Electronic control packages have been developed for providing precise temperature control in refrigeration equipment including, e.g., ultra low freezers, incubators, and walk-in freezers. In refrigeration equipment, particularly in laboratory refrigeration equipment, the desire is to accurately maintain the temperature within the chamber below a desired set point. The selected set point would ordinarily be selected as the temperature necessary to preserve test samples from degradation. In refrigeration equipment, cooling is performed by absorbing heat within an enclosed chamber into a cooled refrigerant gas and transferring that heat into ambient air outside of the refrigeration device.
Similarly, incubators also exchange heat within a chamber to outside ambient air utilizing the same methods. Unlike refrigeration equipment, which operates to keep the chamber below a set point temperature, incubators must maintain the temperatures between lower and upper set point temperatures. While refrigeration equipment is typically used to preserve items placed in the chamber, incubators are used to conduct experiments in controlled temperature environments.
Thus, while refrigeration equipment only requires apparatus for cooling the inner chamber relative to ambient air temperature, an incubator must be able to both cool and heat the chamber to remain within the desired temperature range. In order to maintain highly precise temperature control in the foregoing devices, microprocessor control devices have been employed and are now standard on laboratory equipment.
While an electronic component on these controllers only fails occasionally, the damage an end-user of the refrigerator can suffer from such failure can be quite severe because products stored or being tested in the refrigeration equipment can be damaged or the tests compromised. Thus, the effects can be devastating when an electronic component fails, subjecting the stored products to unintended temperature conditions.
There is therefore a need for a temperature control mechanism which allows for back-up control when a primary controller fails. More particularly, there is a need for a mechanism for refrigeration equipment to cycle within an acceptable temperature range automatically on failure of the primary temperature control thereby reducing the chances of property loss if the primary controller fails.