JPH0692408A - Gas concentration controller - Google Patents

Abstract

PURPOSE:To provide a gas concentration controller constructed to output a permission signal for door opening, when the oxygen concentration and pressure inside a storage chamber are made equal to those of the atmosphere, so as to allow an entrance safely. CONSTITUTION:A control unit 6 supplies N2 gas from a corrected air generating unit 3 or air from an air supply unit 4 into the inside of a storage chamber 2 on the basis of the signal from a O2 sensor 7 and a CO2 sensor 8 provided in the storage chamber 2 so as to keep the constant gas mixture rate inside the storage chamber 2. To open the door of the storage chamber 2, a door opening switch button 24 is operated to be set on so that compressed air is supplied into the storage chamber 2 while corrected air inside the storage chamber 2 is exhausted to the outside for air replacement, and then a door lock mechanism 22 is released when the oxygen concentration and the pressure inside the storage chamber 2 become approximate equivalent of those of the atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas concentration control device, and more particularly to a gas concentration control device configured to open a storage door safely.

[0002]

2. Description of the Related Art Stored foods such as fresh foods are generally stored in a storage cabinet to maintain their freshness until shipment. In addition, for long-term storage of these stored materials, the inside of the storage is inactivated by setting it to a temperature low enough not to freeze the stored storage, and the oxygen concentration in the storage is reduced to the necessary minimum. It is considered to be the best way to suppress this, and these kinds of studies have been ongoing these days. A storage method utilizing this phenomenon is called a CA (Atmosphere Controlled or Controlled Atmosphere) storage method.

In the gas concentration control apparatus using this CA storage method, the inside of the storage is maintained at the minimum necessary oxygen (O ₂ ), the maximum necessary carbon dioxide gas (CO ₂ gas) is put, and the rest is nitrogen. It is necessary to maintain the concentration ratio in the chamber at a constant value with an inert gas such as gas (N ₂ gas).

Further, since the optimum ratio of O ₂ gas to CO ₂ gas and N ₂ gas in the storage is determined depending on the kind of the stored material, it is necessary to keep it constant. However, as described above, since the stored matter breathes, O ₂
The gas is consumed, CO ₂ gas is generated, and the ratio of the gas concentration in the storage changes. Therefore, during the storage period, it is necessary to monitor changes in the gas concentration in the refrigerator and adjust it so that it is always constant.

[0005] O ₂ in reservoir to detect the O ₂ concentration in the refrigerator
A sensor and a CO ₂ sensor that detects the CO ₂ concentration in the refrigerator are connected. The gas supply unit is connected to the storage via a gas supply line, and a gas supply valve is provided in this line.

The control circuit controls the gas supply unit, the gas supply valve, and the exhaust valve so as to maintain the gas concentration set by the operation of the control panel according to the concentration detection signals from the O ₂ sensor and the CO ₂ sensor. Therefore, when the O ₂ concentration and the CO ₂ concentration in the storage are out of the set ranges due to the breathing action of the storage in the storage, the control circuit opens the gas supply valve and the exhaust valve to respond to the gas concentration in the storage. Gas in a concentration ratio is supplied from the gas supply unit to the storage, and the gas in the storage is exhausted to the atmosphere.

[0007]

However, in the conventional gas concentration control apparatus, since the gas is supplied from the gas supply unit, the oxygen concentration in the storage is usually low, and the pressure in the storage is higher than atmospheric pressure. Is pressurized to. Therefore, since the oxygen concentration is usually low in the storage, there is a problem that if the worker enters the storage as it is, the worker will be in an oxygen-deficient state (hereinafter referred to as “oxygen deficiency”).

Further, conventionally, when an operator opens the door of the storage, the pressure inside the storage is higher. Therefore, if the operator attempts to open the door carelessly, the door will be affected by the difference between the pressure inside the storage and the atmospheric pressure. The door suddenly opened, and the operator might be skipped due to the opening operation of the door.

