U.S. patent number 3,691,782 [Application Number 05/051,195] was granted by the patent office on 1972-09-19 for refrigerator thermostat and arrangement thereof.
Invention is credited to Walter U. Holzer.
United States Patent |
3,691,782 |
Holzer |
September 19, 1972 |
REFRIGERATOR THERMOSTAT AND ARRANGEMENT THEREOF
Abstract
A temperature control device for use in a frozen-foods
compartment of a refrigerator, or the like comprises a pair of
temperature-sensitive elements one of which is adapted to be
inserted into the material to be frozen. The two elements are
connected in a logic circuit which in turn controls a switching
device to thereby control the operation of the refrigeration unit
to establish and then maintain a desired temperature in the
compartment.
Inventors: |
Holzer; Walter U. (D-7758
Meersburg, DT) |
Family
ID: |
21969892 |
Appl.
No.: |
05/051,195 |
Filed: |
June 30, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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679356 |
Oct 31, 1967 |
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Current U.S.
Class: |
62/209; 236/78B;
236/78R; 327/459 |
Current CPC
Class: |
G05D
23/24 (20130101); G05D 23/1932 (20130101); G05D
23/1928 (20130101); G05D 23/1909 (20130101); F25D
29/005 (20130101); F25D 2700/16 (20130101) |
Current International
Class: |
F25D
29/00 (20060101); G05D 23/24 (20060101); G05D
23/20 (20060101); G05d 023/24 (); H03k
019/30 () |
Field of
Search: |
;62/213,209,229
;236/78B,15A,15B ;219/516,505 ;307/310,252B |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Wayner; William E.
Parent Case Text
This is a continuation-in-part of an application, Ser. No. 679,356,
filed on Oct. 31, 1967 now abandoned.
Claims
I claim:
1. A temperature control system for establishing and maintaining a
predetermined temperature in a refrigeration chamber in which
frozen material is adapted to be stored, said control system
comprising switch means capable of operating in first, second and
third different states of conduction for controlling the operation
of the refrigeration chamber, control circuit means for controlling
the operation of said switch means, first and second temperature
sensitive resistor sensors arranged in the chamber, one of said
sensors being movable in the chamber for insertion in the frozen
material stored therein, logic means coupled to said resistor
sensors and to the input of said control circuit means, said logic
means being effective in response to the temperatures sensed by
said first and second sensors to provide a control signal to the
input of said control circuit means, the latter in turn being
effective to establish said switch means into one of said first,
second and third states of conduction.
2. The temperature control system of claim 1, in which said control
circuit means comprises an output switching device, a trigger
having an input coupled to said sensors and an output coupled to
the control terminal of said switching device, and variable
resistance means coupled between said input and output for
controlling the response of said trigger to variations in said
first and second temperature sensors.
3. The temperature control system of claim 2, in which said first
and second temperature-sensitive resistors are coupled in an
OR-circuit, said OR-circuit being coupled to the input of said
control circuit means.
4. The temperature control system of claim 3, further comprising
means for selectively inserting resistance elements having
different values of resistance in circuit arrangement with one of
said first and second temperature sensors.
5. The temperature control system of claim 1, in which the movable
one of said first and second temperature sensors is housed in a
tube of heat-conducting material.
6. The temperature control system of claim 1, in which said first
and second temperature-sensitive resistors are coupled in an
OR-circuit, said OR-circuit being coupled to the input of said
control circuit means.
7. The temperature control system of claim 6, further comprising
means for selectively inserting resistance elements having
different values of resistance in circuit arrangement with one of
said first and second temperature sensors.
Description
The invention relates generally to temperature control devices, and
particularly to a device for controlling the operation of a
refrigerating unit for establishing suitable temperatures in a
refrigerating chamber having freezing devices and adapted to
contain frozen goods.
In freezer chests employing freezing devices the refrigerating unit
can be switched from its normal refrigerating power, which
maintains a temperature of at least -18.degree. C, in the
refrigerating chamber, to maximum refrigerating power which is
required for freezing with a so-called cold shock. Since the
refrigerating temperatures should reach up to -35.degree. C, a
considerably higher refrigerating power is required.
