Electricity: electrothermally or thermally actuated switches – Thermally actuated switches – Expansible or vaporizable fluid actuated
Patent
1983-02-07
1985-04-09
Broome, Harold
Electricity: electrothermally or thermally actuated switches
Thermally actuated switches
Expansible or vaporizable fluid actuated
200 83S, 337117, H01H 3738
Patent
active
045104808
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a thermostatic switch unit for controlling the operation of refrigeration apparatus. The invention is applicable to refrigeration plant generally, including freezer equipment and refrigeration systems used in vehicle air conditioning.
Freezers are normally preset to preserve food at a sub-zero freezing temperature, typically -20.degree. C. When loading fresh food or freshly prepared or purchased food into a freezer the newly introduced food is generally at ambient temperature. It is important that the food be cooled rapidly to avoid damage to the individual cells through the formation of large ice crystals. More particularly, cooling from 0.degree. C. to -5.degree. C., the temperature range in which the consolidation of ice crystals occurs, should be carried out as fast as possible, ideally in less than 30 minutes. A slower transition in temperature would permit the formation of large ice crystals which could in turn cause rupture of individual food cells, spoiling the texture and quality of the food.
With a view to effecting rapid freezing of newly introduced food some freezers have the facility for continuous running of the associated compressor in order to exploit the full cooling capacity of the equipment. Such continuous running for rapid cooling is usually achieved by the provision of an override switch in parallel with the normal thermostatic control switch of the compressor motor. The override switch would be a double pole switch which, upon closure, also illuminates a monitoring lamp to indicate that the thermostatic switch has been by-passed and that the compressor is running continuously. Alternatively, the thermostatic control switch may have a temperature setting control shaft which is movable into a position in which it effects direct mechanical operation of the thermostatic switch, effectively by-passing thermostatic control and ensuring continuous running of the compressor motor. With both of these arrangements the overriding or by-passing of the thermostatic control, and therefore the continuous running of the compressor motor, can be cancelled only by manual resetting of the control switch. If the user forgets to reset the switch, or omits to note the time of operation of the override or by-pass switch, the continuous running of the compressor may be terminated at the wrong time: if the override switch is reset prematurely the freezing of the food will be incorrect, while if the user forgets to reset the override switch, or rests it too late, the freezer will attain too low a temperature, and energy will be wasted.
The period of time for which a compressor of a freezer has to operate to effect a desired degree of fast cooling is dependent upon the mass of food to be frozen and the mass of existing frozen food in the freezer. The correct time for effective rapid freezing may, for example, vary from one to thirty hours, making it difficult or impossible for the user to evaluate the required freezing time correctly.
One of the objects of the present invention is to provide a thermostatic control capable of controlling a freezer to effect rapid freezing of newly introduced goods, with automatic resetting of the thermostatic control when a preset temperature has been reached in the fast-freeze condition.
According to the present invention there is provided a thermostatic switch unit for controlling the operation of a refrigeration or freezer apparatus comprising a switch acted upon by a thermostat mechanism associated with a single temperature sensing element responsive to the working temperature of the apparatus, the said mechanism including a switch operating lever and a spring of adjustable force acting on the lever to predetermine upper and lower limits of a normal working range, of the unit, and manually operable means which when operated act upon the switch, or upon the thermostat mechanism, to cause closure of the switch, characterized in that the manually operable means include a latch mechanism which normally retains a pre-load element in an inoperative posit
REFERENCES:
patent: 2114740 (1938-04-01), Henning
Gemma Mario
Rossi Guglielmo
Broome Harold
Ranco Incorporated
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