Therefore, an object of the present invention is to provide a gas concentration control device that solves the above problems.

[0010]

According to a first aspect of the present invention, a storage to which a plurality of types of mixed gas containing oxygen are supplied in order to maintain the freshness of the storage, and an oxygen concentration in the storage. Oxygen concentration detection means for detecting, correction air supply means for supplying correction air so that the mixing ratio of the mixed gas supplied to the storage becomes a predetermined value, and the inside of the storage based on the detection signal from the oxygen concentration detection means When the mixing ratio of exceeds a predetermined upper limit value or a lower limit value, the correction air from the correction air supply means is supplied to the storage, and when the mixing ratio in the storage reaches the lower limit value or the upper limit value, the correction is performed. Concentration control means for stopping the correction air supply from the air supply means, door opening instruction means for outputting an opening signal of the door before opening the door of the storage, and door opening signal from the door opening instruction means. To the storage Air replacement means for supplying compressed air and discharging the correction air in the storage to the outside, and after starting replacement of the correction air in the storage by the air replacement means, based on the detection signal from the oxygen concentration detection means, Oxygen concentration determination means for determining whether or not the oxygen concentration in the storage has reached approximately the same level as the oxygen concentration in the atmosphere, and the oxygen concentration determination means determines that the oxygen concentration in the storage has reached approximately the oxygen concentration in the atmosphere. And a door opening permission unit that outputs a permission signal for permitting the opening of the door.

According to a second aspect of the present invention, in order to maintain the freshness of the stored product, a storage container to which a plurality of kinds of mixed gas containing oxygen are supplied, and an oxygen concentration detecting means for detecting the oxygen concentration in the storage container. And a correction air supply means for supplying correction air so that the mixing ratio of the mixed gas supplied to the storage becomes a predetermined value, and the mixing ratio in the storage is predetermined based on a detection signal from the oxygen concentration detecting means. When the upper limit value or the lower limit value is exceeded, the correction air from the correction air supply means is supplied to the storage, and when the mixing ratio in the storage reaches the lower limit value or the upper limit value, the correction air is supplied from the correction air supply means. Concentration control means for stopping air supply, door opening instruction means for outputting an opening signal of the door before opening the door of the storage, and compressed air for the storage receiving a door opening signal from the door opening instruction means. Supply With the air replacement means for discharging the correction air in the storage to the outside, and after the replacement of the correction air in the storage by the air replacement means is started, the oxygen concentration of the storage is based on the detection signal from the oxygen concentration detection means. Oxygen concentration determination means for determining whether or not it has reached approximately the same level as the oxygen concentration in the atmosphere, and after the replacement of the modified air in the storage by the air replacement means is started, the pressure in the storage is almost atmospheric pressure. Pressure determination means for determining whether or not
When the oxygen concentration determination means determines that the oxygen concentration in the storage reaches the oxygen concentration in the atmosphere and the pressure determination means determines that the pressure in the storage has reached approximately atmospheric pressure, the door And a door opening permission unit that outputs a permission signal that permits the opening of the door.

[0012]

When the oxygen concentration determination means determines that the oxygen concentration in the storage reaches the oxygen concentration in the atmosphere, the door opening permission means permits the opening of the door of the storage. By outputting, it is possible to prevent the worker from becoming oxygen deficient in the storage.

According to the second aspect of the invention, the oxygen concentration determining means determines that the oxygen concentration in the storage reaches almost the atmospheric oxygen concentration, and the pressure determining means determines that the pressure in the storage is approximately atmospheric pressure. When it is determined that the door opening permission means outputs a permission signal for permitting the door to be opened, it is possible to prevent the worker from running out of oxygen in the storage and the door is rapidly opened by the pressure in the storage. Can be prevented.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a configuration diagram of a gas concentration control device 1 which is an embodiment of the present invention.

The gas concentration control device 1 is roughly composed of a storage 2, a modified air generation unit (modified air supply means) 3, an air supply unit 4, a gas concentration detection unit 5, and a control unit 6.