In the known arrangements the switching to the maximum
refrigerating power is effected when goods such as frozen foods
placed in the freezer chest are to be frozen by the intensive
action of the cold shock. The freezing is completed when the goods
have attained a prescribed freezing temperature in their interior.
The time required for this freezing operation depends to a great
extent upon the nature of the goods which are to be frozen. For
example, the freezing of flat and thin pieces is much more rapid
than that of thick pieces.
Heretofore the duration of such a cold shock process was determined
by the operator largely by instinct. But there is a danger that the
operator will switch too quickly from the maximum refrigerating
power to the normal refrigerating power, so that the parts of the
goods inside the freezer will not be subjected to cold-shock, and
it will thus take much longer until the refrigerating chamber
temperature of -18.degree. C is attained. This is harmful for the
quality of the goods to be frozen. The maintaining of high
refrigerating power for an excessive period has the disadvantage
that an excessive demand is placed on the refrigerating unit, which
in turn, results in greater wear and higher operating costs of the
refrigerating unit.
Depending on the nature of the goods to be frozen, differing
deviations from the nominal freezing temperature can be permitted
during normal operation in the freezer chest or the refrigerating
chamber. For example, a material which consists primarily of
protein and fat requires a different accuracy in maintaining the
nominal freezing temperature than a more sensitive material, such
as vegetables. The presently known temperature control devices for
refrigerating units do not provide the possibility for connecting
and disconnecting the refrigerating unit for attaining the desired
nominal temperature dependent on the sensitivity of the material to
deviations in temperature. Only fixed temperature differences are
provided after which the refrigerating unit is connected. For
example, a deviation of plus or minus 1.degree. C is permitted, so
that with a set refrigeration chamber temperature of -18.degree. C,
the refrigerating unit is connected at -17.degree. C and
disconnected at -19.degree. C. This difference of 2.degree. C is
called the connection difference. Regardless of whether the
material requires such a small connection difference, that same
refrigerating power is always expended. It is therefore an object
of the invention to provide a temperature control device which
permits the accurate execution of a rapid freezing process, the
so-called cold shock.
It is another object of the invention to provide a temperature
control device which improves the economy of a refrigerating unit
by providing the possibility of preselecting the connection
difference and adapting it to the respective material to be
frozen.
It is a further object of the invention to provide a temperature
control device which does away with the need for mechanical
switches in its operation.
The operation broadly resides in the provision of two temperature
feelers, of which the feeler that switches the circuit breaker back
to the lower power stage is mounted movably and can be introduced
into the material to be frozen, while the other feeler, which
connects and disconnects the circuit breaker, herein shown as a
triac in the lower power stage, can be set to corresponding
response values by an adjusting device. In order to eliminate
mechanical switches in the temperature control device, which are
susceptible to trouble, the switch-back of the circuit breaker and
the switching in normal operation are controlled by a transistor
ahead of which is arranged a trigger which is in turn connected to
the feelers and which has a variable resistance in its feedback
path.
One of the two temperature feelers determines the period during
which the maximum power stage is in effect, while the other feeler
effects in nominal operation the connection and disconnection of
the refrigerating unit in dependence on the preset nominal
value.
To the accomplishment of the above and to such further objects as
may hereinafter appear, the present invention relates to a
temperature control device for a refrigerating unit substantially
as defined in the appended claims and as described in the following
specification taken together with the accompanying drawings in
which:
FIG. 1 is a circuit diagram of a temperature control device
designed according to the invention; and
FIG. 2, is a schematic perspective view of a temperature feeler
designed as a probe as employed in the temperature control device
of the invention.
In the particular embodiment of the invention herein shown, the
temperature control device of the invention, as shown in FIG. 1,
includes a current source 1 at 220 volts a-c connected to the
terminals 2 and 3 of a refrigerating unit 4. A switching device 5
is arranged in the circuit of refrigerating unit 4, and is herein
shown as a gate-controlled thyristor or triac.
