Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
1999-11-30
2001-12-04
Wayner, William (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S098000, C062S225000
Reexamination Certificate
active
06324857
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention involves a laboratory thermostat having a bath container for a liquid to be tempered as well as a refrigerating unit, wherein the refrigerating unit has a refrigeration cycle having a compressor, a condenser, an evaporator, as well as a mass flow regulator (expansion valve) controlled by a temperature sensor arranged at the outlet of the evaporator, and having a regulation device that is connected to a temperature value sensor for detecting the bath temperature, and, if necessary, having a heating unit for the bath liquid.
In laboratory thermostats of this type cost-effective membrane valves, which are also called thermostatic expansion valves, can be used as the expansion valve. A liquid thermometer, which is arranged at the outlet of the evaporator and measures the temperature in the refrigerant there, generally functions for controlling the membrane valve. Depending on the temperature difference between the intake and outlet of the evaporator, the mass flow is changed in such a way that the evaporator outputs its optimal refrigerating capacity. The temperature of the intake is indirectly measured by the pressure.
Using the thermostatic expansion valve, the refrigerating capacity is thus adapted to the actual requirements and limited accordingly. In order to achieve a thermostatic regulation of the liquids to be tempered in the bath container, i.e., keeping a constant liquid temperature previously set in the regulation device, it is known according to German published patent application DE 38 18 321 A1 to provide, in addition to the output limiter-expansion valve, a hot gas-bypass valve, which is in controlling connection with the regulation device. The bypass valve, which can be magnetically opened or closed, is inserted into a bypass line, which is connected on one end after the compressor and before the condenser and on the other end after the expansion valve and before the evaporator. Thus, the hot refrigerant gas flows through the evaporator when the hot gas-bypass valve is open. In this case, there will be no cooling. For regulation of the temperature of the bath liquid, the bypass valve is opened and closed at appropriate time intervals.
It is disadvantageous therein that the refrigeration capacity is not continuously available, but instead is switched between 0% and 100%. If a high regulation accuracy is necessary with this two point regulation, then to smooth out the temperature fluctuations, the bath volume must be large or the switching intervals must be done at shorter time intervals, which, however, greatly reduces the lifetime of the solenoid valve. Furthermore, during the switching operation large pressure jolts occur in the refrigeration cycle, which strain the components of the refrigeration cycle and can lead to a breakdown of these components, especially the expansion valve with a membrane.
SUMMARY OF THE INVENTION
An object of the present invention is to create a laboratory thermostat of the type mentioned at the outset, which allows at low cost a practically continuous regulation of the refrigerant flow and thus maintenance of a constant bath temperature with high regulation accuracy. A stressing of the components belonging to the refrigerant cycle by the regulation should be avoided, and thus a disturbance-free operation over longer operating time periods should also possible.
In order to achieve this objective, it is proposed that the temperature sensor for the expansion valve be in thermal contact with a heating unit belonging to a tempering apparatus and controlled by the regulation device, to increase the refrigerating capacity of the refrigerating unit when the actual value of the bath liquid temperature measured by the temperature actual value sensor is higher than the bath target value temperature and, on the other hand, to reduce the refrigerating capacity when the actual value of the bath liquid temperature measured by the temperature actual value sensor is lower than the bath target value temperature, on the one hand by heating of the temperature sensor and on the other hand by cooling it off.
In this way, the temperature base level of the temperature sensor for the expansion valve can be varied, and thus the temperature of the bath liquid can be adjusted and regulated to various values. The temperature measured by the temperature sensor is thus not only a function of the temperature of the refrigerant after the evaporator, but also a function of the temperature output by the heating unit controlled by the regulation device. The extent of the heating by the heating unit is determined by the regulation device according to the adjusted bath temperature output and the bath temperature measured by the temperature actual value sensor.
For this regulation a bypass valve, having the aforementioned disadvantages resulting from it, is no longer necessary. Servo-controlled expansion valves are of course known, which control the refrigerant flow by constantly changing a nozzle based on the control of the regulation device. However, such an arrangement entails a considerable cost, which is occasioned by the parts necessary for it, namely the expansion valve itself, a step motor having electronic control, as well as a spindle drive.
With the present invention an available expansion valve, in particular a simple membrane valve, can continue to be used, which is preferably connected to the temperature sensor constructed as a liquid thermometer, via a control line constructed as a tube for the control medium.
In this case, the costs for the continuous control of necessary components can be reduced with the inventive subject matter to approximately one-third of the costs of a servo-controlled expansion valve.
Another independent solution of the objective of the invention is given wherein the temperature sensor, thermally coupled to the tempering apparatus, can be positioned at any location desired, thus even independent from a line to the evaporator outlet.
An additional advantageous embodiment of the invention provides that the tempering apparatus in thermal contact with the temperature sensor of the expansion valve has a refrigerating device in addition to the heating unit. In this way, an increase in the control dynamics is achieved, because a quicker heat discharge is possible in the area of the temperature sensor.
Preferably it is provided that the refrigerating device of the tempering apparatus is connected to the refrigeration cycle of the refrigerating device. In this way, the expense for the refrigeration device is extremely small, since it is possible to fall back on the available main refrigerating flow cycle.
It is advantageous therein, if the refrigerating device connected to the refrigerating cycle of the refrigerating unit is connected via a capillary tube, connected in particular prior to the expansion valve to the refrigerating cycle of the refrigerating unit, that on the other end of the capillary tube an evaporator is connected, which is in thermal contact with the temperature sensor, and that the evaporator of the refrigerating device is connected via a refrigerant return to the refrigerant line between the evaporator and the compressor of the refrigeration cycle.
The refrigeration is accomplished continuously hereby, and the tempering of the temperature sensor to a certain temperature value is achieved, if necessary, by counter-heating using the heating unit. Since the heating and refrigeration output necessary for tempering the temperature sensor is small, even with the counter-heating only very small losses result, which are practically of no consequence.
It is advantageous if the temperature sensor is in thermal contact with both the refrigerating device and the refrigerant line of the refrigeration cycle between the evaporator and the compressor. In this way, a fundamental tempering of the temperature sensor by the available refrigerant line is present, and when the heating unit breaks down, a tempering of the bath liquid remains, which is indeed unregulated but limited, as in the previously k
Akin Gump Strauss Hauer & Feld L.L.P.
Julabo Labortechnik GmbH
Wayner William
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