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P a g e
OPERATION
CO
2
Atmosphere
The incubator also controls and maintains the gas concentration of CO
2
in the chamber atmosphere
by operating an internal injection solenoid valve connected to a gas input port. The incubator
monitors the CO
2
concentration level in the chamber using an infrared sensor located in the
recirculation duct. The sensor operates on the principle that a specific frequency set of infrared light
is absorbed by CO
2
. The more CO
2
present in the chamber, the more of that band of infrared is
absorbed. The sensor is only sensitive to CO
2
, so measurement accuracy is consistent, regardless of
the presence of other gases in the incubator.
The incubator uses Proportional – Integral – Derivative (PID) control to avoid significantly
overshooting the CO
2
setpoint. This means the rate of injection slows as the chamber CO
2
concentration approaches the target CO
2
concentration. When the chamber concentration is stable
CO
2
injections take place in small bursts to correct for deviations less than 0.1%. The incubator is not
provided with a means to actively remove CO
2
from the chamber atmosphere.
The Over Temp Safety System
The over temperature limit system (OTL) is a user-set, mechanical heating cutoff connected to a
hydrostatic sensor probe inside the incubation chamber. The system operates independently of the main
microprocessor temperature controller and routes power away from the incubator heating elements if the
chamber temperature exceeds the OTL temperature cutoff setting. It will continue doing so as long as the
chamber temperature remains above the OTL setting. This helps safeguard the unit by preventing
runaway heating in the event of electronics failures or a sudden external heat spike.
The OTL must be set by the user in order to function
. The manufacturer recommends a setting of
approximately 1°C above the highest temperature setpoint of your heating application. A red indicator
illuminates when the OTL is rerouting power. Failure to set the Over Temperature Limit system voids the
unit manufacturing defect warranty in the event of an overtemperature event.
Physical and Data Access
An access port on the right side of the unit allows sensors such as thermocouple probes to be
inserted and left in the chamber without compromising the CO
2
atmosphere or chamber
temperature. An atmosphere sample port for independently verifying the CO
2
concentration in the
chamber is provided on the right side of the unit. A USB outputs CO
2
and temperature levels once
per minute as a serial-protocol digital log line. Jack ports on the back of the unit provide the same
outputs as analog 4 – 20 milliamp signals for use by a building monitoring system. Please see the
entry on page 41 for more details.
Set CO
2
%
