US20110185755A1 - Cooling apparatus and frost detecting method thereof - Google Patents

Abstract

A cooling apparatus including a frost sensor to sense frost, a multiplexer having a first input terminal, to which the frost sensor is connected, and a second input terminal as a non-connected input terminal, a signal processor to subtract a signal input through the second input terminal from a signal input through the first input terminal, and to output a signal obtained by the subtraction, and a controller to detect an amount of frost sensed by the frost sensor, based on the output signal from the signal processor. It is possible to easily and accurately determine noise contained in a signal received from the frost sensor by determining, as noise, the signal received from the input terminal, to which the frost sensor is not connected, and subtracting the noise from the signal received from each input terminal, to which the frost sensor is connected.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims the benefit of Korean Patent Application No. 2010-8391 filed on Jan. 29, 2010 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in its entirety.
BACKGROUND
• 1. Field
• Embodiments relate to a cooling apparatus and a frost detecting method thereof, and, more particularly, to a cooling apparatus capable of directly detecting frost formed on an evaporator due to heat exchange and a frost detecting method thereof.
• 2. Description of the Related Art
• A cooling apparatus is adapted to cool a confined space by circulating a refrigerant through a refrigeration cycle. As such a cooling apparatus, there are a refrigerator, a Kimchi refrigerator, an air conditioner, etc.
• Here, the refrigeration cycle includes four stages to change the phase of the refrigerant, namely, compression, condensation, expansion, and vaporization stages. To this end, the cooling system should include a compressor, a condenser, an expansion valve, and an evaporator. When a gaseous refrigerant is supplied to the condenser after being compressed in accordance with operation of a compressor, the refrigerant, which is in a compressed state, is cooled as it exchanges heat with air around the condenser. As a result, the refrigerant is condensed into liquid phase. The liquid refrigerant is then injected into the evaporator while flow rate thereof is adjusted by the expansion valve. As a result, the refrigerant is abruptly expanded, so that it is vaporized. As the refrigerant is vaporized, it absorbs heat from air around the evaporator, thereby generating cold air. The cold air is supplied to a confined space such as a storage chamber or a room, thereby cooling the confined space. The refrigerant, which has been changed into the gaseous phase in the evaporator, is again introduced into the compressor, and is then compressed into the liquid phase. Thus, the above stages of the refrigeration cycle are repeated for the refrigerant.
• The surface temperature of the evaporator, which functions to cool a confined space by absorbing heat from the confined space through the refrigeration cycle, is relatively lower than the temperature of air present in the confined space. As a result, moisture condensed from the air in the confined space, which is in a moisture-rich state, is attached to the surface of the evaporator, so that frost is formed on the surface of the evaporator. The frost formed on the surface of the evaporator accumulates over time, so that the thickness of the frost is increased. As a result, the heat exchange efficiency of the cold air flowing around the evaporator is degraded, thereby causing degradation in cooling efficiency and excessive power consumption.
• In order to solve such problems, in conventional cases, an operating time of the compressor is accumulated, and a defrosting operation is carried out when the accumulated operating time exceeds a predetermined time. In the defrosting operation, a heater arranged around the evaporator operates to remove the frost formed on the evaporator.
• However, this method is inefficient to remove the frost formed on the evaporator because the defrosting operation is periodically carried out based on the operating time of the compressor, irrespective of the actual amount of the frost formed on the evaporator. Furthermore, unnecessary power consumption may occur. Also, an increase in temperature may frequently occur due to the defrosting operation.
• To this end, there is a conventional frost detecting apparatus developed to directly detect the amount of frost formed on an evaporator and to efficiently carry out a defrosting operation based on the result of the detection. In the conventional frost detecting apparatus, a voltage corresponding to a drive signal from a multiplexer is supplied to a sensing unit. Based on the supplied voltage, the sensing unit senses a capacitance established at the evaporator and transmits a signal representing the sensed capacitance to a detecting unit. Based on the sensed capacitance, the detecting unit determines the amount of frost formed on the evaporator.
• In such a frost detecting apparatus, noise may be generated due to variation in heat generated in various elements such as a multiplexer and a detector. Noise may also be generated due to a frequency generated from an oscillator. The generated noise may be transmitted to the detector in a state of being included in the sensing signal representing the capacitance established at the evaporator. As a result, it may be difficult to accurately determine the amount of frost. For this reason, it may be difficult to carry out a defrosting operation at an appropriate point in time.
SUMMARY
• It is an aspect to provide a cooling apparatus capable of easily removing noise from a frost detecting signal generated upon detecting frost formed on an evaporator, and accurately detecting the amount of frost formed, and a frost detecting method thereof.
• It is another aspect to provide a cooling apparatus capable of detecting an accurate amount of frost formed in the cooling apparatus, thereby achieving an efficient defrosting operation and a reduction in power consumption, and a frost detecting method thereof.
• In accordance with one aspect, a cooling apparatus includes a frost sensor to sense frost, a multiplexer having a first input terminal, to which the frost sensor is connected, and a second input terminal as a non-connected input terminal, a signal processor to subtract a signal input through the second input terminal from a signal input through the first input terminal, and to output a signal obtained by the subtraction, and a controller to detect an amount of frost sensed by the frost sensor, based on the output signal from the signal processor.
• A peripheral noise signal may be input to the second input terminal.
• The signal processor may remove a noise signal by subtracting the signal input through the second input terminal from a frost sensing signal as the signal input through the first input terminal.
• The controller may control a defrosting operation based on the detected frost amount. The cooling apparatus may further include a heater to operate in accordance with a command from the controller, so as to execute the defrosting operation.
