JPS633254B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a dew point detection device.

Conventionally, various so-called dew point hygrometers that measure temperature from the dew point of gas have been used, but all of these have complex structures and often require skill to perform measurements, with low accuracy and reliability. For example, with a dew point hygrometer that uses visual judgment, it is difficult to judge the dew point and the error is very large. There are also phototube dew point hygrometers and lithium chloride dew point hygrometers, but even these have a dew point accuracy of ±1°C. Therefore, the present invention provides a dew point detection device that can perform highly accurate dew point detection with a simple configuration.

Hereinafter, one embodiment of the present invention will be described based on the drawings. In Figure 1, Q ₁ and Q ₂ are the second
This is a crystal resonator that exhibits linear temperature characteristics as shown in Figures l ₁ and l _2. Crystal resonator Q ₁ is hermetically sealed, and crystal resonator Q ₂ is for dew condensation detection and is not exposed. be. A is the cooling and heating device, and the crystal oscillator
Cool or heat Q ₁ and Q ₂ . M is mixer,
CM ₁ and CM ₂ are comparison circuits, ST ₁ and ST ₂ are setting circuits,
L is a warning lamp, and DR is a drive circuit. Q ₃ is a crystal oscillator for temperature detection, TM is a temperature detection circuit,
CU is an arithmetic circuit that calculates absolute temperature or relative humidity, and DS is a display device.

Next, the operation will be explained. When the power is turned on, one pulse is supplied to the terminal P of the setting circuit ST ₁ , and the output frequency from the mixer M at this time, that is, the difference between the oscillation frequencies of the crystal oscillators Q ₁ and Q ₂ is set as an initial value to the setting circuit ST ₁ . is set to and comparison circuit
In CM ₁ , the output frequency of the mixer M and the initial value of the setting circuit ST ₁ are compared, and if the two are substantially the same, an output is generated from the drive circuit DR based on the output of the comparison circuit CM ₁ . This output causes the heating/cooling device A to operate as a cooler to cool the crystal oscillators Q ₁ and Q ₂ . Since the crystal oscillator Q ₂ is exposed, when the dew point is reached, dew condenses on its surface and its mass increases, causing the resonant frequency to drop as shown in the second diagram. On the other hand, since the crystal resonator _Q1 is hermetically sealed, there is no condensation on its surface.

Therefore, the difference between the two resonance frequencies increases, and when this difference exceeds a predetermined value Δf, the output from the comparator circuit _CM1 is stopped and cooling is stopped. By stopping the output of this comparator circuit CM ₁ , the crystal oscillator
The oscillation frequency of _Q1 is taken into the arithmetic circuit CU, and this frequency is converted to the dew point. At the same time, the output of the temperature detection circuit TM is taken into the arithmetic circuit CU and the temperature is measured. Absolute humidity and relative humidity are determined from the dew point and temperature and displayed on the display device DS.

By the way, once condensation forms on the crystal oscillator _Q2 , measurements cannot be performed until it dries. So set circuit ST ₂
Then, the value f ₁ is slightly larger than the frequency of the difference between the crystal oscillators Q ₁ and Q ₂ when the crystal oscillator Q ₂ is dry.
Set. Therefore, when the switch S is closed, the comparator circuit CM ₂ compares the output of the setting circuit ST ₂ and the output of the mixer M, and the difference between the two is calculated as above.
If it is larger than f ₁ , the lamp L lights up to warn that measurement is impossible, and the heating/cooling device A operates as a heater by the output of the drive circuit DR to heat the crystal oscillator Q ₂ . This heating dries the crystal resonator _Q2 , and when the difference in oscillation frequency with the crystal resonator _Q1 becomes smaller than _f1 , the output of the comparator circuit _CM2 stops.

Note that although the electrodes of the crystal oscillator Q ₂ are made of Au or protected with an oxide film, since they are exposed, the surface gets dirty and the resonant frequency changes when dry. Therefore, as mentioned in the previous explanation, each time the power is turned on, the setting circuit _ST1 sets the output frequency of mixer M to the initial value.
It is set to .

By the way, as a crystal oscillator, at about 10MHz and 1℃
If you use one that changes at 1KHz, the dew point measurement accuracy can be within 0.1℃.

As described above, according to the present invention, the reference value for comparison is reset each time the power is turned on, so even if the resonant frequency of the exposed crystal oscillator changes due to dirt, dew point measurement will not be performed. The effect does not appear,
It is easy to maintain and can provide accurate measurements over a long period of time.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, and Fig. 2 shows the frequency of the crystal resonator used in this example.
FIG. 3 is a characteristic diagram showing temperature characteristics. Q ₁ ... Hermetically sealed crystal, Q ₂ ... Exposed crystal, A ... Heating and cooling device, M ...
...Mixer, CM ₁ ... Comparison circuit, CU ... Arithmetic circuit.

Claims (1)

[Claims] 1. A cooler that cools each crystal oscillator by hermetically sealing one of the two crystal oscillators exhibiting similar linear temperature characteristics and exposing the other to the gas to be detected, and each of the crystal oscillators described above. A detection circuit that detects the frequency difference between the resonant frequencies of , a setting circuit that sets the frequency value of the difference from the above detection circuit every time the power is turned on, and a frequency value of the difference between the settings of this setting circuit and the above detection circuit. a comparison circuit that generates an output to operate the cooler until the difference between the A dew point detection device consisting of a calculation circuit that calculates the dew point of gas.