Switching device 5 permits refrigerating unit 4 to switch between a
maximum power state and a power state for normal operation, in
which refrigerating unit 4 can also be connected and disconnected
in dependence on the temperature in the refrigerating chamber. The
control of the triac is effected by a control transistor 6, ahead
of which is arranged a trigger circuit, which in turn is connected
to the temperature sensors or feelers 21 and 22. The trigger
circuit consists of the two transistors 7, 8 and the resistors 9 to
14 connected in a conventional manner as shown in FIG. 1.
Temperature feelers 21 and 22 are advantageously in the form of
temperature-dependent NTC or PTC resistors. The resistance values
of feelers 21 and 22 vary as a function of temperature. At least
temperature feeler 21 is designed as a probe, by inserting the NTC
or PTC resistor into a metal tube. This probe is adapted to be
introduced into the material to be frozen.
A fixed resistor 19 and a variable resistor 20 connected in series
define a feedback path for the trigger circuit. In addition, a
power supply unit 16 is provided which consists of the conventional
rectifiers, filters and stabilizers for providing the electronic
control with voltages from a supply voltage 17 and a supply
transformer 18. The output of power supply 16 is a stabilized d.c.
voltage which has, as is conventional, a residual hum. A voltage of
3 volts is applied from power supply 16 to the collector electrode
of the control transistor 6, and the rest of the electronic control
circuit is provided with a voltage of 22 volts. The temperature
feeler 22 is series-connected with a fixed resistor 23, and the
feeler 21 is connected parallel thereto and is selectively coupled
to one of three fixed resistors 24, 25, and 26, with which it can
be connected by the operation of a selector switch 27 to form a
voltage divider circuit. The parallel-connected feelers 21 and 22,
which are connected as an "OR" circuit, are provided with rectifier
diodes 30 and 31 for decoupling. In addition, capacitors 32 and 33
are connected in parallel to ground to form along with resistor 11
an a-c filter. The capacitors 32 and 33 serve to suppress high
frequency noise. In an apparatus having poor suppression of radio
noise (e.g., vacuum cleaners or drilling machines, etc.) there can
occur switching sparks which can release the trigger consisting of
the transistors 7, 8. This is avoided by the capacitors 32 and
33.
The method of operation of the electronic temperature control
device of FIG. 1 is as follows:
In order to freeze a material placed in a freezer chest or the
like, with a high refrigerating power by a so-called cold-shock,
refrigerating unit 4 is initially switched by setting switching
device 5 to its maximum power state to supply maximum refrigerating
power to unit 4. This switching can be effected by control elements
(not shown) or by hand. Switching back of switching device 5 to its
normal state is effected when the material in unit 4 has fully
attained the freezing temperature required for cold shock. The
firing (initial setting) of switching device or thyristor 5 occurs
through the gate electrode of that device by means of transistor 6,
which is supplied with a separate supply voltage. The signal at the
base of transistor 6 and indirectly the opening or cut-off times of
switching device 5 is controlled by the trigger consisting of the
transistors 7 and 8. This trigger oscillates according to the
setting of variable resistor 20 and selector switch 27. This
freezing temperature is sensed by the variable-resistance feeler 22
designed as a probe, which is movably mounted and introduced into
the material. When the resistance of feeler 22 reaches a
predetermined value, a determination is made that the material has
attained the required temperature in its interior. When the
interior of the material has reached the freezing temperature, the
resistance value of feeler 22 reaches a level at which switching
device 5 is switched by control transistor 6 to its normal power
state for normal operation at a reduced refrigeration power. In
this normal power stage temperature feeler 21 then takes over the
control of refrigerating unit 4 by connecting refrigerating unit 4
over the trigger and control transistor 6 with switching device 5.