• The cooling apparatus may further include a filter to allow a low-frequency signal component of a frost sensing signal generated by the frost sensor to pass through the filter.
• The signal processor may allow a low-frequency signal component of a frost sensing signal generated by the frost sensor to pass through the signal processor.
• The signal processor may convert an analog signal as a frost sensing signal generated by the frost sensor into a digital signal.
• The signal processor may amplify a frost sensing signal generated by the frost sensor to a predetermined level.
• The frost sensor may be installed on at least one of an evaporator for a refrigerating compartment, an evaporator for a freezing compartment, and an evaporator for an ice making compartment.
• The frost sensor may sense a capacitance established between cooling fins provided at the at least one evaporator.
• The cooling apparatus may further include an oscillator to supply a voltage to the frost sensor.
• The multiplexer may further have a first output terminal, to which the frost sensor is connected, and a second output terminal as a non-connected output terminal, and may supply the voltage to a selected one of the first and second output terminals.
• The frost sensor may include a plurality of sensors. The sensors may be connected to the first output terminal and first input terminal of the multiplexer. The sensors may sequentially receive a voltage, and transmit a frost sensing signal to the first input terminal.
• A frost detecting method in a cooling apparatus includes supplying a voltage to a frost sensor through a first output terminal of a multiplexer, sensing frost by the frost sensor, receiving a frost sensing signal generated by the frost sensor through a first input terminal of the multiplexer, receiving a signal from a second input terminal of the multiplexer, subtracting the signal of the second input terminal from the frost sensing signal, and detecting an amount of frost, based on a signal obtained by the subtraction.
• The subtraction of the signal of the second input terminal from the frost sensing signal may be executed to remove a peripheral noise signal from the frost sensing signal.
• The frost detecting method may further include determining a point in time when a defrosting operation should be begun, based on the detected frost amount, driving a heater at the determined time point when the defrosting operation should be begun, determining, during the defrosting operation, a point in time when the defrosting operation should be ended, and stopping driving of the heater at the determined time point when the defrosting operation should be ended.
• The frost detecting method may further include passing a low-frequency component of the frost sensing signal generated by the frost sensor.
• The frost detecting method may further include converting an analog signal as the frost sensing signal generated by the frost sensor into a digital signal.
• The frost detecting method may further include amplifying the frost sensing signal generated by the frost sensor to a predetermined level.
• The sensing of frost by the frost sensor may include sensing a capacitance established between cooling fins provided on at least one evaporator.
• The frost detecting method may further include supplying a voltage through the second output terminal of the multiplexer.
• The second output terminal and the second input terminal may be non-connected terminals.
• The frost sensor may include a plurality of sensors each connected to the first output terminal and first input terminal of the multiplexer. The supply of the voltage to the frost sensor may include sequentially supplying the voltage to the sensors.
• The reception of the frost sensing signal through the first input terminal of the multiplexer may include sequentially receiving frost sensing signals from the sensors through the first input terminal.
• In accordance with one aspect, it may be possible to easily and accurately determine noise contained in a signal received from the frost sensor by determining, as noise, the signal received from the input terminal, to which the frost sensor is not connected, and subtracting the noise from the signal received from each input terminal, to which the frost sensor is connected.
• As a result, it may be possible to accurately determine whether or not frost has been formed on an evaporator, and to accurately detect the amount of frost formed.
• It may also be possible to execute a defrosting operation at an appropriate point in time as the accuracy of the detection of the amount of frost formed on the evaporator is enhanced. Accordingly, it may be possible to prevent the cooling efficiency of the evaporator from being reduced due to a reduction in air flow rate during heat exchange.
• It may be possible to accurately determine the amount of frost left on the evaporator during the defrosting operation, and thus to accurate determine an appropriate point in time when the defrosting operation should be ended. Accordingly, it may be possible to end the defrosting operation at an appropriate point in time. As a result, it may be possible to reduce energy consumption caused by the defrosting operation. Also, the temperature variation in the cooling apparatus may be minimized in accordance with the defrosting operation. Accordingly, the performance of the cooling apparatus may be enhanced.
• As the defrosting operation may be efficiently begun and ended, the heater may be driven only when the driving of the heater is required. Accordingly, the driving time of the heater and the number of times the heater drives may be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
• These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
• FIG. 1 is a view illustrating a refrigerator according to an exemplary embodiment;
• FIG. 2 is a view illustrating a detailed configuration of an evaporator provided at the refrigerator according to the illustrated embodiment;
• FIG. 3 is a block diagram illustrating a control configuration of the refrigerator according to an exemplary embodiment;
• FIGS. 4A and 4B are sectional views respectively illustrating frost detecting devices according to exemplary embodiments;
• FIG. 5 is a block diagram illustrating a control configuration of the refrigerator according to an exemplary embodiment;
• FIG. 6 is a block diagram illustrating a connection between a frost sensor and a detector in a frost detecting device provided at the refrigerator in accordance with an exemplary embodiment;
• FIGS. 7 and 8 are schematic views respectively illustrating connections between the evaporator and frost detecting device provided at the refrigerator in accordance with embodiments;
• FIG. 9 is a flow chart illustrating frost detection carried out in the refrigerator in accordance with an exemplary embodiment; and
• FIGS. 10A-10C depicts graphs of frost sensing signals generated in a refrigerator in accordance with an exemplary embodiment.
DETAILED DESCRIPTION
• Hereinafter, exemplary embodiments will be described in order to explain the present invention by referring to the figures.
