JPS6326772Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a water activity value measuring device that can accurately measure the water activity value of foods containing alcohol.

In recent years, the water activity value AW defined by the following formula (1)
It is becoming known that measuring the edible period of food is effective for predicting the edible period of food.

AW=P/Ps...(1) However, P is the water vapor pressure exhibited by the food at a temperature of T°C, and Ps is the saturated water vapor pressure of water at a temperature of T°C.

By the way, some foods contain alcohol due to fermentation or addition, and when measuring the water activity of such foods, conventional water activity measuring instruments are affected by alcohol and cannot be accurate. It was not possible to obtain water activity values.

FIG. 1 is a block diagram showing an example of a conventional water activity value measuring device, in which 1 is a sample case containing a food 2 whose water activity value is to be measured, and 3 is a sample case in which a humidity sensor 4 and a temperature sensor 5 are housed. A sensor housing case, 6 is a hole provided in the sensor housing case 3, 7 and 8 are amplifiers, 9 is an arithmetic circuit, and 10 is a display circuit. The sample case 1 and the sensor housing case 3 are removable and are configured to have a sealed structure when measuring a water activity value.

FIG. 2 is a circuit diagram showing an example of the configuration of the humidity sensor 4, which includes a thermistor Th1 held so as to be able to freely contact the outside air, a thermistor Th2 held in a zero humidity state, a resistor R1, The power source E is connected to the bridge circuit through a current control resistor R3. In addition, thermistor Th1,
Th2 is built into a dustproof filter (not shown), and is placed in close proximity to the filter so that their temperatures are equal in an atmosphere of zero humidity. Also, when measuring water activity value, thermistor Th1,
Th2 is approximately 200 depending on the current supplied from power supply E.
The constants of each part are set so that it self-heats to ℃, and the bridge unbalance voltage that appears between terminals a and b becomes zero when the thermistor Th1 is kept in an atmosphere with zero humidity. Resistor R1,
This is to set the value of R2.

To measure the water activity value using the water activity value measuring device shown in Fig. 1, first put a certain amount of the food 2 whose water activity value is to be measured into the sample case 1, and then attach the sensor housing case 3 as shown in the figure. , the sample case 1 is sealed. In this case, it is necessary to prevent the volume of the food 2 from becoming too small compared to the volume of the sample case 1. Next, the sample case 1 sealed with the sensor housing case 3 is placed in a constant temperature bath and held for a certain period of time. During this time, the food 2 either absorbs the water vapor in the sample case 1 or
Or release the water vapor in the food, sample case 1
The inside is in a state of humidity equilibrium.

By the way, when the humidity sensor 4 having the configuration shown in FIG. 2 is kept in an atmosphere containing water vapor, the thermal conductivity of the air containing water vapor is higher than that of dry air, so it is separated from the outside air. The amount of heat dissipated by the thermistor Th1, which is held so as to be in contact with the thermistor Th1, is greater than the amount of heat dissipated by the thermistor Th2, and the temperature of the thermistor Th1 becomes lower than the temperature of thermistor Th2. This results in
The resistance value of thermistor Th1 becomes greater than the resistance value of thermistor Th2, the bridge circuit does not lose its balance, and a humidity signal proportional to the absolute humidity of the atmosphere in which thermistor Th1 is held is output between terminals a and b. It is something. Note that this has been confirmed through experiments.

Therefore, in this case, the humidity sensor 4 outputs a humidity signal proportional to the absolute humidity inside the sample case 1. And this humidity signal is
The signal is applied to an arithmetic circuit 9 via an amplifier 7. Based on the temperature signal applied from the temperature sensor 5 via the amplifier 8, the arithmetic circuit 9 calculates the saturated water vapor amount Ds of pure water at that temperature.
The calculation shown in the following equation (2) is performed using a humidity signal indicating the absolute humidity D in the sample case 1, which is applied via the .

D÷Ds...(2) By the way, the absolute humidity D, saturated water vapor amount Ds, water vapor pressure P of food 2, and saturated water vapor pressure Ps after reaching the humidity equilibrium state are expressed by the following equations (3) and (4). ).

D=804/1+0.000366t・P/Po……(3) Ds=804/1+0.00366t・Ps/Po……(4) However, Po is the atmospheric pressure and t is the temperature of the thermostatic chamber.
By substituting these equations (3) and (4) into equation (2), the following equation (5) is obtained.

D/Ds=P/Ps... (5) Therefore, after reaching the humidity equilibrium state, as can be seen from equations (5) and (1), the calculation result of the calculation circuit 9 is the water activity value of the food. Therefore, after reaching the humidity equilibrium state, the value displayed on the display circuit 9 indicates the water activity value of the food.