The storehouse 2 stores stored items such as fresh foods therein.
It is stored and is stored inside by a refrigerator
Is constructed so that the stored material is maintained at a temperature that does not freeze
Has been done. In addition, the storage 2 is, as shown in FIG.
Keep it airtight with the door 2b for loading and unloading
And a fan 2a is provided inside the cabinet.
The inside air can be agitated. This savings
O inside the warehouse 2 ₂Sensor (oxygen concentration detection means)
7, CO₂Sensor 8 and pressure sensor 21 are provided
It

Reference numeral 9 denotes a modified air supply pipe connected to the modified air generating unit 3 (hereinafter referred to as N ₂ pipe), and 10 denotes an oxygen supply pipe connected to the air supply unit 4 (hereinafter, referred to as N ₂ pipe).
O ₂ pipes) and 11 are discharge pipes connected to the storage box 2, respectively.

The N ₂ pipe 9 is provided with a N ₂ supply valve 12 which is an electromagnetic valve. The modified air from the modified air generation unit 3 is supplied into the storage 2 when the N ₂ supply valve 12 is opened. Further, an O ₂ supply valve 13 composed of a solenoid valve is arranged in the O ₂ pipe 10, and the air from the air supply unit 4 is supplied into the storage 2 by opening the O ₂ supply valve 13. .

Further, an exhaust valve 14 which is an electromagnetic valve is arranged in the exhaust pipe 11, and when the exhaust valve 14 is opened, the gas in the refrigerator is exhausted to the atmosphere.

The modified air generating unit 3 is a gas separation device which is supplied with air, which is a mixed gas of nitrogen and oxygen, to separate and generate the modified air, nitrogen and oxygen. The modified air generation unit 3 is connected to the air supply unit 4 via a pipe 16.

The air supply unit 4 is a compressor 17
And a dryer 18 for drying the compressed air from the compressor 17. And the dryer 18 is the pipe 1
6 and 10 to supply dry compressed air to the storage 2 and the modified air generating unit 3.

The modified air generating unit 3 is a PSA (Pressu
Re-Swing Adsorption) type nitrogen generator is built in, and a gas in which O ₂ gas and N ₂ gas are mixed at a desired ratio is supplied to the storage 2 as described later.

The gas concentration detection unit 5 is O₂Densitometer 1
9, CO₂It has a densitometer 20. Each O ₂Densitometer 19, C
O₂Densitometer 20 is O₂Sensor 7, CO₂With sensor 8
It is connected, and by the detection signal from each sensor 7,8
Outputs whether the density is within the set range. This mind
The signal output from the body concentration detection unit 5 is the control unit.
It is input to G.6.

As shown in FIG. 2, the door 2b of the storage 2 is normally locked by the door lock mechanism 22 so that the two handles 23 cannot be opened without permission. The door lock mechanism 22 is, for example, a lock mechanism of a type incorporating a solenoid (not shown), and when a lock release signal is output from the control unit 6, the door 2
It is configured to perform the unlock operation of b.

A door opening switch button (door opening instruction means) 2 that is operated when the door 2b is opened is provided near the door 2b.
4, a lock release lamp 25 and a buzzer 26 for notifying the lock release of the door lock mechanism 22 when the door open permission is given as will be described later.

The control unit 6 controls the modified air generation unit 3 and the air supply unit 4 based on the detection signals from the respective sensors.
The concentration for controlling the opening and closing of each solenoid valve so that the O ₂ concentration and the CO ₂ concentration in the storage 2 become the set predetermined values by switching the N ₂ supply valve 12 and the O ₂ supply valve 13 It has a control means 6A.

When the door open switch button 24 is turned on and the door open signal is output, the control unit 6 supplies compressed air to the storage 2 and discharges the correction air in the storage 2 to the outside. When the oxygen concentration in the storage 2 reaches almost the atmospheric oxygen concentration and the pressure in the storage 2 becomes substantially atmospheric pressure, the door 2b has a door lock releasing means 6B for unlocking the door 2b. .