• Exemplary embodiments are adapted to enhance the defrosting efficiency of a cooling apparatus and thus to reduce power consumption by accurately detecting whether or not frost has been formed on an evaporator of the cooling apparatus and the amount of frost formed, and controlling driving of a heater based on the results of the detection, thereby controlling a defrosting operation.
• The exemplary embodiments are described in conjunction with an example in which the cooling apparatus is applied to a refrigerator.
• FIG. 1 is a view illustrating a refrigerator according to an exemplary embodiment.FIG. 2 is a view illustrating a detailed configuration of an evaporator provided at the refrigerator according to the illustrated embodiment.FIG. 3 is a block diagram illustrating a control configuration of the refrigerator according to an exemplary embodiment.
• A refrigerator is adapted to store food in a fresh state for a prolonged period of time by maintaining a storage chamber in a low-temperature state through repetition of a refrigeration cycle to sequentially compress, condense, expand, and vaporize a refrigerant.
• As shown inFIG. 1, such a refrigerator, which is designated byreference numeral100, includes abody110 having an open front side, and astorage chamber120 defined in thebody110, to store food. Thestorage chamber120 is laterally divided into arefrigerating compartment121 and a freezingcompartment122 by an intermediate barrier wall.
• Each of therefrigerating compartment121 and freezingcompartment122 is open at a front side thereof.Doors131 and132 are provided at respective open front sides of the refrigerating and freezingcompartments121 and122, to shield thecompartments121 and122 from the outside of thecompartments121 and122.
• A duct (not shown), through which air flows, is formed between thebody110 and one wall of thestorage chamber120. A plurality of holes are formed through the wall of thestorage chamber120. Through the holes, air flows between thestorage chamber120 and the duct.
• Installed in the duct areevaporators141 and142 to cool ambient air present around theevaporators141 and142 in accordance with a cooling operation of absorbing latent heat from the ambient air while evaporating a refrigerant supplied from a condenser (not shown), afan150 to suck air from thestorage chamber120 while supplying air passing around theevaporators141 and142 to thestorage chamber120, and aheater160 to remove frost formed on theevaporators141 and142.
• The refrigerator shown inFIG. 1 includes theevaporator141, which is installed for therefrigerating compartment121, and theevaporator142, which is installed for the freezingcompartment122. Using therefrigerating compartment evaporator141 and freezingcompartment evaporator142, it may be possible to cool therefrigerating compartment121 and freezingcompartment122, respectively. Alternatively, it may be possible to cool therefrigerating compartment121 and freezingcompartment122, using a single evaporator.
• Of course, an evaporator for an ice making compartment (not shown) may also be installed in the ice making compartment, to achieve ice making in the ice making compartment.
• Acompressor170 to compress and then supply the refrigerant is installed in a machinery chamber defined in a lower portion of thebody110. The condenser (not shown) is also installed in the machinery chamber, to discharge heat from the refrigerant, which has been compressed into a high-temperature and high-pressure state, thereby condensing the refrigerant.
• As shown inFIG. 2, theevaporator141 includes a refrigerant tube141a,through which the refrigerant flows, and a plurality of coolingfins141b(141b₁and141b₂) mounted to therefrigerant tube141, to achieve an enhancement in heat exchange efficiency. Theevaporator142 also has the same configuration as theevaporator141. Accordingly, the following description will be given mainly in conjunction with theevaporator141.
• Theevaporators141 and142 function to heat-exchange the refrigerant, which is maintained in a low-temperature and low-pressure state, with air present in the storage chamber at a higher temperature than the refrigerant, and thus to evaporate the refrigerant under low-pressure and low-temperature conditions, thereby lowering the internal temperature of the storage chamber.
• Since the surface temperatures of theevaporators141 and142 are lower than the temperature of the air in the storage chamber, moisture condensed from the air in the storage chamber is attached to the surfaces of theevaporators141 and142, thereby forming frost.
• In order to remove the frost formed on theevaporators141 and142, a defrosting operation is carried out. To control the defrosting operation, driving of theheater160 is controlled under control of thecontroller180.
• In order to control the defrosting operation, it is necessary to know whether or not frost has been formed on theevaporator141 and the amount of frost formed.
• To this end, the refrigerator, which is an example of the cooling apparatus, includes afrost detecting device200 to detect the amount of frost formed on theevaporator141.
• As shown inFIG. 2, thefrost detecting device200 includes afrost sensor210 installed at at least one of the refrigerant tubes141aandplural cooling fins141bof theevaporator141, to sense a capacitance established at theevaporator141, and adetector220 to determine the amount of frost corresponding to the capacitance sensed by thefrost sensor210.
• In this case, thefrost sensor210 includes two electrodes and two insulators, as shown inFIGS. 4A and 4B.
• In detail, as shown inFIG. 4A, thefrost sensor210 includes afirst electrode210ato sense frost formed between thefirst electrode210aand thesecond cooling fin141b₂of theevaporator141, afirst insulator210barranged in contact with thefirst electrode210a,asecond electrode210carranged in contact with thefirst insulator210b,and asecond insulator210dinstalled on thefirst cooling fin141b₁arranged opposite to thesecond cooling fin141b₂such that thesecond insulator210dis in contact with thesecond electrode210c.
• Thefirst insulator210binsulates thefirst electrode210afrom thesecond electrode210c.Thesecond insulator210dinsulates thefirst cooling fin141b1 arranged opposite to thesecond cooling fin141b2 from thesecond electrode210c.
• Thefirst electrode210ais connected to a sensor terminal A. Thesecond electrode210cis connected to a shield terminal B. Voltages of equal phase and magnitude are applied to the first andsecond electrodes210aand210cvia the sensor terminal A and shield terminal B, respectively. Accordingly, it may be possible to prevent an electric field from being established at the side of thefirst cooling fin141b₁.
• An electric field may also be generated between thefirst electrode210aand thesecond cooling fin141b₂. When frost is formed between thefirst electrode210aand thesecond cooling fin141b₂, the electric field generated between thefirst electrode210aand thesecond cooling fin141b₂may be varied, thereby causing a variation in dielectric field between thefirst electrode210aand thesecond cooling fin141b₂. As a result, a variation in capacitance occurs. The varied capacitance is output in the form of a voltage signal.
• Based on the output voltage, it may be possible to determine whether or not frost has been formed, and the amount of frost formed.
