Apparatus for maintaining liquid temperature at a constant level

An apparatus for maintaining liquid temperature at a constant level comprises a reaction vessel for containing liquid, a cooling device connected with the reaction vessel for cooling the liquid, a heating device connected with the cooling device for heating the liquid cooled by the cooling device, a circulating device for circulating the liquid through and among the reaction vessel, the cooling device and the heating device, a temperature detecting device for detecting the temperature of the liquid heated by the heating device, a heat exchange rate control device for controlling the heat exchange rate between the cooling device and the liquid, and a control device for controlling the heating device and the heat exchange rate control device based on a control state of the apparatus and on the temperature difference between the detected temperature and a desired temperature.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus for maintaining liquid 
temperature in a vessel at a constant level, and in particular, to an 
apparatus for maintaining liquid temperature in a reaction vessel of an 
automatic biochemical analyzer for clinic examination at a constant level. 
An automatic biochemical analyzer for clinic examination, require a short 
rise time for the liquid temperature in the reaction vessel, i.e. a short 
time length from the start of the power supply to the time when a desired 
temperature of the liquid has been reached, and a precise control of the 
liquid temperature at a desired level, i.e. a control including only small 
temperature ripples. 
Automatic biochemical analyzers for clinical examination generally provide 
a cooling device which is continuously operated for cooling the liquid, 
and a heating device which is intermittently operated for heating the 
cooled liquid for maintaining the liquid temperature in a desired 
temperature range. In this arrangement of the prior art, in order to 
obtain a short rise time, the cooling device and the heating device are 
required to have a rather large capacity. However, the large capacities of 
the cooling and heating devices cause greater temperature ripples. In 
contrast with this, smaller temperature ripples may be obtained by using 
cooling and heating devices each having a smaller capacity. However, this 
arrangement will cause a rather long rise time. Since the above-mentioned 
two requirements are contradictory to each other, in conventional 
automatic biochemical analyzers of clinic examination, the capacity of 
each device is so determined as to obtain a short rise time at the 
sacrifice of precise liquid temperature control, or to obtain precise 
liquid temperature control at the sacrifice of a short rise time. Or else, 
these two contradictory requirements are compromised. In short, no 
automatic biochemical analyzer for clinic examination of the prior art has 
satisfied these two requirements at the same time. 
In addition, in automatic biochemical analyzers for clinic examination of 
the prior art, the cooling device is operated to cool the liquid at all 
times, even when, at the start of the analyzer operation, the liquid 
temperature is lower than the desired value. In such circumstances of 
lower initial temperature, it is obvious that the heating operation alone 
including no cooling operation is more effective to obtain a shorter rise 
time. Namely, the analyzer of the prior art has a demerit that an 
unnecessary cooling operation is carried out even in the case of the 
liquid having a lower initial temperature. Further, since the cooling 
device is in operation at all times, the refrigerator of the cooling 
device is always applied on by a maximum load, which causes a shorter life 
of the refrigerator. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an apparatus for 
maintaining liquid temperature at a constant level, which can assure a 
shorter rise time of an automatic analyzer as well as small ripples of the 
liquid temperature. 
Another object of the present invention is to provide an apparatus for 
maintaining liquid temperature at a constant level, wherein the operation 
time of the refrigerator at a full load condition can be decreased. 
An apparatus for maintaining liquid temperature at a constant level 
according to the present invention comprises a reaction vessel for 
containing the liquid, cooling means for cooling the liquid and connected 
with the reaction vessel, heating means connected with the cooling means 
for heating the liquid cooled by the cooling means, circulating means for 
circulating the liquid through and among the reaction vessel, the cooling 
means and the heating means, temperature detecting means for detecting the 
temperature of the liquid heated by the heating means, heat exchange rate 
control means for controlling the heat exchange rate between the cooling 
means and the liquid, and control means for controlling the heating means 
and the heat exchange rate control means based on the control state of the 
apparatus and on the temperature difference between the detected 
temperature and a desired temperature. 