Next, the gas concentration control device 1 having the above structure
The operation will be described with reference to FIGS. 2 to 6.

In this embodiment, the control unit 6 previously sets the O ₂ concentration to 2% <O ₂ ≦ 4% and the CO ₂ concentration to 5%.
% <CO ₂ ≦ 7% shall be set.

Here, when the operator turns on the start switch (not shown), the control unit 6 executes the processing shown in FIGS. 3 and 4.

In FIG. 3, step S1 (hereinafter "step")
The dryer 1 is turned on by turning on the start switch.
8 and the compressor 17 are simultaneously activated. Subsequently, in S2, the operation of the modified air generation unit 3 is started, and the compressed air generated by the compressor 17 is transferred to the dryer 1
After being dehumidified in 8, it is supplied to the modified air generating unit 3. Then, in the modified air generating unit 3, each solenoid valve is controlled to open and close, and the operation of the nitrogen generating cycle is executed. At this time, the modified air generating unit 3 lowers the O ₂ concentration in the storage 2 in a short time, so that the gas having the lowest O ₂ concentration, that is, the high-purity nitrogen gas is generated. In this way, high-purity nitrogen gas is stored in the modified air generation unit 3.

Before starting the apparatus, air (O₂concentration
About 21%), so N ₂Supply valve 12 opens
Adjusted air from the adjusted air generation unit 3 (low concentration
Oxygen, N₂99%) is supplied into the storage 2 (S
3).

The gas mixture ratio in the storage 2 is constantly detected by the O ₂ sensor 7 and the CO ₂ sensor 8, and the O ₂ sensor 7
The detection signals from the CO ₂ sensor 8 and the O ₂ concentration meter 19,
It is output to the CO ₂ concentration meter 20. In the above operation of the modified air generating unit 3, the O ₂ sensor 7 causes the inside of the storage 2 to be O ₂ ≦
Continue until 4% (O ₂ concentration upper limit) (S
4). After a while, the oxygen concentration in the storage 2 becomes O ₂ ≦ 4
When the ratio becomes%, the N ₂ supply valve 12 is closed to stop the nitrogen gas supply from the modified air generating unit 3 (S5), and subsequently the modified air generating unit 3 is stopped (S6). Then, the compressor 17 and the dryer 18 are stopped (S
7).

When fresh food or the like is stored in the storage 2, the oxygen concentration in the storage 2 decreases with time due to the breathing action of the fresh food, and conversely carbon dioxide increases. Therefore, in the next step S9, it is monitored by the O ₂ sensor 7 whether or not the oxygen concentration in the storage 2 becomes O ₂ <2% (O ₂ concentration lower limit value) due to the breathing action.

The O ₂ concentration and CO ₂ concentration that can maintain the freshness of fresh food for a long time vary depending on the type of food, but are optimum values within a certain range. However, if the storage 2 is hermetically sealed and kept as it is, the O ₂ concentration will drop to near the lower limit value of 2% due to the above-mentioned breathing action.
_{2 The} concentration will be too low and the freshness of the food will decrease.

Therefore, when O ₂ <2% in S8, the compressor 17 and the dryer 18 of the air supply unit 4 are restarted (S9).

Subsequently, the O ₂ supply valve 13 is opened to supply the compressed air from the air supply unit 4 into the storage 2. This process is continued until the oxygen concentration in the storage 2 reaches O ₂ ≧ 4% (upper limit value) (steps S10 and S1).
1).

In step S11, the air on standby is dehumidified and introduced into the storage 2. About 21% oxygen, 0.03% carbon dioxide and most of the rest of nitrogen are in the air. Therefore, by supplying air in the storage 2 to the atmosphere, the O ₂ concentration ratio in the storage 2 can be increased in a short time. Like this, O
_The air having a high concentration of 2 is supplied to the storage 2 in order to prevent the gas in the storage 2 having a high CO ₂ concentration from being discharged to the outside as much as possible due to the breathing action of the storage.

