Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2002-06-11
2004-12-14
Goins, Davetta W. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S632000, C073S023200, C073S037000, C137S014000
Reexamination Certificate
active
06831564
ABSTRACT:
FIELD OF THE INVENTION
Embodiments of the present invention generally relate to an apparatus and method for use with a controlled gas atmosphere. More particularly, the apparatus and method of the present invention relates to notifying a user when the gas pressure is at or below a threshold pressure in an incubator.
BACKGROUND OF THE INVENTION
There are a number of commercial applications that utilize a controlled gas atmosphere enclosure. For example, in the semiconductor industry, gases are injected into an enclosed chamber wherein one of the gases is plasmarized and hits a target on a chamber lid causing the target's materials to deposit on a wafer. Other commercial applications include using controlled gases to cultivate biological cultures in an enclosed chamber such as an incubator. It is desirable to maintain optimal conditions inside the incubator in order to promote the desired growth of the cultures. In a conventional incubator, gases such as O
2
, N
2
, and CO
2
are introduced from their respective tanks into the chamber depending on the growing conditions desired. Typically, the user sets the CO
2
and O
2
setpoints and the appropriate gases are added. N
2
can be used to purge excess O
2
from the incubator when the O
2
level in the chamber is too high for the setpoints.
A conventional incubator is generally rectangular and has up to five insulated walls (top, bottom, left side, right side, and rear). Each wall may have an inner space defined by the inner and outer surfaces of the insulated wall and the inner spaces are in communication with each other. An insulated front door together with the insulated walls completes the inner chamber of the incubator. The door is typically mounted on hinges on the front side of one of the sidewalls. The door allows access into the inner chamber where culture plates are placed or removed from the shelves provided therein.
Most biological incubators are either water jacket or forced draft. In the water jacket incubator, a water jacket is inserted in the inner space of the incubator. A heater is used to heat the water in the water jacket to the desired temperature. Because water can be heated evenly, the water jacket can evenly distribute the desired heat throughout the inner chamber. Such even heating is desired in order to provide a uniform temperature (for the biological cultures) throughout the chamber and to prevent “cold spots,” which can cause condensation on the inner chamber walls.
Although heating of the chamber walls in the water jacket incubator is substantially uniform, the chamber atmosphere can stratify thermally if the chamber atmosphere is undisturbed. Due to the stratification, the temperature of the chamber is greater at the top of the chamber than at the bottom of the chamber. Therefore, it is desirable to maintain a certain flow rate of constituent gases within the chamber to assure uniformity of the temperature. The pressure set by the user on the constituent gas tanks contributes to the flow of the gases, and thus, needs to be monitored.
For proper culture growth, it is desirable to maintain certain pressure levels and flow rates of N
2
, CO
2
, and O
2
in the chamber. Rapid recovery of these gas concentrations are of significant importance for proper cell growth. Wide ranges of gas inlet pressure can be troublesome and hinder gas concentration recovery efforts, thus monitoring this pressure is critical. Deterministic flow rate(s) offer the capability for a system to optimize its gas concentration recovery. If a flow of gas is less than 10 psig, then control algorithms cannot adequately recover using a linear model of flow injection. Furthermore, if gas inlet pressure(s) exceed 30 psig, the system integrity is at risk. Once an orifice with a set diameter and the specific gravity of the particular gas being injected are known, then flow rates can be accurately predicted with the exceptions aforementioned; i.e., at low pressures flow rate prediction becomes much more complex and at high pressures component specification failures can occur. Typically, the user sets the pressure of the gas being injected by turning a lever on the tank until the gauge on the tank reads around 15 psig or the desired pressure. However, the pressure that actually flows into the incubator can vary as much as ±15 psig. The user can set the pressure, but can not be certain as to how much pressure is actually flowing through the orifice due to possible errors in the gauge of the tanks, the orifice and the gas line being clogged, or other factors that can affect the gas pressure and flow rate. At pressures between 15 to 30 psig, flow variations are essentially linear, and are easy to compensate. In the range of 10 to 15 psig, variations are more non-linear, but the errors can still be acceptable. Below 10 psig, other factors such as viscosity and surface tension will make the errors in the flow rate and pressure unacceptable. Once the error becomes unacceptable, then the results of the culture being grown in the incubator will be affected destroying months to years of research. Thus, it is important to know if the pressure level is at or below 10 psig or a predetermined level that is independent of the gauge on the tanks, so that action can be taken by the user to increase the pressure.
Therefore, there is a need for a notification system to allow a user to know when the pressure of the gas is at or below a predetermined threshold level in the incubator for improved culture growth.
SUMMARY OF THE INVENTION
The present invention generally relates to a notification system to allow a user to know when the pressures at the gas inlets of the incubator are below a predetermined level. The notification system helps to ensure that the incubator is operating at the desired pressure for optimal growth of the cultures.
One embodiment of the present invention can include a notification apparatus for an enclosed chamber that includes a threshold pressure setter that can set a threshold pressure for a gas, a gas pressure evaluator that may determine the gas pressure of the gas, a gas pressure comparator that may compare the gas pressure and the threshold pressure, and an indicator that can indicate when the gas pressure reaches the threshold pressure, wherein the setter, evaluator, and indicator can be in communication with each other. The threshold pressure can be about 10 psig or less and the gas pressure evaluator can be a transducer. The gas pressure comparator can compare the gas pressure relayed by a transducer with the threshold pressure and can communicate with the indicator when the threshold pressure is reached. The transducer can relay the gas pressure to the comparator via a wire or a wireless means. The indicator can indicate visually and/or audibly. The can notify a user that the pressure of the gas is at or below the threshold pressure.
Another embodiment of the invention can include a method of notifying a user of a gas pressure and can include setting a threshold pressure of an injected gas, evaluating a current gas pressure of the gas with the threshold pressure of the gas, and displaying a result to the user. The method further includes injecting the gas at a predetermined pressure. Setting the threshold pressure can be done via a user interface. Evaluating the current gas pressure with the threshold pressure to determine if the current gas pressure is at or below the threshold pressure. A transducer can be used to relay the current gas pressure to a controller and displaying the result can include informing the user when the current gas pressure is at or below the threshold pressure.
In another embodiment of the invention a notification system for an enclosed chamber that includes a means for setting a threshold pressure of a gas; a means for evaluating a pressure of the gas, a means for comparing the gas pressure and the threshold pressure, and a means for indicating a result to the user. The means for setting can be a user interface and the gas can be selected from a group consisting of CO
2
, O
2
, and N
2
. Th
Bair, III Richard H.
Elwood Bryan M.
Baker & Hostetler LLP
Goins Davetta W.
Kendro Laboratory Products, Inc.
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