• As shown inFIG. 4B, thefrost sensor210 is installed on thefirst cooling fin141b₁, to sense frost formed between thefirst cooling fin141b₁and thesecond cooling fin141b₂.
• Thefrost sensor210 includes afirst electrode210ato sense formation of frost, afirst insulator210barranged in contact with thefirst electrode210a,asecond electrode210carranged in contact with thefirst insulator210b,and asecond insulator210darranged in contact with thesecond electrode210c.
• In detail, thesecond electrode210cis arranged in contact with the back surface of thefirst insulator210b.Thesecond electrode210cextends around an exposed portion of thefirst insulator210b,so as to surround the exposed portion of thefirst insulator210b.
• Thus, thesecond electrode210cextends along the surfaces of thefirst electrode210a,except for the front surface of thefirst electrode210a,so as to surround the side surfaces of thefirst electrode210a.In accordance with this arrangement, thesecond electrode210cfunctions as a shield to cut off an electric field leaking from side surface edges of thefirst insulator210bandfirst electrode210a.
• An insulation gap g is formed between thesecond electrode210band thefirst electrode210a,to insulate thesecond electrode210cfrom thefirst electrode210a.
• Thefirst electrode210ais connected to a sensor terminal A, whereas thesecond electrode210cis connected to a shield terminal B. Voltages of equal phase and magnitude are applied to thefirst electrode210aandsecond electrode210c,respectively. As a result, it may be possible to prevent an electric field from being established at the side of thefirst cooling fin141b₁.
• Thefrost sensor210 may prevent the electric field generated from thefirst electrode210 from leaking from the side surface edges of the first insulatinglayer210binto a frost sensing region. Thus, it may be possible to prevent the electric field of thefirst electrode210a,which defines a frost detection region, from being varied.
• Also, the second electrode230 may prevent the electric field from leaking from the side surface edges of thefirst insulator210beven when the dielectric constant of thefirst insulator210bvaries in accordance with a variation in temperature, thus preventing electric field variation.
• That is, the electric field of thefirst electrode210ain thefrost sensor210 is guided only to thesecond cooling fin141b₂by thesecond electrode210c.Accordingly, the electric field of thefirst electrode210amay be varied only by frost formed between thefirst electrode210aand thesecond cooling fin141b₂.
• FIG. 3 is a block diagram illustrating a control configuration of the refrigerator according to an exemplary embodiment of the present invention. The refrigerator includes thefan150,heater160,compressor170,controller180, and frost detectingdevice200.
• Thefan150 rotates in accordance with a command from thecontroller180 in a cooling mode, to suck air from thestorage chamber120, and to supply air passing around theevaporators141 and142 to thestorage chamber120.
• Theheater160 generates heat in accordance with a command from thecontroller180 in a defrosting mode, to remove frost formed on theevaporators141 and142.
• Thecompressor170 compresses a refrigerant in accordance with a command from thecontroller180 in a cooling mode, to supply the compressed refrigerant to a condenser (not shown). As the compressed refrigerant is supplied, a cooling cycle operates to cool the storage chamber.
• When a voltage output from thedetector220 is lower than a first reference voltage, thecontroller180 determines that a defrosting operation should be begun. In this case, thecontroller180 performs a control to stop driving of thefan150 andcompressor170, and to drive theheater160. Thus, a defrosting operation is carried out.
• On the other hand, when the voltage output from thedetector220 during the defrosting operation is higher than a second reference voltage, thecontroller180 determines that the defrosting operation should be completed. In this case, thecontroller180 performs a control to stop driving of theheater160, and to drive thefan150 andcompressor170. Thus, a cooling operation is again carried out.
• In this case, thecontroller180 drives thecompressor170 in a cooling cycle corresponding to an operation mode set by the user while controlling rotation of thefan150, to keep the storage chamber at a predetermined temperature.
• Amounts of frost respectively corresponding to various voltage values may be experimentally acquired. Based on the acquired frost amounts, a first reference voltage corresponding to a point in time when a defrosting operation should be begun and a second reference voltage corresponding to a point in time when the defrosting operation should be ended may be determined. The determined first and second reference voltages may be previously stored in a memory (not shown).
• Alternatively, an initial voltage generated between thefrost sensor210 and the coolingfin141bof theevaporator141 may be experimentally acquired under the condition that thefrost sensor210 is installed at the coolingfin141b.In this case, a saturation voltage corresponding to a frost saturation state may also be experimentally acquired. The initial voltage and saturation voltage may be compared with each other, to obtain a comparison voltage. The comparison voltage may be set to the first reference voltage, and the initial voltage may be set to the second reference voltage. The first and second reference voltages may be previously stored in the memory (not shown).
• The reason why the second reference voltage is set to the initial voltage is that, when the frost formed on theevaporator141 is completely removed, the initial voltage is output because there is no frost present between thefrost detecting device200.
• The distance between thesecond cooling fin141b₂, formation of frost upon which is determined, and thefrost sensor210 is varied in accordance with the distance between thefirst cooling fin141b₁, at which thefrost sensor210 is installed, and thesecond cooling fin141b₂. As a result, the capacitance C established between thesecond cooling fin141b2 and thefrost sensor210 is varied (C=kε₀A/d, A: the area of the first electrode, d: the distance between the cooling fins, k: the dielectric constant established between the electrodes, and ε₀: the dielectric constant of a free space.) Since a variation in voltage occurs as the capacitance varies, it may be necessary to take into consideration the distance between the cooling fins when the first and second reference voltages are set.
• It may be possible to optimize the defrosting operation by starting the defrosting operation at an appropriate point in time, and completing the defrosting operation at an appropriate point in time. Thus, consumption of electric power may be minimized.
• Thefrost detecting device200 is installed at each of theevaporators141 and142, to detect the amount of frost formed on the associatedevaporator141 or142. Thefrost detecting device200 transmits data representing the detected frost amount to thecontroller180.
• Thefrost detecting device200 includes thefrost sensor210 anddetector220. The configuration of thefrost detecting device200 will be described with reference toFIGS. 5 to 8.