Then, in step S11, O ₂ ≧
When it becomes 4%, the O ₂ supply valve 13 is closed and the air supply is stopped (S12).

Subsequently, the compressor 17 and the dryer 1
8 is stopped (S13).

The change in the O ₂ concentration according to the opening and closing of the O ₂ supply valve 13 can be represented by a triangular waveform indicated by the solid line A in FIG.

The control unit 6 returns to S8 after the processing of S13 is completed and repeats the processing of S8 to S13.

Next, in S8, when the O ₂ concentration in the storage 2 is not O ₂ <2%, that is, when the O ₂ concentration is 2% or more, the process proceeds to S14, and in the next S14, the CO ₂ in the storage 2 is changed.
It is checked whether the concentration exceeds 7% (upper limit value). When CO ₂ > 7%, the process moves to S15, the compressor 17 and the dryer 18 are started, and S1
At 6 the operation of the modified air supply unit 3 is started.

Then, the N ₂ supply valve 12 is opened to supply the N ₂ gas (modified air) generated by the modified air supply unit 3 to the storage 2 (S17). As a result, the CO ₂ concentration in the storage 2 changes, and when the CO ₂ sensor 8 detects that CO ₂ ≦ 5% (S18),
It closes the N ₂ supply valve 12, and stops the N ₂ gas supply to the reservoir 2 (S19).

Subsequently, the modified air generating unit 3 is stopped (S20), and the compressor 17 and the dryer 18 are stopped (S21).

When the process of S21 is completed, the process returns to the step before S8.

The change in the CO ₂ concentration depending on the opening / closing of the N ₂ supply valve 12 can be represented by a triangular waveform indicated by a broken line B in FIG.

When the CO ₂ concentration in the storage 2 is not CO ₂ > 7% in S14, that is, when the CO ₂ concentration is 7% or less, the process returns to the step before S8.

As described above, the O ₂ concentration in the storage 2 is 2%.
The gas mixing ratio is adjusted so that <O ₂ ≦ 4% and CO ₂ concentration is 5% <CO ₂ ≦ 7%, and if the worker enters the storage 2 as it is, the worker will be in an oxygen-deficient state. . or,
Since the pressure inside the storage 2 is higher than the atmospheric pressure,
If the door 2b is opened carelessly, the internal pressure causes the door 2b to open.
Opens vigorously.

Therefore, when the worker enters the storage 2, it is necessary to replace the inside of the storage 2 with the atmosphere and reduce the pressure to the atmospheric pressure in advance. In this embodiment, since the door 2b of the storage 2 is locked by the door lock mechanism 22, even if the operator tries to open the door 2b by grasping the handle 23, the door 2b is not opened immediately.

Here, the operation for opening the door 2b of the storage 2 and the processing executed by the control unit 6 will be described.

When the operator turns on the door opening switch button 24, the control unit 6 executes the processing shown in FIG.

That is, the control unit 6 checks in S31 whether or not the door open switch button 24 is turned on. When the door open switch button 24 is turned on and a door open signal is output, the compressor 17 and the dryer 18 are turned on. To start.

Subsequently, the O ₂ supply valve 13 and the exhaust valve 14
The valve is opened to supply compressed air into the storage 2 and the corrected air in the storage 2 is exhausted to the outside to replace the corrected air in the storage 2 with the atmospheric state (S33). Further, the fan 2a is activated to stir the inside of the storage 2 to promote air replacement in the storage 2 (S34). Incidentally, the above S32 to S3
Reference numeral 4 constitutes a replacement means for replacing the modified air in the storage 2 with the atmospheric state.