In an embodiment of the present invention, the heat exchange rate control 
means includes a plurality of cooling tubes disposed in the cooling means 
for passing the liquid therethrough each having a different heat exchange 
capacity, and valve means for opening or closing each of passages 
communicating with each of the cooling tubes. 
In another embodiment, the heat exchange rate control means includes a 
cooling tube disposed in the cooling means and valve means for controlling 
the liquid flow directed towards the cooling tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1, 2 and 3, an apparatus for maintaining liquid 
temperature at a constant level according to an embodiment of the present 
invention will be described below. FIG. 1 shows the apparatus applied to 
an automatic biochemical analyzer for clinic examination. In FIG. 1, 
liquid 33 is contained in an annular cylindrical reaction vessel 27, which 
has an U-shaped axial cross-section and an upper opening. The reaction 
vessel 27 is connected at its bottom with an inlet port 28 and an outlet 
port 29 for circulating the liquid 33, and coated on its outer surface 
with insulation material 30. Numeral 31 denotes a cylindrical reaction 
cell, which is made of transparent material having a good optical feature 
and a high heat conductivity, such as glass, for example, and poured with 
a predetermined amount of analite and a predetermined amount of reagent to 
be mixed with each other. A plurality of reaction cells are supported by a 
reaction disk 32, and immersed at their lower portions into the 
temperature controlled liquid 33 in the reaction vessel 27 for maintaining 
the liquid in the reaction cells at a reaction temperature. 
The outlet 29 of reaction vessel 27 is connected with a pipe 38, which is 
connected with a first switching valve 34. The first switching valve 34 
includes an inlet port, a first outlet port and a second outlet port and 
has two valve positions, i.e. a valve position 34a where the first outlet 
port is communicated with the inlet port, while the the second outlet port 
is closed, and a valve position 34b where the second outlet port is 
communicated with the inlet port, while the first outlet port is closed. 
The first outlet port of the first switching valve 34 is connected with 
one end of a first cooling tube 7 through a pipe 39, while the second 
outlet port is connected with an inlet port of a second switching valve 35 
through a pipe 40. The second switching valve 35 includes, similarly to 
the first switching valve 34, an inlet port, a first outlet port and a 
second outlet port and has two valve positions, i.e. a valve position 35a 
where the first outlet port is communicated with the inlet port, while the 
the second outlet port is closed, and a valve position 35b where the 
second outlet port is communicated with the inlet port, while the first 
outlet port is closed. The first outlet port of the second switching valve 
35 is connected with one end of a second cooling tube 8 through a pipe 43, 
while the second outlet port is connected through a pipe 44 with a pump 21 
for circulating the liquid 33. The first switching valve 34 and the second 
switching valve 35 are controlled based on signals from control means 53, 
which will be described later. 
A cooling device 1 is a refrigerator using, for example, Freon gas as 
refrigerant, and includes a compressor 2, a condenser 3 for condensing the 
refrigerant, an expansion valve 4 for expanding the refrigerant, an 
evaporator 5 for evaporating the refrigerant and a cooling water tank 6 
containing water 11. The outer surface of the cooling water tank 6 is 
coated with insulation material 9, and the upper opening of the tank is 
closed with a cover 10 made of insulation material. The water 11 in the 
cooling water tank 6 is cooled by utilizing evaporation heat of the 
refrigerant in the evaporator 5. 
The first cooling tube 7 extends in the cooling water tank 6 and then to 
outside of the tank 6 and is connected at the end, other than the one end 
of the tube 7, with the pipe 40 through a pipe 41. Similarly, the second 
cooling tube 8 extends in the cooling water tank 6 and is then to outside 
of the tank 6 and connected at the end, other than the one end of the tube 
8 with the pipe 44 through a pipe 45. The heat exchange capacity of the 
first cooling tube 7 is determined correspondingly to the maximum cooling 
capacity of the cooling device 1, while the heat exchange capacity of the 
second cooling tube 8 is so determined as to suit the normal control state 
of the apparatus. 
The discharge side of the pump 21 is connected through a pipe 36 with an 
inlet port 23 of a heating device 22, an outlet port 24 of which is 
connected with the inlet port 28 of the reaction vessel 27 through a pipe 
37. The heating device 22 is of a cylindrical shape and includes therein a 
rod-shaped heater 25 and a temperature sensor 26 for detecting the liquid 
temperature Tp. 
