M W Labs, LLC

CO2 Incubator Operation
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Service & PM
CO2 Incubator Operation

1     Understanding CO2 Sensing
2    Temperature Control
3     Distilled water in waterjacket
4    Maintenance tips & installation

(1)    Understanding CO2 Sensing:  Infrared (IR) and Thermal Conductivity (TC)  are the two types of  CO2 sensors.

Thermal Conductivity (TC)  works by measuring the resistance between two thermistors, one exposed to the chamber and the other enclosed. The presence of CO2 in the chamber changes the resistance between the two thermistors. The level of CO2 is determined by measuring the resistance. One drawback of the TC  system is that changes in temperature and relative humidity can affect the accuracy of the sensor. Door openings, which cause change in temperature and relative humidity in addition to CO2 levels, can affect the thermal TC  sensor.

The infrared (IR)  system was developed as an alternative to the TC sensor and is a more accurate controller of CO2 levels. The IR detects CO2 levels with an optical sensor. The chamber air passes over an IR emitter (a light source) and the sensor. The sensor detects a reduction in the IR  from the emitter as the CO2 in the chamber air absorbs the IR. The amount of IR absorbed is relative to the levels of CO2 in the chamber air. The IR sensor is not effected by variations in temperature and humidity so it is more accurate than the TC sensor especially following door openings. The IR  is more expensive than the TC.

Time injection or constant flow is a third type of CO2 control. In this method filtered air is injected from outside the chamber at a specified flow rate and CO2 is injected at the same flow rate. These are alternated on a time sequence. Different manufacturers use different timings. Example if you want to control 5% CO2. Air is injected for 95 seconds and CO2 is injected for 5 seconds.  The door switch detects when the door is opened and a recovery time inject pure CO2 so that the unit recovers  to set point.

(2)    Temperature Control (Waterjacketed incubators at 37C)
Older incubators keep the water surrounding the chamber at 37.5C. The door heat would on a time cycle would pulse on and off to keep moisture from condensating on the door.
Most  incubators in the past 5 years keep the waterjacket at 36.5 to 36.8C. The door heater on a time cycle pulses on and off to keep the chamber at 37C.
Note that the temp is controlled by time and not temperature. In each case  heat is being added to control temperature at a given rate.  Heat is also being lost to the room at a given rate. If the room temp warms up or cools down the  temp of the unit will change. Most cases it will be 5-10F before the unit will notice. Manufactures are now starting to over coming this problem in the past two years. 

(3) Distilled water for Waterjacket
Most manufactures recommend distilled water in waterjackets and RH% pans. Most research labs have switched to de-ionized water which is very corrosive. This is because the de-ionized water free ions and some electrons are removed from the water creating an unnatural state. This state is similar to an acid in that the water becomes very aggressive and attacks, and tries to strip away ions and electrons, any material that it becomes in contact. This is very important when dealing with metal such as stainless steel.
Most manufactures water level is checked by the resistance of the water. De-ionized water is so high that it will not detect the water.

(4)    Maintenance Tips & Installation
Daily Checks:
visually inspect temperature and CO2 display to make sure they match the set points.  Record these temperatures.

Weekly Checks:
1   Check CO2 with independent analyzer, take two readings, record this reading. If reading is more
than .5% from set point. Do not enter unit for one hour and take two more readings. If still more
than .5% check manual factory recommendations. Some users wait until the next day.
2   Check display temperature with internal thermometer located in the geometric center of the chamber.
3   Inspect humidity pan and to make sure pan is at proper level.(If applicable)
Check humidity display and record.
4   Check high pressure gauge on CO2 tank regulator.
5   Check low  pressure gauge on CO2 tank regulator. See manual for factory recommendation.
(most manufactures recommendations are between 15-20 psig.)
6   Check to make sure not material is stored on top of unit. Many manufactures do not recommend
the storage of on top because of heat disapation.
Six Month Check:
1   Check all filters for discoloration. Replace if discolored.
2   Check gas lines and CO2 regulator for leaks.
3   Check air flow or fan blade for rotation and discoloration. This depend so on manufacturers and models.
4   Check CO2 tank switcher for proper operation.
Yearly Inspections & Calibrations:
1   Use factory procedures to calibrate CO2 and Temperature. Most manufacturers recommend a trained
technician to preform component level reclaibration. See user manual.
2   Inspect power cord for wear. This includes cracks, exposed wires and burn marks on power plug.
3   Disinfect interior and autoclave all removalble parts if so desired. See manual for manufactors
recommendation. Do not use Purex, Clorox, strong alkaline or caustic on stainless steel. Stainless
Steel is corrosion-resistant but not corrosion-proof. These can cause corrosion or pitting in
stainless steel.
4   Check all filters for discoloration. Replace if discolored.
Check air flow or fan blade for rotation and discoloration. This dependso on manufacturers and models.
5   Check CO2 tank switcher for proper operation.

Common over looked items on installation:
 Follow factory recommendations (see manual)
1   Verify proper voltage.
2   Do not install unit in direct sun light or direct path of heating or air conditioning vents.
Both of these can cause temperature control problems or condensation problems.
3   Make sure you install unit to insure technician can service contorl panel.
4   Check the level of the unit before filling with water. Check both the out side cabinet and
the internal shelves.
5   Check all CO2 lines, connections and the regualtor for leaks.
6   Insure you install two stage regulator and set to factory settings. (see factory manual)