• FIG. 5 is a block diagram illustrating a detailed configuration of thefrost detecting device200 provided at the refrigerator in accordance with an exemplary embodiment.FIG. 6 is a block diagram illustrating a connection between thefrost sensor210 anddetector220 in thefrost detecting device200 provided at the refrigerator in accordance with an exemplary embodiment.FIGS. 7 and 8 are schematic views respectively illustrating connections between the evaporator and frost detecting device provided at the refrigerator in accordance with embodiments.
• As shown inFIG. 5, thefrost detecting device200 includes thefrost sensor210 anddetector220.
• Thefrost sensor210 includes a plurality of sensors S(1), S(2), . . . , and S(n−1). The sensors S(1), S(2), . . . , and S(n−1) are installed at selected ones of the coolingfins141bof the evaporator.
• Each of the sensors S(1), S(2), . . . , and S(n−1) of thefrost sensor210 senses frost formed between the cooling fin, at which the sensor is installed, and the cooling fin facing the sensor-installed cooling fin.
• Here, sensing frost means sensing a capacitance established between the sensor-installed cooling fin and the cooling fin facing the sensor-installed cooling fin.
• As shown inFIG. 6, the sensors of thefrost sensor210, namely, the first sensor S(1), second sensor S(2), . . . , and n−1-th sensor S(n−1), are connected to a plurality of first output terminals of anoutput stage221ain amultiplexer221, namely, an A₁output terminal a(1), an A₂output terminal a(2), . . . , and an A_n-1, output terminal a(n−1), respectively, while being connected to a plurality of first input terminals of aninput stage221bin themultiplexer221, namely, a B₁input terminal b(1), a B₂input terminal b(2), . . . , and a B_n-1input terminal b(n−1), respectively.
• A voltage is sequentially supplied to the first sensor S(1), second sensor S(2), . . . , and n−1-th sensor S(n−1) of thefrost sensor210 via theoutput stage221aof themultiplexer221. Each sensor, to which the voltage is supplied, senses a capacitance between the associated facing cooling fins, and transmits a signal representing the sensed capacitance to theinput stage221bof themultiplexer221.
• The sensors S(1), S(2), . . . , and S(n−1) of thefrost sensor210 may be installed on at least one of therefrigerating compartment evaporator141, freezingcompartment evaporator142, and ice making compartment evaporator (not shown). This will be described with reference toFIGS. 7 and 8.
• FIG. 7 is a schematic view illustrating the case in which a plurality of sensors are installed at one evaporator. The sensors S(1), S(2), . . . , and S(n−1) are installed at different cooling fins of therefrigerating compartment evaporator141, respectively. Each sensor senses frost formed between the cooling fin, at which the sensor is installed, and the cooling fin facing the sensor-installed cooling fin, and transmits a frost sensing signal to theinput stage221bof themultiplexer221.
• Of course, a single sensor may be installed at one cooling fin of one evaporator.
• FIG. 8 is a schematic view illustrating the case in which a plurality of sensors are installed at a plurality of evaporators. The sensors S(1), S(2), . . . , and S(n−1) are installed at different cooling fins of therefrigerating compartment evaporator141, and freezingcompartment evaporator142, respectively.
• Referring toFIG. 8, it can be seen that the first and second sensors S(1) and S(2) are installed at different cooling fins of therefrigerating compartment evaporator141, respectively, whereas the n−1-th sensor S(n−1) is installed at one cooling fin of the freezingcompartment evaporator142.
• Each of the sensors S(1), S(2), . . . , and S(n−1) senses frost formed between the cooling fin, at which the sensor is installed, and the cooling fin facing the sensor-installed cooling fin, and transmits a frost sensing signal to theinput stage221bof themultiplexer221.
• That is, each of the sensors S(1), S(2), . . . , and S(n−1) transmit a frost sensing signal to an associated one of the input terminals b(1), B(2), . . . , and b(n−1) provided at the input stage121bof themultiplexer121.
• Thedetector220 removes a noise signal from the frost sensing signal received from thefrost sensor210, to more accurately detect the frost sensing signal. Thedetector220 then transmits the detected frost sensing signal (namely, a voltage signal corresponding to a sensed capacitance) to thecontroller180.
• As thedetector220 removes the noise signal, it may be possible to obtain only a voltage signal corresponding to the capacitance varied due to the frost formed on the cooling fin of the evaporator.
• Thedetector220 includes, in addition to themultiplexer221, anoscillator222, afilter223, and asignal processor224.
• Themultiplexer221 includes theoutput stage221a,which outputs a voltage generated from theoscillator222, and aninput stage221b,which receives a frost sensing signal generated from thefrost sensor210. This will be described with reference toFIG. 6.
• Theoutput stage221aincludes a plurality of first output terminals a(1), a(2), . . . , and a(n−1), and a single second output terminal a(n).
• The first output terminals a(1), a(2), . . . , and a(n−1) are connected to the sensors S(1), S(2), . . . , and S(n−1), respectively, whereas the single second output terminal a(n) is a non-connected (NC) terminal which is not connected to any sensor.
• Theoutput stage221areceives an output terminal select signal from thesignal processor224.
• That is, upon connection of the first output terminals a(1), a(2), . . . , and a(n−1) to the sensors S(1), S(2), . . . , and S(n−1) of thefrost sensor210, respectively, theoutput stage221aselects one first output terminal, which corresponds to a command from thesignal processor224. Theoutput stage221athen connects the selected first output terminal to the sensor corresponding to the first output terminal.
• When theoutput stage221areceives an AC signal having a reference frequency from theoscillator222, it outputs the received reference-frequency AC signal to the first output terminals a(1), a(2), . . . , and a(n−1) and the second output terminal a(n).
• Theoutput stage221aselects one sensor corresponding to an output terminal select signal, to connect the selected sensor thereto, and outputs a voltage generated from theoscillator222 to the connected sensor.
• Theoutput stage221aalso outputs the voltage generated from theoscillator222 to the second output terminal a(n), which is not connected to any sensor.
• That is, the voltage from theoscillator222 is output to the second output terminal a(n) when signal sensing is achieved at the second input terminal b(n) corresponding to the second output terminal a(n), in order to cause the noise signal generated due to an oscillation operation of theoscillator222 and effected on the first input terminals b(1), b(2), . . . , and b(n−1) to be effected on the second input terminal b(n) in the same manner.
• Theinput stage221bincludes a plurality of first input terminals b(1), b(2), . . . , and b(n−1), and a single second input terminal b(n).
• The first input terminals b(1), b(2), . . . , and b(n−1) are connected to the sensors S(1), S(2), . . . , and S(n−1), respectively, whereas the single second input terminal b(n) is a non-connected (NC) terminal which is not connected to any sensor.