The output signal of the temperature sensor 26 is transformed into an 
amplified voltage signal through an amplifier 51, and transferred to a A/D 
converter 52, where the signal is digitized, and then to the control means 
53 which includes a micro-computer. The liquid temperature detecting 
actions of temperature sensor 26 are usually carried out every 20 msec. 
Further, there are shown an electric alternating current source 54 for the 
heater 25, and a solid-state relay 55 which controls the alternating 
current from the current source 54 in an on-off way based on control 
signals from the control means 53. 
The function of the apparatus will be described below. 
The electric power is supplied to the automatic biochemical analyzer for 
clinic examination, and a desired temperature value Ti is input into the 
control means 53. The desired temperature Ti is usually selected from 
among 25.degree. C., 30.degree. C. and 37.degree. C. 
In a starting time of the analyzer operation, wherein the temperature Tp of 
the liquid 33 detected by the temperature sensor 26 is lower than the 
desired temperature Ti, the control means 53 instructs to energize the 
heater 25 of the heating device 22, and to switch the first switching 
valve 34 and the second switching valve 35 to the position 34b and the 
position 35b, respectively (refer to FIG. 2). In consequence, the liquid 
33 in the reaction vessel 27 is flowed through the outlet port 29, the 
pipe 38, the inlet port of the first switching valve 34, the second outlet 
port of the first switching valve 34, the inlet port of the second 
switching valve 35, the second outlet port of the second switching valve 
35 to the heating device 22, where the liquid is heated, and then is 
returned to the reaction vessel 27. In this case, since the liquid 33 is 
not cooled by the cooling device 1, but only heated by the heater 25, the 
liquid 33 can be rapidly heated to the desired temperature Ti. 
On the other hand, in a starting time of the analyzer operation, wherein 
the temperature Tp of the liquid 33 detected by the temperature sensor 26 
is higher than the desired temperature Ti, the control means 53 instructs 
to deenergize the heater 25 of the heating device 22, and to switch the 
first switching valve 34 and the second switching valve 35 to the position 
34a and the position 35b, respectively (refer to FIG. 3). In consequence, 
the liquid 33 in the reaction vessel 27 is flowed through the outlet port 
29, the pipe 38, the inlet port of the first switching valve 34, the first 
outlet port of the first switching valve 34, the first cooling tube 7, the 
pipe 41, the inlet port of the second switching valve 35, the second 
outlet port of the second switching valve 35 to the heating device 22, and 
then is returned to the reaction vessel 27. In this case, since the liquid 
33 is not heated by the heating device 22 because the heater 25 is 
deenergized, the liquid 33 can be rapidly cooled to the desired 
temperature Ti. 
After the liquid temperature Tp has reached the desired temperature Ti, the 
apparatus for maintaining the liquid temperature at a constant level is 
shifted to a normal control state (FIG. 1). Namely, the control means 53 
instructs the first switching valve 34 and the second switching valve 35 
to switch to the position 34b and the position 35a, respectively. In 
consequence, the liquid 33 in the reaction vessel 27 is flowed through the 
outlet port 29, the pipe 38, the inlet port of the first switching valve 
34, the second outlet port of the first switching valve 34, the pipe 40, 
the inlet port of the second switching valve 35, the first outlet port of 
the second switching valve 35, the pipe 43, the second cooling tube 8, and 
the pipe 45, to the heating device 22, where the liquid is suitably 
heated, and then is returned to the reaction vessel 27. The control means 
53 controls the power supply to the heater 25 of the heating device 22 in 
on-off way based on temperature difference between the desired temperature 
Ti and the temperature Tp detected by the temperature sensor 26 every 20 
mses. In this case, since the liquid 33 is cooled only by the second 
cooling tube 8 which has a smaller heat exchange capacity selected 
correspondingly to the normal temperature control state, a temperature 
control having a high precision and suppressed temperature ripples can be 
obtained. 
