready,
PUSH the button; cootwo will show the
screen on the right and initiate a 60
seconds countdown.
During a Carbon Monoxide sensor
calibration it is very important to expose
cootwo to a known source of gas
flowing at a constant rate.