• Theinput stage221breceives an input terminal select signal from thesignal processor224.
• That is, upon connecting the first input terminals b(1), b(2), . . . , and b(n−1) to the sensors S(1), S(2), . . . , and S(n−1), respectively, theinput stage221bselects one first input terminal, which corresponds to a command from thesignal processor224. Theinput stage221bthen connects the selected first input terminal to the sensor corresponding to the first input terminal.
• Theinput stage221bconnects one of the first input terminals b(1), b(2), . . . , and b(n−1) to a sensor corresponding to the sensor in accordance with a command from thesignal processor224. When theinput stage221breceives a frost sensing signal from the connected sensor, it transmits the received frost sensing signal to thefilter223.
• Theinput stage221btransmits a signal generated from the second input terminal b(n), to which any sensor is not connected, to thefilter223.
• The signal received from the second input terminal b(n) includes noise signals generated from theoscillator222 andmultiplexer221.
• Themultiplexer221 sequentially connects the sensors to theoscillator222 in the order determined in accordance with a command from thesignal processor222, to sequentially supply a voltage to the sensors, and thus to sequentially drive the sensors. Accordingly, formation of frost is sensed through the sensors in a sequential manner. A frost sensing signal generated by each sensor is transmitted to thefilter223.
• As shown inFIGS. 7 and 8, theinput stage221aof themultiplexer221 transmits the frost sensing signals received from the sensors S(1), S(2), . . . , and S(n−1) to thefilter223, while transmitting a signal from the second input terminal b(n) to thefilter223.
• Theoscillator222 generates an AC signal having a reference frequency, and supplies the AC signal to the sensors of thefrost sensor210.
• Theoscillator222 supplies voltages to the sensor terminal A and shield terminal B of thefrost sensor210 via themultiplexer221. In this case, the voltages supplied to the sensor terminal A and shield terminal B have the same phase and magnitude.
• Thefilter223 filters the frost sensing signal received through each input terminal of theinput stage221bof themultiplexer221, and transmits the filtered frost sensing signal to thesignal processor224.
• That is, thefilter223 receives the frost sensing signal, which has a reference signal component, from themultiplexer221, and then removes the reference signal component.
• Thefilter223 allows only the frequency components of the frost sensing signal, which have a frequency not higher than a predetermined frequency, to pass therethrough, while preventing the remaining frequency components of the frost sensing signal from passing therethrough. For thefilter223, a low-pass filter (LPF) may be used.
• Here, the predetermined frequency is a frequency lower than the reference frequency generated from theoscillator222.
• The reason why the frost sensing signal is filtered to have a frequency lower than the reference frequency of theoscillator222 will be described hereinafter. The dielectric constant established between the sensor and the cooling fin is varied in accordance with the amount of frost formed between the sensor and the cooling fin. In accordance with the variation in dielectric constant, a variation in capacitance occurs, thereby causing a variation in the impedance of the sensor terminal of the sensor. The impedance variation causes the voltage of the sensor terminal to be lower than the voltage of the reference signal in accordance with a voltage division rule. As a result, the frequency of the frost sensing signal is lower than the reference frequency. That is, the reference voltage is removed, in order to obtain a pure frost sensing signal.
• Thesignal processor224 converts the filtered frost sensing signal into a digital signal. Thesignal processor224 then subtracts a non-sensing signal from the frost sensing signal, which has been converted into a digital signal, thereby obtaining a noise-removed frost sensing signal. Thereafter, thesignal processor224 transmits the obtained signal to thecontroller180. Here, the filtered frost sensing signal is an analog signal.
• That is, thesignal processor224 subtracts the signal input to one of the input terminals b(1), b(2), . . . b(n−1), and b(n), which is not connected to any of the sensors S(1), S(2), . . . , S(n−1), and S(n), namely, the input terminal b(n), from each of the frost sensing signals input to the remaining input terminals, thereby removing offset noise generated from theoscillator222 andmultiplexer221.
• Since the filtered frost sensing signal has a very small level, it may be difficult to discriminate the frost sensing signal. Accordingly, thesignal processor224 may convert the filtered frost sensing signal into a digital signal after amplifying the frost sensing signal to a predetermined level.
• Thesignal processor224 then performs offset adjustment upon the filtered frost sensing signal.
• Thesignal processor224 transmits, to themultiplexer221, a select signal to select one of the plural sensors, when frost sensing is to be performed. In accordance with the select signal, one output terminal and one input terminal of the output and input stages221aand221bin themultiplexer221 are connected to the selected sensor.
• Software for a low-pass filter function may be loaded in thesignal processor224, in order to allow thesignal processor224 to pass only the frequency components of the frost sensing signal, which have a frequency not higher than a predetermined frequency, while blocking the remaining frequency components. In this case, thefilter223 may be dispensed with.
• When thesignal processor224 receives a frost sensing signal from theinput stage221bof themultiplexer221, it executes the software, thereby passing only the frequency components of the frost sensing signal, which have a frequency not higher than the predetermined frequency. Accordingly, thesignal processor224 converts the resultant frost sensing signal, which only has desired frequency components, into a digital signal.
• FIG. 9 is a flow chart illustrating frost detection carried out in the refrigerator in accordance with an exemplary embodiment.
• Thesignal processor224 selects one of the plural sensors in accordance with a predetermined order (301), and transmits a signal representing sensing of the sensor, namely, a sensor select signal, to themultiplexer221.
• Themultiplexer221 selects the first output terminal corresponding to the sensor select signal from thesignal processor224, thereby causing the selected sensor to be connected to theoscillator222. Themultiplexer221 then supplies a voltage to the selected sensor (302).
• Thereafter, themultiplexer221 selects the first input terminal corresponding to the sensor select signal from thesignal processor224, thereby causing the selected sensor to be connected to thefilter223. Subsequently, themultiplexer221 receives a frost sensing signal (303), and then transmits the received frost sensing signal to thefilter223.
• Thereafter, thefilter223 filters the frost sensing signal received from the input terminal of theinput stage221bof themultiplexer221, and transmits the filtered frost sensing signal to thesignal processor224.
