C (E3) 08/2015 page 13/93
2. Unit description
The CO
2
incubators C 170 are equipped with a microprocessor controller for temperature and CO
2
levels
and a digital display accurate to one-tenth of a degree resp. 0.1 vol.-%
The inner chamber, the pre-heating chamber and the inside of the doors are all made of stainless steel
V2A (German material no. 1.4301, US equivalent AISI 304). The inner surfaces are smooth and therefore
easy to clean. The inner chamber is deep-drawn from one piece, polished (suitable for pharmaceutical
applications) and has no welds or inaccessible corners. The hinges and the seal of the inner glass door
are glued from the outside to aid cleaning of the inner chamber. When operating the chamber at high
temperatures (sterilization), the impact of the oxygen in the air may cause discoloration of the metallic
surfaces (yellowish-brown or blue) by natural oxidation processes. These colorations are harmless and
will in no way impair the function or quality of the unit.
The perforated shelves and the shelf holder are also made of stainless steel (German material no.
1.4016, US equivalent AISI 430). You can insert a maximum of 8 shelves. The shelf holder is demounta-
ble without any tool. In this way, you can clean it hygienically in every laboratory dishwasher before hot-
air sterilization.
The housing is RAL 7035 powder-coated. All corners and edges are also completely coated.
The heating system of the CO
2
incubator permits hot-air auto-sterilization at 190 °C / 374°F. Thus, a tem-
perature of at least 180 °C / 356°F is maintained on all internal surfaces, resulting in sterilization of the
entire inner chamber.
Thanks to the standard safety device (class 3.1 according to DIN 12880:2007), the set temperature is
maintained in case of failure.
The gas enters the chamber via a fine filter (aseptic filter) with a high filtration efficiency that also filters
the smallest particles.
A highly precise, drift-free CO
2
infrared measuring system in combination with the permanent mixture of
CO
2
gas through a special proprietary gas mixing head developed by BINDER allows precise and con-
stant CO
2
concentrations for long periods. This creates optimum growth conditions for cultures. The CO
2
sensor can be removed from the inner chamber by hand and cleaned with suitable detergents if needed.
The CO
2
incubator can be operated in a temperature range from 7 °C / 12.6 °F above ambient tempera-
ture up to +50 °C / 122°F and a CO
2
range of 0 vol.-% up to 20 vol.-%.
2.1 The CO
2
measuring principle
Fast reaction times, as well as the highest accuracy and selectivity, characterize the CO
2
measuring pro-
cedure of the C 170 incubator series. The accuracy of the CO
2
measuring system is based on a single-
beam infrared measuring cell, which measures in differential mode using the permanently alternating
transmission feature of its semi-conductor filter.
Due to this highly developed single-beam principle with Fabry-Perot interferometer (FPI), disturbance
variables and aging phenomena in the measuring system are almost completely eliminated, so that this
measuring system, in contrast to other measuring procedures, remains practically drift-free between cali-
brations and is absolutely selective for CO
2
.
The CO
2
measuring cell contains a measuring section inside, in which the absorption of infrared light
depends on the number of CO
2
molecules in the beam path. This number of CO
2
molecules changes with
the ambient pressure in relation to a constant volume. The distances between the molecules are conse-
quently pressure-dependent. The collision frequency of the IR-beam with CO
2
molecules increases there-
fore by increasing pressure. For this reason, the ambient pressure must be compensated in order to cor-
rect the display reading of the CO
2
concentration in vol.-%. This is achieved by entering the altitude of the
site above the sea (chap. 8.1).
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