As mentioned above, the water activity value measuring device shown in Figure 1 can measure the water activity value of foods with high accuracy, but it is difficult to measure the water activity value of foods that contain alcohol through fermentation, addition, etc. In this case, it was not possible to obtain accurate water activity values due to the influence of alcohol. That is, the water activity value measuring device shown in FIG. 1 uses a humidity sensor 4 that detects absolute humidity based on the thermal conductivity of gas, and the thermal conductivity of alcohol vapor is Since the thermal conductivity is lower than that of large steam,
If the food contains alcohol, the bridge unbalance voltage that appears between terminals a and b due to the influence of alcohol vapor will be lower than when there is no alcohol, making it difficult to accurately measure water activity values. I couldn't do it.

FIG. 3 shows that alcohol is put into the sample case 1 when the display circuit 10 shows "1".
This is a graph showing the display value of the display circuit 10 as the alcohol concentration in the sample case 1 is increased.As can be seen from the figure, the value displayed on the display circuit 10, that is, the output signal of the arithmetic circuit 9 decreases approximately in proportion to the alcohol concentration.

The present invention has improved the above-mentioned drawbacks, and its purpose is to enable accurate measurement of water activity even when food contains alcohol. Examples will be described in detail below.

FIG. 4 is a block diagram of an embodiment of the present invention, in which 11 is a sample case, 12 is a food product, 13 is a sensor storage case, 14 is a gas sensor, 15 is a temperature sensor, and 16 is provided in the sensor storage case 13. 17 and 18 are amplifier circuits, 19 is an arithmetic circuit, and 20 is an adder, and the same reference numerals as in FIG. 1 represent the same parts. In addition, the gas sensor 14
needs to have characteristics of low sensitivity to water vapor and high sensitivity to alcohol vapor, and for example, a catalytic combustion type sensor using a platinum catalyst can be applied. Moreover, foods 2 and 12 are foods containing alcohol sampled from the same food.

The gas sensor 14 detects the amount of alcohol vapor contained in a unit volume, and sends an alcohol signal proportional to the amount of alcohol vapor as shown in FIG. 5 to the amplifier 1.
7 to the arithmetic circuit 19.
Further, based on the temperature signal applied from the temperature sensor 15 via the amplifier 18, the arithmetic circuit 19 calculates the amount of saturated alcohol vapor A at that temperature, and calculates the amount of alcohol vapor per unit volume added via the amplifier 17. The alcohol signal indicating the amount A is used to perform the calculation shown in the following equation (6) to obtain the alcohol concentration in the sample case 11 and add it to the adder 20.

A÷As (6) Therefore, the output signal of the arithmetic circuit 19 increases in proportion to the alcohol concentration in the sample case 11, as seen from equation (6) and FIG. On the other hand, since the output signal of the arithmetic circuit 9 decreases in proportion to the alcohol concentration in the sample case 1 as described above, by adding the output signals of the arithmetic circuits 9 and 19 in the adder 20,
The display circuit 10 can display accurate water activity values. In this case, it goes without saying that the amplification factors of the amplifiers 7 and 17 should be set so that the addition result indicates an accurate water activity value.

In the embodiment, two sample cases are used, but it goes without saying that a humidity sensor, a gas sensor, and a temperature sensor may be provided in one sample case.

As explained above, the present invention includes a gas sensor that detects the amount of alcohol vapor in a unit volume, a temperature sensor that detects the temperature of a predetermined atmosphere, and an arithmetic circuit 1.
9. Since it is equipped with a correction means for correcting the water activity value, which includes an adder 20, etc., it has the advantage that it is possible to accurately measure the water activity value even when the food contains alcohol.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional example, Fig. 2 is a circuit diagram of a humidity sensor, Fig. 3 is a graph showing the relationship between alcohol concentration and water activity value displayed on the display circuit 10, and Fig. 4 is a diagram of the present invention. The block diagram of the embodiment of the invention, FIG. 5, is a graph showing the relationship between the amount of alcohol vapor and the output signal of the gas sensor. 1 and 11 are sample cases, 2 and 12 are food,
3 and 13 are sensor housing cases, 4 is a humidity sensor,
5, 15 are temperature sensors, 6, 16 are holes, 7, 8,
17 and 18 are amplifiers, 9 and 19 are arithmetic circuits, and 10
is a display circuit, 14 is a gas sensor, 20 is an adder,
E is a power supply, Th1 and Th2 are thermistors, R1 to R
3 is resistance.

Claims (1)

[Scope of utility model registration request] A humidity sensor that detects the absolute humidity inside the airtight container and outputs a humidity signal based on the thermal conductivity of the gas inside the airtight container containing the food; a temperature sensor that detects the ambient temperature and outputs a temperature signal; a calculation circuit that calculates a water activity value of the food based on the humidity signal and the temperature signal; a gas sensor that detects the amount of alcohol vapor contained in a unit volume and outputs an alcohol signal; and a calculation circuit that calculates the water activity value of the food based on the humidity signal and the temperature signal; A water activity value measuring device comprising a correction means for correcting the water activity value based on.