• That is, thefilter223, which is a low pass filter (LPF), receives a frost sensing signal containing a reference frequency component from themultiplexer221, and removes the reference frequency component from the received frost sensing signal.
• The reason why the frost sensing signal is filtered to have a frequency lower than the reference frequency of theoscillator222 will be described hereinafter. The dielectric constant established between the sensor of the frost sensor and the cooling fin is varied in accordance with the amount of frost formed between the sensor and the cooling fin. In accordance with the variation in dielectric constant, a variation in capacitance occurs, thereby causing a variation in the impedance of the sensor terminal of the sensor. The impedance variation causes the voltage of the sensor terminal to be lower than the voltage of the reference signal in accordance with a voltage division rule. As a result, the frequency of the frost sensing signal is lower than the reference frequency. That is, the reference voltage is removed, in order to obtain a pure frost sensing signal.
• It may be possible to allow thesignal processor224 to pass only the frequency components of the frost sensing signal, which have a frequency not higher than a predetermined frequency, while preventing the remaining frequency components, using software loaded in thesignal processor224, for a low-pass filter function. In this case, thefilter223 may be dispensed with.
• Since the filtered frost sensing signal has a very small level, it may be difficult to discriminate the frost sensing signal. Accordingly, thesignal processor224 may convert the filtered frost sensing signal into a digital signal after amplifying the frost sensing signal to a predetermined level. Here, the filtered frost sensing signal is an analog signal.
• It is then determined whether the frost sensing operation has been completed for all sensors (304). When it is not determined that the frost sensing operation has been completed for all sensors, thesignal processor224 selects a next one of the plural sensors, and transmits a signal representing sensing of the sensor, namely, a sensor select signal, to themultiplexer221.
• In this case, the sensor select signal has been predetermined. If the frost sensing operation has been completed for all sensors, thesignal processor224 then transmits a voltage supply signal to the second output terminal a(n).
• Thereafter, frost formed on each cooling fin is sensed through an associated one of the plural sensors while executing the above-describedoperations302 to304.
• When the frost sensing operation has been completely executed through the plural sensor, a voltage is supplied to the second output terminal a(n), which is not connected to any sensor (305). Thesignal processor224 then receives a signal from the second input terminal b(n), which is not connected to any sensor (306).
• Subsequently, thesignal processor224 subtracts the output signal of the NC second input terminal b(n) from the frost sensing signal received from each of the first input terminal b(1), b(2), b(n−1), and b(n), and transmits the resultant signal to the controller180 (307).
• Thecontroller180 then determines the amount of frost formed on the cooling fin of each evaporator, using the received signal (308). Based on the result of the determination, thecontroller180 controls a defrosting operation.
• Thus, it may be possible to remove offset noise generated at theoscillator222 andmultiplexer221 by subtracting the output signal of the second input terminal b(n) from the signal output from each of the first input terminal b(1), b(2), b(n−1), and b(n).
• That is, thedetector220 may obtain only the voltage signal corresponding to a capacitance varied due to the frost formed on the cooling fin of the evaporator in accordance with removal of noise signals.
• FIGS. 10A-10C depict graphs of frost sensing signals generated in a refrigerator in accordance with an exemplary embodiment.
• In detail,FIGS. 10A-10C depict graphs of frost sensing signals representing results of frost sensing experiments carried out for about 16 hours using 6 sensors. In the experiments, low-pass filtering was executed for signals obtained after signal subtraction.
• InFIG. 10A, the graphs S(1) to S(6) represent frost sensing signals from sensors, which are applied to the first input terminals of the multiplexer, whereas the graph S(7) represents a signal applied to the second input terminal, which is not connected to any sensor.
• Referring toFIG. 10A, it may be seen that a signal containing a common noise component and noise from the oscillator is input to each of 7 input terminals.
• InFIG. 10B, each of the graphs S(1) to S(6) represents a signal obtained by subtracting the signal represented by the graph S(7) from each of the frost sensing signals depicted inFIG. 10A.
• Referring toFIG. 10B, it can be seen that although common noise is removed from each frost sensing signal depicted inFIG. 10A in accordance with subtraction of the signal represented by the graph S(7), noise of about 10 mV from the oscillator is still output.
• InFIG. 10C, each of the graphs S(1) to S(6) represents a signal obtained after filtering an associated one of the signals depicted by the graphs S(1) to S(6) ofFIG. 10B through a low-pass filter.
• Referring toFIG. 10C, it may be seen that signals, which do not pass through the filter for low-pass filtering to remove noise caused by oscillation of the oscillator exhibit a standard deviation of about 1.9 mV, whereas signals passing through the filter exhibit a standard deviation of about 0.7 mV. From this, it may be seen that noise reduction of about 61% is obtained, as compared to signals not passing through the filter.
• Thus, it may be possible to easily and accurately determine noise contained in a signal received from the frost sensor by determining, as noise, the signal received from the input terminal, to which the frost sensor is not connected, and subtracting the noise from the signal received from each input terminal, to which the frost sensor is connected.
• As a result, it may be possible to accurately determine whether or not frost has been formed on an evaporator, and to accurately detect the amount of frost formed.
• Accordingly, it may be possible to more accurately determine whether or not frost has been formed on the refrigerant tube and cooling fins of the evaporator, and to accurately detect the amount of frost formed. Also, it may be possible to accurately determine the point in time when a defrosting operation should be begun, and the point in time when the defrosting operation should be ended.
• Thus, it may be possible to drive and stop the heater for the defrosting operation at appropriate points in time as the amount of frost formed on the evaporator and the defrosting operation completion time are accurately determined, and thus to optimize the defrosting operation. As a result, the heat exchange performance of the evaporator may be enhanced. Also, consumption of energy for the defrosting operation may be reduced. Thus, an enhancement in energy efficiency may be achieved.
• Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Claims (24)