In the next step S35, the detection signal from the O ₂ concentration meter 19 is read and it is determined whether the oxygen concentration in the storage 2 is approximately the same as the oxygen concentration in the atmosphere (oxygen concentration determination means). That is, the oxygen concentration in the storage 2 rises due to the opening of the O ₂ supply valve 13 and the exhaust valve 14, and eventually the O ₂
When ≧ 20%, the process moves to S36 and the compressor 17
And the dryer 18 is stopped. In this embodiment, since the air compressed by the compressor 17 is forcibly supplied into the storage 2 and the inside of the storage 2 is agitated by the fan 2a, the oxygen concentration in the storage 2 is relatively short in the atmosphere. Oxygen concentration (about O ₂ 21%).

Next, the O ₂ supply valve 13 is closed to stop the air supply (S37). Since the exhaust valve 14 remains open even after the O ₂ supply valve 13 is closed, the air in the storage 2 is gradually exhausted via the exhaust valve 14, and the pressure in the storage 2 is reduced.

Subsequently, in S38, the detection signal from the pressure sensor 21 is read to determine whether or not the pressure in the storage 2 has been reduced to almost atmospheric pressure.

In S38, when the pressure in the storage 2 becomes almost atmospheric pressure, the process proceeds to S39, and the exhaust valve 14 is closed. Then, the fan 2a is stopped (S40).

Further, in S41, a lock release signal (permission signal) is output to the door lock mechanism 22, and the door lock mechanism 2
Unlock 2 (door opening permission means). Then, a buzzer sound is emitted from the buzzer 26 and the lock release lamp 25 is turned on to notify the operator that the door 2b is unlocked (S42, S43).

As described above, when the oxygen concentration in the storage 2 becomes almost the same as the oxygen concentration in the atmosphere and the pressure in the storage 2 becomes almost atmospheric pressure, the door 2b is unlocked. Even if the operator accidentally tries to open the door 2b without operating the door opening switch button 24, the door lock mechanism 2
2 has locked the door 2b and therefore cannot enter the storage 2. Therefore, the worker is prevented from running out of oxygen in the storage 2, and when the worker opens the door 2b of the storage 2, the pressure in the storage 2 causes the door 2 to open.
b is prevented from opening suddenly, and since the pressure inside the storage 2 and the pressure of the outside air are almost the same, the door 2b can be opened smoothly, and it is possible to enter the storage 2 more safely than before. .

In the above embodiment, when the oxygen concentration in the storage 2 becomes approximately the same as the atmospheric oxygen concentration,
You may make it unlock the door 2b. In that case, the pressure in the storage 2 is manually operated by a worker to operate the exhaust valve 14
Is opened and closed to reduce the pressure in the storage 2 to almost atmospheric pressure.

Although the door 2b is unlocked on the basis of the oxygen concentration and pressure in the storage 2 in the above embodiment, it is not always necessary to unlock the door 2b, and the oxygen concentration in the storage 2 is atmospheric. The buzzer 26 may notify that the oxygen concentration is almost the same as the above, or the lock release lamp 25 may be turned on to notify.

[0063]

As described above, in the gas concentration control apparatus according to the present invention, when the oxygen concentration determination means determines that the oxygen concentration in the storage reaches the oxygen concentration in the atmosphere according to the first aspect. Since the door opening permission means outputs the permission signal for permitting the opening of the door of the storage, the worker can be prevented from running out of oxygen in the storage and can enter the storage more safely.

Further, according to claim 2, the oxygen concentration judging means judges that the oxygen concentration in the storage reaches almost the atmospheric oxygen concentration, and the pressure judging means makes the pressure in the storage almost atmospheric pressure. When it is determined that the door opening permission means outputs a permission signal for permitting the opening of the door, it is possible to prevent the worker from running out of oxygen in the storage,
The door can be prevented from opening suddenly due to the pressure in the storage, and since the pressure inside the storage and the pressure of the outside air are almost the same, the door can be opened smoothly.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a gas concentration control device according to the present invention.

FIG. 2 is a front view showing a front surface and a door of the storage.

FIG. 3 is a flowchart for explaining a process executed by a control unit.

FIG. 4 is a flowchart illustrating a process that is executed subsequent to the process shown in FIG.

