JPS6123793Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a relative hygrometer that electrically measures relative humidity. Various types of relative hygrometers are known, such as a wet and dry bulb type, a hair type, and a semiconductor type. However, none of the types that convert humidity into electrical signals and output them is completely satisfactory in terms of stability, and the output voltage also changes due to temperature changes, so similar to the wet-and-dry bulb type, , the relative humidity must be measured with correction according to the temperature at that time,
It was not possible to easily measure relative humidity. The present invention has improved the above-mentioned drawbacks, and its purpose is to enable direct reading of relative humidity within the operating temperature range. Examples will be described in detail below. FIG. 1 is an explanatory diagram of an embodiment of the present invention, in which a thermistor, a heat-sensitive element Rs made of platinum, etc., is held so that it can freely contact the outside air, and a thermistor, a heat-sensitive element Rs, made of platinum, etc., kept in an absolutely dry state. Temperature compensation element Rc and 2
A bridge circuit consisting of two resistors R ₂ , R ₃ and a variable resistor R ₄ for zero point adjustment, a power supply E connected to this bridge circuit via a current control resistor R ₁ , and terminals T ₁ , T ₂ A temperature compensation amplifier 1 that amplifies the unbalanced voltage that appears between the two and whose amplification factor changes depending on the temperature of the outside air, and this temperature compensation amplifier 1
It is comprised of a voltmeter 2 that measures the output voltage of. In addition, the heat-sensitive element Rs used in this example
has the structure shown in FIG. 2, for example, in which 3 is a glass-coated thermistor, 4 is a metal cap, 5 is a hermetic seal, 6 and 6' are lead wires, and 7 is a hole. The metal cap 4 is hermetically sealed by a hermetic seal 5, and has, for example, four to eight holes 7 with a diameter of about 0.5 mm, thereby maintaining contact with the outside air. . On the other hand, the temperature compensation element
Since Rc must be kept in an absolutely dry state, the metal cap 4 of the heat-sensitive element Rs shown in FIG. 2 is not provided with a hole 7. However, it is necessary that the heat-sensitive element Rs and the temperature-compensating element Rc have almost the same current-voltage characteristics, and that they are placed close to each other so that the temperature of both is maintained in an atmosphere of zero relative humidity. It is necessary to keep them the same. When measuring relative humidity with the relative hygrometer shown in Fig. 1, as an initial adjustment, the heat-sensitive element Rs is first held in an atmosphere of zero relative humidity, and the power source E
Apply a voltage from
Adjust variable resistor _R4 so that the bridge unbalanced output voltage appearing across _R5 is zero. After the initial adjustment is completed, the heat-sensitive element Rs is brought into contact with the outside air to start measuring relative humidity. Heat sensitive element Rs
When the heat-sensitive element is brought into contact with the outside air, when there is a large amount of water vapor in the outside air, that is, when the humidity is high, the heat-sensitive element
The heat dissipation amount of Rs increases and its temperature decreases. Although this temperature drop is very small, the bridge circuit becomes unbalanced and a bridge unbalanced output voltage occurs between terminals T ₁ and T ₂ . This output voltage increases as the relative humidity increases at a constant temperature;
Under constant relative humidity, it exhibits a characteristic that increases as the temperature of the outside air increases, and also corresponds one-to-one with the absolute humidity of the outside air. FIG. 3 is an example of a characteristic showing the relationship between temperature and unbalanced output voltage using relative humidity as a parameter when the heat sensitive element Rs and the temperature compensating element Rc are constituted by thermistors. As shown in Figure 3, the unbalanced output voltage gradually increases as the temperature rises, so even if the relative humidity is constant, if the outside temperature differs, the bridge unbalanced output voltage will differ. becomes. Therefore, in order to determine the relative humidity from the bridge unbalanced output voltage appearing at terminals T ₁ and T ₂ , in addition to the bridge unbalanced output voltage, the temperature of the outside air is measured, and a characteristic diagram such as the one shown in Fig. 3 is used. It is necessary to convert using Therefore, in the present invention, by connecting the temperature compensation amplifier 1 whose amplification factor changes depending on the temperature of the outside air to the terminals T ₁ and T ₂ of the bridge circuit, the output voltage from the temperature compensation amplifier 1 is adjusted to the relative humidity. If is constant, it will always be constant regardless of the outside temperature. Therefore, since the output voltage from the temperature compensation amplifier 1 corresponds to the relative humidity, the relative humidity can be directly read by measuring this output voltage with the voltmeter 2. Furthermore, by adding the output of the temperature compensation amplifier 1 to an AD converter (not shown) and converting it into a digital signal, it is also possible to digitally display the relative humidity. FIG. 4 shows an example of the temperature compensation amplifier 1 of FIG. 1, in which OP ₁ and OP ₂ are operational amplifiers, Th ₁ and Th ₂ are thermistors, and R ₆ to R ₁₈ are The resistor _C1 is a capacitor, and the same symbols as in FIG. 1 represent the same parts. The bridge unbalanced output voltage generated at the terminals T ₁ and T ₂ of the bridge circuit is amplified by the operational amplifier OP ₁ and applied to the operational amplifier OP ₂ . In this case, since the thermistor Th ₁ is connected to the feedback circuit of the operational amplifier 1, the amplification factor of the operational amplifier OP ₁ changes in response to temperature changes. Since the resistance value of the thermistor _Th1 increases as the temperature decreases, the amplification factor of the operational amplifier _OP1 increases as the temperature decreases. Furthermore, since the thermistor _Th2 is also connected to the feedback circuit of the operational amplifier _OP2 , its amplification factor increases as the temperature decreases. Therefore, like this,
When the temperature compensation amplifier 1 whose amplification factor changes in response to temperature changes is connected to the terminals T ₁ and T ₂ of the bridge circuit, the output voltage from the temperature compensation amplifier 1 can be changed to the ambient temperature if the relative humidity is constant. Since the relative humidity can be kept constant regardless of changes in the relative humidity, the relative humidity can be determined by measuring this output voltage. It goes without saying that the temperature compensation amplifier 1 may be of any type as long as it has characteristics that can be used for the above purpose. The above explanation assumes that the bridge unbalanced output voltage from the bridge circuit shown in Figure 1 changes as shown in Figure 3 in response to changes in relative humidity and ambient temperature. Below are the results of measuring the relationship between temperature and bridge unbalanced output voltage using relative humidity as a parameter. [1] In the circuit shown in Figure 1, the heat-sensitive element Rs
When a thermistor is used as the temperature compensation element Rc, the thermistor used at this time has the current-voltage characteristics (at an ambient temperature of 25°C) shown in Table 1, and Figure 5 shows the characteristics shown in Table 1. FIG.