1. A cooling apparatus comprising:

a frost sensor to sense frost;

a multiplexer having a first input terminal, to which the frost sensor is connected, and a second input terminal as a non-connected input terminal;

a signal processor to subtract a signal input through the second input terminal from a signal input through the first input terminal, and to output a signal obtained by the subtraction; and

a controller to detect an amount of frost sensed by the frost sensor, based on the output signal from the signal processor.

2. The cooling apparatus according toclaim 1, wherein a peripheral noise signal is input to the second input terminal.

3. The cooling apparatus according toclaim 1, wherein the signal processor removes a noise signal by subtracting the signal input through the second input terminal from a frost sensing signal as the signal input through the first input terminal.

4. The cooling apparatus according toclaim 1, wherein:

the controller controls a defrosting operation based on the detected frost amount; and

the cooling apparatus further comprises a heater to operate in accordance with a command from the controller, so as to execute the defrosting operation.

5. The cooling apparatus according toclaim 1, further comprising:

a filter to allow a low-frequency signal component of a frost sensing signal generated by the frost sensor to pass through the filter.

6. The cooling apparatus according toclaim 1, wherein the signal processor allows a low-frequency signal component of a frost sensing signal generated by the frost sensor to pass through the signal processor.

7. The cooling apparatus according toclaim 1, wherein the signal processor converts an analog signal as a frost sensing signal generated by the frost sensor into a digital signal.

8. The cooling apparatus according toclaim 1, wherein the signal processor amplifies a frost sensing signal generated by the frost sensor to a predetermined level.

9. The cooling apparatus according toclaim 1, wherein the frost sensor is installed on at least one of an evaporator for a refrigerating compartment, an evaporator for a freezing compartment, and an evaporator for an ice making compartment.

10. The cooling apparatus according toclaim 9, wherein the frost sensor senses a capacitance established between cooling fins provided at the at least one evaporator.

11. The cooling apparatus according toclaim 1, further comprising:

an oscillator to supply a voltage to the frost sensor.

12. The cooling apparatus according toclaim 11, wherein the multiplexer further has a first output terminal, to which the frost sensor is connected, and a second output terminal as a non-connected output terminal, and supplies the voltage to a selected one of the first and second output terminals.

13. The cooling apparatus according toclaim 1, wherein:

the frost sensor comprises a plurality of sensors; and

the sensors are connected to the first output terminal and first input terminal of the multiplexer, and the sensors sequentially receive a voltage, and transmit a frost sensing signal to the first input terminal.

14. A frost detecting method in a cooling apparatus, comprising:

supplying a voltage to a frost sensor through a first output terminal of a multiplexer;

sensing frost by the frost sensor;

receiving a frost sensing signal generated by the frost sensor through a first input terminal of the multiplexer;

receiving a signal from a second input terminal of the multiplexer;

subtracting the signal of the second input terminal from the frost sensing signal; and

detecting an amount of frost, based on a signal obtained by the subtraction.

15. The frost detecting method according toclaim 14, wherein the subtraction of the signal of the second input terminal from the frost sensing signal is executed to remove a peripheral noise signal from the frost sensing signal.

16. The frost detecting method according toclaim 14, further comprising:

determining a point in time when a defrosting operation should be begun, based on the detected frost amount;

driving a heater at the determined time point when the defrosting operation should be begun;

determining, during the defrosting operation, a point in time when the defrosting operation should be ended; and

stopping driving of the heater at the determined time point when the defrosting operation should be ended.

17. The frost detecting method according toclaim 14, further comprising:

passing a low-frequency component of the frost sensing signal generated by the frost sensor.

18. The frost detecting method according toclaim 14, further comprising:

converting an analog signal as the frost sensing signal generated by the frost sensor into a digital signal.

19. The frost detecting method according toclaim 14, further comprising:

amplifying the frost sensing signal generated by the frost sensor to a predetermined level.

20. The frost detecting method according toclaim 14, wherein the sensing of frost by the frost sensor comprises sensing a capacitance established between cooling fins provided on at least one evaporator.

21. The frost detecting method according toclaim 14, further comprising:

supplying a voltage through the second output terminal of the multiplexer.

22. The frost detecting method according toclaim 14, wherein the second output terminal and the second input terminal are non-connected terminals.

23. The frost detecting method according toclaim 14, wherein:

the frost sensor comprises a plurality of sensors each connected to the first output terminal and first input terminal of the multiplexer; and

the supply of the voltage to the frost sensor comprises sequentially supplying the voltage to the sensors.

24. The frost detecting method according toclaim 23, wherein the reception of the frost sensing signal through the first input terminal of the multiplexer comprises sequentially receiving frost sensing signals from the sensors through the first input terminal.

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