FIG. 5 is a diagram for explaining changes in the concentrations of oxygen and carbon dioxide due to the concentration control operation.

FIG. 6 is a flowchart for explaining a process executed when an instruction to open the door of the storage is given.

[Explanation of symbols]

1 Gas Concentration Control Device 2 Storage 2b Door 3 Modified Air Generation Unit 4 Air Supply Unit 5 Gas Concentration Detection Unit 6 Control Unit 6A Concentration Control Means 6B Door Lock Release Means 7 O ₂ Sensor 8 CO ₂ Sensor 12 N ₂ Supply Valve 13 O ₂ supply valve 14 Exhaust valve 19 O ₂ concentration meter 20 CO ₂ concentration meter 21 Pressure sensor 22 Door lock mechanism 24 Door open switch button 25 Lock release lamp 26 Buzzer

Claims (2)

[Claims] 1. A storage to which a plurality of types of mixed gas containing oxygen are supplied in order to maintain the freshness of the stored material, an oxygen concentration detecting means for detecting an oxygen concentration in the storage, and a storage inside the storage. Correcting air supply means for supplying correcting air so that the mixing ratio of the supplied mixed gas becomes a predetermined value, and the upper limit value or the lower limit value of the mixing ratio in the refrigerator determined in advance based on the detection signal from the oxygen concentration detecting means. Concentration for supplying the correction air from the correction air supply means to the storage when the value exceeds the value, and stopping the correction air supply from the correction air supply means when the mixing ratio in the storage reaches the lower limit value or the upper limit value. Control means, door opening instructing means for outputting an opening signal of the door before opening the door of the storage, and supplying compressed air to the storage while receiving the door opening signal from the door opening instructing means. After the air replacement means for discharging the correction air in the storage to the outside and the replacement air for the correction air in the storage by the air replacement means is started, the oxygen concentration of the storage is in the atmosphere based on the detection signal from the oxygen concentration detection means. The oxygen concentration determining means for determining whether or not the oxygen concentration in the storage has reached almost the same level as the oxygen concentration in the storage, and the oxygen concentration determining means determines that the oxygen concentration in the storage has reached the oxygen concentration in the atmosphere. A gas concentration control device comprising: a door opening permission unit that outputs a permission signal for permitting the opening of a door. 2. A storage to which a plurality of kinds of mixed gas containing oxygen are supplied in order to maintain the freshness of the stored material, an oxygen concentration detecting means for detecting an oxygen concentration in the storage, and a storage in the storage. Correcting air supply means for supplying correcting air so that the mixing ratio of the supplied mixed gas becomes a predetermined value, and the upper limit value or the lower limit value of the mixing ratio in the refrigerator determined in advance based on the detection signal from the oxygen concentration detecting means. Concentration for supplying the correction air from the correction air supply means to the storage when the value exceeds the value, and stopping the correction air supply from the correction air supply means when the mixing ratio in the storage reaches the lower limit value or the upper limit value. Control means, door opening instructing means for outputting an opening signal of the door before opening the door of the storage, and supplying compressed air to the storage while receiving the door opening signal from the door opening instructing means. After the air replacement means for discharging the correction air in the storage to the outside and the replacement air for the correction air in the storage by the air replacement means is started, the oxygen concentration of the storage is in the atmosphere based on the detection signal from the oxygen concentration detection means. Oxygen concentration determination means for determining whether or not the oxygen concentration has reached approximately the same level as the oxygen concentration in the storage compartment, and whether the pressure in the storage compartment has become substantially atmospheric pressure after the replacement of the correction air in the storage compartment by the air replacement means is started Pressure determining means for determining whether or not the oxygen concentration in the storage has reached almost the atmospheric oxygen concentration by the oxygen concentration determining means, and the pressure in the storage is determined to be substantially atmospheric pressure by the pressure determining means. And a door opening permission unit that outputs a permission signal for permitting the opening of the door when it is determined that the gas concentration control device.