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CB-S / CB-S-UL (E7) 06/2020 page 76/119
Example:
If a pH of 7.2 is measured in a medium buffered with 2.20 g NaHC0
3
per liter, there must be 8 vol.-% CO
2
surrounding this medium.
19.1.2 Measuring CO
2
directly via chemical indicator tubes
This is a common do-it-yourself test for many users. A chemical color reaction in a glass tube shows the
CO
2
concentration. A standardized volume of air from inside the incubator has to be suctioned through
this glass tube to get a quantitative test result. Therefore, use a special hand pump with a standardized
suction volume.
Procedure (example):
(1) Break off both ends of the glass tube or remove the plugs.
(2) Pin the end with the higher end of the scale to the adapter of the hand pump that belongs to that
test system.
(3) Pin the other end through the silicone access port of the inner chamber door.
(4) Take one sample volume out of the inner chamber volume by pressing the pump fully together and
releasing it afterwards.
(5) The standardized volume is suctioned through the glass tube and the chemical indicator changes
its color beginning from the side pinned into the chamber in the direction of the hand pump.
(6) The more CO
2
is inside the chamber the more the chemical reaction will cause a color change of
the chemical reactor.
(7) You can read the CO
2
concentration by the scale directly printed on the glass tube or a delivered
reference-reading rule.
(8) The result must then be corrected to the current ambient pressure. The required formula is printed
on the instruction sheet of such systems.
All the necessary equipment must be supplied by one manufacturer only and in a defined test system.
Note: These test systems are not very accurate. A typical accuracy is around 10% of the full-scale value.
These test systems are not suitable for calibrating the BINDER FPI sensor system.
Figure 17: Example of chemical indicator
tubes
Figure 18: Example of a hand pump (foreground) and elec-
trical pump (background)
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