Temperature feelers or sensors 21 and 22 supply a voltage
proportional to the temperature which voltage is decoupled through
diodes 30 and 31. That voltage is supplied through resistor 11 to
the input of the trigger. The diodes 31 and 32 are provided to
carry out an "OR" function. The following conditions may exist:
"OR" function: Sensor 22 Sensor 21 1 1 Everything is switched
off
1 0 The trigger and thus 0 1 switching device 5 0 0 is switched
on
It can be seen that in case of a temperature difference between the
sensors (condition 0/1 ) cooling will continue between the sensors
21 and 22 until such time as the sensors reach the same preselected
temperature (1/1 ). That temperature is preselected by the setting
of selector switch 27. The condition 0/0 will be avoided by
resistor 23. At a sufficiently low temperature the same voltage is
present at the sensors 21 and 22 and thus at the common connection
of the diodes 30 and 31 at the resistor 11. Thereby a cut-off
effect occurs after the "OR" function, and the cooling will be
interrupted through the trigger.
The thyristor 5 functions in three possible states in a known
manner; the energy control takes place through its gate
electrode:
a. Switched off: The trigger blocks the transistor 6; no necessary
positive control voltage is applied to the control electrode of the
thyristor 5.
b. Fully switched on: The trigger oscillates and supplies a number
(N) or half-waves to the control electrode so that the thyristor
fully connects through.
c. Half switched off: The trigger supplies only (N/2) half-wave to
the control electrode of the thyristor and thereby supplies
electrical energy to refrigerating unit 4 only half of the time as
in b). By switching to the various fixed resistors 24, 25 or 26 by
means of the selector switch 27, a certain temperature range can be
selected over which the temperature feeler 21 operates to control
the operation of circuit breaker 5. By means of the variable
resistor 20 provided in the feedback path across transistors 7 and
8, it is also possible to select the deviation from the nominal
value over which temperature feeler 21 is effective to connect and
disconnect circuit breaker 5. In dependence on the material to be
frozen, it is then possible to determine what deviations from the
nominal value of the refrigerating temperature are permitted in the
refrigerating chamber. By means of variable resistor 20 it is
possible, for example, to provide that the connection and
disconnection of refrigerating unit 4 should be effected after a
deviation of plus or minus 1.degree. C from the required
refrigerating chamber temperature of -18.degree. C, for example.
But it can also be provided that refrigerating unit 4 should only
be connected or disconnected at much greater temperature
differences, for example, at deviations of 7-1/2.degree. C from the
nominal value. The connection difference can be adjusted between
2.degree. and 15.degree. C.
The switching of refrigerating unit 4 over circuit breaker 5, which
is in turn switched by control transistor 6, is effected when the
predetermined temperature has been sensed by temperature feelers 21
and 22 in such a way that the respective voltage variation is
transmitted over diode 30 or 31 and resistor 11 to transistor 7.
This transistor is cut off, so that transistor 8, connected in
series with transistor 7 via the resistor 14, is turned on and the
switching transistor 6 is in turn, cut off. As a result, circuit
breaker 5 is cut off on one side so that refrigerating unit 4 is
switched to the lower power stage, in the manner described above.
Depending on the temperature, which is measured by feelers 21 and
22 respectively, the circuit breaker 5 is opened for both
half-cycles or only for one half-cycle so that refrigerating unit 4
works at full or partial load.
FIG. 2 illustrates a possible configuration of temperature feeler
22 which as noted above is designed as a movable probe, for
insertion into the material to be frozen. As shown, feeler 22 is
secured in a metal tube 35 over a ring bush 34 of thermally
conductive material, which may be, for example, a suitable metal.
The two leads 36, 37 extending from temperature feeler 22 leave
tube 35 through a plug 38. two leads are also represented in the
circuit diagram of FIG. 1.
To make sure that the temperature can be sensed without delay, the
generally stationary temperature feeler 21 is preferably also
surrounded by a metallic body, for example, a metal plate which is
in contact with the interior of the refrigerator.
Thus, while only a single embodiment of the present invention has
been herein specifically described it will be apparent that
modifications may be made therein without departing from the spirit
and the scope of the invention.
* * * * *