Forma Scientific 3158 - Control Panel

Forma Scientific, Inc.
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5-2
When monitoring the effects of CO
2
, absolute humidity must be held constant so any
change in thermal conductivity is caused only by a change in the CO
2
concentration.
Under the worst circumstances, a change in absolute humidity could cause such a
significant change in thermal conductivity that the controller could shift the CO
2
content
by as much as 4%.
Maintaining the water level inside the incubator is a simple procedure, but an
important one to keep the humidity in the incubator constant. Any water pan, used in lieu
of flooding the incubator floor, must be stainless steel and at least 187 square inches of
surface area. Tests indicate that smaller pans, bowls or non-metallic pans do not provide
adequate humidification, which can lead to incubator humidity variations with ambient
humidity shifts, resulting in CO
2
changes in the incubator.
When operating a dry incubator, as opposed to a humidified one, ambient humidity
fluctuations will affect CO
2
calibrations. Since the fluctuations possible in extreme
ambient changes have less effect on the total absolute humidity, the CO
2
calibration can
be affected by as much as 1.5%.
When a change in humidity or temperature is needed, the CO
2
control can be easily
zeroed for the new condition.
Temperature changes have little affect on CO
2
calibration, but do cause large changes
in the absolute humidity which is reflected in changes in CO
2
calibration.
5.3 CONTROL PANEL (Figure 5-2)
a. Fill Fitting, Drain Fitting/Valve and Vent Hole
The fill and drain fittings are conveniently located on the front of the incubator. The
water jacket fill fitting is located directly above the incubator door. The drain fitting is
located below the door, behind a protective metal cover. A small valve is located adjacent
to the drain fitting for convenience when draining the water jacket.
The vent hole, located adjacent to the fill fitting, allows the air displaced by water
entering the jacket to escape. It also prevents distortion of the chamber by allowing air to
escape as the unit expands and contracts during heating and cooling. Under no
circumstances should the vent be plugged.