[Table] Also, the resistors R ₁ to R ₃ and R ₅ used are
They are 0.398KΩ, 10.04KΩ, 10.04KΩ, and 49.47KΩ, and the power supply E is 9.88V. At this time, the current flowing through the heat sensitive element Rs and temperature compensation element Rc is 14.98 mA (at an ambient temperature of 10°C), and the temperature of the heat sensitive element Rs and temperature compensation element Rc is approximately 200 mA.
It was warm at ℃. Therefore, when the relative humidity is high, the amount of heat dissipated increases, the resistance value of the heat sensitive element Rs increases, and the unbalanced output voltage increases. The relationship between the bridge unbalanced output voltage and the ambient temperature was measured by setting the constants of each part in this way and using the relative humidity as a parameter. This is illustrated in Figure 3 above, and Table 2 below. shows part of the data of this measurement result.

【table】

[Table] [2] In the circuit shown in Figure 6, the heat-sensitive element
When platinum elements are used as Rs' and temperature compensation element Rc', the platinum element used as heat-sensitive element Rs' has the current-voltage characteristics shown in Table 3 (ambient temperature 25
temperature compensation element).
The platinum element used as Rc' has the current-voltage characteristics (at an ambient temperature of 25°C) shown in Table 4, and Figures 7 and 8 are plots of Tables 3 and 4, respectively. FIG.

【table】

[Table] The resistors R ₆₁ and R ₆₂ used are each 1.025KΩ,
It is 0.992KΩ. The constants of each part were set as described above, and the relationship between the bridge unbalanced output voltage generated at terminals T' ₁ and T' ₂ and the ambient humidity was measured using the relative humidity as a parameter. Table 5 below shows part of the data of this measurement result. However, in this case, the power source E' was adjusted so that the current flowing through the heat sensitive element Rs' and the temperature compensating element Rc' was always 130 mA.

【table】

[Table] The resistance value of platinum decreases as the temperature decreases, and the resistance of the heated thermistor described above increases as the temperature decreases, contrary to platinum. The polarity of the unbalanced output voltage is opposite when using a thermistor and when using a thermistor, but as shown in Figures 2 and 9, the change in the unbalanced output voltage is different when using a thermistor. Both cases and the use of platinum change in the same way with changes in relative humidity and changes in ambient temperature. Therefore, it goes without saying that any heat sensitive element or temperature compensating element may be used as long as its resistance value changes with temperature changes. As explained above, the present invention uses a temperature compensation amplifier whose amplification factor changes in response to changes in ambient temperature to amplify bridge unbalanced output voltage that changes in accordance with changes in relative humidity and ambient temperature. Therefore, if the relative humidity is constant, a constant output voltage can be obtained from the temperature compensation amplifier regardless of changes in the ambient temperature. Therefore, there is an advantage that the relative humidity can be directly read, and the relative humidity can be controlled using the output voltage from the temperature compensation amplifier as it is.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention;
Figure 2 is a structural diagram of the heat-sensitive element, Figure 3 is the relative humidity,
A characteristic diagram showing an example of the relationship between temperature and output voltage, FIG. 4 is a circuit diagram showing the configuration of an example of a temperature compensation amplifier, FIG. 5 is a diagram showing the current-voltage characteristics of the thermistor, and FIG. 6 is the circuit diagram used in the experiment, Figures 7 and 8 are diagrams showing the current-voltage characteristics of the platinum element, and Figure 9 is an example of the relationship between relative humidity, temperature, and output voltage when platinum is used. FIG. 1 is a temperature compensation amplifier, 2 is a voltmeter, 3 is a thermistor, 4 is a metal case, 5 is a hermetic seal, 6 and 6' are lead wires, 7 is a hole, R ₁ to R ₁₈ ,
R ₆₁ and R ₆₂ are resistors, R ₅ and Rs′ are heat sensitive elements, Rc,
Rc′ is a temperature compensation element, C ₁ is a capacitor, OP ₁ ,
OP ₂ is an operational amplifier, E and E' are power supplies, and Th ₁ and Th ₂ are thermistors.

Claims (1)

[Scope of utility model registration request] A heat-sensitive element held so as to be able to freely contact the outside air, a temperature-compensating element that has almost the same resistance temperature characteristics as the heat-sensitive element and kept in an absolutely dry state, and two resistors are bridged. a bridge circuit that is connected to the circuit and outputs an unbalanced voltage according to the absolute temperature of the outside air by passing a current so as to heat the heat-sensitive element and the temperature compensation element to a temperature higher than the outside air temperature, and an amplification corresponding to the temperature of the outside air. 1. A relative hygrometer comprising a temperature compensation amplifier that amplifies the unbalanced voltage output from the bridge circuit at a constant rate and outputs a signal indicating the relative humidity of the outside air.