Refrigeration – Processes – Defrosting or frost inhibiting
Reexamination Certificate
2000-10-31
2002-04-30
Wayner, William (Department: 3744)
Refrigeration
Processes
Defrosting or frost inhibiting
C062S175000, C236S051000, C236S07800D
Reexamination Certificate
active
06378315
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to monitoring and controlling temperature of food display cases and, more specifically, to a method and apparatus for monitoring and controlling food temperature.
BACKGROUND OF THE INVENTION
Produced food travels from processing plants to grocery stores, where the food product remains on display case shelves for extended periods of time. For improved food quality, the food product should not exceed critical temperature limits while being displayed in the grocery store display cases. For uncooked food products, the product temperature should not exceed 41° F. For cooked food products, the product temperature should not be less than 140° F. In other words, the critical temperature limits are approximately 41° and 140° F. Between these critical temperature limits, bacteria grow at a faster rate.
One attempt to maintain food product temperature within safe limits is to monitor the discharge air temperature to ensure that the display case does not become too warm or too cold. But the food product temperature and discharge air temperature do not necessarily correlate; that is, discharge air temperature and food product temperature will not necessarily have the same temperature trend because food product temperatures can vary significantly from discharge air temperature due to the thermal mass of the food product. Further, during initial startup and display case defrost, the air temperature can be as high as 70° F., while food product temperature is much lower for this typically short interval. Finally, it is impractical to measure the temperature of food products at regular intervals in order to monitor food product temperature in a display case.
More specifically, in a conventional refrigeration system, a main controller typically logs or controls temperature. Conventionally, the main controller is installed in the compressor room, which is located on the roof or back of the grocery store. The conventional method for monitoring and controlling the display case temperature requires a discharge air temperature sensor mounted in the display case. The discharge air temperature sensor is typically connected to an analog input board, which is also typically located in the compressor room. A temperature wire must be pulled from the display case to the compressor room, which is typically difficult and increasingly expensive depending on how far away the compressor room is from the display case. Further, this wiring and installation process is more expensive and extremely cumbersome when retrofitting a store.
Additionally, display cases require periodic cleaning or maintenance during which, display case temperature may vary. Therefore, during these periods, it is undesirable for a controller to monitor and control the display case temperature.
SUMMARY OF THE INVENTION
An apparatus, system, and method for controlling a refrigeration system according to the invention overcomes the limitations of the prior art by providing wireless transmission of simulated product data. An apparatus according to the invention includes a plurality of circuits having at least one refrigeration case and a compressor rack. An electronic evaporator pressure regulator in communication with each circuit controls the temperature of one of the circuits. A sensor in communication with each circuit measures a parameter from the circuit, and a transceiver in communication with the sensor wirelessly transmits the measured parameter. A receiver receives the wirelessly transmitted measured parameter. A controller in communication with the receiver controls each electronic evaporator pressure regulator and a suction pressure of said compressor rack based upon the wirelessly transmitted measured parameter from each of the circuits.
Preferably, the transceivers of the present invention are low power. Low-power transceivers have a limited transmission range and would therefore be required to be located in closer proximity to the receiver. Because using a low-power transceiver could limit the distance which a refrigerator case may be located from the receiver, the present invention includes a series of repeaters that receive and transmit signals between the receiver and the refrigerator case. The repeaters act as a bridge, enabling greater distances between the refrigerator case and the receiver.
The present invention also preferably includes a mode switch that is operable in either a first or second mode. The mode switch is usable to signal the controller to suspend temperature recording and regulation. This switch is usable during cleaning or maintenance of a refrigerator case.
REFERENCES:
patent: 5951900 (1999-09-01), Smrke
patent: 6116512 (2000-09-01), Dushane et al.
Aggers John
Gelber Scott Michael
Singh Abtar
Computer Process Controls Inc.
Harness & Dickey & Pierce P.L.C.
Wayner William
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