Further, since the cooling device 1 is required to run with full load only 
in a starting time of the analyzer operation, but with minimum load in an 
operation time of the normal temperature control state, the time duration 
of which is much longer than the starting time, the life of the cooling 
device becomes longer. 
Another embodiment of the present invention is described below by referring 
to FIG. 4. Descriptions are shortened with respect to the portions 
identical with those of the embodiment shown in FIG. 1. 
In this embodiment, at the position where the first switching valve 34 is 
located in the above mentioned first embodiment, a flow dividing valve 55 
is instead arranged, and the second switching valve 35 and the second 
cooling tube 8 are both omitted. The flow dividing valve 55 includes an 
inlet port connected with the pipe 38, a first outlet port connected with 
one end of the first cooling tube 7, and a second outlet port connected 
with the pump 21 through a pipe 47, the other end of the first cooling 
tube 7 being connected with the pipe 47 through the pipe 41. The flow 
dividing valve 55 controls the flow rate of the liquid 33 into the first 
cooling tube 7 based on signals from the control means 53. 
In a starting time of the analyzer operation, wherein the temperature Tp of 
the liquid 33 detected by the temperature sensor 26 is lower than the 
desired temperature Ti, the control means 53 instructs to energize the 
heater 25 of the heating device 22, and to control the flow dividing valve 
55 so as to prevent the liquid 33 from flowing into the cooling tube 7. In 
consequence, the liquid 33 in the reaction vessel 27 is flowed through the 
outlet port 29, the pipe 38, the flow dividing valve 55 and the pipe 47 to 
the heating device 22, where the liquid is heated, and then returned to 
the reaction vessel 27. In this case, since the liquid 33 is not cooled by 
the cooling device 1, but only heated by the heater 25, the liquid 33 can 
be rapidly heated to the desired temperature Ti. 
On the the hand, in a starting time of the analyzer operation, wherein the 
temperature Tp of the liquid 33 detected by the temperature sensor 26 is 
higher than the desired temperature Ti, the control means 53 instructs to 
deenergize the heater 25 of the heating device 22 and to control the flow 
dividing valve 55 so as to make the whole liquid 33 flow from the pipe 38 
into the cooling tube 7. In consequence, the liquid 33 in the reaction 
vessel 27 is flowed through the outlet port 29, the pipe 38, the flow 
dividing valve 55, the first cooling tube 7, where the liquid is cooled by 
the cooling water 11, to the heating device 22, and then returned to the 
reaction vessel 27. In this case, since the liquid 33 is not heated by the 
heating device 22 because the heater 25 is deenergized, but cooled by the 
first cooling tube 7 having maximum cooling capacity, the liquid 33 can be 
rapidly cooled to the desired temperature Ti. 
After the liquid temperature Tp has reached the desired temperature Ti, the 
operation of the apparatus for maintaining the liquid temperature at a 
constant level is shifted to a normal control state. Namely, the control 
means 53 instructs the flow dividing valve 55 to divide the the liquid 33 
and to control the flow rate to the first cooling tube 7 by an amount 
corresponding to the normal control state. In consequence, a certain 
amount of the liquid 33 corresponding to the normal control state is 
cooled by the first cooling tube 7, and then joined with the liquid flow 
from the pipe 47. The joined liquid is then flowed to the heating device 
22, where the liquid is suitably heated, and returned to the reaction 
vessel 27. The control means 53 controls the power supply to the heater 25 
of the heating device 22 in on-off way based on the temperature difference 
between the desired temperature Ti and the liquid temperature Tp detected 
by the temperature sensor 26 every 20 msec. In this way, a temperature 
control having suppressed temperature ripples can be obtained. 
As described above, in the present invention, in case the liquid 33 is 
required to be rapidly cooled, a greater cooling capacity is selected, 
while in case the liquid 33 is not required to be cooled, the liquid 33 is 
not cooled, and in the normal control state, a suitable cooling capacity 
corresponding to the normal control state is selected. By virtue of these 
arrangements and processes, a short rise time of the apparatus and a 
highly precise control of the temperature can be obtained. In addition, 
the life of the cooling apparatus becomes longer by virtue of the 
decreased load on the cooling apparatus.